Implementing generic parser plugins and documentation

This constitutes a large change in how we will parse different data
formats going forward (for the plugins that support it)

This is working off @henrypfhu's changes.

plugins/inputs/exec/exec.go

@@ -9,66 +9,40 @@ import (
 	"github.com/gonuts/go-shellquote"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/internal/encoding"
 	"github.com/influxdata/telegraf/plugins/inputs"
-
-	_ "github.com/influxdata/telegraf/internal/encoding/graphite"
-	_ "github.com/influxdata/telegraf/internal/encoding/influx"
-	_ "github.com/influxdata/telegraf/internal/encoding/json"
+	"github.com/influxdata/telegraf/plugins/parsers"
 )
 
 const sampleConfig = `
-  # Shell/commands array
-  # compatible with old version
-  # we can still use the old command configuration
-  # command = "/usr/bin/mycollector --foo=bar"
-  commands = ["/tmp/test.sh","/tmp/test2.sh"]
+  ### Commands array
+  commands = ["/tmp/test.sh", "/usr/bin/mycollector --foo=bar"]
 
-  # Data format to consume. This can be "json", "influx" or "graphite" (line-protocol)
-  # NOTE json only reads numerical measurements, strings and booleans are ignored.
-  data_format = "json"
-
-  # measurement name suffix (for separating different commands)
+  ### measurement name suffix (for separating different commands)
   name_suffix = "_mycollector"
 
-  ### Below configuration will be used for data_format = "graphite", can be ignored for other data_format
-  ### If matching multiple measurement files, this string will be used to join the matched values.
-  separator = "."
-
-  ### Each template line requires a template pattern.  It can have an optional
-  ### filter before the template and separated by spaces.  It can also have optional extra
-  ### tags following the template.  Multiple tags should be separated by commas and no spaces
-  ### similar to the line protocol format.  The can be only one default template.
-  ### Templates support below format:
-  ### 1. filter + template
-  ### 2. filter + template + extra tag
-  ### 3. filter + template with field key
-  ### 4. default template
-  templates = [
-    "*.app env.service.resource.measurement",
-    "stats.* .host.measurement* region=us-west,agent=sensu",
-    "stats2.* .host.measurement.field",
-    "measurement*"
- ]
+  ### Data format to consume. This can be "json", "influx" or "graphite"
+  ### Each data format has it's own unique set of configuration options, read
+  ### more about them here:
+  ### https://github.com/influxdata/telegraf/blob/master/DATA_FORMATS.md
+  data_format = "influx"
 `
 
 type Exec struct {
-	Commands   []string
-	Command    string
-	DataFormat string
+	Commands []string
+	Command  string
 
-	Separator string
-	Templates []string
-
-	encodingParser encoding.Parser
-
-	initedConfig bool
+	parser parsers.Parser
 
 	wg sync.WaitGroup
-	sync.Mutex
 
-	runner Runner
-	errc   chan error
+	runner  Runner
+	errChan chan error
+}
+
+func NewExec() *Exec {
+	return &Exec{
+		runner: CommandRunner{},
+	}
 }
 
 type Runner interface {
@@ -95,22 +69,18 @@ func (c CommandRunner) Run(e *Exec, command string) ([]byte, error) {
 	return out.Bytes(), nil
 }
 
-func NewExec() *Exec {
-	return &Exec{runner: CommandRunner{}}
-}
-
 func (e *Exec) ProcessCommand(command string, acc telegraf.Accumulator) {
 	defer e.wg.Done()
 
 	out, err := e.runner.Run(e, command)
 	if err != nil {
-		e.errc <- err
+		e.errChan <- err
 		return
 	}
 
-	metrics, err := e.encodingParser.Parse(out)
+	metrics, err := e.parser.Parse(out)
 	if err != nil {
-		e.errc <- err
+		e.errChan <- err
 	} else {
 		for _, metric := range metrics {
 			acc.AddFields(metric.Name(), metric.Fields(), metric.Tags(), metric.Time())
@@ -118,66 +88,33 @@ func (e *Exec) ProcessCommand(command string, acc telegraf.Accumulator) {
 	}
 }
 
-func (e *Exec) initConfig() error {
-	e.Lock()
-	defer e.Unlock()
-
-	if e.Command != "" && len(e.Commands) < 1 {
-		e.Commands = []string{e.Command}
-	}
-
-	if e.DataFormat == "" {
-		e.DataFormat = "json"
-	}
-
-	var err error
-
-	configs := make(map[string]interface{})
-	configs["Separator"] = e.Separator
-	configs["Templates"] = e.Templates
-
-	e.encodingParser, err = encoding.NewParser(e.DataFormat, configs)
-
-	if err != nil {
-		return fmt.Errorf("exec configuration is error: %s ", err.Error())
-	}
-
-	return nil
-}
-
 func (e *Exec) SampleConfig() string {
 	return sampleConfig
 }
 
 func (e *Exec) Description() string {
-	return "Read metrics from one or more commands that can output JSON, influx or graphite line protocol to stdout"
+	return "Read metrics from one or more commands that can output to stdout"
+}
+
+func (e *Exec) SetParser(parser parsers.Parser) {
+	e.parser = parser
 }
 
 func (e *Exec) Gather(acc telegraf.Accumulator) error {
+	e.errChan = make(chan error, len(e.Commands))
 
-	if !e.initedConfig {
-		if err := e.initConfig(); err != nil {
-			return err
-		}
-		e.initedConfig = true
-	}
-
-	e.Lock()
-	e.errc = make(chan error, 10)
-	e.Unlock()
-
+	e.wg.Add(len(e.Commands))
 	for _, command := range e.Commands {
-		e.wg.Add(1)
 		go e.ProcessCommand(command, acc)
 	}
 	e.wg.Wait()
 
 	select {
 	default:
-		close(e.errc)
+		close(e.errChan)
 		return nil
-	case err := <-e.errc:
-		close(e.errc)
+	case err := <-e.errChan:
+		close(e.errChan)
 		return err
 	}