utils.Debugf -> log.Printf, move jsonlog to own package.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)

jsonlog/jsonlog.go

@@ -0,0 +1,45 @@
+package jsonlog
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"time"
+)
+
+type JSONLog struct {
+	Log     string    `json:"log,omitempty"`
+	Stream  string    `json:"stream,omitempty"`
+	Created time.Time `json:"time"`
+}
+
+func (jl *JSONLog) Format(format string) (string, error) {
+	if format == "" {
+		return jl.Log, nil
+	}
+	if format == "json" {
+		m, err := json.Marshal(jl)
+		return string(m), err
+	}
+	return fmt.Sprintf("[%s] %s", jl.Created.Format(format), jl.Log), nil
+}
+
+func WriteLog(src io.Reader, dst io.WriteCloser, format string) error {
+	dec := json.NewDecoder(src)
+	for {
+		l := &JSONLog{}
+
+		if err := dec.Decode(l); err == io.EOF {
+			return nil
+		} else if err != nil {
+			log.Printf("Error streaming logs: %s", err)
+			return err
+		}
+		line, err := l.Format(format)
+		if err != nil {
+			return err
+		}
+		fmt.Fprintf(dst, "%s", line)
+	}
+}