introduce timestamps to file content and path

new parameter to allow timestamp prefix to each line in file.  Also, add
ability to introduce time parameters in path and file name.  Will also
create missing directories if required.

plugins/outputs/file/file.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"strings"
+	"time"
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/outputs"
@@ -13,6 +15,8 @@ import (
 type File struct {
 	Files []string
 
+	Timestamp bool
+
 	writer  io.Writer
 	closers []io.Closer
 
@@ -23,6 +27,9 @@ var sampleConfig = `
   ## Files to write to, "stdout" is a specially handled file.
   files = ["stdout", "/tmp/metrics.out"]
 
+  ## Prefix each output line with timestamp
+  timestamp = true
+
   ## Data format to output.
   ## Each data format has it's own unique set of configuration options, read
   ## more about them here:
@@ -48,13 +55,24 @@ func (f *File) Connect() error {
 		} else {
 			var of *os.File
 			var err error
-			if _, err := os.Stat(file); os.IsNotExist(err) {
-				of, err = os.Create(file)
+			generatedFile := generateFileName(file)
+			fmt.Printf("writing to output file [%s]", generatedFile)
+			if _, err := os.Stat(generatedFile); os.IsNotExist(err) {
+				// create directory f it doesn't exist
+				lastSlash := strings.LastIndex(generatedFile, "/")
+				if lastSlash != -1 {
+					err = os.MkdirAll(generatedFile[:lastSlash], os.ModeDir)
+				}
+				// create file if it doesn't exist
+				if err == nil {
+					of, err = os.Create(generatedFile)
+				}
 			} else {
-				of, err = os.OpenFile(file, os.O_APPEND|os.O_WRONLY, os.ModeAppend)
+				of, err = os.OpenFile(generatedFile, os.O_APPEND|os.O_WRONLY, os.ModeAppend)
 			}
 
 			if err != nil {
+				fmt.Errorf("Failed to initialise file [%s] [%s]", generatedFile, err)
 				return err
 			}
 			writers = append(writers, of)
@@ -91,6 +109,12 @@ func (f *File) Write(metrics []telegraf.Metric) error {
 		return nil
 	}
 
+	prefix := ""
+	if f.Timestamp {
+		t := time.Now().UTC()
+		prefix = t.Format(time.RFC3339) + " "
+	}
+
 	for _, metric := range metrics {
 		values, err := f.serializer.Serialize(metric)
 		if err != nil {
@@ -98,7 +122,7 @@ func (f *File) Write(metrics []telegraf.Metric) error {
 		}
 
 		for _, value := range values {
-			_, err = f.writer.Write([]byte(value + "\n"))
+			_, err = f.writer.Write([]byte(prefix + value + "\n"))
 			if err != nil {
 				return fmt.Errorf("FAILED to write message: %s, %s", value, err)
 			}
@@ -107,6 +131,29 @@ func (f *File) Write(metrics []telegraf.Metric) error {
 	return nil
 }
 
+// Generate filename, replace tokens enclosed by { and } with time format
+func generateFileName(s string) string {
+	t := time.Now().UTC()
+	//split on opening brace
+	tokens := strings.Split(s, "{")
+	// first token has no left bracket
+	outputString := tokens[0]
+	// cycle through remaining tokens
+	for j := 1; j < len(tokens); j++ {
+		//find closing brace
+		index := strings.Index(tokens[j], "}")
+		// if -1 we have opening brace with no closing brace so we don't format
+		if index == -1 {
+			outputString += tokens[j]
+		} else {
+			// Extract enclosed token and format, concatenate anything after closing brace on output
+			generatedString := t.Format(tokens[j][:index])
+			outputString += generatedString + tokens[j][index+1:]
+		}
+	}
+	return outputString
+}
+
 func init() {
 	outputs.Add("file", func() telegraf.Output {
 		return &File{}