Improve prometheus plugin

closes #707

plugins/inputs/prometheus/prometheus.go

@@ -5,9 +5,7 @@ import (
 	"fmt"
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/inputs"
-	"github.com/prometheus/common/expfmt"
-	"github.com/prometheus/common/model"
-	"io"
+	"io/ioutil"
 	"net/http"
 	"sync"
 	"time"
@@ -62,6 +60,7 @@ var client = &http.Client{
 }
 
 func (g *Prometheus) gatherURL(url string, acc telegraf.Accumulator) error {
+	collectDate := time.Now()
 	resp, err := client.Get(url)
 	if err != nil {
 		return fmt.Errorf("error making HTTP request to %s: %s", url, err)
@@ -70,38 +69,33 @@ func (g *Prometheus) gatherURL(url string, acc telegraf.Accumulator) error {
 	if resp.StatusCode != http.StatusOK {
 		return fmt.Errorf("%s returned HTTP status %s", url, resp.Status)
 	}
-	format := expfmt.ResponseFormat(resp.Header)
 
-	decoder := expfmt.NewDecoder(resp.Body, format)
-
-	options := &expfmt.DecodeOptions{
-		Timestamp: model.Now(),
-	}
-	sampleDecoder := &expfmt.SampleDecoder{
-		Dec:  decoder,
-		Opts: options,
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return fmt.Errorf("error reading body: %s", err)
 	}
 
-	for {
-		var samples model.Vector
-		err := sampleDecoder.Decode(&samples)
-		if err == io.EOF {
-			break
-		} else if err != nil {
-			return fmt.Errorf("error getting processing samples for %s: %s",
-				url, err)
-		}
-		for _, sample := range samples {
-			tags := make(map[string]string)
-			for key, value := range sample.Metric {
-				if key == model.MetricNameLabel {
-					continue
-				}
-				tags[string(key)] = string(value)
-			}
-			acc.Add("prometheus_"+string(sample.Metric[model.MetricNameLabel]),
-				float64(sample.Value), tags)
-		}
+	// Headers
+	headers := make(map[string]string)
+	for key, value := range headers {
+		headers[key] = value
+	}
+
+	// Prepare Prometheus parser config
+	promparser := PrometheusParser{
+		PromFormat: headers,
+	}
+
+	metrics, err := promparser.Parse(body)
+	if err != nil {
+		return fmt.Errorf("error getting processing samples for %s: %s",
+			url, err)
+	}
+	// Add (or not) collected metrics
+	for _, metric := range metrics {
+		tags := metric.Tags()
+		tags["url"] = url
+		acc.AddFields(metric.Name(), metric.Fields(), tags, collectDate)
 	}
 
 	return nil