Add prometheus serializer and use it in prometheus output (#6703)

Gopkg.lock

@@ -1750,6 +1750,7 @@
     "github.com/go-sql-driver/mysql",
     "github.com/gobwas/glob",
     "github.com/gofrs/uuid",
+    "github.com/gogo/protobuf/proto",
     "github.com/golang/protobuf/proto",
     "github.com/golang/protobuf/ptypes/duration",
     "github.com/golang/protobuf/ptypes/empty",

docs/DATA_FORMATS_OUTPUT.md

@@ -5,10 +5,11 @@ standard data formats that may be selected from when configuring many output
 plugins.
 
 1. [InfluxDB Line Protocol](/plugins/serializers/influx)
-1. [JSON](/plugins/serializers/json)
-1. [Graphite](/plugins/serializers/graphite)
-1. [SplunkMetric](/plugins/serializers/splunkmetric)
 1. [Carbon2](/plugins/serializers/carbon2)
+1. [Graphite](/plugins/serializers/graphite)
+1. [JSON](/plugins/serializers/json)
+1. [Prometheus](/plugins/serializers/prometheus)
+1. [SplunkMetric](/plugins/serializers/splunkmetric)
 1. [Wavefront](/plugins/serializers/wavefront)
 
 You will be able to identify the plugins with support by the presence of a

internal/http.go

@@ -2,6 +2,7 @@ package internal
 
 import (
 	"crypto/subtle"
+	"net"
 	"net/http"
 )
 
@@ -43,3 +44,49 @@ func (h *basicAuthHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request)
 
 	h.next.ServeHTTP(rw, req)
 }
+
+// IPRangeHandler returns a http handler that requires the remote address to be
+// in the specified network.
+func IPRangeHandler(network []*net.IPNet, onError ErrorFunc) func(h http.Handler) http.Handler {
+	return func(h http.Handler) http.Handler {
+		return &ipRangeHandler{
+			network: network,
+			onError: onError,
+			next:    h,
+		}
+	}
+}
+
+type ipRangeHandler struct {
+	network []*net.IPNet
+	onError ErrorFunc
+	next    http.Handler
+}
+
+func (h *ipRangeHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	if len(h.network) == 0 {
+		h.next.ServeHTTP(rw, req)
+		return
+	}
+
+	remoteIPString, _, err := net.SplitHostPort(req.RemoteAddr)
+	if err != nil {
+		h.onError(rw, http.StatusForbidden)
+		return
+	}
+
+	remoteIP := net.ParseIP(remoteIPString)
+	if remoteIP == nil {
+		h.onError(rw, http.StatusForbidden)
+		return
+	}
+
+	for _, net := range h.network {
+		if net.Contains(remoteIP) {
+			h.next.ServeHTTP(rw, req)
+			return
+		}
+	}
+
+	h.onError(rw, http.StatusForbidden)
+}

plugins/inputs/prometheus/README.md

@@ -11,8 +11,14 @@ in Prometheus format.
   ## An array of urls to scrape metrics from.
   urls = ["http://localhost:9100/metrics"]
 
-  ## Metric version (optional, default=1, supported values are 1 and 2)
+  ## Metric version controls the mapping from Prometheus metrics into
-  # metric_version = 2
+  ## Telegraf metrics.  When using the prometheus_client output, use the same
+  ## value in both plugins to ensure metrics are round-tripped without
+  ## modification.
+  ##
+  ##   example: metric_version = 1; deprecated in 1.13
+  ##            metric_version = 2; recommended version
+  # metric_version = 1
 
   ## An array of Kubernetes services to scrape metrics from.
   # kubernetes_services = ["http://my-service-dns.my-namespace:9100/metrics"]

plugins/inputs/prometheus/prometheus.go

@@ -62,8 +62,14 @@ var sampleConfig = `
   ## An array of urls to scrape metrics from.
   urls = ["http://localhost:9100/metrics"]
 
-  ## Metric version (optional, default=1, supported values are 1 and 2)
+  ## Metric version controls the mapping from Prometheus metrics into
-  # metric_version = 2
+  ## Telegraf metrics.  When using the prometheus_client output, use the same
+  ## value in both plugins to ensure metrics are round-tripped without
+  ## modification.
+  ##
+  ##   example: metric_version = 1; deprecated in 1.13
+  ##            metric_version = 2; recommended version
+  # metric_version = 1
 
   ## Url tag name (tag containing scrapped url. optional, default is "url")
   # url_tag = "scrapeUrl"
@@ -95,7 +101,7 @@ var sampleConfig = `
   # username = ""
   # password = ""
 
-	## Specify timeout duration for slower prometheus clients (default is 3s)
+  ## Specify timeout duration for slower prometheus clients (default is 3s)
   # response_timeout = "3s"
 
   ## Optional TLS Config
@@ -114,6 +120,13 @@ func (p *Prometheus) Description() string {
 	return "Read metrics from one or many prometheus clients"
 }
 
+func (p *Prometheus) Init() error {
+	if p.MetricVersion != 2 {
+		p.Log.Warnf("Use of deprecated configuration: 'metric_version = 1'; please update to 'metric_version = 2'")
+	}
+	return nil
+}
+
 var ErrProtocolError = errors.New("prometheus protocol error")
 
 func (p *Prometheus) AddressToURL(u *url.URL, address string) *url.URL {
@@ -311,7 +324,9 @@ func (p *Prometheus) gatherURL(u URLAndAddress, acc telegraf.Accumulator) error
 		tags := metric.Tags()
 		// strip user and password from URL
 		u.OriginalURL.User = nil
-		tags[p.URLTag] = u.OriginalURL.String()
+		if p.URLTag != "" {
+			tags[p.URLTag] = u.OriginalURL.String()
+		}
 		if u.Address != "" {
 			tags["address"] = u.Address
 		}

plugins/outputs/file/README.md

@@ -9,6 +9,11 @@ This plugin writes telegraf metrics to files
   ## Files to write to, "stdout" is a specially handled file.
   files = ["stdout", "/tmp/metrics.out"]
 
+  ## Use batch serialization format instead of line based delimiting.  The
+  ## batch format allows for the production of non line based output formats and
+  ## may more effiently encode and write metrics.
+  # use_batch_format = false
+
   ## The file will be rotated after the time interval specified.  When set
   ## to 0 no time based rotation is performed.
   # rotation_interval = "0h"

plugins/outputs/file/file.go

@@ -3,7 +3,6 @@ package file
 import (
 	"fmt"
 	"io"
-	"log"
 	"os"
 
 	"github.com/influxdata/telegraf"
@@ -18,6 +17,8 @@ type File struct {
 	RotationInterval    internal.Duration `toml:"rotation_interval"`
 	RotationMaxSize     internal.Size     `toml:"rotation_max_size"`
 	RotationMaxArchives int               `toml:"rotation_max_archives"`
+	UseBatchFormat      bool              `toml:"use_batch_format"`
+	Log                 telegraf.Logger   `toml:"-"`
 
 	writer     io.Writer
 	closers    []io.Closer
@@ -28,6 +29,11 @@ var sampleConfig = `
   ## Files to write to, "stdout" is a specially handled file.
   files = ["stdout", "/tmp/metrics.out"]
 
+  ## Use batch serialization format instead of line based delimiting.  The
+  ## batch format allows for the production of non line based output formats and
+  ## may more effiently encode metric groups.
+  # use_batch_format = false
+
   ## The file will be rotated after the time interval specified.  When set
   ## to 0 no time based rotation is performed.
   # rotation_interval = "0d"
@@ -98,15 +104,27 @@ func (f *File) Description() string {
 func (f *File) Write(metrics []telegraf.Metric) error {
 	var writeErr error = nil
 
-	for _, metric := range metrics {
+	if f.UseBatchFormat {
-		b, err := f.serializer.Serialize(metric)
+		octets, err := f.serializer.SerializeBatch(metrics)
 		if err != nil {
-			log.Printf("D! [outputs.file] Could not serialize metric: %v", err)
+			f.Log.Errorf("Could not serialize metric: %v", err)
 		}
 
-		_, err = f.writer.Write(b)
+		_, err = f.writer.Write(octets)
 		if err != nil {
-			writeErr = fmt.Errorf("E! [outputs.file] failed to write message: %v", err)
+			f.Log.Errorf("Error writing to file: %v", err)
+		}
+	} else {
+		for _, metric := range metrics {
+			b, err := f.serializer.Serialize(metric)
+			if err != nil {
+				f.Log.Debugf("Could not serialize metric: %v", err)
+			}
+
+			_, err = f.writer.Write(b)
+			if err != nil {
+				writeErr = fmt.Errorf("E! [outputs.file] failed to write message: %v", err)
+			}
 		}
 	}
 

plugins/outputs/prometheus_client/README.md

@@ -1,6 +1,7 @@
-# Prometheus Client Service Output Plugin
+# Prometheus Output Plugin
 
-This plugin starts a [Prometheus](https://prometheus.io/) Client, it exposes all metrics on `/metrics` (default) to be polled by a Prometheus server.
+This plugin starts a [Prometheus](https://prometheus.io/) Client, it exposes
+all metrics on `/metrics` (default) to be polled by a Prometheus server.
 
 ## Configuration
 
@@ -10,6 +11,14 @@ This plugin starts a [Prometheus](https://prometheus.io/) Client, it exposes all
   ## Address to listen on.
   listen = ":9273"
 
+  ## Metric version controls the mapping from Telegraf metrics into
+  ## Prometheus format.  When using the prometheus input, use the same value in
+  ## both plugins to ensure metrics are round-tripped without modification.
+  ##
+  ##   example: metric_version = 1; deprecated in 1.13
+  ##            metric_version = 2; recommended version
+  # metric_version = 1
+
   ## Use HTTP Basic Authentication.
   # basic_username = "Foo"
   # basic_password = "Bar"

plugins/outputs/prometheus_client/prometheus_client.go

@@ -1,18 +1,12 @@
-package prometheus_client
+package prometheus
 
 import (
 	"context"
-	"crypto/subtle"
 	"crypto/tls"
 	"fmt"
-	"log"
 	"net"
 	"net/http"
 	"net/url"
-	"regexp"
-	"sort"
-	"strconv"
-	"strings"
 	"sync"
 	"time"
 
@@ -20,73 +14,30 @@ import (
 	"github.com/influxdata/telegraf/internal"
 	tlsint "github.com/influxdata/telegraf/internal/tls"
 	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/plugins/outputs/prometheus_client/v1"
+	"github.com/influxdata/telegraf/plugins/outputs/prometheus_client/v2"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 var (
-	invalidNameCharRE = regexp.MustCompile(`[^a-zA-Z0-9_:]`)
+	defaultListen             = ":9273"
-	validNameCharRE   = regexp.MustCompile(`^[a-zA-Z_][a-zA-Z0-9_]*`)
+	defaultPath               = "/metrics"
+	defaultExpirationInterval = internal.Duration{Duration: 60 * time.Second}
 )
 
-// SampleID uniquely identifies a Sample
-type SampleID string
-
-// Sample represents the current value of a series.
-type Sample struct {
-	// Labels are the Prometheus labels.
-	Labels map[string]string
-	// Value is the value in the Prometheus output. Only one of these will populated.
-	Value          float64
-	HistogramValue map[float64]uint64
-	SummaryValue   map[float64]float64
-	// Histograms and Summaries need a count and a sum
-	Count uint64
-	Sum   float64
-	// Metric timestamp
-	Timestamp time.Time
-	// Expiration is the deadline that this Sample is valid until.
-	Expiration time.Time
-}
-
-// MetricFamily contains the data required to build valid prometheus Metrics.
-type MetricFamily struct {
-	// Samples are the Sample belonging to this MetricFamily.
-	Samples map[SampleID]*Sample
-	// Need the telegraf ValueType because there isn't a Prometheus ValueType
-	// representing Histogram or Summary
-	TelegrafValueType telegraf.ValueType
-	// LabelSet is the label counts for all Samples.
-	LabelSet map[string]int
-}
-
-type PrometheusClient struct {
-	Listen             string
-	BasicUsername      string            `toml:"basic_username"`
-	BasicPassword      string            `toml:"basic_password"`
-	IPRange            []string          `toml:"ip_range"`
-	ExpirationInterval internal.Duration `toml:"expiration_interval"`
-	Path               string            `toml:"path"`
-	CollectorsExclude  []string          `toml:"collectors_exclude"`
-	StringAsLabel      bool              `toml:"string_as_label"`
-	ExportTimestamp    bool              `toml:"export_timestamp"`
-
-	tlsint.ServerConfig
-
-	server *http.Server
-	url    string
-
-	sync.Mutex
-	// fam is the non-expired MetricFamily by Prometheus metric name.
-	fam map[string]*MetricFamily
-	// now returns the current time.
-	now func() time.Time
-}
-
 var sampleConfig = `
   ## Address to listen on
   listen = ":9273"
 
+  ## Metric version controls the mapping from Telegraf metrics into
+  ## Prometheus format.  When using the prometheus input, use the same value in
+  ## both plugins to ensure metrics are round-tripped without modification.
+  ##
+  ##   example: metric_version = 1; deprecated in 1.13
+  ##            metric_version = 2; recommended version
+  # metric_version = 1
+
   ## Use HTTP Basic Authentication.
   # basic_username = "Foo"
   # basic_password = "Bar"
@@ -121,46 +72,42 @@ var sampleConfig = `
   # export_timestamp = false
 `
 
