Add Serializer plugins, and 'file' output plugin

plugins/outputs/file/README.md

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+# file Output Plugin

plugins/outputs/file/file.go

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+package file
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/plugins/serializers"
+)
+
+type File struct {
+	Files []string
+
+	writer  io.Writer
+	closers []io.Closer
+
+	serializer serializers.Serializer
+}
+
+var sampleConfig = `
+  ### Files to write to, "stdout" is a specially handled file.
+  files = ["stdout", "/tmp/metrics.out"]
+
+  ### Data format to output. This can be "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_OUTPUT.md
+  data_format = "influx"
+`
+
+func (f *File) SetSerializer(serializer serializers.Serializer) {
+	f.serializer = serializer
+}
+
+func (f *File) Connect() error {
+	writers := []io.Writer{}
+	for _, file := range f.Files {
+		if file == "stdout" {
+			writers = append(writers, os.Stdout)
+			f.closers = append(f.closers, os.Stdout)
+		} else {
+			var of *os.File
+			var err error
+			if _, err := os.Stat(file); os.IsNotExist(err) {
+				of, err = os.Create(file)
+			} else {
+				of, err = os.OpenFile(file, os.O_APPEND|os.O_WRONLY, os.ModeAppend)
+			}
+
+			if err != nil {
+				return err
+			}
+			writers = append(writers, of)
+			f.closers = append(f.closers, of)
+		}
+	}
+	f.writer = io.MultiWriter(writers...)
+	return nil
+}
+
+func (f *File) Close() error {
+	var errS string
+	for _, c := range f.closers {
+		if err := c.Close(); err != nil {
+			errS += err.Error() + "\n"
+		}
+	}
+	if errS != "" {
+		return fmt.Errorf(errS)
+	}
+	return nil
+}
+
+func (f *File) SampleConfig() string {
+	return sampleConfig
+}
+
+func (f *File) Description() string {
+	return "Send telegraf metrics to file(s)"
+}
+
+func (f *File) Write(metrics []telegraf.Metric) error {
+	if len(metrics) == 0 {
+		return nil
+	}
+
+	for _, metric := range metrics {
+		values, err := f.serializer.Serialize(metric)
+		if err != nil {
+			return err
+		}
+
+		for _, value := range values {
+			_, err = f.writer.Write([]byte(value + "\n"))
+			if err != nil {
+				return fmt.Errorf("FAILED to write message: %s, %s", value, err)
+			}
+		}
+	}
+	return nil
+}
+
+func init() {
+	outputs.Add("file", func() telegraf.Output {
+		return &File{}
+	})
+}

plugins/outputs/file/file_test.go

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+package file