Add the ability to discard an event from a hook

The Discard method has been added to the Event type so it can be called
from a hook to prevent the event from behing printed. This new method
works outside of the context of a hook too.

Fixes #90

event.go

@@ -60,11 +60,13 @@ func (e *Event) write() (err error) {
 	if e == nil {
 		return nil
 	}
+	if e.level != Disabled {
 		e.buf = enc.AppendEndMarker(e.buf)
 		e.buf = enc.AppendLineBreak(e.buf)
 		if e.w != nil {
 			_, err = e.w.WriteLevel(e.level, e.buf)
 		}
+	}
 	eventPool.Put(e)
 	return
 }
@@ -72,7 +74,13 @@ func (e *Event) write() (err error) {
 // Enabled return false if the *Event is going to be filtered out by
 // log level or sampling.
 func (e *Event) Enabled() bool {
-	return e != nil
+	return e != nil && e.level != Disabled
+}
+
+// Discard disables the event so Msg(f) won't print it.
+func (e *Event) Discard() *Event {
+	e.level = Disabled
+	return nil
 }
 
 // Msg sends the *Event with msg added as the message field if not empty.

hook.go

@@ -6,6 +6,15 @@ type Hook interface {
 	Run(e *Event, level Level, message string)
 }
 
+// HookFunc is an adaptor to allow the use of an ordinary function
+// as a Hook.
+type HookFunc func(e *Event, level Level, message string)
+
+// Run implements the Hook interface.
+func (h HookFunc) Run(e *Event, level Level, message string) {
+	h(e, level, message)
+}
+
 // LevelHook applies a different hook for each level.
 type LevelHook struct {
 	NoLevelHook, DebugHook, InfoHook, WarnHook, ErrorHook, FatalHook, PanicHook Hook

hook_test.go

@@ -6,205 +6,136 @@ import (
 	"testing"
 )
 
-type LevelNameHook struct{}
+var (
-
+	levelNameHook = HookFunc(func(e *Event, level Level, msg string) {
-func (h LevelNameHook) Run(e *Event, level Level, msg string) {
 		levelName := level.String()
 		if level == NoLevel {
 			levelName = "nolevel"
 		}
 		e.Str("level_name", levelName)
-}
+	})
-
+	simpleHook = HookFunc(func(e *Event, level Level, msg string) {
-type SimpleHook struct{}
-
-func (h SimpleHook) Run(e *Event, level Level, msg string) {
 		e.Bool("has_level", level != NoLevel)
 		e.Str("test", "logged")
-}
+	})
-
+	copyHook = HookFunc(func(e *Event, level Level, msg string) {
-type CopyHook struct{}
-
-func (h CopyHook) Run(e *Event, level Level, msg string) {
 		hasLevel := level != NoLevel
 		e.Bool("copy_has_level", hasLevel)
 		if hasLevel {
 			e.Str("copy_level", level.String())
 		}
 		e.Str("copy_msg", msg)
-}
+	})
-
+	nopHook = HookFunc(func(e *Event, level Level, message string) {
-type NopHook struct{}
+	})
-
+	discardHook = HookFunc(func(e *Event, level Level, message string) {
-func (h NopHook) Run(e *Event, level Level, msg string) {
+		e.Discard()
-}
+	})
-
-var (
-	levelNameHook LevelNameHook
-	simpleHook    SimpleHook
-	copyHook      CopyHook
-	nopHook       NopHook
 )
 
