Add support for custom object marshaling

benchmark_test.go

@@ -72,12 +72,19 @@ func BenchmarkLogFields(b *testing.B) {
 	})
 }
 
-func BenchmarkLogFieldType(b *testing.B) {
-	type obj struct {
+type obj struct {
 	Pub  string
 	Tag  string `json:"tag"`
 	priv int
-	}
+}
+
+func (o obj) MarshalZerologObject(e *Event) {
+	e.Str("Pub", o.Pub).
+		Str("Tag", o.Tag).
+		Int("priv", o.priv)
+}
+
+func BenchmarkLogFieldType(b *testing.B) {
 	bools := []bool{true, false, true, false, true, false, true, false, true, false}
 	ints := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
 	floats := []float64{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
@@ -143,6 +150,9 @@ func BenchmarkLogFieldType(b *testing.B) {
 		"Interface": func(e *Event) *Event {
 			return e.Interface("k", o)
 		},
+		"Object": func(e *Event) *Event {
+			return e.Object("k", o)
+		},
 	}
 	logger := New(ioutil.Discard)
 	b.ResetTimer()

context.go

@@ -1,6 +1,9 @@
 package zerolog
 
-import "time"
+import (
+	"io/ioutil"
+	"time"
+)
 
 // Context configures a new sub-logger with contextual fields.
 type Context struct {
@@ -26,6 +29,16 @@ func (c Context) Dict(key string, dict *Event) Context {
 	return c
 }
 
+// Object marshals an object that implement the LogObjectMarshaler interface.
+func (c Context) Object(key string, obj LogObjectMarshaler) Context {
+	e := newEvent(levelWriterAdapter{ioutil.Discard}, 0, true)
+	e.Object(key, obj)
+	e.buf[0] = ',' // A new event starts as an object, we want to embed it.
+	c.l.context = append(c.l.context, e.buf...)
+	eventPool.Put(e)
+	return c
+}
+
 // Str adds the field key with val as a string to the logger context.
 func (c Context) Str(key, val string) Context {
 	c.l.context = appendString(c.l.context, key, val)

event.go

@@ -26,6 +26,10 @@ type Event struct {
 	done    func(msg string)
 }
 
+type LogObjectMarshaler interface {
+	MarshalZerologObject(e *Event)
+}
+
 func newEvent(w LevelWriter, level Level, enabled bool) *Event {
 	if !enabled {
 		return &Event{}
@@ -121,6 +125,23 @@ func Dict() *Event {
 	return newEvent(levelWriterAdapter{ioutil.Discard}, 0, true)
 }
 
+// Object marshals an object that implement the LogObjectMarshaler interface.
+func (e *Event) Object(key string, obj LogObjectMarshaler) *Event {
+	e.buf = appendKey(e.buf, key)
+	pos := len(e.buf)
+	obj.MarshalZerologObject(e)
+	if pos < len(e.buf) {
+		// As MarshalZerologObject will use event API, the first field will be
+		// preceded by a coma. If at least one field has been added (buf grew),
+		// we replace this coma by the opening bracket.
+		e.buf[pos] = '{'
+	} else {
+		e.buf = append(e.buf, '{')
+	}
+	e.buf = append(e.buf, '}')
+	return e
+}
+
 // Str adds the field key with val as a string to the *Event context.
 func (e *Event) Str(key, val string) *Event {
 	if !e.enabled {

log_example_test.go

@@ -138,6 +138,31 @@ func ExampleEvent_Dict() {
 	// Output: {"foo":"bar","dict":{"bar":"baz","n":1},"message":"hello world"}
 }
 
+type User struct {
+	Name    string
+	Age     int
+	Created time.Time
+}
+
+func (u User) MarshalZerologObject(e *zerolog.Event) {
+	e.Str("name", u.Name).
+		Int("age", u.Age).
+		Time("created", u.Created)
+}
+
+func ExampleEvent_Object() {
+	log := zerolog.New(os.Stdout)
+
+	u := User{"John", 35, time.Time{}}
+
+	log.Log().
+		Str("foo", "bar").
+		Object("user", u).
+		Msg("hello world")
+
+	// Output: {"foo":"bar","user":{"name":"John","age":35,"created":"0001-01-01T00:00:00Z"},"message":"hello world"}
+}
+
 func ExampleEvent_Interface() {
 	log := zerolog.New(os.Stdout)
 
@@ -197,6 +222,19 @@ func ExampleContext_Dict() {
 	// Output: {"foo":"bar","dict":{"bar":"baz","n":1},"message":"hello world"}
 }
 
+func ExampleContext_Object() {
+	u := User{"John", 35, time.Time{}}
+
+	log := zerolog.New(os.Stdout).With().
+		Str("foo", "bar").
+		Object("user", u).
+		Logger()
+
+	log.Log().Msg("hello world")
+
+	// Output: {"foo":"bar","user":{"name":"John","age":35,"created":"0001-01-01T00:00:00Z"},"message":"hello world"}
+}
+
 func ExampleContext_Interface() {
 	obj := struct {
 		Name string `json:"name"`