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log/slog: add multiple handlers support for logger #74840
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log/slog: add multiple handlers support for logger
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6 changes: 6 additions & 0 deletions
api/next/65954.txt
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,6 @@ | ||
| pkg log/slog, func NewMultiHandler(...Handler) *MultiHandler #65954 | ||
| pkg log/slog, method (*MultiHandler) Enabled(context.Context, Level) bool #65954 | ||
| pkg log/slog, method (*MultiHandler) Handle(context.Context, Record) error #65954 | ||
| pkg log/slog, method (*MultiHandler) WithAttrs([]Attr) Handler #65954 | ||
| pkg log/slog, method (*MultiHandler) WithGroup(string) Handler #65954 | ||
| pkg log/slog, type MultiHandler struct #65954 |
6 changes: 6 additions & 0 deletions
doc/next/6-stdlib/99-minor/log/slog/65954.md
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,6 @@ | ||
| The [`NewMultiHandler`](/pkg/log/slog#NewMultiHandler) function creates a | ||
| [`MultiHandler`](/pkg/log/slog#MultiHandler) that invokes all the given Handlers. | ||
| Its `Enable` method reports whether any of the handlers' `Enabled` methods | ||
| return true. | ||
| Its `Handle`, `WithAttr` and `WithGroup` methods call the corresponding method | ||
| on each of the enabled handlers. |
39 changes: 39 additions & 0 deletions
src/log/slog/example_multi_handler_test.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,39 @@ | ||
| // Copyright 2025 The Go Authors. All rights reserved. | ||
| // Use of this source code is governed by a BSD-style | ||
| // license that can be found in the LICENSE file. | ||
|
|
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| package slog_test | ||
|
|
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| import ( | ||
| "bytes" | ||
| "log/slog" | ||
| "os" | ||
| ) | ||
|
|
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| func ExampleMultiHandler() { | ||
| removeTime := func(groups []string, a slog.Attr) slog.Attr { | ||
| if a.Key == slog.TimeKey && len(groups) == 0 { | ||
| return slog.Attr{} | ||
| } | ||
| return a | ||
| } | ||
|
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| var textBuf, jsonBuf bytes.Buffer | ||
| textHandler := slog.NewTextHandler(&textBuf, &slog.HandlerOptions{ReplaceAttr: removeTime}) | ||
| jsonHandler := slog.NewJSONHandler(&jsonBuf, &slog.HandlerOptions{ReplaceAttr: removeTime}) | ||
|
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| multiHandler := slog.NewMultiHandler(textHandler, jsonHandler) | ||
| logger := slog.New(multiHandler) | ||
|
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| logger.Info("login", | ||
| slog.String("name", "whoami"), | ||
| slog.Int("id", 42), | ||
| ) | ||
|
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| os.Stdout.WriteString(textBuf.String()) | ||
| os.Stdout.WriteString(jsonBuf.String()) | ||
|
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| // Output: | ||
| // level=INFO msg=login name=whoami id=42 | ||
| // {"level":"INFO","msg":"login","name":"whoami","id":42} | ||
| } |
61 changes: 61 additions & 0 deletions
src/log/slog/multi_handler.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,61 @@ | ||
| // Copyright 2025 The Go Authors. All rights reserved. | ||
| // Use of this source code is governed by a BSD-style | ||
| // license that can be found in the LICENSE file. | ||
|
|
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| package slog | ||
|
|
||
| import ( | ||
| "context" | ||
| "errors" | ||
| ) | ||
|
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| // NewMultiHandler creates a [MultiHandler] with the given Handlers. | ||
| func NewMultiHandler(handlers ...Handler) *MultiHandler { | ||
| h := make([]Handler, len(handlers)) | ||
| copy(h, handlers) | ||
| return &MultiHandler{multi: h} | ||
| } | ||
|
|
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| // MultiHandler is a [Handler] that invokes all the given Handlers. | ||
| // Its Enable method reports whether any of the handlers' Enabled methods return true. | ||
| // Its Handle, WithAttr and WithGroup methods call the corresponding method on each of the enabled handlers. | ||
