Add --since argument to docker logs cmd

Added --since argument to `docker logs` command. Accept unix
timestamps and shows logs only created after the specified date.

Default value is 0 and passing default value or not specifying
the value in the request causes parameter to be ignored (behavior
prior to this change).

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>

jsonlog/jsonlog.go

@@ -32,16 +32,20 @@ func (jl *JSONLog) Reset() {
 	jl.Created = time.Time{}
 }
 
-func WriteLog(src io.Reader, dst io.Writer, format string) error {
+func WriteLog(src io.Reader, dst io.Writer, format string, since time.Time) error {
 	dec := json.NewDecoder(src)
 	l := &JSONLog{}
 	for {
+		l.Reset()
 		if err := dec.Decode(l); err == io.EOF {
 			return nil
 		} else if err != nil {
 			logrus.Printf("Error streaming logs: %s", err)
 			return err
 		}
+		if !since.IsZero() && l.Created.Before(since) {
+			continue
+		}
 		line, err := l.Format(format)
 		if err != nil {
 			return err
@@ -49,6 +53,5 @@ func WriteLog(src io.Reader, dst io.Writer, format string) error {
 		if _, err := io.WriteString(dst, line); err != nil {
 			return err
 		}
-		l.Reset()
 	}
 }

jsonlog/jsonlog_test.go

@@ -21,7 +21,7 @@ func TestWriteLog(t *testing.T) {
 	}
 	w := bytes.NewBuffer(nil)
 	format := timeutils.RFC3339NanoFixed
-	if err := WriteLog(&buf, w, format); err != nil {
+	if err := WriteLog(&buf, w, format, time.Time{}); err != nil {
 		t.Fatal(err)
 	}
 	res := w.String()
@@ -52,7 +52,7 @@ func BenchmarkWriteLog(b *testing.B) {
 	b.SetBytes(int64(r.Len()))
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		if err := WriteLog(r, w, format); err != nil {
+		if err := WriteLog(r, w, format, time.Time{}); err != nil {
 			b.Fatal(err)
 		}
 		b.StopTimer()

timeutils/utils.go

@@ -0,0 +1,22 @@
+package timeutils
+
+import (
+	"strconv"
+	"time"
+)
+
+// GetTimestamp tries to parse given string as RFC3339 time
+// or Unix timestamp, if successful returns a Unix timestamp
+// as string otherwise returns value back.
+func GetTimestamp(value string) string {
+	format := RFC3339NanoFixed
+	loc := time.FixedZone(time.Now().Zone())
+	if len(value) < len(format) {
+		format = format[:len(value)]
+	}
+	t, err := time.ParseInLocation(format, value, loc)
+	if err != nil {
+		return value
+	}
+	return strconv.FormatInt(t.Unix(), 10)
+}