-func (p *PrometheusClient) auth(h http.Handler) http.Handler {
+type Collector interface {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	Describe(ch chan<- *prometheus.Desc)
-		if p.BasicUsername != "" && p.BasicPassword != "" {
+	Collect(ch chan<- prometheus.Metric)
-			w.Header().Set("WWW-Authenticate", `Basic realm="Restricted"`)
+	Add(metrics []telegraf.Metric) error
-
-			username, password, ok := r.BasicAuth()
-			if !ok ||
-				subtle.ConstantTimeCompare([]byte(username), []byte(p.BasicUsername)) != 1 ||
-				subtle.ConstantTimeCompare([]byte(password), []byte(p.BasicPassword)) != 1 {
-				http.Error(w, "Not authorized", 401)
-				return
-			}
-		}
-
-		if len(p.IPRange) > 0 {
-			matched := false
-			remoteIPs, _, _ := net.SplitHostPort(r.RemoteAddr)
-			remoteIP := net.ParseIP(remoteIPs)
-			for _, iprange := range p.IPRange {
-				_, ipNet, err := net.ParseCIDR(iprange)
-				if err != nil {
-					http.Error(w, "Config Error in ip_range setting", 500)
-					return
-				}
-				if ipNet.Contains(remoteIP) {
-					matched = true
-					break
-				}
-			}
-			if !matched {
-				http.Error(w, "Not authorized", 401)
-				return
-			}
-		}
-
-		h.ServeHTTP(w, r)
-	})
 }
 
-func (p *PrometheusClient) Connect() error {
+type PrometheusClient struct {
+	Listen             string            `toml:"listen"`
+	MetricVersion      int               `toml:"metric_version"`
+	BasicUsername      string            `toml:"basic_username"`
+	BasicPassword      string            `toml:"basic_password"`
+	IPRange            []string          `toml:"ip_range"`
+	ExpirationInterval internal.Duration `toml:"expiration_interval"`
+	Path               string            `toml:"path"`
+	CollectorsExclude  []string          `toml:"collectors_exclude"`
+	StringAsLabel      bool              `toml:"string_as_label"`
+	ExportTimestamp    bool              `toml:"export_timestamp"`
+	tlsint.ServerConfig
+
+	Log telegraf.Logger `toml:"-"`
+
+	server    *http.Server
+	url       *url.URL
+	collector Collector
+	wg        sync.WaitGroup
+}
+
+func (p *PrometheusClient) Description() string {
+	return "Configuration for the Prometheus client to spawn"
+}
+
+func (p *PrometheusClient) SampleConfig() string {
+	return sampleConfig
+}
+
+func (p *PrometheusClient) Init() error {
 	defaultCollectors := map[string]bool{
 		"gocollector": true,
 		"process":     true,
@@ -181,421 +128,137 @@ func (p *PrometheusClient) Connect() error {
 		}
 	}
 
-	err := registry.Register(p)
+	switch p.MetricVersion {
-	if err != nil {
+	default:
-		return err
+		fallthrough
+	case 1:
+		p.Log.Warnf("Use of deprecated configuration: metric_version = 1; please update to metric_version = 2")
+		p.collector = v1.NewCollector(p.ExpirationInterval.Duration, p.StringAsLabel, p.Log)
+		err := registry.Register(p.collector)
+		if err != nil {
+			return err
+		}
+	case 2:
+		p.collector = v2.NewCollector(p.ExpirationInterval.Duration, p.StringAsLabel)
+		err := registry.Register(p.collector)
+		if err != nil {
+			return err
+		}
 	}
 
-	if p.Listen == "" {
+	ipRange := make([]*net.IPNet, 0, len(p.IPRange))
-		p.Listen = "localhost:9273"
+	for _, cidr := range p.IPRange {
+		_, ipNet, err := net.ParseCIDR(cidr)
+		if err != nil {
+			return fmt.Errorf("error parsing ip_range: %v", err)
+		}
+
+		ipRange = append(ipRange, ipNet)
 	}
 
-	if p.Path == "" {
+	authHandler := internal.AuthHandler(p.BasicUsername, p.BasicPassword, onAuthError)
-		p.Path = "/metrics"
+	rangeHandler := internal.IPRangeHandler(ipRange, onError)
-	}
+	promHandler := promhttp.HandlerFor(registry, promhttp.HandlerOpts{ErrorHandling: promhttp.ContinueOnError})
 
 	mux := http.NewServeMux()
-	mux.Handle(p.Path, p.auth(promhttp.HandlerFor(
+	if p.Path == "" {
-		registry, promhttp.HandlerOpts{ErrorHandling: promhttp.ContinueOnError})))
+		p.Path = "/"
+	}
+	mux.Handle(p.Path, authHandler(rangeHandler(promHandler)))
 
 	tlsConfig, err := p.TLSConfig()
 	if err != nil {
 		return err
 	}
+
 	p.server = &http.Server{
 		Addr:      p.Listen,
 		Handler:   mux,
 		TLSConfig: tlsConfig,
 	}
 
-	var listener net.Listener
+	return nil
-	if tlsConfig != nil {
+}
-		listener, err = tls.Listen("tcp", p.Listen, tlsConfig)
+
+func (p *PrometheusClient) listen() (net.Listener, error) {
+	if p.server.TLSConfig != nil {
+		return tls.Listen("tcp", p.Listen, p.server.TLSConfig)
 	} else {
-		listener, err = net.Listen("tcp", p.Listen)
+		return net.Listen("tcp", p.Listen)
 	}
+}
+
+func (p *PrometheusClient) Connect() error {
+	listener, err := p.listen()
 	if err != nil {
 		return err
 	}
 
-	p.url = createURL(tlsConfig, listener, p.Path)
+	scheme := "http"
+	if p.server.TLSConfig != nil {
+		scheme = "https"
+	}
 
+	p.url = &url.URL{
+		Scheme: scheme,
+		Host:   listener.Addr().String(),
+		Path:   p.Path,
+	}
+
+	p.Log.Infof("Listening on %s", p.URL())
+
+	p.wg.Add(1)
 	go func() {
+		defer p.wg.Done()
 		err := p.server.Serve(listener)
 		if err != nil && err != http.ErrServerClosed {
-			log.Printf("E! Error creating prometheus metric endpoint, err: %s\n",
+			p.Log.Errorf("Server error: %v", err)
-				err.Error())
 		}
 	}()
 
 	return nil
 }
 
+func onAuthError(rw http.ResponseWriter, code int) {
+	rw.Header().Set("WWW-Authenticate", `Basic realm="Restricted"`)
+	http.Error(rw, http.StatusText(code), code)
+}
+
+func onError(rw http.ResponseWriter, code int) {
+	http.Error(rw, http.StatusText(code), code)
+}
+
 // Address returns the address the plugin is listening on.  If not listening
 // an empty string is returned.
 func (p *PrometheusClient) URL() string {
-	return p.url
+	if p.url != nil {
-}
+		return p.url.String()
-
-func createURL(tlsConfig *tls.Config, listener net.Listener, path string) string {
-	u := url.URL{
-		Scheme: "http",
-		Host:   listener.Addr().String(),
-		Path:   path,
 	}
-
+	return ""
-	if tlsConfig != nil {
-		u.Scheme = "https"
-	}
-	return u.String()
 }
 
 func (p *PrometheusClient) Close() error {
-	ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
+
 	err := p.server.Shutdown(ctx)
-	prometheus.Unregister(p)
+	p.wg.Wait()
-	p.url = ""
+	p.url = nil
+	prometheus.Unregister(p.collector)
 	return err
 }
 
-func (p *PrometheusClient) SampleConfig() string {
-	return sampleConfig
-}
-
-func (p *PrometheusClient) Description() string {
-	return "Configuration for the Prometheus client to spawn"
-}
-
-// Implements prometheus.Collector
-func (p *PrometheusClient) Describe(ch chan<- *prometheus.Desc) {
-	prometheus.NewGauge(prometheus.GaugeOpts{Name: "Dummy", Help: "Dummy"}).Describe(ch)
-}
-
-// Expire removes Samples that have expired.
-func (p *PrometheusClient) Expire() {
-	now := p.now()
-	for name, family := range p.fam {
-		for key, sample := range family.Samples {
-			if p.ExpirationInterval.Duration != 0 && now.After(sample.Expiration) {
-				for k := range sample.Labels {
-					family.LabelSet[k]--
-				}
-				delete(family.Samples, key)
-
-				if len(family.Samples) == 0 {
-					delete(p.fam, name)
-				}
-			}
-		}
-	}
-}
-
-// Collect implements prometheus.Collector
-func (p *PrometheusClient) Collect(ch chan<- prometheus.Metric) {
-	p.Lock()
-	defer p.Unlock()
-
-	p.Expire()
-
-	for name, family := range p.fam {
-		// Get list of all labels on MetricFamily
-		var labelNames []string
-		for k, v := range family.LabelSet {
-			if v > 0 {
-				labelNames = append(labelNames, k)
-			}
-		}
-		desc := prometheus.NewDesc(name, "Telegraf collected metric", labelNames, nil)
-
-		for _, sample := range family.Samples {
-			// Get labels for this sample; unset labels will be set to the
-			// empty string
-			var labels []string
-			for _, label := range labelNames {
-				v := sample.Labels[label]
-				labels = append(labels, v)
-			}
-
-			var metric prometheus.Metric
-			var err error
-			switch family.TelegrafValueType {
-			case telegraf.Summary:
-				metric, err = prometheus.NewConstSummary(desc, sample.Count, sample.Sum, sample.SummaryValue, labels...)
-			case telegraf.Histogram:
-				metric, err = prometheus.NewConstHistogram(desc, sample.Count, sample.Sum, sample.HistogramValue, labels...)
-			default:
-				metric, err = prometheus.NewConstMetric(desc, getPromValueType(family.TelegrafValueType), sample.Value, labels...)
-			}
-			if err != nil {
-				log.Printf("E! Error creating prometheus metric, "+
-					"key: %s, labels: %v,\nerr: %s\n",
-					name, labels, err.Error())
-				continue
-			}
-
-			if p.ExportTimestamp {
-				metric = prometheus.NewMetricWithTimestamp(sample.Timestamp, metric)
-			}
-			ch <- metric
-		}
-	}
-}
-
-func sanitize(value string) string {
-	return invalidNameCharRE.ReplaceAllString(value, "_")
-}
-
-func isValidTagName(tag string) bool {
-	return validNameCharRE.MatchString(tag)
-}
-
-func getPromValueType(tt telegraf.ValueType) prometheus.ValueType {
-	switch tt {
-	case telegraf.Counter:
-		return prometheus.CounterValue
-	case telegraf.Gauge:
-		return prometheus.GaugeValue
-	default:
-		return prometheus.UntypedValue
-	}
-}
-
-// CreateSampleID creates a SampleID based on the tags of a telegraf.Metric.
-func CreateSampleID(tags map[string]string) SampleID {
-	pairs := make([]string, 0, len(tags))
-	for k, v := range tags {
-		pairs = append(pairs, fmt.Sprintf("%s=%s", k, v))
-	}
-	sort.Strings(pairs)
-	return SampleID(strings.Join(pairs, ","))
-}
-
-func addSample(fam *MetricFamily, sample *Sample, sampleID SampleID) {
-
-	for k := range sample.Labels {
-		fam.LabelSet[k]++
-	}
-
-	fam.Samples[sampleID] = sample
-}
-
-func (p *PrometheusClient) addMetricFamily(point telegraf.Metric, sample *Sample, mname string, sampleID SampleID) {
-	var fam *MetricFamily
-	var ok bool
-	if fam, ok = p.fam[mname]; !ok {
-		fam = &MetricFamily{
-			Samples:           make(map[SampleID]*Sample),
-			TelegrafValueType: point.Type(),
-			LabelSet:          make(map[string]int),
-		}
-		p.fam[mname] = fam
-	}
-
-	addSample(fam, sample, sampleID)
-}
-
-// Sorted returns a copy of the metrics in time ascending order.  A copy is
-// made to avoid modifying the input metric slice since doing so is not
-// allowed.
-func sorted(metrics []telegraf.Metric) []telegraf.Metric {
-	batch := make([]telegraf.Metric, 0, len(metrics))
-	for i := len(metrics) - 1; i >= 0; i-- {
-		batch = append(batch, metrics[i])
-	}
-	sort.Slice(batch, func(i, j int) bool {
-		return batch[i].Time().Before(batch[j].Time())
-	})
-	return batch
-}
-
 func (p *PrometheusClient) Write(metrics []telegraf.Metric) error {
-	p.Lock()
+	return p.collector.Add(metrics)
-	defer p.Unlock()
-
-	now := p.now()
-
-	for _, point := range sorted(metrics) {
-		tags := point.Tags()
-		sampleID := CreateSampleID(tags)
-
-		labels := make(map[string]string)
-		for k, v := range tags {
-			tName := sanitize(k)
-			if !isValidTagName(tName) {
-				continue
-			}
-			labels[tName] = v
-		}
-
-		// Prometheus doesn't have a string value type, so convert string
-		// fields to labels if enabled.
-		if p.StringAsLabel {
-			for fn, fv := range point.Fields() {
-				switch fv := fv.(type) {
-				case string:
-					tName := sanitize(fn)
-					if !isValidTagName(tName) {
-						continue
-					}
-					labels[tName] = fv
-				}
-			}
-		}
-
-		switch point.Type() {
-		case telegraf.Summary:
-			var mname string
-			var sum float64
-			var count uint64
-			summaryvalue := make(map[float64]float64)
-			for fn, fv := range point.Fields() {
-				var value float64
-				switch fv := fv.(type) {
-				case int64:
-					value = float64(fv)
-				case uint64:
-					value = float64(fv)
-				case float64:
-					value = fv
-				default:
-					continue
-				}
-
-				switch fn {
-				case "sum":
-					sum = value
-				case "count":
-					count = uint64(value)
-				default:
-					limit, err := strconv.ParseFloat(fn, 64)
-					if err == nil {
-						summaryvalue[limit] = value
-					}
-				}
-			}
-			sample := &Sample{
-				Labels:       labels,
-				SummaryValue: summaryvalue,
-				Count:        count,
-				Sum:          sum,
-				Timestamp:    point.Time(),
-				Expiration:   now.Add(p.ExpirationInterval.Duration),
-			}
-			mname = sanitize(point.Name())
-
-			if !isValidTagName(mname) {
-				continue
-			}
-
-			p.addMetricFamily(point, sample, mname, sampleID)
-
-		case telegraf.Histogram:
-			var mname string
-			var sum float64
-			var count uint64
-			histogramvalue := make(map[float64]uint64)
-			for fn, fv := range point.Fields() {
-				var value float64
-				switch fv := fv.(type) {
-				case int64:
-					value = float64(fv)
-				case uint64:
-					value = float64(fv)
-				case float64:
-					value = fv
-				default:
-					continue
-				}
-
-				switch fn {
-				case "sum":
-					sum = value
-				case "count":
-					count = uint64(value)
-				default:
-					limit, err := strconv.ParseFloat(fn, 64)
-					if err == nil {
-						histogramvalue[limit] = uint64(value)
-					}
-				}
-			}
-			sample := &Sample{
-				Labels:         labels,
-				HistogramValue: histogramvalue,
-				Count:          count,
-				Sum:            sum,
-				Timestamp:      point.Time(),
-				Expiration:     now.Add(p.ExpirationInterval.Duration),
-			}
-			mname = sanitize(point.Name())
-
-			if !isValidTagName(mname) {
-				continue
-			}
-
-			p.addMetricFamily(point, sample, mname, sampleID)
-
-		default:
-			for fn, fv := range point.Fields() {
-				// Ignore string and bool fields.
-				var value float64
-				switch fv := fv.(type) {
-				case int64:
-					value = float64(fv)
-				case uint64:
-					value = float64(fv)
-				case float64:
-					value = fv
-				default:
-					continue
-				}
-
-				sample := &Sample{
-					Labels:     labels,
-					Value:      value,
-					Timestamp:  point.Time(),
-					Expiration: now.Add(p.ExpirationInterval.Duration),
-				}
-
-				// Special handling of value field; supports passthrough from
-				// the prometheus input.
-				var mname string
-				switch point.Type() {
-				case telegraf.Counter:
-					if fn == "counter" {
-						mname = sanitize(point.Name())
-					}
-				case telegraf.Gauge:
-					if fn == "gauge" {
-						mname = sanitize(point.Name())
-					}
-				}
-				if mname == "" {
-					if fn == "value" {
-						mname = sanitize(point.Name())
-					} else {
-						mname = sanitize(fmt.Sprintf("%s_%s", point.Name(), fn))
-					}
-				}
-				if !isValidTagName(mname) {
-					continue
-				}
-				p.addMetricFamily(point, sample, mname, sampleID)
-
-			}
-		}
-	}
-	return nil
 }
 