| type MultiHandler struct { | ||
| multi []Handler | ||
| } | ||
|
|
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| func (h *MultiHandler) Enabled(ctx context.Context, l Level) bool { | ||
| for i := range h.multi { | ||
| if h.multi[i].Enabled(ctx, l) { | ||
| return true | ||
| } | ||
| } | ||
| return false | ||
| } | ||
|
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| func (h *MultiHandler) Handle(ctx context.Context, r Record) error { | ||
| var errs []error | ||
| for i := range h.multi { | ||
| if h.multi[i].Enabled(ctx, r.Level) { | ||
| if err := h.multi[i].Handle(ctx, r.Clone()); err != nil { | ||
| errs = append(errs, err) | ||
| } | ||
| } | ||
| } | ||
| return errors.Join(errs...) | ||
| } | ||
|
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| func (h *MultiHandler) WithAttrs(attrs []Attr) Handler { | ||
| handlers := make([]Handler, 0, len(h.multi)) | ||
| for i := range h.multi { | ||
| handlers = append(handlers, h.multi[i].WithAttrs(attrs)) | ||
| } | ||
| return &MultiHandler{multi: handlers} | ||
| } | ||
|
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| func (h *MultiHandler) WithGroup(name string) Handler { | ||
| handlers := make([]Handler, 0, len(h.multi)) | ||
| for i := range h.multi { | ||
| handlers = append(handlers, h.multi[i].WithGroup(name)) | ||
| } | ||
| return &MultiHandler{multi: handlers} | ||
| } |
139 changes: 139 additions & 0 deletions
src/log/slog/multi_handler_test.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,139 @@ | ||
| // Copyright 2025 The Go Authors. All rights reserved. | ||
| // Use of this source code is governed by a BSD-style | ||
| // license that can be found in the LICENSE file. | ||
|
|
||
| package slog | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "context" | ||
| "errors" | ||
| "testing" | ||
| "time" | ||
| ) | ||
|
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| // mockFailingHandler is a handler that always returns an error | ||
| // from its Handle method. | ||
| type mockFailingHandler struct { | ||
| Handler | ||
| err error | ||
| } | ||
|
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| func (h *mockFailingHandler) Handle(ctx context.Context, r Record) error { | ||
| _ = h.Handler.Handle(ctx, r) | ||
| return h.err | ||
| } | ||
|
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| func TestMultiHandler(t *testing.T) { | ||
| t.Run("Handle sends log to all handlers", func(t *testing.T) { | ||
| var buf1, buf2 bytes.Buffer | ||
| h1 := NewTextHandler(&buf1, nil) | ||
| h2 := NewJSONHandler(&buf2, nil) | ||
|
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| multi := NewMultiHandler(h1, h2) | ||
| logger := New(multi) | ||
|
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| logger.Info("hello world", "user", "test") | ||
|
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| checkLogOutput(t, buf1.String(), "time="+textTimeRE+` level=INFO msg="hello world" user=test`) | ||
| checkLogOutput(t, buf2.String(), `{"time":"`+jsonTimeRE+`","level":"INFO","msg":"hello world","user":"test"}`) | ||
| }) | ||
|
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| t.Run("Enabled returns true if any handler is enabled", func(t *testing.T) { | ||
| h1 := NewTextHandler(&bytes.Buffer{}, &HandlerOptions{Level: LevelError}) | ||
| h2 := NewTextHandler(&bytes.Buffer{}, &HandlerOptions{Level: LevelInfo}) | ||
|
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| multi := NewMultiHandler(h1, h2) | ||
|
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| if !multi.Enabled(context.Background(), LevelInfo) { | ||
| t.Error("Enabled should be true for INFO level, but got false") | ||
| } | ||
| if !multi.Enabled(context.Background(), LevelError) { | ||
| t.Error("Enabled should be true for ERROR level, but got false") | ||
| } | ||
| }) | ||
|
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| t.Run("Enabled returns false if no handlers are enabled", func(t *testing.T) { | ||
| h1 := NewTextHandler(&bytes.Buffer{}, &HandlerOptions{Level: LevelError}) | ||
| h2 := NewTextHandler(&bytes.Buffer{}, &HandlerOptions{Level: LevelInfo}) | ||
|
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| multi := NewMultiHandler(h1, h2) | ||
