Support log summary cloning.

entity.go

@@ -65,6 +65,12 @@ type Summary interface {
 
 	// Size returns the log content size.
 	Size() int
+
+	// Clone returns a copy of the current log summary (excluding context).
+	Clone() Summary
+
+	// CloneWithContext returns a copy of the current log summary and sets its context to the given value.
+	CloneWithContext(context.Context) Summary
 }
 
 // The logEntity type is a built-in implementation of the Entity interface.
@@ -141,6 +147,43 @@ func (o *logEntity) Size() int {
 	return o.buffer.Len()
 }
 
+// Clone returns a copy of the current log summary (excluding context).
+func (o *logEntity) Clone() Summary {
+	return o.CloneWithContext(nil)
+}
+
+// CloneWithContext returns a copy of the current log summary and sets its context to the given value.
+func (o *logEntity) CloneWithContext(ctx context.Context) Summary {
+	var buffer *bytes.Buffer
+	if bs := o.buffer.Bytes(); len(bs) > 0 {
+		cp := make([]byte, len(bs))
+		copy(cp, bs)
+		buffer = bytes.NewBuffer(cp)
+	} else {
+		buffer = new(bytes.Buffer)
+	}
+
+	var fields map[string]interface{}
+	if n := len(o.fields); n > 0 {
+		fields = make(map[string]interface{}, n)
+		for k, v := range o.fields {
+			fields[k] = v
+		}
+	}
+
+	return &logEntity{
+		name:       o.name,
+		time:       o.time,
+		timeFormat: o.timeFormat,
+		level:      o.level,
+		message:    o.message,
+		fields:     fields,
+		ctx:        ctx,
+		buffer:     *buffer,
+		caller:     o.caller,
+	}
+}
+
 // Read is the implementation of io.Reader interface.
 func (o *logEntity) Read(p []byte) (int, error) {
 	return o.buffer.Read(p)

entity_test.go

@@ -16,6 +16,7 @@ package logger
 
 import (
 	"bytes"
+	"context"
 	"fmt"
 	"io/ioutil"
 	"testing"
@@ -69,11 +70,27 @@ func TestLogEntityAndSummary(t *testing.T) {
 	if got := o.Size(); got != 4 {
 		t.Fatalf("Summary.Size(): %d", got)
 	}
+
+	if o.Clone() == nil {
+		t.Fatalf("Summary.Clone(): nil")
+	}
+	if o.CloneWithContext(context.Background()) == nil {
+		t.Fatalf("Summary.CloneWithContext(): nil")
+	}
+
 	if got, err := ioutil.ReadAll(o); err == nil {
 		if !bytes.Equal(got, []byte("test")) {
 			t.Fatalf("Summary.Read(): %s", string(got))
 		}
 	} else {
 		t.Fatalf("Summary.Read(): %s", err)
 	}
+	// empty buffer
+	if o.Clone() == nil {
+		t.Fatalf("Summary.Clone(): nil")
+	}
+	// empty buffer
+	if o.CloneWithContext(context.Background()) == nil {
+		t.Fatalf("Summary.CloneWithContext(): nil")
+	}
 }