 func init() {
 	outputs.Add("prometheus_client", func() telegraf.Output {
 		return &PrometheusClient{
-			ExpirationInterval: internal.Duration{Duration: time.Second * 60},
+			Listen:             defaultListen,
+			Path:               defaultPath,
+			ExpirationInterval: defaultExpirationInterval,
 			StringAsLabel:      true,
-			fam:                make(map[string]*MetricFamily),
-			now:                time.Now,
 		}
 	})
 }

plugins/outputs/prometheus_client/prometheus_client_test.go

@@ -1,693 +1,304 @@
-package prometheus_client
+package prometheus
 
 import (
+	"io/ioutil"
+	"net/http"
+	"strings"
 	"testing"
 	"time"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/internal"
-	"github.com/influxdata/telegraf/metric"
-	prometheus_input "github.com/influxdata/telegraf/plugins/inputs/prometheus"
 	"github.com/influxdata/telegraf/testutil"
 	"github.com/stretchr/testify/require"
 )
 
-func setUnixTime(client *PrometheusClient, sec int64) {
+func TestMetricVersion1(t *testing.T) {
-	client.now = func() time.Time {
+	tests := []struct {
-		return time.Unix(sec, 0)
+		name     string
-	}
+		output   *PrometheusClient
-}
+		metrics  []telegraf.Metric
-
+		expected []byte
-// NewClient initializes a PrometheusClient.
-func NewClient() *PrometheusClient {
-	return &PrometheusClient{
-		ExpirationInterval: internal.Duration{Duration: time.Second * 60},
-		StringAsLabel:      true,
-		fam:                make(map[string]*MetricFamily),
-		now:                time.Now,
-	}
-}
-
-func TestWrite_Basic(t *testing.T) {
-	now := time.Now()
-	pt1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 0.0},
-		now)
-	var metrics = []telegraf.Metric{
-		pt1,
-	}
-
-	client := NewClient()
-	err = client.Write(metrics)
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, telegraf.Untyped, fam.TelegrafValueType)
-	require.Equal(t, map[string]int{}, fam.LabelSet)
-
-	sample, ok := fam.Samples[CreateSampleID(pt1.Tags())]
-	require.True(t, ok)
-
-	require.Equal(t, 0.0, sample.Value)
-	require.True(t, now.Before(sample.Expiration))
-}
-
-func TestWrite_IntField(t *testing.T) {
-	client := NewClient()
-
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 42},
-		time.Now())
-	err = client.Write([]telegraf.Metric{p1})
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	for _, v := range fam.Samples {
-		require.Equal(t, 42.0, v.Value)
-	}
-
-}
-
-func TestWrite_FieldNotValue(t *testing.T) {
-	client := NewClient()
-
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"howdy": 0.0},
-		time.Now())
-	err = client.Write([]telegraf.Metric{p1})
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo_howdy"]
-	require.True(t, ok)
-	for _, v := range fam.Samples {
-		require.Equal(t, 0.0, v.Value)
-	}
-}
-
-func TestWrite_SkipNonNumberField(t *testing.T) {
-	client := NewClient()
-
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": "howdy"},
-		time.Now())
-	err = client.Write([]telegraf.Metric{p1})
-	require.NoError(t, err)
-
-	_, ok := client.fam["foo"]
-	require.False(t, ok)
-}
-
-func TestWrite_Counters(t *testing.T) {
-	type args struct {
-		measurement string
-		tags        map[string]string
-		fields      map[string]interface{}
-		valueType   telegraf.ValueType
-	}
-	var tests = []struct {
-		name       string
-		args       args
-		err        error
-		metricName string
-		valueType  telegraf.ValueType
 	}{
 		{
-			name: "field named value is not added to metric name",
+			name: "simple",
-			args: args{
+			output: &PrometheusClient{
-				measurement: "foo",
+				Listen:            ":0",
-				fields:      map[string]interface{}{"value": 42},
+				MetricVersion:     1,
-				valueType:   telegraf.Counter,
+				CollectorsExclude: []string{"gocollector", "process"},
+				Path:              "/metrics",
+				Log:               testutil.Logger{},
 			},
-			metricName: "foo",
+			metrics: []telegraf.Metric{
-			valueType:  telegraf.Counter,
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"host": "example.org",
+					},
+					map[string]interface{}{
+						"time_idle": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle{host="example.org"} 42
+`),
 		},
 		{
-			name: "field named counter is not added to metric name",
+			name: "prometheus untyped",
-			args: args{
+			output: &PrometheusClient{
-				measurement: "foo",
+				Listen:            ":0",
-				fields:      map[string]interface{}{"counter": 42},
+				MetricVersion:     1,
-				valueType:   telegraf.Counter,
+				CollectorsExclude: []string{"gocollector", "process"},
+				Path:              "/metrics",
+				Log:               testutil.Logger{},
 			},
-			metricName: "foo",
+			metrics: []telegraf.Metric{
-			valueType:  telegraf.Counter,
+				testutil.MustMetric(
+					"cpu_time_idle",
+					map[string]string{
+						"host": "example.org",
+					},
+					map[string]interface{}{
+						"value": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle{host="example.org"} 42
+`),
 		},
 		{
-			name: "field with any other name is added to metric name",
+			name: "prometheus counter",
-			args: args{
+			output: &PrometheusClient{
-				measurement: "foo",
+				Listen:            ":0",
-				fields:      map[string]interface{}{"other": 42},
+				MetricVersion:     1,
-				valueType:   telegraf.Counter,
+				CollectorsExclude: []string{"gocollector", "process"},
+				Path:              "/metrics",
+				Log:               testutil.Logger{},
 			},
-			metricName: "foo_other",
+			metrics: []telegraf.Metric{
-			valueType:  telegraf.Counter,
+				testutil.MustMetric(
+					"cpu_time_idle",
+					map[string]string{
+						"host": "example.org",
+					},
+					map[string]interface{}{
+						"counter": 42.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Counter,
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle counter
+cpu_time_idle{host="example.org"} 42
+`),
 		},
 		{
-			name: "uint64 fields are output",
+			name: "prometheus gauge",
-			args: args{
+			output: &PrometheusClient{
-				measurement: "foo",
+				Listen:            ":0",
-				fields:      map[string]interface{}{"value": uint64(42)},
+				MetricVersion:     1,
-				valueType:   telegraf.Counter,
+				CollectorsExclude: []string{"gocollector", "process"},
+				Path:              "/metrics",
+				Log:               testutil.Logger{},
 			},
-			metricName: "foo",
+			metrics: []telegraf.Metric{
-			valueType:  telegraf.Counter,
+				testutil.MustMetric(
+					"cpu_time_idle",
+					map[string]string{
+						"host": "example.org",
+					},
+					map[string]interface{}{
+						"gauge": 42.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Gauge,
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle gauge
+cpu_time_idle{host="example.org"} 42
+`),
+		},
+		{
+			name: "prometheus histogram",
+			output: &PrometheusClient{
+				Listen:            ":0",
+				MetricVersion:     1,
+				CollectorsExclude: []string{"gocollector", "process"},
+				Path:              "/metrics",
+				Log:               testutil.Logger{},
+			},
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"http_request_duration_seconds",
+					map[string]string{},
+					map[string]interface{}{
+						"sum":   53423,
+						"0.05":  24054,
+						"0.1":   33444,
+						"0.2":   100392,
+						"0.5":   129389,
+						"1":     133988,
+						"+Inf":  144320,
+						"count": 144320,
+					},
+					time.Unix(0, 0),
+					telegraf.Histogram,
+				),
+			},
+			expected: []byte(`
+# HELP http_request_duration_seconds Telegraf collected metric
+# TYPE http_request_duration_seconds histogram
+http_request_duration_seconds_bucket{le="0.05"} 24054
+http_request_duration_seconds_bucket{le="0.1"} 33444
+http_request_duration_seconds_bucket{le="0.2"} 100392
+http_request_duration_seconds_bucket{le="0.5"} 129389
+http_request_duration_seconds_bucket{le="1"} 133988
+http_request_duration_seconds_bucket{le="+Inf"} 144320
+http_request_duration_seconds_sum 53423
+http_request_duration_seconds_count 144320
+`),
+		},
+		{
+			name: "prometheus summary",
+			output: &PrometheusClient{
+				Listen:            ":0",
+				MetricVersion:     1,
+				CollectorsExclude: []string{"gocollector", "process"},
+				Path:              "/metrics",
+				Log:               testutil.Logger{},
+			},
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"rpc_duration_seconds",
+					map[string]string{},
+					map[string]interface{}{
+						"0.01":  3102,
+						"0.05":  3272,
+						"0.5":   4773,
+						"0.9":   9001,
+						"0.99":  76656,
+						"count": 2693,
+						"sum":   17560473,
+					},
+					time.Unix(0, 0),
+					telegraf.Summary,
+				),
+			},
+			expected: []byte(`
+# HELP rpc_duration_seconds Telegraf collected metric
+# TYPE rpc_duration_seconds summary
+rpc_duration_seconds{quantile="0.01"} 3102
+rpc_duration_seconds{quantile="0.05"} 3272
+rpc_duration_seconds{quantile="0.5"} 4773
+rpc_duration_seconds{quantile="0.9"} 9001
+rpc_duration_seconds{quantile="0.99"} 76656
+rpc_duration_seconds_sum 1.7560473e+07
+rpc_duration_seconds_count 2693
+`),
 		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			m, err := metric.New(
+			err := tt.output.Init()
-				tt.args.measurement,
+			require.NoError(t, err)
-				tt.args.tags,
-				tt.args.fields,
-				time.Now(),
-				tt.args.valueType,
-			)
-			client := NewClient()
-			err = client.Write([]telegraf.Metric{m})
-			require.Equal(t, tt.err, err)
 
-			fam, ok := client.fam[tt.metricName]
+			err = tt.output.Connect()
-			require.True(t, ok)
+			require.NoError(t, err)
-			require.Equal(t, tt.valueType, fam.TelegrafValueType)
+
+			defer func() {
+				err := tt.output.Close()
+				require.NoError(t, err)
+			}()
+
+			err = tt.output.Write(tt.metrics)
+			require.NoError(t, err)
+
+			resp, err := http.Get(tt.output.URL())
+			require.NoError(t, err)
+			require.Equal(t, http.StatusOK, resp.StatusCode)
+			defer resp.Body.Close()
+			body, err := ioutil.ReadAll(resp.Body)
+			require.NoError(t, err)
+
+			require.Equal(t,
+				strings.TrimSpace(string(tt.expected)),
+				strings.TrimSpace(string(body)))
 		})
 	}
 }
 
