Support arbitrary hook for fatal logs (#1088)

This adds a new WithFatalHook option that allows specifying arbitrary
behavior overrides messages logged with FatalLevel.

This supersedes the previous OnFatal option that relied on a
CheckWriteAction enum.

The enum is replaced by a CheckWriteHook--a hook that runs after write.

Refs #1086

Co-authored-by: Sung Yoon Whang <sungyoon@uber.com>
Co-authored-by: Abhinav Gupta <abg@uber.com>

internal/exit/exit.go

@@ -24,24 +24,32 @@ package exit
 
 import "os"
 
-var real = func() { os.Exit(1) }
+var _exit = os.Exit
 
 // Exit normally terminates the process by calling os.Exit(1). If the package
 // is stubbed, it instead records a call in the testing spy.
+// Deprecated: use With() instead.
 func Exit() {
-	real()
+	With(1)
+}
+
+// With terminates the process by calling os.Exit(code). If the package is
+// stubbed, it instead records a call in the testing spy.
+func With(code int) {
+	_exit(code)
 }
 
 // A StubbedExit is a testing fake for os.Exit.
 type StubbedExit struct {
 	Exited bool
-	prev   func()
+	Code   int
+	prev   func(code int)
 }
 
 // Stub substitutes a fake for the call to os.Exit(1).
 func Stub() *StubbedExit {
-	s := &StubbedExit{prev: real}
-	real = s.exit
+	s := &StubbedExit{prev: _exit}
+	_exit = s.exit
 	return s
 }
 
@@ -56,9 +64,10 @@ func WithStub(f func()) *StubbedExit {
 
 // Unstub restores the previous exit function.
 func (se *StubbedExit) Unstub() {
-	real = se.prev
+	_exit = se.prev
 }
 
-func (se *StubbedExit) exit() {
+func (se *StubbedExit) exit(code int) {
 	se.Exited = true
+	se.Code = code
 }

internal/exit/exit_test.go

@@ -18,25 +18,32 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
-package exit
+package exit_test
 
 import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"go.uber.org/zap/internal/exit"
 )
 
 func TestStub(t *testing.T) {
+	type want struct {
+		exit bool
+		code int
+	}
 	tests := []struct {
 		f    func()
-		want bool
+		want want
 	}{
-		{Exit, true},
-		{func() {}, false},
+		{func() { exit.With(42) }, want{exit: true, code: 42}},
+		{exit.Exit, want{exit: true, code: 1}},
+		{func() {}, want{}},
 	}
 
 	for _, tt := range tests {
-		s := WithStub(tt.f)
-		assert.Equal(t, tt.want, s.Exited, "Stub captured unexpected exit value.")
+		s := exit.WithStub(tt.f)
+		assert.Equal(t, tt.want.exit, s.Exited, "Stub captured unexpected exit value.")
+		assert.Equal(t, tt.want.code, s.Code, "Stub captured unexpected exit value.")
 	}
 }

logger.go

@@ -42,7 +42,7 @@ type Logger struct {
 
 	development bool
 	addCaller   bool
-	onFatal     zapcore.CheckWriteAction // default is WriteThenFatal
+	onFatal     zapcore.CheckWriteHook // default is WriteThenFatal
 
 	name        string
 	errorOutput zapcore.WriteSyncer
@@ -288,12 +288,12 @@ func (log *Logger) check(lvl zapcore.Level, msg string) *zapcore.CheckedEntry {
 		ce = ce.Should(ent, zapcore.WriteThenPanic)
 	case zapcore.FatalLevel:
 		onFatal := log.onFatal
-		// Noop is the default value for CheckWriteAction, and it leads to
+		// nil is the default value for CheckWriteAction, and it leads to
 		// continued execution after a Fatal which is unexpected.
-		if onFatal == zapcore.WriteThenNoop {
+		if onFatal == nil {
 			onFatal = zapcore.WriteThenFatal
 		}
-		ce = ce.Should(ent, onFatal)
+		ce = ce.After(ent, onFatal)
 	case zapcore.DPanicLevel:
 		if log.development {
 			ce = ce.Should(ent, zapcore.WriteThenPanic)

logger_test.go

@@ -579,6 +579,23 @@ func TestLoggerCustomOnFatal(t *testing.T) {
 	}
 }
 
+type customWriteHook struct {
+	called bool
+}
+
+func (h *customWriteHook) OnWrite(_ *zapcore.CheckedEntry, _ []Field) {
+	h.called = true
+}
+
+func TestLoggerWithFatalHook(t *testing.T) {
+	var h customWriteHook
+	withLogger(t, InfoLevel, opts(WithFatalHook(&h)), func(logger *Logger, logs *observer.ObservedLogs) {
+		logger.Fatal("great sadness")
+		assert.True(t, h.called)
+		assert.Equal(t, 1, logs.FilterLevelExact(FatalLevel).Len())
+	})
+}
+
 func TestNopLogger(t *testing.T) {
 	logger := NewNop()
 

options.go

@@ -133,9 +133,15 @@ func IncreaseLevel(lvl zapcore.LevelEnabler) Option {
 }
 
 // OnFatal sets the action to take on fatal logs.
+// Deprecated: Use WithFatalHook instead.
 func OnFatal(action zapcore.CheckWriteAction) Option {
+	return WithFatalHook(action)
+}
+
+// WithFatalHook sets a CheckWriteHook to run on fatal logs.
+func WithFatalHook(hook zapcore.CheckWriteHook) Option {
 	return optionFunc(func(log *Logger) {
-		log.onFatal = action
+		log.onFatal = hook
 	})
 }
 

zapcore/entry.go

@@ -27,10 +27,9 @@ import (
 	"sync"
 	"time"
 
