add opentracing spans for metrics

vendor/github.com/go-logfmt/logfmt/example_test.go

@@ -0,0 +1,60 @@
+package logfmt_test
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/go-logfmt/logfmt"
+)
+
+func ExampleEncoder() {
+	check := func(err error) {
+		if err != nil {
+			panic(err)
+		}
+	}
+
+	e := logfmt.NewEncoder(os.Stdout)
+
+	check(e.EncodeKeyval("id", 1))
+	check(e.EncodeKeyval("dur", time.Second+time.Millisecond))
+	check(e.EndRecord())
+
+	check(e.EncodeKeyval("id", 1))
+	check(e.EncodeKeyval("path", "/path/to/file"))
+	check(e.EncodeKeyval("err", errors.New("file not found")))
+	check(e.EndRecord())
+
+	// Output:
+	// id=1 dur=1.001s
+	// id=1 path=/path/to/file err="file not found"
+}
+
+func ExampleDecoder() {
+	in := `
+id=1 dur=1.001s
+id=1 path=/path/to/file err="file not found"
+`
+
+	d := logfmt.NewDecoder(strings.NewReader(in))
+	for d.ScanRecord() {
+		for d.ScanKeyval() {
+			fmt.Printf("k: %s v: %s\n", d.Key(), d.Value())
+		}
+		fmt.Println()
+	}
+	if d.Err() != nil {
+		panic(d.Err())
+	}
+
+	// Output:
+	// k: id v: 1
+	// k: dur v: 1.001s
+	//
+	// k: id v: 1
+	// k: path v: /path/to/file
+	// k: err v: file not found
+}