-func TestWrite_Sanitize(t *testing.T) {
+func TestMetricVersion2(t *testing.T) {
-	client := NewClient()
+	tests := []struct {
-
+		name     string
-	p1, err := metric.New(
+		output   *PrometheusClient
-		"foo.bar:colon",
+		metrics  []telegraf.Metric
-		map[string]string{"tag-with-dash": "localhost.local"},
+		expected []byte
-		map[string]interface{}{"field-with-dash-and:colon": 42},
-		time.Now(),
-		telegraf.Counter)
-	err = client.Write([]telegraf.Metric{p1})
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo_bar:colon_field_with_dash_and:colon"]
-	require.True(t, ok)
-	require.Equal(t, map[string]int{"tag_with_dash": 1}, fam.LabelSet)
-
-	sample1, ok := fam.Samples[CreateSampleID(p1.Tags())]
-	require.True(t, ok)
-
-	require.Equal(t, map[string]string{
-		"tag_with_dash": "localhost.local"}, sample1.Labels)
-}
-
-func TestWrite_Gauge(t *testing.T) {
-	type args struct {
-		measurement string
-		tags        map[string]string
-		fields      map[string]interface{}
-		valueType   telegraf.ValueType
-	}
-	var tests = []struct {
-		name       string
-		args       args
-		err        error
-		metricName string
-		valueType  telegraf.ValueType
 	}{
 		{
-			name: "field named value is not added to metric name",
+			name: "simple",
-			args: args{
+			output: &PrometheusClient{
-				measurement: "foo",
+				Listen:            ":0",
-				fields:      map[string]interface{}{"value": 42},
+				MetricVersion:     2,
-				valueType:   telegraf.Gauge,
+				CollectorsExclude: []string{"gocollector", "process"},
+				Path:              "/metrics",
+				Log:               testutil.Logger{},
 			},
-			metricName: "foo",
+			metrics: []telegraf.Metric{
-			valueType:  telegraf.Gauge,
+				testutil.MustMetric(
-		},
+					"cpu",
-		{
+					map[string]string{
-			name: "field named gauge is not added to metric name",
+						"host": "example.org",
-			args: args{
+					},
-				measurement: "foo",
+					map[string]interface{}{
-				fields:      map[string]interface{}{"gauge": 42},
+						"time_idle": 42.0,
-				valueType:   telegraf.Gauge,
+					},
+					time.Unix(0, 0),
+				),
 			},
-			metricName: "foo",
+			expected: []byte(`
-			valueType:  telegraf.Gauge,
+# HELP cpu_time_idle Telegraf collected metric
-		},
+# TYPE cpu_time_idle untyped
-		{
+cpu_time_idle{host="example.org"} 42
-			name: "field with any other name is added to metric name",
+`),
-			args: args{
-				measurement: "foo",
-				fields:      map[string]interface{}{"other": 42},
-				valueType:   telegraf.Gauge,
-			},
-			metricName: "foo_other",
-			valueType:  telegraf.Gauge,
-		},
-		{
-			name: "uint64 fields are output",
-			args: args{
-				measurement: "foo",
-				fields:      map[string]interface{}{"value": uint64(42)},
-				valueType:   telegraf.Counter,
-			},
-			metricName: "foo",
-			valueType:  telegraf.Counter,
 		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			m, err := metric.New(
+			err := tt.output.Init()
-				tt.args.measurement,
+			require.NoError(t, err)
-				tt.args.tags,
-				tt.args.fields,
-				time.Now(),
-				tt.args.valueType,
-			)
-			client := NewClient()
-			err = client.Write([]telegraf.Metric{m})
-			require.Equal(t, tt.err, err)
 
-			fam, ok := client.fam[tt.metricName]
+			err = tt.output.Connect()
-			require.True(t, ok)
+			require.NoError(t, err)
-			require.Equal(t, tt.valueType, fam.TelegrafValueType)
 
+			defer func() {
+				err := tt.output.Close()
+				require.NoError(t, err)
+			}()
+
+			err = tt.output.Write(tt.metrics)
+			require.NoError(t, err)
+
+			resp, err := http.Get(tt.output.URL())
+			require.NoError(t, err)
+			require.Equal(t, http.StatusOK, resp.StatusCode)
+			defer resp.Body.Close()
+			body, err := ioutil.ReadAll(resp.Body)
+			require.NoError(t, err)
+
+			require.Equal(t,
+				strings.TrimSpace(string(tt.expected)),
+				strings.TrimSpace(string(body)))
 		})
 	}
 }
-
-func TestWrite_Summary(t *testing.T) {
-	client := NewClient()
-
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"sum": 84, "count": 42, "0": 2, "0.5": 3, "1": 4},
-		time.Now(),
-		telegraf.Summary)
-
-	err = client.Write([]telegraf.Metric{p1})
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, 1, len(fam.Samples))
-
-	sample1, ok := fam.Samples[CreateSampleID(p1.Tags())]
-	require.True(t, ok)
-
-	require.Equal(t, 84.0, sample1.Sum)
-	require.Equal(t, uint64(42), sample1.Count)
-	require.Equal(t, 3, len(sample1.SummaryValue))
-}
-
-func TestWrite_Histogram(t *testing.T) {
-	client := NewClient()
-
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"sum": 84, "count": 42, "0": 2, "0.5": 3, "1": 4},
-		time.Now(),
-		telegraf.Histogram)
-
-	err = client.Write([]telegraf.Metric{p1})
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, 1, len(fam.Samples))
-
-	sample1, ok := fam.Samples[CreateSampleID(p1.Tags())]
-	require.True(t, ok)
-
-	require.Equal(t, 84.0, sample1.Sum)
-	require.Equal(t, uint64(42), sample1.Count)
-	require.Equal(t, 3, len(sample1.HistogramValue))
-}
-
-func TestWrite_MixedValueType(t *testing.T) {
-	now := time.Now()
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 1.0},
-		now,
-		telegraf.Counter)
-	p2, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 2.0},
-		now,
-		telegraf.Gauge)
-	var metrics = []telegraf.Metric{p1, p2}
-
-	client := NewClient()
-	err = client.Write(metrics)
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, 1, len(fam.Samples))
-}
-
-func TestWrite_MixedValueTypeUpgrade(t *testing.T) {
-	now := time.Now()
-	p1, err := metric.New(
-		"foo",
-		map[string]string{"a": "x"},
-		map[string]interface{}{"value": 1.0},
-		now,
-		telegraf.Untyped)
-	p2, err := metric.New(
-		"foo",
-		map[string]string{"a": "y"},
-		map[string]interface{}{"value": 2.0},
-		now,
-		telegraf.Gauge)
-	var metrics = []telegraf.Metric{p1, p2}
-
-	client := NewClient()
-	err = client.Write(metrics)
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, 2, len(fam.Samples))
-}
-
-func TestWrite_MixedValueTypeDowngrade(t *testing.T) {
-	now := time.Now()
-	p1, err := metric.New(
-		"foo",
-		map[string]string{"a": "x"},
-		map[string]interface{}{"value": 1.0},
-		now,
-		telegraf.Gauge)
-	p2, err := metric.New(
-		"foo",
-		map[string]string{"a": "y"},
-		map[string]interface{}{"value": 2.0},
-		now,
-		telegraf.Untyped)
-	var metrics = []telegraf.Metric{p1, p2}
-
-	client := NewClient()
-	err = client.Write(metrics)
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, 2, len(fam.Samples))
-}
-
-func TestWrite_Tags(t *testing.T) {
-	now := time.Now()
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 1.0},
-		now)
-	p2, err := metric.New(
-		"foo",
-		map[string]string{"host": "localhost"},
-		map[string]interface{}{"value": 2.0},
-		now)
-	var metrics = []telegraf.Metric{p1, p2}
-
-	client := NewClient()
-	err = client.Write(metrics)
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, telegraf.Untyped, fam.TelegrafValueType)
-
-	require.Equal(t, map[string]int{"host": 1}, fam.LabelSet)
-
-	sample1, ok := fam.Samples[CreateSampleID(p1.Tags())]
-	require.True(t, ok)
-
-	require.Equal(t, 1.0, sample1.Value)
-	require.True(t, now.Before(sample1.Expiration))
-
-	sample2, ok := fam.Samples[CreateSampleID(p2.Tags())]
-	require.True(t, ok)
-
-	require.Equal(t, 2.0, sample2.Value)
-	require.True(t, now.Before(sample2.Expiration))
-}
-
-func TestWrite_StringFields(t *testing.T) {
-	now := time.Now()
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 1.0, "status": "good"},
-		now,
-		telegraf.Counter)
-	p2, err := metric.New(
-		"bar",
-		make(map[string]string),
-		map[string]interface{}{"status": "needs numeric field"},
-		now,
-		telegraf.Gauge)
-	var metrics = []telegraf.Metric{p1, p2}
-
-	client := NewClient()
-	err = client.Write(metrics)
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, 1, fam.LabelSet["status"])
-
-	fam, ok = client.fam["bar"]
-	require.False(t, ok)
-}
-
-func TestDoNotWrite_StringFields(t *testing.T) {
-	now := time.Now()
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 1.0, "status": "good"},
-		now,
-		telegraf.Counter)
-	p2, err := metric.New(
-		"bar",
-		make(map[string]string),
-		map[string]interface{}{"status": "needs numeric field"},
-		now,
-		telegraf.Gauge)
-	var metrics = []telegraf.Metric{p1, p2}
-
-	client := &PrometheusClient{
-		ExpirationInterval: internal.Duration{Duration: time.Second * 60},
-		StringAsLabel:      false,
-		fam:                make(map[string]*MetricFamily),
-		now:                time.Now,
-	}
-
-	err = client.Write(metrics)
-	require.NoError(t, err)
-
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, 0, fam.LabelSet["status"])
-
-	fam, ok = client.fam["bar"]
-	require.False(t, ok)
-}
-
-func TestExpire(t *testing.T) {
-	client := NewClient()
-
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 1.0},
-		time.Now())
-	setUnixTime(client, 0)
-	err = client.Write([]telegraf.Metric{p1})
-	require.NoError(t, err)
-
-	p2, err := metric.New(
-		"bar",
-		make(map[string]string),
-		map[string]interface{}{"value": 2.0},
-		time.Now())
-	setUnixTime(client, 1)
-	err = client.Write([]telegraf.Metric{p2})
-
-	setUnixTime(client, 61)
-	require.Equal(t, 2, len(client.fam))
-	client.Expire()
-	require.Equal(t, 1, len(client.fam))
-}
-
-func TestExpire_TagsNoDecrement(t *testing.T) {
-	client := NewClient()
-
-	p1, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 1.0},
-		time.Now())
-	setUnixTime(client, 0)
-	err = client.Write([]telegraf.Metric{p1})
-	require.NoError(t, err)
-
-	p2, err := metric.New(
-		"foo",
-		map[string]string{"host": "localhost"},
-		map[string]interface{}{"value": 2.0},
-		time.Now())
-	setUnixTime(client, 1)
-	err = client.Write([]telegraf.Metric{p2})
-
-	setUnixTime(client, 61)
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, 2, len(fam.Samples))
-	client.Expire()
-	require.Equal(t, 1, len(fam.Samples))
-
-	require.Equal(t, map[string]int{"host": 1}, fam.LabelSet)
-}
-
-func TestExpire_TagsWithDecrement(t *testing.T) {
-	client := NewClient()
-
-	p1, err := metric.New(
-		"foo",
-		map[string]string{"host": "localhost"},
-		map[string]interface{}{"value": 1.0},
-		time.Now())
-	setUnixTime(client, 0)
-	err = client.Write([]telegraf.Metric{p1})
-	require.NoError(t, err)
-
-	p2, err := metric.New(
-		"foo",
-		make(map[string]string),
-		map[string]interface{}{"value": 2.0},
-		time.Now())
-	setUnixTime(client, 1)
-	err = client.Write([]telegraf.Metric{p2})
-
-	setUnixTime(client, 61)
-	fam, ok := client.fam["foo"]
-	require.True(t, ok)
-	require.Equal(t, 2, len(fam.Samples))
-	client.Expire()
-	require.Equal(t, 1, len(fam.Samples))
-
-	require.Equal(t, map[string]int{"host": 0}, fam.LabelSet)
-}
-
-var pTesting *PrometheusClient
-
-func TestPrometheusWritePointEmptyTag(t *testing.T) {
-	if testing.Short() {
-		t.Skip("Skipping integration test in short mode")
-	}
-
-	pClient, p, err := setupPrometheus()
-	require.NoError(t, err)
-	defer pClient.Close()
-
-	now := time.Now()
-	tags := make(map[string]string)
-	pt1, _ := metric.New(
-		"test_point_1",
-		tags,
-		map[string]interface{}{"value": 0.0},
-		now)
-	pt2, _ := metric.New(
-		"test_point_2",
-		tags,
-		map[string]interface{}{"value": 1.0},
-		now)
-	var metrics = []telegraf.Metric{
-		pt1,
-		pt2,
-	}
-	require.NoError(t, pClient.Write(metrics))
-
-	expected := []struct {
-		name  string
-		value float64
-		tags  map[string]string
-	}{
-		{"test_point_1", 0.0, tags},
-		{"test_point_2", 1.0, tags},
-	}
-
-	var acc testutil.Accumulator
-
-	require.NoError(t, p.Gather(&acc))
-	for _, e := range expected {
-		acc.AssertContainsFields(t, e.name,
-			map[string]interface{}{"value": e.value})
-	}
-
-	tags = make(map[string]string)
-	tags["testtag"] = "testvalue"
-	pt3, _ := metric.New(
-		"test_point_3",
-		tags,
-		map[string]interface{}{"value": 0.0},
-		now)
-	pt4, _ := metric.New(
-		"test_point_4",
-		tags,
-		map[string]interface{}{"value": 1.0},
-		now)
-	metrics = []telegraf.Metric{
-		pt3,
-		pt4,
-	}
-	require.NoError(t, pClient.Write(metrics))
-
-	expected2 := []struct {
-		name  string
-		value float64
-	}{
-		{"test_point_3", 0.0},
-		{"test_point_4", 1.0},
-	}
-
-	require.NoError(t, p.Gather(&acc))
-	for _, e := range expected2 {
-		acc.AssertContainsFields(t, e.name,
-			map[string]interface{}{"value": e.value})
-	}
-}
-
-func setupPrometheus() (*PrometheusClient, *prometheus_input.Prometheus, error) {
-	if pTesting == nil {
-		pTesting = NewClient()
-		pTesting.Listen = "localhost:9127"
-		pTesting.Path = "/metrics"
-		err := pTesting.Connect()
-		if err != nil {
-			return nil, nil, err
-		}
-	} else {
-		pTesting.fam = make(map[string]*MetricFamily)
-	}
-
-	time.Sleep(time.Millisecond * 200)
-
-	p := &prometheus_input.Prometheus{
-		URLs: []string{"http://localhost:9127/metrics"},
-	}
-
-	return pTesting, p, nil
-}