+	"go.uber.org/multierr"
 	"go.uber.org/zap/internal/bufferpool"
 	"go.uber.org/zap/internal/exit"
-
-	"go.uber.org/multierr"
 )
 
 var (
@@ -152,6 +151,13 @@ type Entry struct {
 	Stack      string
 }
 
+// CheckWriteHook allows to customize the action to take after a Fatal log entry
+// is processed.
+type CheckWriteHook interface {
+	// OnWrite gets invoked when an entry is written
+	OnWrite(*CheckedEntry, []Field)
+}
+
 // CheckWriteAction indicates what action to take after a log entry is
 // processed. Actions are ordered in increasing severity.
 type CheckWriteAction uint8
@@ -164,10 +170,25 @@ const (
 	WriteThenGoexit
 	// WriteThenPanic causes a panic after Write.
 	WriteThenPanic
-	// WriteThenFatal causes a fatal os.Exit after Write.
+	// WriteThenFatal causes an os.Exit(1) after Write.
 	WriteThenFatal
 )
 
+// OnWrite implements the OnWrite method to keep CheckWriteAction compatible
+// with the new CheckWriteHook interface which deprecates CheckWriteAction.
+func (a CheckWriteAction) OnWrite(ce *CheckedEntry, _ []Field) {
+	switch a {
+	case WriteThenGoexit:
+		runtime.Goexit()
+	case WriteThenPanic:
+		panic(ce.Message)
+	case WriteThenFatal:
+		exit.Exit()
+	}
+}
+
+var _ CheckWriteHook = CheckWriteAction(0)
+
 // CheckedEntry is an Entry together with a collection of Cores that have
 // already agreed to log it.
 //
@@ -178,15 +199,15 @@ type CheckedEntry struct {
 	Entry
 	ErrorOutput WriteSyncer
 	dirty       bool // best-effort detection of pool misuse
-	should      CheckWriteAction
+	after       CheckWriteHook
 	cores       []Core
 }
 
 func (ce *CheckedEntry) reset() {
 	ce.Entry = Entry{}
 	ce.ErrorOutput = nil
 	ce.dirty = false
-	ce.should = WriteThenNoop
+	ce.after = nil
 	for i := range ce.cores {
 		// don't keep references to cores
 		ce.cores[i] = nil
@@ -224,17 +245,11 @@ func (ce *CheckedEntry) Write(fields ...Field) {
 		ce.ErrorOutput.Sync()
 	}
 
-	should, msg := ce.should, ce.Message
-	putCheckedEntry(ce)
-
-	switch should {
-	case WriteThenPanic:
-		panic(msg)
-	case WriteThenFatal:
-		exit.Exit()
-	case WriteThenGoexit:
-		runtime.Goexit()
+	hook := ce.after
+	if hook != nil {
+		hook.OnWrite(ce, fields)
 	}
+	putCheckedEntry(ce)
 }
 
 // AddCore adds a Core that has agreed to log this CheckedEntry. It's intended to be
@@ -252,11 +267,19 @@ func (ce *CheckedEntry) AddCore(ent Entry, core Core) *CheckedEntry {
 // Should sets this CheckedEntry's CheckWriteAction, which controls whether a
 // Core will panic or fatal after writing this log entry. Like AddCore, it's
 // safe to call on nil CheckedEntry references.
+// Deprecated: Use After(ent Entry, after CheckWriteHook) instead.
 func (ce *CheckedEntry) Should(ent Entry, should CheckWriteAction) *CheckedEntry {
+	return ce.After(ent, should)
+}
+
+// After sets this CheckEntry's CheckWriteHook, which will be called after this
+// log entry has been written. It's safe to call this on nil CheckedEntry
+// references.
+func (ce *CheckedEntry) After(ent Entry, hook CheckWriteHook) *CheckedEntry {
 	if ce == nil {
 		ce = getCheckedEntry()
 		ce.Entry = ent
 	}
-	ce.should = should
+	ce.after = hook
 	return ce
 }

zapcore/entry_test.go

@@ -64,7 +64,7 @@ func TestPutNilEntry(t *testing.T) {
 			assert.NotNil(t, ce, "Expected only non-nil CheckedEntries in pool.")
 			assert.False(t, ce.dirty, "Unexpected dirty bit set.")
 			assert.Nil(t, ce.ErrorOutput, "Non-nil ErrorOutput.")
-			assert.Equal(t, WriteThenNoop, ce.should, "Unexpected terminal behavior.")
+			assert.Nil(t, ce.after, "Unexpected terminal behavior.")
 			assert.Equal(t, 0, len(ce.cores), "Expected empty slice of cores.")
 			assert.True(t, cap(ce.cores) > 0, "Expected pooled CheckedEntries to pre-allocate slice of Cores.")
 		}
@@ -128,5 +128,22 @@ func TestCheckedEntryWrite(t *testing.T) {
 			ce.Write()
 		})
 		assert.True(t, stub.Exited, "Expected to exit when WriteThenFatal is set.")
+		assert.Equal(t, 1, stub.Code, "Expected to exit when WriteThenFatal is set.")
 	})
+
+	t.Run("After", func(t *testing.T) {
+		var ce *CheckedEntry
+		hook := &customHook{}
+		ce = ce.After(Entry{}, hook)
+		ce.Write()
+		assert.True(t, hook.called, "Expected to call custom action after Write.")
+	})
+}
+
+type customHook struct {
+	called bool
+}
+
+func (c *customHook) OnWrite(_ *CheckedEntry, _ []Field) {
+	c.called = true
 }