Add support for the duration field

context.go

@@ -128,6 +128,18 @@ func (c Context) Time(key string, t time.Time) Context {
 	return c
 }
 
+// Dur adds the fields key with d divided by unit and stored as a float.
+func (c Context) Dur(key string, d, unit time.Duration) Context {
+	c.l.context = appendDuration(c.l.context, key, d, unit, true)
+	return c
+}
+
+// DurInt adds the fields key with d divided by unit and stored as a int.
+func (c Context) DurInt(key string, d, unit time.Duration) Context {
+	c.l.context = appendDuration(c.l.context, key, d, unit, true)
+	return c
+}
+
 // Interface adds the field key with obj marshaled using reflection.
 func (c Context) Interface(key string, i interface{}) Context {
 	c.l.context = appendInterface(c.l.context, key, i)

event.go

@@ -262,6 +262,24 @@ func (e *Event) Time(key string, t time.Time) *Event {
 	return e
 }
 
+// Dur adds the fields key with d divided by unit and stored as a float.
+func (e *Event) Dur(key string, d, unit time.Duration) *Event {
+	if !e.enabled {
+		return e
+	}
+	e.buf = appendDuration(e.buf, key, d, unit, true)
+	return e
+}
+
+// DurInt adds the fields key with d divided by unit and stored as a int.
+func (e *Event) DurInt(key string, d, unit time.Duration) *Event {
+	if !e.enabled {
+		return e
+	}
+	e.buf = appendDuration(e.buf, key, d, unit, true)
+	return e
+}
+
 // Interface adds the field key with i marshaled using reflection.
 func (e *Event) Interface(key string, i interface{}) *Event {
 	if !e.enabled {

field.go

@@ -88,6 +88,13 @@ func appendTimestamp(dst []byte) []byte {
 	return appendTime(dst, TimestampFieldName, now())
 }
 
+func appendDuration(dst []byte, key string, d, unit time.Duration, float bool) []byte {
+	if float {
+		return appendFloat64(dst, key, float64(d)/float64(unit))
+	}
+	return appendInt64(dst, key, int64(d/unit))
+}
+
 func appendInterface(dst []byte, key string, i interface{}) []byte {
 	marshaled, err := json.Marshal(i)
 	if err != nil {

log_example_test.go

@@ -3,6 +3,7 @@ package zerolog_test
 import (
 	"errors"
 	"os"
+	"time"
 
 	"github.com/rs/zerolog"
 )
@@ -131,6 +132,19 @@ func ExampleEvent_Interface() {
 	// Output: {"foo":"bar","obj":{"name":"john"},"message":"hello world"}
 }
 
+func ExampleEvent_Dur() {
+	d := time.Duration(10 * time.Millisecond)
+
+	log := zerolog.New(os.Stdout)
+
+	log.Log().
+		Str("foo", "bar").
+		Dur("dur", d, time.Second).
+		Msg("hello world")
+
+	// Output: {"foo":"bar","dur":0.01,"message":"hello world"}
+}
+
 func ExampleContext_Dict() {
 	log := zerolog.New(os.Stdout).With().
 		Str("foo", "bar").
@@ -160,3 +174,16 @@ func ExampleContext_Interface() {
 
 	// Output: {"foo":"bar","obj":{"name":"john"},"message":"hello world"}
 }
+
+func ExampleContext_Dur() {
+	d := time.Duration(10 * time.Millisecond)
+
+	log := zerolog.New(os.Stdout).With().
+		Str("foo", "bar").
+		Dur("dur", d, time.Second).
+		Logger()
+
+	log.Log().Msg("hello world")
+
+	// Output: {"foo":"bar","dur":0.01,"message":"hello world"}
+}