plugins/outputs/prometheus_client/v1/collector.go

@@ -0,0 +1,391 @@
+package v1
+
+import (
+	"fmt"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	invalidNameCharRE = regexp.MustCompile(`[^a-zA-Z0-9_:]`)
+	validNameCharRE   = regexp.MustCompile(`^[a-zA-Z_][a-zA-Z0-9_]*`)
+)
+
+// SampleID uniquely identifies a Sample
+type SampleID string
+
+// Sample represents the current value of a series.
+type Sample struct {
+	// Labels are the Prometheus labels.
+	Labels map[string]string
+	// Value is the value in the Prometheus output. Only one of these will populated.
+	Value          float64
+	HistogramValue map[float64]uint64
+	SummaryValue   map[float64]float64
+	// Histograms and Summaries need a count and a sum
+	Count uint64
+	Sum   float64
+	// Metric timestamp
+	Timestamp time.Time
+	// Expiration is the deadline that this Sample is valid until.
+	Expiration time.Time
+}
+
+// MetricFamily contains the data required to build valid prometheus Metrics.
+type MetricFamily struct {
+	// Samples are the Sample belonging to this MetricFamily.
+	Samples map[SampleID]*Sample
+	// Need the telegraf ValueType because there isn't a Prometheus ValueType
+	// representing Histogram or Summary
+	TelegrafValueType telegraf.ValueType
+	// LabelSet is the label counts for all Samples.
+	LabelSet map[string]int
+}
+
+type Collector struct {
+	ExpirationInterval time.Duration
+	StringAsLabel      bool
+	ExportTimestamp    bool
+	Log                telegraf.Logger
+
+	sync.Mutex
+	fam map[string]*MetricFamily
+}
+
+func NewCollector(expire time.Duration, stringsAsLabel bool, logger telegraf.Logger) *Collector {
+	return &Collector{
+		ExpirationInterval: expire,
+		StringAsLabel:      stringsAsLabel,
+		Log:                logger,
+		fam:                make(map[string]*MetricFamily),
+	}
+}
+
+func (c *Collector) Describe(ch chan<- *prometheus.Desc) {
+	prometheus.NewGauge(prometheus.GaugeOpts{Name: "Dummy", Help: "Dummy"}).Describe(ch)
+}
+
+func (c *Collector) Collect(ch chan<- prometheus.Metric) {
+	c.Lock()
+	defer c.Unlock()
+
+	c.Expire(time.Now(), c.ExpirationInterval)
+
+	for name, family := range c.fam {
+		// Get list of all labels on MetricFamily
+		var labelNames []string
+		for k, v := range family.LabelSet {
+			if v > 0 {
+				labelNames = append(labelNames, k)
+			}
+		}
+		desc := prometheus.NewDesc(name, "Telegraf collected metric", labelNames, nil)
+
+		for _, sample := range family.Samples {
+			// Get labels for this sample; unset labels will be set to the
+			// empty string
+			var labels []string
+			for _, label := range labelNames {
+				v := sample.Labels[label]
+				labels = append(labels, v)
+			}
+
+			var metric prometheus.Metric
+			var err error
+			switch family.TelegrafValueType {
+			case telegraf.Summary:
+				metric, err = prometheus.NewConstSummary(desc, sample.Count, sample.Sum, sample.SummaryValue, labels...)
+			case telegraf.Histogram:
+				metric, err = prometheus.NewConstHistogram(desc, sample.Count, sample.Sum, sample.HistogramValue, labels...)
+			default:
+				metric, err = prometheus.NewConstMetric(desc, getPromValueType(family.TelegrafValueType), sample.Value, labels...)
+			}
+			if err != nil {
+				c.Log.Errorf("Error creating prometheus metric: "+
+					"key: %s, labels: %v, err: %v",
+					name, labels, err)
+				continue
+			}
+
+			if c.ExportTimestamp {
+				metric = prometheus.NewMetricWithTimestamp(sample.Timestamp, metric)
+			}
+			ch <- metric
+		}
+	}
+}
+
+func sanitize(value string) string {
+	return invalidNameCharRE.ReplaceAllString(value, "_")
+}
+
+func isValidTagName(tag string) bool {
+	return validNameCharRE.MatchString(tag)
+}
+
+func getPromValueType(tt telegraf.ValueType) prometheus.ValueType {
+	switch tt {
+	case telegraf.Counter:
+		return prometheus.CounterValue
+	case telegraf.Gauge:
+		return prometheus.GaugeValue
+	default:
+		return prometheus.UntypedValue
+	}
+}
+
+// CreateSampleID creates a SampleID based on the tags of a telegraf.Metric.
+func CreateSampleID(tags map[string]string) SampleID {
+	pairs := make([]string, 0, len(tags))
+	for k, v := range tags {
+		pairs = append(pairs, fmt.Sprintf("%s=%s", k, v))
+	}
+	sort.Strings(pairs)
+	return SampleID(strings.Join(pairs, ","))
+}
+
+func addSample(fam *MetricFamily, sample *Sample, sampleID SampleID) {
+
+	for k := range sample.Labels {
+		fam.LabelSet[k]++
+	}
+
+	fam.Samples[sampleID] = sample
+}
+
+func (c *Collector) addMetricFamily(point telegraf.Metric, sample *Sample, mname string, sampleID SampleID) {
+	var fam *MetricFamily
+	var ok bool
+	if fam, ok = c.fam[mname]; !ok {
+		fam = &MetricFamily{
+			Samples:           make(map[SampleID]*Sample),
+			TelegrafValueType: point.Type(),
+			LabelSet:          make(map[string]int),
+		}
+		c.fam[mname] = fam
+	}
+
+	addSample(fam, sample, sampleID)
+}
+
+// Sorted returns a copy of the metrics in time ascending order.  A copy is
+// made to avoid modifying the input metric slice since doing so is not
+// allowed.
+func sorted(metrics []telegraf.Metric) []telegraf.Metric {
+	batch := make([]telegraf.Metric, 0, len(metrics))
+	for i := len(metrics) - 1; i >= 0; i-- {
+		batch = append(batch, metrics[i])
+	}
+	sort.Slice(batch, func(i, j int) bool {
+		return batch[i].Time().Before(batch[j].Time())
+	})
+	return batch
+}
+
+func (c *Collector) Add(metrics []telegraf.Metric) error {
+	c.Lock()
+	defer c.Unlock()
+
+	now := time.Now()
+
+	for _, point := range sorted(metrics) {
+		tags := point.Tags()
+		sampleID := CreateSampleID(tags)
+
+		labels := make(map[string]string)
+		for k, v := range tags {
+			tName := sanitize(k)
+			if !isValidTagName(tName) {
+				continue
+			}
+			labels[tName] = v
+		}
+
+		// Prometheus doesn't have a string value type, so convert string
+		// fields to labels if enabled.
+		if c.StringAsLabel {
+			for fn, fv := range point.Fields() {
+				switch fv := fv.(type) {
+				case string:
+					tName := sanitize(fn)
+					if !isValidTagName(tName) {
+						continue
+					}
+					labels[tName] = fv
+				}
+			}
+		}
+
+		switch point.Type() {
+		case telegraf.Summary:
+			var mname string
+			var sum float64
+			var count uint64
+			summaryvalue := make(map[float64]float64)
+			for fn, fv := range point.Fields() {
+				var value float64
+				switch fv := fv.(type) {
+				case int64:
+					value = float64(fv)
+				case uint64:
+					value = float64(fv)
+				case float64:
+					value = fv
+				default:
+					continue
+				}
+
+				switch fn {
+				case "sum":
+					sum = value
+				case "count":
+					count = uint64(value)
+				default:
+					limit, err := strconv.ParseFloat(fn, 64)
+					if err == nil {
+						summaryvalue[limit] = value
+					}
+				}
+			}
+			sample := &Sample{
+				Labels:       labels,
+				SummaryValue: summaryvalue,
+				Count:        count,
+				Sum:          sum,
+				Timestamp:    point.Time(),
+				Expiration:   now.Add(c.ExpirationInterval),
+			}
+			mname = sanitize(point.Name())
+
+			if !isValidTagName(mname) {
+				continue
+			}
+
+			c.addMetricFamily(point, sample, mname, sampleID)
+
+		case telegraf.Histogram:
+			var mname string
+			var sum float64
+			var count uint64
+			histogramvalue := make(map[float64]uint64)
+			for fn, fv := range point.Fields() {
+				var value float64
+				switch fv := fv.(type) {
+				case int64:
+					value = float64(fv)
+				case uint64:
+					value = float64(fv)
+				case float64:
+					value = fv
+				default:
+					continue
+				}
+
+				switch fn {
+				case "sum":
+					sum = value
+				case "count":
+					count = uint64(value)
+				default:
+					limit, err := strconv.ParseFloat(fn, 64)
+					if err == nil {
+						histogramvalue[limit] = uint64(value)
+					}
+				}
+			}
+			sample := &Sample{
+				Labels:         labels,
+				HistogramValue: histogramvalue,
+				Count:          count,
+				Sum:            sum,
+				Timestamp:      point.Time(),
+				Expiration:     now.Add(c.ExpirationInterval),
+			}
+			mname = sanitize(point.Name())
+
+			if !isValidTagName(mname) {
+				continue
+			}
+
+			c.addMetricFamily(point, sample, mname, sampleID)
+
+		default:
+			for fn, fv := range point.Fields() {
+				// Ignore string and bool fields.
+				var value float64
+				switch fv := fv.(type) {
+				case int64:
+					value = float64(fv)
+				case uint64:
+					value = float64(fv)
+				case float64:
+					value = fv
+				default:
+					continue
+				}
+
+				sample := &Sample{
+					Labels:     labels,
+					Value:      value,
+					Timestamp:  point.Time(),
+					Expiration: now.Add(c.ExpirationInterval),
+				}
+
+				// Special handling of value field; supports passthrough from
+				// the prometheus input.
+				var mname string
+				switch point.Type() {
+				case telegraf.Counter:
+					if fn == "counter" {
+						mname = sanitize(point.Name())
+					}
+				case telegraf.Gauge:
+					if fn == "gauge" {
+						mname = sanitize(point.Name())
+					}
+				}
+				if mname == "" {
+					if fn == "value" {
+						mname = sanitize(point.Name())
+					} else {
+						mname = sanitize(fmt.Sprintf("%s_%s", point.Name(), fn))
+					}
+				}
+				if !isValidTagName(mname) {
+					continue
+				}
+				c.addMetricFamily(point, sample, mname, sampleID)
+
+			}
+		}
+	}
+	return nil
+}
+
+func (c *Collector) Expire(now time.Time, age time.Duration) {
+	if age == 0 {
+		return
+	}
+
+	for name, family := range c.fam {
+		for key, sample := range family.Samples {
+			if age != 0 && now.After(sample.Expiration) {
+				for k := range sample.Labels {
+					family.LabelSet[k]--
+				}
+				delete(family.Samples, key)
+
+				if len(family.Samples) == 0 {
+					delete(c.fam, name)
+				}
+			}
+		}
+	}
+}

plugins/outputs/prometheus_client/v2/collector.go

@@ -0,0 +1,87 @@
+package v2
+
+import (
+	"sync"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	serializer "github.com/influxdata/telegraf/plugins/serializers/prometheus"
+	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
+)
+
+type Metric struct {
+	family *dto.MetricFamily
+	metric *dto.Metric
+}
+
+func (m *Metric) Desc() *prometheus.Desc {
+	labelNames := make([]string, 0, len(m.metric.Label))
+	for _, label := range m.metric.Label {
+		labelNames = append(labelNames, *label.Name)
+	}
+
+	desc := prometheus.NewDesc(*m.family.Name, *m.family.Help, labelNames, nil)
+
+	return desc
+}
+
+func (m *Metric) Write(out *dto.Metric) error {
+	out.Label = m.metric.Label
+	out.Counter = m.metric.Counter
+	out.Untyped = m.metric.Untyped
+	out.Gauge = m.metric.Gauge
+	out.Histogram = m.metric.Histogram
+	out.Summary = m.metric.Summary
+	out.TimestampMs = m.metric.TimestampMs
+	return nil
+}
+
+type Collector struct {
+	sync.Mutex
+	expireDuration time.Duration
+	coll           *serializer.Collection
+}
+
+func NewCollector(expire time.Duration, stringsAsLabel bool) *Collector {
+	config := serializer.FormatConfig{}
+	if stringsAsLabel {
+		config.StringHandling = serializer.StringAsLabel
+	}
+	return &Collector{
+		expireDuration: expire,
+		coll:           serializer.NewCollection(config),
+	}
+}
+
+func (c *Collector) Describe(ch chan<- *prometheus.Desc) {
+	// Sending no descriptor at all marks the Collector as "unchecked",
+	// i.e. no checks will be performed at registration time, and the
+	// Collector may yield any Metric it sees fit in its Collect method.
+	return
+}
+
+func (c *Collector) Collect(ch chan<- prometheus.Metric) {
+	c.Lock()
+	defer c.Unlock()
+
+	for _, family := range c.coll.GetProto() {
+		for _, metric := range family.Metric {
+			ch <- &Metric{family: family, metric: metric}
+		}
+	}
+}
+
+func (c *Collector) Add(metrics []telegraf.Metric) error {
+	c.Lock()
+	defer c.Unlock()
+
+	for _, metric := range metrics {
+		c.coll.Add(metric)
+	}
+
+	if c.expireDuration != 0 {
+		c.coll.Expire(time.Now(), c.expireDuration)
+	}
+	return nil
+}

