1 files changed, 76 insertions, 0 deletions
diff --git a/pkg/log/json.go b/pkg/log/json.go
new file mode 100644
index 000000000..a278c8fc8
--- /dev/null
+++ b/pkg/log/json.go
@@ -0,0 +1,76 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package log
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+type jsonLog struct {
+	Msg   string    `json:"msg"`
+	Level Level     `json:"level"`
+	Time  time.Time `json:"time"`
+}
+
+// MarshalJSON implements json.Marshaler.MarashalJSON.
+func (lv Level) MarshalJSON() ([]byte, error) {
+	switch lv {
+	case Warning:
+		return []byte(`"warning"`), nil
+	case Info:
+		return []byte(`"info"`), nil
+	case Debug:
+		return []byte(`"debug"`), nil
+	default:
+		return nil, fmt.Errorf("unknown level %v", lv)
+	}
+}
+
+// UnmarshalJSON implements json.Unmarshaler.UnmarshalJSON.  It can unmarshal
+// from both string names and integers.
+func (lv *Level) UnmarshalJSON(b []byte) error {
+	switch s := string(b); s {
+	case "0", `"warning"`:
+		*lv = Warning
+	case "1", `"info"`:
+		*lv = Info
+	case "2", `"debug"`:
+		*lv = Debug
+	default:
+		return fmt.Errorf("unknown level %q", s)
+	}
+	return nil
+}
+
+// JSONEmitter logs messages in json format.
+type JSONEmitter struct {
+	Writer
+}
+
+// Emit implements Emitter.Emit.
+func (e JSONEmitter) Emit(level Level, timestamp time.Time, format string, v ...interface{}) {
+	j := jsonLog{
+		Msg:   fmt.Sprintf(format, v...),
+		Level: level,
+		Time:  timestamp,
+	}
+	b, err := json.Marshal(j)
+	if err != nil {
+		panic(err)
+	}
+	e.Writer.Write(b)
+}