From 3f54be87164ba1c4dd94433c9fb36f6e82aec33e Mon Sep 17 00:00:00 2001
From: Olivier Poitrey <rs@rhapsodyk.net>
Date: Sat, 20 May 2017 00:22:37 -0700
Subject: [PATCH] Improve context.Context logging

---
 README.md   | 19 ++++++++++++++++---
 ctx.go      | 18 +++++++++++++-----
 ctx_test.go | 16 +++++-----------
 event.go    |  2 +-
 log/log.go  |  7 +++++++
 5 files changed, 42 insertions(+), 20 deletions(-)

diff --git a/README.md b/README.md
index f4f9783..8edbeda 100644
--- a/README.md
+++ b/README.md
@@ -190,6 +190,16 @@ sampled.Info().Msg("will be logged every 10 messages")
 // Output: {"time":1494567715,"sample":10,"message":"will be logged every 10 messages"}
 ```
 
+### Pass a sub-logger by context
+
+```go
+ctx := log.With("component", "module").Logger().FromContext(ctx)
+
+log.Ctx(ctx).Info().Msg("hello world")
+
+// Output: {"component":"module","level":"info","message":"hello world"}
+```
+
 ## Global Settings
 
 Some settings can be changed and will by applied to all loggers:
@@ -202,7 +212,7 @@ Some settings can be changed and will by applied to all loggers:
 * `zerolog.MessageFieldName`: Can be set to customize message field name.
 * `zerolog.ErrorFieldName`: Can be set to customize `Err` field name.
 * `zerolog.SampleFieldName`: Can be set to customize the field name added when sampling is enabled.
-* `zerolog.TimeFieldFormat`: Can be set to customize `Time` field value formatting.
+* `zerolog.TimeFieldFormat`: Can be set to customize `Time` field value formatting. If set with an empty string, times are formated as UNIX timestamp.
 
 ## Field Types
 
@@ -216,7 +226,10 @@ Some settings can be changed and will by applied to all loggers:
 
 ### Advanced Fields
 
-* `Timestamp`: Insert UNIX timestamp field with `zerolog.TimestampFieldName` field name.
-* `Time`: Add a field with the time formated with the `zerolog.TimeFieldFormat`.
 * `Err`: Takes an `error` and render it as a string using the `zerolog.ErrorFieldName` field name.
+* `Timestamp`: Insert a timestamp field with `zerolog.TimestampFieldName` field name and formatted using `zerolog.TimeFieldFormat`.
+* `Time`: Adds a field with the time formated with the `zerolog.TimeFieldFormat`.
+* `Dur`: Adds a field with a `time.Duration` formatted as a `float`. For `int` value, use `DurInt`.
+* `Dict`: Adds a sub-key/value as a field of the event.
+* `Interface`: Uses reflection to marshal the type.
 
diff --git a/ctx.go b/ctx.go
index d5616bc..4abf062 100644
--- a/ctx.go
+++ b/ctx.go
@@ -1,6 +1,11 @@
 package zerolog
 
-import "context"
+import (
+	"context"
+	"io/ioutil"
+)
+
+var disabledLogger = New(ioutil.Discard).Level(Disabled)
 
 type ctxKey struct{}
 
@@ -9,8 +14,11 @@ func (l Logger) WithContext(ctx context.Context) context.Context {
 	return context.WithValue(ctx, ctxKey{}, l)
 }
 
-// FromContext returns the Logger associated with the ctx.
-func FromContext(ctx context.Context) (l Logger, ok bool) {
-	l, ok = ctx.Value(ctxKey{}).(Logger)
-	return
+// Ctx returns the Logger associated with the ctx. If no logger
+// is associated, a disabled logger is returned.
+func Ctx(ctx context.Context) Logger {
+	if l, ok := ctx.Value(ctxKey{}).(Logger); ok {
+		return l
+	}
+	return disabledLogger
 }
diff --git a/ctx_test.go b/ctx_test.go
index 770e670..dc9943f 100644
--- a/ctx_test.go
+++ b/ctx_test.go
@@ -10,19 +10,13 @@ import (
 func TestCtx(t *testing.T) {
 	log := New(ioutil.Discard)
 	ctx := log.WithContext(context.Background())
-	log2, ok := FromContext(ctx)
-	if !ok {
-		t.Error("Expected ok=true from FromContext")
-	}
+	log2 := Ctx(ctx)
 	if !reflect.DeepEqual(log, log2) {
-		t.Error("FromContext did not return the expected logger")
+		t.Error("Ctx did not return the expected logger")
 	}
 
-	log2, ok = FromContext(context.Background())
-	if ok {
-		t.Error("Expected ok=false from FromContext")
-	}
-	if !reflect.DeepEqual(log2, Logger{}) {
-		t.Error("FromContext did not return the expected logger")
+	log2 = Ctx(context.Background())
+	if !reflect.DeepEqual(log2, disabledLogger) {
+		t.Error("Ctx did not return the expected logger")
 	}
 }
diff --git a/event.go b/event.go
index 6c8fb18..91bff3a 100644
--- a/event.go
+++ b/event.go
@@ -89,7 +89,7 @@ func (e *Event) Msgf(format string, v ...interface{}) (n int, err error) {
 	return e.write()
 }
 
-// Dict adds the field key with a dict to the *Event context.
+// Dict adds the field key with a dict to the event context.
 // Use zerolog.Dict() to create the dictionary.
 func (e *Event) Dict(key string, dict *Event) *Event {
 	if !e.enabled {
diff --git a/log/log.go b/log/log.go
index c516dd0..a478596 100644
--- a/log/log.go
+++ b/log/log.go
@@ -2,6 +2,7 @@
 package log
 
 import (
+	"context"
 	"os"
 
 	"github.com/rs/zerolog"
@@ -76,3 +77,9 @@ func Panic() *zerolog.Event {
 func Log() *zerolog.Event {
 	return Logger.Log()
 }
+
+// Ctx returns the Logger associated with the ctx. If no logger
+// is associated, a disabled logger is returned.
+func Ctx(ctx context.Context) zerolog.Logger {
+	return zerolog.Ctx(ctx)
+}