plugins/serializers/prometheus/README.md

@@ -0,0 +1,68 @@
+# Prometheus
+
+The `prometheus` data format converts metrics into the Prometheus text
+exposition format.  When used with the `prometheus` input, the input should be
+use the `metric_version = 2` option in order to properly round trip metrics.
+
+**Warning**: When generating histogram and summary types, output may
+not be correct if the metric spans multiple batches.  This issue can be
+somewhat, but not fully, mitigated by using outputs that support writing in
+"batch format".  When using histogram and summary types, it is recommended to
+use only the `prometheus_client` output.
+
+## Configuration
+
+```toml
+[[outputs.file]]
+  files = ["stdout"]
+  use_batch_format = true
+
+  ## Include the metric timestamp on each sample.
+  prometheus_export_timestamp = false
+
+  ## Sort prometheus metric families and metric samples.  Useful for
+  ## debugging.
+  prometheus_sort_metrics = false
+
+  ## Output string fields as metric labels; when false string fields are
+  ## discarded.
+  prometheus_string_as_label = false
+
+  ## Data format to output.
+  ## Each data format has its own unique set of configuration options, read
+  ## more about them here:
+  ##   https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md
+  data_format = "prometheus"
+```
+
+### Example
+
+**Example Input**
+```
+cpu,cpu=cpu0 time_guest=8022.6,time_system=26145.98,time_user=92512.89 1574317740000000000
+cpu,cpu=cpu1 time_guest=8097.88,time_system=25223.35,time_user=96519.58 1574317740000000000
+cpu,cpu=cpu2 time_guest=7386.28,time_system=24870.37,time_user=95631.59 1574317740000000000
+cpu,cpu=cpu3 time_guest=7434.19,time_system=24843.71,time_user=93753.88 1574317740000000000
+```
+
+**Example Output**
+```
+# HELP cpu_time_guest Telegraf collected metric
+# TYPE cpu_time_guest counter
+cpu_time_guest{cpu="cpu0"} 9582.54
+cpu_time_guest{cpu="cpu1"} 9660.88
+cpu_time_guest{cpu="cpu2"} 8946.45
+cpu_time_guest{cpu="cpu3"} 9002.31
+# HELP cpu_time_system Telegraf collected metric
+# TYPE cpu_time_system counter
+cpu_time_system{cpu="cpu0"} 28675.47
+cpu_time_system{cpu="cpu1"} 27779.34
+cpu_time_system{cpu="cpu2"} 27406.18
+cpu_time_system{cpu="cpu3"} 27404.97
+# HELP cpu_time_user Telegraf collected metric
+# TYPE cpu_time_user counter
+cpu_time_user{cpu="cpu0"} 99551.84
+cpu_time_user{cpu="cpu1"} 103468.52
+cpu_time_user{cpu="cpu2"} 102591.45
+cpu_time_user{cpu="cpu3"} 100717.05
+```

plugins/serializers/prometheus/collection.go

@@ -0,0 +1,464 @@
+package prometheus
+
+import (
+	"hash/fnv"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/gogo/protobuf/proto"
+	"github.com/influxdata/telegraf"
+	dto "github.com/prometheus/client_model/go"
+)
+
+const helpString = "Telegraf collected metric"
+
+type MetricFamily struct {
+	Name string
+	Type telegraf.ValueType
+}
+
+type Metric struct {
+	Labels    []LabelPair
+	Time      time.Time
+	Scaler    *Scaler
+	Histogram *Histogram
+	Summary   *Summary
+}
+
+type LabelPair struct {
+	Name  string
+	Value string
+}
+
+type Scaler struct {
+	Value float64
+}
+
+type Bucket struct {
+	Bound float64
+	Count uint64
+}
+
+type Quantile struct {
+	Quantile float64
+	Value    float64
+}
+
+type Histogram struct {
+	Buckets []Bucket
+	Count   uint64
+	Sum     float64
+}
+
+type Summary struct {
+	Quantiles []Quantile
+	Count     uint64
+	Sum       float64
+}
+
+type MetricKey uint64
+
+func MakeMetricKey(labels []LabelPair) MetricKey {
+	h := fnv.New64a()
+	for _, label := range labels {
+		h.Write([]byte(label.Name))
+		h.Write([]byte("\x00"))
+		h.Write([]byte(label.Value))
+		h.Write([]byte("\x00"))
+	}
+	return MetricKey(h.Sum64())
+}
+
+type Entry struct {
+	Family  MetricFamily
+	Metrics map[MetricKey]*Metric
+}
+
+type Collection struct {
+	config  FormatConfig
+	Entries map[MetricFamily]Entry
+}
+
+func NewCollection(config FormatConfig) *Collection {
+	cache := &Collection{
+		config:  config,
+		Entries: make(map[MetricFamily]Entry),
+	}
+	return cache
+}
+
+func hasLabel(name string, labels []LabelPair) bool {
+	for _, label := range labels {
+		if name == label.Name {
+			return true
+		}
+	}
+	return false
+}
+
+func (c *Collection) createLabels(metric telegraf.Metric) []LabelPair {
+	labels := make([]LabelPair, 0, len(metric.TagList()))
+	for _, tag := range metric.TagList() {
+		// Ignore special tags for histogram and summary types.
+		switch metric.Type() {
+		case telegraf.Histogram:
+			if tag.Key == "le" {
+				continue
+			}
+		case telegraf.Summary:
+			if tag.Key == "quantile" {
+				continue
+			}
+		}
+
+		name, ok := SanitizeName(tag.Key)
+		if !ok {
+			continue
+		}
+
+		labels = append(labels, LabelPair{Name: name, Value: tag.Value})
+	}
+
+	if c.config.StringHandling != StringAsLabel {
+		return labels
+	}
+
+	addedFieldLabel := false
+	for _, field := range metric.FieldList() {
+		value, ok := field.Value.(string)
+		if !ok {
+			continue
+		}
+
+		name, ok := SanitizeName(field.Key)
+		if !ok {
+			continue
+		}
+
+		// If there is a tag with the same name as the string field, discard
+		// the field and use the tag instead.
+		if hasLabel(name, labels) {
+			continue
+		}
+
+		labels = append(labels, LabelPair{Name: name, Value: value})
+		addedFieldLabel = true
+
+	}
+
+	if addedFieldLabel {
+		sort.Slice(labels, func(i, j int) bool {
+			return labels[i].Name < labels[j].Name
+		})
+	}
+
+	return labels
+}
+
+func (c *Collection) Add(metric telegraf.Metric) {
+	labels := c.createLabels(metric)
+	for _, field := range metric.FieldList() {
+		metricName := MetricName(metric.Name(), field.Key, metric.Type())
+		metricName, ok := SanitizeName(metricName)
+		if !ok {
+			continue
+		}
+
+		family := MetricFamily{
+			Name: metricName,
+			Type: metric.Type(),
+		}
+
+		entry, ok := c.Entries[family]
+		if !ok {
+			entry = Entry{
+				Family:  family,
+				Metrics: make(map[MetricKey]*Metric),
+			}
+			c.Entries[family] = entry
+
+		}
+
+		metricKey := MakeMetricKey(labels)
+
+		m, ok := entry.Metrics[metricKey]
+		if ok {
+			// A batch of metrics can contain multiple values for a single
+			// Prometheus sample.  If this metric is older than the existing
+			// sample then we can skip over it.
+			if metric.Time().Before(m.Time) {
+				continue
+			}
+		}
+
+		switch metric.Type() {
+		case telegraf.Counter:
+			fallthrough
+		case telegraf.Gauge:
+			fallthrough
+		case telegraf.Untyped:
+			value, ok := SampleValue(field.Value)
+			if !ok {
+				continue
+			}
+
+			m = &Metric{
+				Labels: labels,
+				Time:   metric.Time(),
+				Scaler: &Scaler{Value: value},
+			}
+
+			// what if already here
+			entry.Metrics[metricKey] = m
+		case telegraf.Histogram:
+			if m == nil {
+				m = &Metric{
+					Labels:    labels,
+					Time:      metric.Time(),
+					Histogram: &Histogram{},
+				}
+			}
+			switch {
+			case strings.HasSuffix(field.Key, "_bucket"):
+				le, ok := metric.GetTag("le")
+				if !ok {
+					continue
+				}
+				bound, err := strconv.ParseFloat(le, 64)
+				if err != nil {
+					continue
+				}
+
+				count, ok := SampleCount(field.Value)
+				if !ok {
+					continue
+				}
+
+				m.Histogram.Buckets = append(m.Histogram.Buckets, Bucket{
+					Bound: bound,
+					Count: count,
+				})
+			case strings.HasSuffix(field.Key, "_sum"):
+				sum, ok := SampleSum(field.Value)
+				if !ok {
+					continue
+				}
+
+				m.Histogram.Sum = sum
+			case strings.HasSuffix(field.Key, "_count"):
+				count, ok := SampleCount(field.Value)
+				if !ok {
+					continue
+				}
+
+				m.Histogram.Count = count
+			default:
+				continue
+			}
+
+			entry.Metrics[metricKey] = m
+		case telegraf.Summary:
+			if m == nil {
+				m = &Metric{
+					Labels:  labels,
+					Time:    metric.Time(),
+					Summary: &Summary{},
+				}
+			}
+			switch {
+			case strings.HasSuffix(field.Key, "_sum"):
+				sum, ok := SampleSum(field.Value)
+				if !ok {
+					continue
+				}
+
+				m.Summary.Sum = sum
+			case strings.HasSuffix(field.Key, "_count"):
+				count, ok := SampleCount(field.Value)
+				if !ok {
+					continue
+				}
+
+				m.Summary.Count = count
+			default:
+				quantileTag, ok := metric.GetTag("quantile")
+				if !ok {
+					continue
+				}
+				quantile, err := strconv.ParseFloat(quantileTag, 64)
+				if err != nil {
+					continue
+				}
+
+				value, ok := SampleValue(field.Value)
+				if !ok {
+					continue
+				}
+
+				m.Summary.Quantiles = append(m.Summary.Quantiles, Quantile{
+					Quantile: quantile,
+					Value:    value,
+				})
+			}
+
+			entry.Metrics[metricKey] = m
+		}
+	}
+}
+
+func (c *Collection) Expire(now time.Time, age time.Duration) {
+	expireTime := now.Add(-age)
+	for _, entry := range c.Entries {
+		for key, metric := range entry.Metrics {
+			if metric.Time.Before(expireTime) {
+				delete(entry.Metrics, key)
+				if len(entry.Metrics) == 0 {
+					delete(c.Entries, entry.Family)
+				}
+			}
+		}
+	}
+}
+
+func (c *Collection) GetEntries(order MetricSortOrder) []Entry {
+	entries := make([]Entry, 0, len(c.Entries))
+	for _, entry := range c.Entries {
+		entries = append(entries, entry)
+	}
+
+	switch order {
+	case SortMetrics:
+		sort.Slice(entries, func(i, j int) bool {
+			lhs := entries[i].Family
+			rhs := entries[j].Family
+			if lhs.Name != rhs.Name {
+				return lhs.Name < rhs.Name
+			}
+
+			return lhs.Type < rhs.Type
+		})
+	}
+	return entries
+}
+
+func (c *Collection) GetMetrics(entry Entry, order MetricSortOrder) []*Metric {
+	metrics := make([]*Metric, 0, len(entry.Metrics))
+	for _, metric := range entry.Metrics {
+		metrics = append(metrics, metric)
+	}
+
+	switch order {
+	case SortMetrics:
+		sort.Slice(metrics, func(i, j int) bool {
+			lhs := metrics[i].Labels
+			rhs := metrics[j].Labels
+			if len(lhs) != len(rhs) {
+				return len(lhs) < len(rhs)
+			}
+
+			for index := range lhs {
+				l := lhs[index]
+				r := rhs[index]
+
+				if l.Name != r.Name {
+					return l.Name < r.Name
+				}
+
+				if l.Value != r.Value {
+					return l.Value < r.Value
+				}
+			}
+
+			return false
+		})
+	}
+
+	return metrics
+}
+
+func (c *Collection) GetProto() []*dto.MetricFamily {
+	result := make([]*dto.MetricFamily, 0, len(c.Entries))
+
+	for _, entry := range c.GetEntries(c.config.MetricSortOrder) {
+		mf := &dto.MetricFamily{
+			Name: proto.String(entry.Family.Name),
+			Help: proto.String(helpString),
+			Type: MetricType(entry.Family.Type),
+		}
+
+		for _, metric := range c.GetMetrics(entry, c.config.MetricSortOrder) {
+			l := make([]*dto.LabelPair, 0, len(metric.Labels))
+			for _, label := range metric.Labels {
+				l = append(l, &dto.LabelPair{
+					Name:  proto.String(label.Name),
+					Value: proto.String(label.Value),
+				})
+			}
+
+			m := &dto.Metric{
+				Label: l,
+			}
+
+			if c.config.TimestampExport == ExportTimestamp {
+				m.TimestampMs = proto.Int64(metric.Time.UnixNano() / int64(time.Millisecond))
+			}
+
+			switch entry.Family.Type {
+			case telegraf.Gauge:
+				m.Gauge = &dto.Gauge{Value: proto.Float64(metric.Scaler.Value)}
+			case telegraf.Counter:
+				m.Counter = &dto.Counter{Value: proto.Float64(metric.Scaler.Value)}
+			case telegraf.Untyped:
+				m.Untyped = &dto.Untyped{Value: proto.Float64(metric.Scaler.Value)}
+			case telegraf.Histogram:
+				buckets := make([]*dto.Bucket, 0, len(metric.Histogram.Buckets))
+				for _, bucket := range metric.Histogram.Buckets {
+					buckets = append(buckets, &dto.Bucket{
+						UpperBound:      proto.Float64(bucket.Bound),
+						CumulativeCount: proto.Uint64(bucket.Count),
+					})
+				}
+
+				if len(buckets) == 0 {
+					continue
+				}
+
+				m.Histogram = &dto.Histogram{
+					Bucket:      buckets,
+					SampleCount: proto.Uint64(metric.Histogram.Count),
+					SampleSum:   proto.Float64(metric.Histogram.Sum),
+				}
+			case telegraf.Summary:
+				quantiles := make([]*dto.Quantile, 0, len(metric.Summary.Quantiles))
+				for _, quantile := range metric.Summary.Quantiles {
+					quantiles = append(quantiles, &dto.Quantile{
+						Quantile: proto.Float64(quantile.Quantile),
+						Value:    proto.Float64(quantile.Value),
+					})
+				}
+
+				if len(quantiles) == 0 {
+					continue
+				}
+
+				m.Summary = &dto.Summary{
+					Quantile:    quantiles,
+					SampleCount: proto.Uint64(metric.Summary.Count),
+					SampleSum:   proto.Float64(metric.Summary.Sum),
+				}
+			default:
+				panic("unknown telegraf.ValueType")
+			}
+
+			mf.Metric = append(mf.Metric, m)
+		}
+
+		if len(mf.Metric) != 0 {
+			result = append(result, mf)
+		}
+	}
+
+	return result
+}