 func TestHook(t *testing.T) {
-	t.Run("Message", func(t *testing.T) {
+	tests := []struct {
-		out := &bytes.Buffer{}
+		name string
-		log := New(out).Hook(levelNameHook)
+		want string
+		test func(log Logger)
+	}{
+		{"Message", `{"level_name":"nolevel","message":"test message"}` + "\n", func(log Logger) {
+			log = log.Hook(levelNameHook)
 			log.Log().Msg("test message")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level_name":"nolevel","message":"test message"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"NoLevel", `{"level_name":"nolevel"}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(levelNameHook)
-	})
-	t.Run("NoLevel", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(levelNameHook)
 			log.Log().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level_name":"nolevel"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Print", `{"level":"debug","level_name":"debug"}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(levelNameHook)
-	})
-	t.Run("Print", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(levelNameHook)
 			log.Print("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"debug","level_name":"debug"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Error", `{"level":"error","level_name":"error"}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(levelNameHook)
-	})
-	t.Run("Error", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(levelNameHook)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","level_name":"error"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Copy/1", `{"copy_has_level":false,"copy_msg":""}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(copyHook)
-	})
-	t.Run("Copy/1", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(copyHook)
 			log.Log().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"copy_has_level":false,"copy_msg":""}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Copy/2", `{"level":"info","copy_has_level":true,"copy_level":"info","copy_msg":"a message","message":"a message"}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(copyHook)
-	})
-	t.Run("Copy/2", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(copyHook)
 			log.Info().Msg("a message")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"info","copy_has_level":true,"copy_level":"info","copy_msg":"a message","message":"a message"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Multi", `{"level":"error","level_name":"error","has_level":true,"test":"logged"}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(levelNameHook).Hook(simpleHook)
-	})
-	t.Run("Multi", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(levelNameHook).Hook(simpleHook)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","level_name":"error","has_level":true,"test":"logged"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Multi/Message", `{"level":"error","level_name":"error","has_level":true,"test":"logged","message":"a message"}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(levelNameHook).Hook(simpleHook)
-	})
-	t.Run("Multi/Message", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(levelNameHook).Hook(simpleHook)
 			log.Error().Msg("a message")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","level_name":"error","has_level":true,"test":"logged","message":"a message"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Output/single/pre", `{"level":"error","level_name":"error"}` + "\n", func(log Logger) {
-		}
-	})
-	t.Run("Output/single/pre", func(t *testing.T) {
 			ignored := &bytes.Buffer{}
-		out := &bytes.Buffer{}
+			log = New(ignored).Hook(levelNameHook).Output(log.w)
-		log := New(ignored).Hook(levelNameHook).Output(out)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","level_name":"error"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Output/single/post", `{"level":"error","level_name":"error"}` + "\n", func(log Logger) {
-		}
-	})
-	t.Run("Output/single/post", func(t *testing.T) {
 			ignored := &bytes.Buffer{}
-		out := &bytes.Buffer{}
+			log = New(ignored).Output(log.w).Hook(levelNameHook)
-		log := New(ignored).Output(out).Hook(levelNameHook)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","level_name":"error"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Output/multi/pre", `{"level":"error","level_name":"error","has_level":true,"test":"logged"}` + "\n", func(log Logger) {
-		}
-	})
-	t.Run("Output/multi/pre", func(t *testing.T) {
 			ignored := &bytes.Buffer{}
-		out := &bytes.Buffer{}
+			log = New(ignored).Hook(levelNameHook).Hook(simpleHook).Output(log.w)
-		log := New(ignored).Hook(levelNameHook).Hook(simpleHook).Output(out)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","level_name":"error","has_level":true,"test":"logged"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Output/multi/post", `{"level":"error","level_name":"error","has_level":true,"test":"logged"}` + "\n", func(log Logger) {
-		}
-	})
-	t.Run("Output/multi/post", func(t *testing.T) {
 			ignored := &bytes.Buffer{}
-		out := &bytes.Buffer{}
+			log = New(ignored).Output(log.w).Hook(levelNameHook).Hook(simpleHook)
-		log := New(ignored).Output(out).Hook(levelNameHook).Hook(simpleHook)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","level_name":"error","has_level":true,"test":"logged"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Output/mixed", `{"level":"error","level_name":"error","has_level":true,"test":"logged"}` + "\n", func(log Logger) {
-		}
-	})
-	t.Run("Output/mixed", func(t *testing.T) {
 			ignored := &bytes.Buffer{}
-		out := &bytes.Buffer{}
+			log = New(ignored).Hook(levelNameHook).Output(log.w).Hook(simpleHook)
-		log := New(ignored).Hook(levelNameHook).Output(out).Hook(simpleHook)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","level_name":"error","has_level":true,"test":"logged"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"With/single/pre", `{"level":"error","with":"pre","level_name":"error"}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(levelNameHook).With().Str("with", "pre").Logger()
-	})
-	t.Run("With/single/pre", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(levelNameHook).With().Str("with", "pre").Logger()
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","with":"pre","level_name":"error"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"With/single/post", `{"level":"error","with":"post","level_name":"error"}` + "\n", func(log Logger) {
-		}
+			log = log.With().Str("with", "post").Logger().Hook(levelNameHook)
-	})
-	t.Run("With/single/post", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).With().Str("with", "post").Logger().Hook(levelNameHook)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","with":"post","level_name":"error"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"With/multi/pre", `{"level":"error","with":"pre","level_name":"error","has_level":true,"test":"logged"}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(levelNameHook).Hook(simpleHook).With().Str("with", "pre").Logger()
-	})
-	t.Run("With/multi/pre", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(levelNameHook).Hook(simpleHook).With().Str("with", "pre").Logger()
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","with":"pre","level_name":"error","has_level":true,"test":"logged"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"With/multi/post", `{"level":"error","with":"post","level_name":"error","has_level":true,"test":"logged"}` + "\n", func(log Logger) {
-		}
+			log = log.With().Str("with", "post").Logger().Hook(levelNameHook).Hook(simpleHook)
-	})
-	t.Run("With/multi/post", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).With().Str("with", "post").Logger().Hook(levelNameHook).Hook(simpleHook)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","with":"post","level_name":"error","has_level":true,"test":"logged"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"With/mixed", `{"level":"error","with":"mixed","level_name":"error","has_level":true,"test":"logged"}` + "\n", func(log Logger) {
-		}
+			log = log.Hook(levelNameHook).With().Str("with", "mixed").Logger().Hook(simpleHook)
-	})
-	t.Run("With/mixed", func(t *testing.T) {
-		out := &bytes.Buffer{}
-		log := New(out).Hook(levelNameHook).With().Str("with", "mixed").Logger().Hook(simpleHook)
 			log.Error().Msg("")
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error","with":"mixed","level_name":"error","has_level":true,"test":"logged"}`+"\n"; got != want {
+		}},
-			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		{"Discard", "", func(log Logger) {
+			log = log.Hook(discardHook)
+			log.Log().Msg("test message")
+		}},
+		{"None", `{"level":"error"}` + "\n", func(log Logger) {
+			log.Error().Msg("")
+		}},
 	}
-	})
+	for _, tt := range tests {
-	t.Run("None", func(t *testing.T) {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
 			out := &bytes.Buffer{}
 			log := New(out)
-		log.Error().Msg("")
+			tt.test(log)
-		if got, want := decodeIfBinaryToString(out.Bytes()), `{"level":"error"}`+"\n"; got != want {
+			if got, want := decodeIfBinaryToString(out.Bytes()), tt.want; got != want {
 				t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
 			}
 		})
 	}
+}
 
 func BenchmarkHooks(b *testing.B) {
 	logger := New(ioutil.Discard)