|
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| if multi.Enabled(context.Background(), LevelDebug) { | ||
| t.Error("Enabled should be false for DEBUG level, but got true") | ||
| } | ||
| }) | ||
|
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| t.Run("WithAttrs propagates attributes to all handlers", func(t *testing.T) { | ||
| var buf1, buf2 bytes.Buffer | ||
| h1 := NewTextHandler(&buf1, nil) | ||
| h2 := NewJSONHandler(&buf2, nil) | ||
|
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| multi := NewMultiHandler(h1, h2).WithAttrs([]Attr{String("request_id", "123")}) | ||
| logger := New(multi) | ||
|
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| logger.Info("request processed") | ||
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| checkLogOutput(t, buf1.String(), "time="+textTimeRE+` level=INFO msg="request processed" request_id=123`) | ||
| checkLogOutput(t, buf2.String(), `{"time":"`+jsonTimeRE+`","level":"INFO","msg":"request processed","request_id":"123"}`) | ||
| }) | ||
|
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| t.Run("WithGroup propagates group to all handlers", func(t *testing.T) { | ||
| var buf1, buf2 bytes.Buffer | ||
| h1 := NewTextHandler(&buf1, &HandlerOptions{AddSource: false}) | ||
| h2 := NewJSONHandler(&buf2, &HandlerOptions{AddSource: false}) | ||
|
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| multi := NewMultiHandler(h1, h2).WithGroup("req") | ||
| logger := New(multi) | ||
|
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| logger.Info("user login", "user_id", 42) | ||
|
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| checkLogOutput(t, buf1.String(), "time="+textTimeRE+` level=INFO msg="user login" req.user_id=42`) | ||
| checkLogOutput(t, buf2.String(), `{"time":"`+jsonTimeRE+`","level":"INFO","msg":"user login","req":{"user_id":42}}`) | ||
| }) | ||
|
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| t.Run("Handle propagates errors from handlers", func(t *testing.T) { | ||
| errFail := errors.New("mock failing") | ||
|
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| var buf1, buf2 bytes.Buffer | ||
| h1 := NewTextHandler(&buf1, nil) | ||
| h2 := &mockFailingHandler{Handler: NewJSONHandler(&buf2, nil), err: errFail} | ||
|
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| multi := NewMultiHandler(h2, h1) | ||
|
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| err := multi.Handle(context.Background(), NewRecord(time.Now(), LevelInfo, "test message", 0)) | ||
| if !errors.Is(err, errFail) { | ||
| t.Errorf("Expected error: %v, but got: %v", errFail, err) | ||
| } | ||
|
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| checkLogOutput(t, buf1.String(), "time="+textTimeRE+` level=INFO msg="test message"`) | ||
| checkLogOutput(t, buf2.String(), `{"time":"`+jsonTimeRE+`","level":"INFO","msg":"test message"}`) | ||
| }) | ||
|
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| t.Run("Handle with no handlers", func(t *testing.T) { | ||
| multi := NewMultiHandler() | ||
| logger := New(multi) | ||
|
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| logger.Info("nothing") | ||
|
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| err := multi.Handle(context.Background(), NewRecord(time.Now(), LevelInfo, "test", 0)) | ||
| if err != nil { | ||
| t.Errorf("Handle with no sub-handlers should return nil, but got: %v", err) | ||
| } | ||
| }) | ||
| } | ||
|
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| // Test that NewMultiHandler copies the input slice and is insulated from future modification. | ||
| func TestNewMultiHandlerCopy(t *testing.T) { | ||
| var buf1 bytes.Buffer | ||
| h1 := NewTextHandler(&buf1, nil) | ||
| slice := []Handler{h1} | ||
| multi := NewMultiHandler(slice...) | ||
| slice[0] = nil | ||
|
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| err := multi.Handle(context.Background(), NewRecord(time.Now(), LevelInfo, "test message", 0)) | ||
| if err != nil { | ||
| t.Errorf("Expected nil error, but got: %v", err) | ||
| } | ||
| checkLogOutput(t, buf1.String(), "time="+textTimeRE+` level=INFO msg="test message"`) | ||
| } |
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