plugins/serializers/prometheus/collection_test.go

@@ -0,0 +1,116 @@
+package prometheus
+
+import (
+	"testing"
+	"time"
+
+	"github.com/gogo/protobuf/proto"
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/testutil"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCollectionExpire(t *testing.T) {
+	tests := []struct {
+		name     string
+		now      time.Time
+		age      time.Duration
+		metrics  []telegraf.Metric
+		expected []*dto.MetricFamily
+	}{
+		{
+			name: "not expired",
+			now:  time.Unix(1, 0),
+			age:  10 * time.Second,
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"time_idle": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []*dto.MetricFamily{
+				{
+					Name: proto.String("cpu_time_idle"),
+					Help: proto.String(helpString),
+					Type: dto.MetricType_UNTYPED.Enum(),
+					Metric: []*dto.Metric{
+						{
+							Label:   []*dto.LabelPair{},
+							Untyped: &dto.Untyped{Value: proto.Float64(42.0)},
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "expired single metric in metric family",
+			now:  time.Unix(20, 0),
+			age:  10 * time.Second,
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"time_idle": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []*dto.MetricFamily{},
+		},
+		{
+			name: "expired one metric in metric family",
+			now:  time.Unix(20, 0),
+			age:  10 * time.Second,
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"time_idle": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"time_guest": 42.0,
+					},
+					time.Unix(15, 0),
+				),
+			},
+			expected: []*dto.MetricFamily{
+				{
+					Name: proto.String("cpu_time_guest"),
+					Help: proto.String(helpString),
+					Type: dto.MetricType_UNTYPED.Enum(),
+					Metric: []*dto.Metric{
+						{
+							Label:   []*dto.LabelPair{},
+							Untyped: &dto.Untyped{Value: proto.Float64(42.0)},
+						},
+					},
+				},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			c := NewCollection(FormatConfig{})
+			for _, metric := range tt.metrics {
+				c.Add(metric)
+			}
+			c.Expire(tt.now, tt.age)
+
+			actual := c.GetProto()
+
+			require.Equal(t, tt.expected, actual)
+		})
+	}
+}

plugins/serializers/prometheus/convert.go

@@ -0,0 +1,175 @@
+package prometheus
+
+import (
+	"strings"
+	"unicode"
+
+	"github.com/influxdata/telegraf"
+	dto "github.com/prometheus/client_model/go"
+)
+
+var FirstTable = &unicode.RangeTable{
+	R16: []unicode.Range16{
+		{0x0041, 0x005A, 1}, // A-Z
+		{0x005F, 0x005F, 1}, // _
+		{0x0061, 0x007A, 1}, // a-z
+	},
+	LatinOffset: 3,
+}
+
+var RestTable = &unicode.RangeTable{
+	R16: []unicode.Range16{
+		{0x0030, 0x0039, 1}, // 0-9
+		{0x0041, 0x005A, 1}, // A-Z
+		{0x005F, 0x005F, 1}, // _
+		{0x0061, 0x007A, 1}, // a-z
+	},
+	LatinOffset: 4,
+}
+
+func isValid(name string) bool {
+	if name == "" {
+		return false
+	}
+
+	for i, r := range name {
+		switch {
+		case i == 0:
+			if !unicode.In(r, FirstTable) {
+				return false
+			}
+		default:
+			if !unicode.In(r, RestTable) {
+				return false
+			}
+		}
+	}
+
+	return true
+}
+
+// SanitizeName check if the name is a valid Prometheus metric name and label
+// name.  If not, it attempts to replaces invalid runes with an underscore to
+// create a valid name.  Returns the metric name and true if the name is valid
+// to use.
+func SanitizeName(name string) (string, bool) {
+	if isValid(name) {
+		return name, true
+	}
+
+	var b strings.Builder
+
+	for i, r := range name {
+		switch {
+		case i == 0:
+			if unicode.In(r, FirstTable) {
+				b.WriteRune(r)
+			}
+		default:
+			if unicode.In(r, RestTable) {
+				b.WriteRune(r)
+			} else {
+				b.WriteString("_")
+			}
+		}
+	}
+
+	name = strings.Trim(b.String(), "_")
+	if name == "" {
+		return "", false
+	}
+
+	return name, true
+}
+
+// MetricName returns the Prometheus metric name.
+func MetricName(measurement, fieldKey string, valueType telegraf.ValueType) string {
+	switch valueType {
+	case telegraf.Histogram, telegraf.Summary:
+		switch {
+		case strings.HasSuffix(fieldKey, "_bucket"):
+			fieldKey = strings.TrimSuffix(fieldKey, "_bucket")
+		case strings.HasSuffix(fieldKey, "_sum"):
+			fieldKey = strings.TrimSuffix(fieldKey, "_sum")
+		case strings.HasSuffix(fieldKey, "_count"):
+			fieldKey = strings.TrimSuffix(fieldKey, "_count")
+		}
+	}
+
+	if measurement == "prometheus" {
+		return fieldKey
+	}
+	return measurement + "_" + fieldKey
+}
+
+func MetricType(valueType telegraf.ValueType) *dto.MetricType {
+	switch valueType {
+	case telegraf.Counter:
+		return dto.MetricType_COUNTER.Enum()
+	case telegraf.Gauge:
+		return dto.MetricType_GAUGE.Enum()
+	case telegraf.Summary:
+		return dto.MetricType_SUMMARY.Enum()
+	case telegraf.Untyped:
+		return dto.MetricType_UNTYPED.Enum()
+	case telegraf.Histogram:
+		return dto.MetricType_HISTOGRAM.Enum()
+	default:
+		panic("unknown telegraf.ValueType")
+	}
+}
+
+// SampleValue converts a field value into a value suitable for a simple sample value.
+func SampleValue(value interface{}) (float64, bool) {
+	switch v := value.(type) {
+	case float64:
+		return v, true
+	case int64:
+		return float64(v), true
+	case uint64:
+		return float64(v), true
+	case bool:
+		if v {
+			return 1.0, true
+		}
+		return 0.0, true
+	default:
+		return 0, false
+	}
+}
+
+// SampleCount converts a field value into a count suitable for a metric family
+// of the Histogram or Summary type.
+func SampleCount(value interface{}) (uint64, bool) {
+	switch v := value.(type) {
+	case float64:
+		if v < 0 {
+			return 0, false
+		}
+		return uint64(v), true
+	case int64:
+		if v < 0 {
+			return 0, false
+		}
+		return uint64(v), true
+	case uint64:
+		return v, true
+	default:
+		return 0, false
+	}
+}
+
+// SampleSum converts a field value into a sum suitable for a metric family
+// of the Histogram or Summary type.
+func SampleSum(value interface{}) (float64, bool) {
+	switch v := value.(type) {
+	case float64:
+		return v, true
+	case int64:
+		return float64(v), true
+	case uint64:
+		return float64(v), true
+	default:
+		return 0, false
+	}
+}

plugins/serializers/prometheus/prometheus.go

@@ -0,0 +1,69 @@
+package prometheus
+
+import (
+	"bytes"
+
+	"github.com/influxdata/telegraf"
+	"github.com/prometheus/common/expfmt"
+)
+
+// TimestampExport controls if the output contains timestamps.
+type TimestampExport int
+
+const (
+	NoExportTimestamp TimestampExport = iota
+	ExportTimestamp
+)
+
+// MetricSortOrder controls if the output is sorted.
+type MetricSortOrder int
+
+const (
+	NoSortMetrics MetricSortOrder = iota
+	SortMetrics
+)
+
+// StringHandling defines how to process string fields.
+type StringHandling int
+
+const (
+	DiscardStrings StringHandling = iota
+	StringAsLabel
+)
+
+type FormatConfig struct {
+	TimestampExport TimestampExport
+	MetricSortOrder MetricSortOrder
+	StringHandling  StringHandling
+}
+
+type Serializer struct {
+	config FormatConfig
+}
+
+func NewSerializer(config FormatConfig) (*Serializer, error) {
+	s := &Serializer{config: config}
+	return s, nil
+}
+
+func (s *Serializer) Serialize(metric telegraf.Metric) ([]byte, error) {
+	return s.SerializeBatch([]telegraf.Metric{metric})
+}
+
+func (s *Serializer) SerializeBatch(metrics []telegraf.Metric) ([]byte, error) {
+	coll := NewCollection(s.config)
+	for _, metric := range metrics {
+		coll.Add(metric)
+	}
+
+	var buf bytes.Buffer
+	for _, mf := range coll.GetProto() {
+		enc := expfmt.NewEncoder(&buf, expfmt.FmtText)
+		err := enc.Encode(mf)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return buf.Bytes(), nil
+}

plugins/serializers/prometheus/prometheus_test.go

@@ -0,0 +1,589 @@
+package prometheus
+
+import (
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/testutil"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSerialize(t *testing.T) {
+	tests := []struct {
+		name     string
+		config   FormatConfig
+		metric   telegraf.Metric
+		expected []byte
+	}{
+		{
+			name: "simple",
+			metric: testutil.MustMetric(
+				"cpu",
+				map[string]string{
+					"host": "example.org",
+				},
+				map[string]interface{}{
+					"time_idle": 42.0,
+				},
+				time.Unix(0, 0),
+			),
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle{host="example.org"} 42
+`),
+		},
+		{
+			name: "prometheus input untyped",
+			metric: testutil.MustMetric(
+				"prometheus",
+				map[string]string{
+					"code":   "400",
+					"method": "post",
+				},
+				map[string]interface{}{
+					"http_requests_total": 3.0,
+				},
+				time.Unix(0, 0),
+				telegraf.Untyped,
+			),
+			expected: []byte(`
+# HELP http_requests_total Telegraf collected metric
+# TYPE http_requests_total untyped
+http_requests_total{code="400",method="post"} 3
+`),
+		},
+		{
+			name: "prometheus input counter",
+			metric: testutil.MustMetric(
+				"prometheus",
+				map[string]string{
+					"code":   "400",
+					"method": "post",
+				},
+				map[string]interface{}{
+					"http_requests_total": 3.0,
+				},
+				time.Unix(0, 0),
+				telegraf.Counter,
+			),
+			expected: []byte(`
+# HELP http_requests_total Telegraf collected metric
+# TYPE http_requests_total counter
+http_requests_total{code="400",method="post"} 3
+`),
+		},
+		{
+			name: "prometheus input gauge",
+			metric: testutil.MustMetric(
+				"prometheus",
+				map[string]string{
+					"code":   "400",
+					"method": "post",
+				},
+				map[string]interface{}{
+					"http_requests_total": 3.0,
+				},
+				time.Unix(0, 0),
+				telegraf.Gauge,
+			),
+			expected: []byte(`
+# HELP http_requests_total Telegraf collected metric
+# TYPE http_requests_total gauge
+http_requests_total{code="400",method="post"} 3
+`),
+		},
+		{
+			name: "prometheus input histogram no buckets",
+			metric: testutil.MustMetric(
+				"prometheus",
+				map[string]string{},
+				map[string]interface{}{
+					"http_request_duration_seconds_sum":   53423,
+					"http_request_duration_seconds_count": 144320,
+				},
+				time.Unix(0, 0),
+				telegraf.Histogram,
+			),
+			expected: []byte(`
+`),
+		},
+		{
+			name: "prometheus input histogram only bucket",
+			metric: testutil.MustMetric(
+				"prometheus",
+				map[string]string{
+					"le": "0.5",
+				},
+				map[string]interface{}{
+					"http_request_duration_seconds_bucket": 129389.0,
+				},
+				time.Unix(0, 0),
+				telegraf.Histogram,
+			),
+			expected: []byte(`
+# HELP http_request_duration_seconds Telegraf collected metric
+# TYPE http_request_duration_seconds histogram
+http_request_duration_seconds_bucket{le="0.5"} 129389
+http_request_duration_seconds_bucket{le="+Inf"} 0
+http_request_duration_seconds_sum 0
+http_request_duration_seconds_count 0
+`),
+		},
+		{
+			name: "simple with timestamp",
+			config: FormatConfig{
+				TimestampExport: ExportTimestamp,
+			},
+			metric: testutil.MustMetric(
+				"cpu",
+				map[string]string{
+					"host": "example.org",
+				},
+				map[string]interface{}{
+					"time_idle": 42.0,
+				},
+				time.Unix(1574279268, 0),
+			),
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle{host="example.org"} 42 1574279268000
+`),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			s, err := NewSerializer(FormatConfig{
+				MetricSortOrder: SortMetrics,
+				TimestampExport: tt.config.TimestampExport,
+				StringHandling:  tt.config.StringHandling,
+			})
+			require.NoError(t, err)
+			actual, err := s.Serialize(tt.metric)
+			require.NoError(t, err)
+
+			require.Equal(t, strings.TrimSpace(string(tt.expected)),
+				strings.TrimSpace(string(actual)))
+		})
+	}
+}
+
+func TestSerializeBatch(t *testing.T) {
+	tests := []struct {
+		name     string
+		config   FormatConfig
+		metrics  []telegraf.Metric
+		expected []byte
+	}{
+		{
+			name: "simple",
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"host": "one.example.org",
+					},
+					map[string]interface{}{
+						"time_idle": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"host": "two.example.org",
+					},
+					map[string]interface{}{
+						"time_idle": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle{host="one.example.org"} 42
+cpu_time_idle{host="two.example.org"} 42
+`),
+		},
+		{
+			name: "multiple metric families",
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"host": "one.example.org",
+					},
+					map[string]interface{}{
+						"time_idle":  42.0,
+						"time_guest": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_guest Telegraf collected metric
+# TYPE cpu_time_guest untyped
+cpu_time_guest{host="one.example.org"} 42
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle{host="one.example.org"} 42
+`),
+		},
+		{
+			name: "histogram",
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{},
+					map[string]interface{}{
+						"http_request_duration_seconds_sum":   53423,
+						"http_request_duration_seconds_count": 144320,
+					},
+					time.Unix(0, 0),
+					telegraf.Histogram,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"le": "0.05"},
+					map[string]interface{}{
+						"http_request_duration_seconds_bucket": 24054.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Histogram,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"le": "0.1"},
+					map[string]interface{}{
+						"http_request_duration_seconds_bucket": 33444.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Histogram,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"le": "0.2"},
+					map[string]interface{}{
+						"http_request_duration_seconds_bucket": 100392.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Histogram,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"le": "0.5"},
+					map[string]interface{}{
+						"http_request_duration_seconds_bucket": 129389.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Histogram,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"le": "1.0"},
+					map[string]interface{}{
+						"http_request_duration_seconds_bucket": 133988.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Histogram,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"le": "+Inf"},
+					map[string]interface{}{
+						"http_request_duration_seconds_bucket": 144320.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Histogram,
+				),
+			},
+			expected: []byte(`
+# HELP http_request_duration_seconds Telegraf collected metric
+# TYPE http_request_duration_seconds histogram
+http_request_duration_seconds_bucket{le="0.05"} 24054
+http_request_duration_seconds_bucket{le="0.1"} 33444
+http_request_duration_seconds_bucket{le="0.2"} 100392
+http_request_duration_seconds_bucket{le="0.5"} 129389
+http_request_duration_seconds_bucket{le="1"} 133988
+http_request_duration_seconds_bucket{le="+Inf"} 144320
+http_request_duration_seconds_sum 53423
+http_request_duration_seconds_count 144320
+`),
+		},
+		{
+			name: "",
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{},
+					map[string]interface{}{
+						"rpc_duration_seconds_sum":   1.7560473e+07,
+						"rpc_duration_seconds_count": 2693,
+					},
+					time.Unix(0, 0),
+					telegraf.Summary,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"quantile": "0.01"},
+					map[string]interface{}{
+						"rpc_duration_seconds": 3102.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Summary,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"quantile": "0.05"},
+					map[string]interface{}{
+						"rpc_duration_seconds": 3272.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Summary,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"quantile": "0.5"},
+					map[string]interface{}{
+						"rpc_duration_seconds": 4773.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Summary,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"quantile": "0.9"},
+					map[string]interface{}{
+						"rpc_duration_seconds": 9001.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Summary,
+				),
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{"quantile": "0.99"},
+					map[string]interface{}{
+						"rpc_duration_seconds": 76656.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Summary,
+				),
+			},
+			expected: []byte(`
+# HELP rpc_duration_seconds Telegraf collected metric
+# TYPE rpc_duration_seconds summary
+rpc_duration_seconds{quantile="0.01"} 3102
+rpc_duration_seconds{quantile="0.05"} 3272
+rpc_duration_seconds{quantile="0.5"} 4773
+rpc_duration_seconds{quantile="0.9"} 9001
+rpc_duration_seconds{quantile="0.99"} 76656
+rpc_duration_seconds_sum 1.7560473e+07
+rpc_duration_seconds_count 2693
+`),
+		},
+		{
+			name: "newer sample",
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"time_idle": 43.0,
+					},
+					time.Unix(1, 0),
+				),
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"time_idle": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle 43
+`),
+		},
+		{
+			name: "invalid label",
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"host-name": "example.org",
+					},
+					map[string]interface{}{
+						"time_idle": 42.0,
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle{host_name="example.org"} 42
+`),
+		},
+		{
+			name: "discard strings",
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"time_idle": 42.0,
+						"cpu":       "cpu0",
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle 42
+`),
+		},
+		{
+			name: "string as label",
+			config: FormatConfig{
+				StringHandling: StringAsLabel,
+			},
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"time_idle": 42.0,
+						"cpu":       "cpu0",
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle{cpu="cpu0"} 42
+`),
+		},
+		{
+			name: "string as label duplicate tag",
+			config: FormatConfig{
+				StringHandling: StringAsLabel,
+			},
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"cpu": "cpu0",
+					},
+					map[string]interface{}{
+						"time_idle": 42.0,
+						"cpu":       "cpu1",
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_idle Telegraf collected metric
+# TYPE cpu_time_idle untyped
+cpu_time_idle{cpu="cpu0"} 42
+`),
+		},
+		{
+			name: "multiple fields grouping",
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"cpu": "cpu0",
+					},
+					map[string]interface{}{
+						"time_guest":  8106.04,
+						"time_system": 26271.4,
+						"time_user":   92904.33,
+					},
+					time.Unix(0, 0),
+				),
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"cpu": "cpu1",
+					},
+					map[string]interface{}{
+						"time_guest":  8181.63,
+						"time_system": 25351.49,
+						"time_user":   96912.57,
+					},
+					time.Unix(0, 0),
+				),
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"cpu": "cpu2",
+					},
+					map[string]interface{}{
+						"time_guest":  7470.04,
+						"time_system": 24998.43,
+						"time_user":   96034.08,
+					},
+					time.Unix(0, 0),
+				),
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"cpu": "cpu3",
+					},
+					map[string]interface{}{
+						"time_guest":  7517.95,
+						"time_system": 24970.82,
+						"time_user":   94148,
+					},
+					time.Unix(0, 0),
+				),
+			},
+			expected: []byte(`
+# HELP cpu_time_guest Telegraf collected metric
+# TYPE cpu_time_guest untyped
+cpu_time_guest{cpu="cpu0"} 8106.04
+cpu_time_guest{cpu="cpu1"} 8181.63
+cpu_time_guest{cpu="cpu2"} 7470.04
+cpu_time_guest{cpu="cpu3"} 7517.95
+# HELP cpu_time_system Telegraf collected metric
+# TYPE cpu_time_system untyped
+cpu_time_system{cpu="cpu0"} 26271.4
+cpu_time_system{cpu="cpu1"} 25351.49
+cpu_time_system{cpu="cpu2"} 24998.43
+cpu_time_system{cpu="cpu3"} 24970.82
+# HELP cpu_time_user Telegraf collected metric
+# TYPE cpu_time_user untyped
+cpu_time_user{cpu="cpu0"} 92904.33
+cpu_time_user{cpu="cpu1"} 96912.57
+cpu_time_user{cpu="cpu2"} 96034.08
+cpu_time_user{cpu="cpu3"} 94148
+`),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			s, err := NewSerializer(FormatConfig{
+				MetricSortOrder: SortMetrics,
+				TimestampExport: tt.config.TimestampExport,
+				StringHandling:  tt.config.StringHandling,
+			})
+			require.NoError(t, err)
+			actual, err := s.SerializeBatch(tt.metrics)
+			require.NoError(t, err)
+
+			require.Equal(t,
+				strings.TrimSpace(string(tt.expected)),
+				strings.TrimSpace(string(actual)))
+		})
+	}
+}

plugins/serializers/registry.go

@@ -10,6 +10,7 @@ import (
 	"github.com/influxdata/telegraf/plugins/serializers/influx"
 	"github.com/influxdata/telegraf/plugins/serializers/json"
 	"github.com/influxdata/telegraf/plugins/serializers/nowmetric"
+	"github.com/influxdata/telegraf/plugins/serializers/prometheus"
 	"github.com/influxdata/telegraf/plugins/serializers/splunkmetric"
 	"github.com/influxdata/telegraf/plugins/serializers/wavefront"
 )
@@ -45,43 +46,54 @@ type Serializer interface {
 // and can be used to instantiate _any_ of the serializers.
 type Config struct {
 	// Dataformat can be one of the serializer types listed in NewSerializer.
-	DataFormat string
+	DataFormat string `toml:"data_format"`
 
 	// Support tags in graphite protocol
-	GraphiteTagSupport bool
+	GraphiteTagSupport bool `toml:"graphite_tag_support"`
 
 	// Maximum line length in bytes; influx format only
-	InfluxMaxLineBytes int
+	InfluxMaxLineBytes int `toml:"influx_max_line_bytes"`
 
 	// Sort field keys, set to true only when debugging as it less performant
 	// than unsorted fields; influx format only
-	InfluxSortFields bool
+	InfluxSortFields bool `toml:"influx_sort_fields"`
 
 	// Support unsigned integer output; influx format only
-	InfluxUintSupport bool
+	InfluxUintSupport bool `toml:"influx_uint_support"`
 
 	// Prefix to add to all measurements, only supports Graphite
-	Prefix string
+	Prefix string `toml:"prefix"`
 
 	// Template for converting telegraf metrics into Graphite
 	// only supports Graphite
-	Template string
+	Template string `toml:"template"`
 
 	// Timestamp units to use for JSON formatted output
-	TimestampUnits time.Duration
+	TimestampUnits time.Duration `toml:"timestamp_units"`
 
 	// Include HEC routing fields for splunkmetric output
-	HecRouting bool
+	HecRouting bool `toml:"hec_routing"`
 
 	// Enable Splunk MultiMetric output (Splunk 8.0+)
-	SplunkmetricMultiMetric bool
+	SplunkmetricMultiMetric bool `toml:"splunkmetric_multi_metric"`
 
 	// Point tags to use as the source name for Wavefront (if none found, host will be used).
-	WavefrontSourceOverride []string
+	WavefrontSourceOverride []string `toml:"wavefront_source_override"`
 
 	// Use Strict rules to sanitize metric and tag names from invalid characters for Wavefront
 	// When enabled forward slash (/) and comma (,) will be accepted
-	WavefrontUseStrict bool
+	WavefrontUseStrict bool `toml:"wavefront_use_strict"`
+
+	// Include the metric timestamp on each sample.
+	PrometheusExportTimestamp bool `toml:"prometheus_export_timestamp"`
+
+	// Sort prometheus metric families and metric samples.  Useful for
+	// debugging.
+	PrometheusSortMetrics bool `toml:"prometheus_sort_metrics"`
+
+	// Output string fields as metric labels; when false string fields are
+	// discarded.
+	PrometheusStringAsLabel bool `toml:"prometheus_string_as_label"`
 }
 
 // NewSerializer a Serializer interface based on the given config.
@@ -103,12 +115,37 @@ func NewSerializer(config *Config) (Serializer, error) {
 		serializer, err = NewCarbon2Serializer()
 	case "wavefront":
 		serializer, err = NewWavefrontSerializer(config.Prefix, config.WavefrontUseStrict, config.WavefrontSourceOverride)
+	case "prometheus":
+		serializer, err = NewPrometheusSerializer(config)
 	default:
 		err = fmt.Errorf("Invalid data format: %s", config.DataFormat)
 	}
 	return serializer, err
 }
 
+func NewPrometheusSerializer(config *Config) (Serializer, error) {
+	exportTimestamp := prometheus.NoExportTimestamp
+	if config.PrometheusExportTimestamp {
+		exportTimestamp = prometheus.ExportTimestamp
+	}
+
+	sortMetrics := prometheus.NoSortMetrics
+	if config.PrometheusExportTimestamp {
+		sortMetrics = prometheus.SortMetrics
+	}
+
+	stringAsLabels := prometheus.DiscardStrings
+	if config.PrometheusStringAsLabel {
+		stringAsLabels = prometheus.StringAsLabel
+	}
+
+	return prometheus.NewSerializer(prometheus.FormatConfig{
+		TimestampExport: exportTimestamp,
+		MetricSortOrder: sortMetrics,
+		StringHandling:  stringAsLabels,
+	})
+}
+
 func NewWavefrontSerializer(prefix string, useStrict bool, sourceOverride []string) (Serializer, error) {
 	return wavefront.NewSerializer(prefix, useStrict, sourceOverride)
 }