src/log/slog/handler_test.go

// Copyright 2022 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.

// TODO: verify that the output of Marshal{Text,JSON} is suitably escaped.

package slog

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log/slog/internal/buffer"
	"os"
	"path/filepath"
	"slices"
	"strconv"
	"strings"
	"sync"
	"testing"
	"time"
)

func TestDefaultHandle(t *testing.T) {
	ctx := context.Background()
	preAttrs := []Attr{Int("pre", 0)}
	attrs := []Attr{Int("a", 1), String("b", "two")}
	for _, test := range []struct {
		name  string
		with  func(Handler) Handler
		attrs []Attr
		want  string
	}{
		{
			name: "no attrs",
			want: "INFO message",
		},
		{
			name:  "attrs",
			attrs: attrs,
			want:  "INFO message a=1 b=two",
		},
		{
			name:  "preformatted",
			with:  func(h Handler) Handler { return h.WithAttrs(preAttrs) },
			attrs: attrs,
			want:  "INFO message pre=0 a=1 b=two",
		},
		{
			name: "groups",
			attrs: []Attr{
				Int("a", 1),
				Group("g",
					Int("b", 2),
					Group("h", Int("c", 3)),
					Int("d", 4)),
				Int("e", 5),
			},
			want: "INFO message a=1 g.b=2 g.h.c=3 g.d=4 e=5",
		},
		{
			name:  "group",
			with:  func(h Handler) Handler { return h.WithAttrs(preAttrs).WithGroup("s") },
			attrs: attrs,
			want:  "INFO message pre=0 s.a=1 s.b=two",
		},
		{
			name: "preformatted groups",
			with: func(h Handler) Handler {
				return h.WithAttrs([]Attr{Int("p1", 1)}).
					WithGroup("s1").
					WithAttrs([]Attr{Int("p2", 2)}).
					WithGroup("s2")
			},
			attrs: attrs,
			want:  "INFO message p1=1 s1.p2=2 s1.s2.a=1 s1.s2.b=two",
		},
		{
			name: "two with-groups",
			with: func(h Handler) Handler {
				return h.WithAttrs([]Attr{Int("p1", 1)}).
					WithGroup("s1").
					WithGroup("s2")
			},
			attrs: attrs,
			want:  "INFO message p1=1 s1.s2.a=1 s1.s2.b=two",
		},
	} {
		t.Run(test.name, func(t *testing.T) {
			var got string
			var h Handler = newDefaultHandler(func(_ uintptr, b []byte) error {
				got = string(b)
				return nil
			})
			if test.with != nil {
				h = test.with(h)
			}
			r := NewRecord(time.Time{}, LevelInfo, "message", 0)
			r.AddAttrs(test.attrs...)
			if err := h.Handle(ctx, r); err != nil {
				t.Fatal(err)
			}
			if got != test.want {
				t.Errorf("\ngot  %s\nwant %s", got, test.want)
			}
		})
	}
}

func TestConcurrentWrites(t *testing.T) {
	ctx := context.Background()
	count := 1000
	for _, handlerType := range []string{"text", "json"} {
		t.Run(handlerType, func(t *testing.T) {
			var buf bytes.Buffer
			var h Handler
			switch handlerType {
			case "text":
				h = NewTextHandler(&buf, nil)
			case "json":
				h = NewJSONHandler(&buf, nil)
			default:
				t.Fatalf("unexpected handlerType %q", handlerType)
			}
			sub1 := h.WithAttrs([]Attr{Bool("sub1", true)})
			sub2 := h.WithAttrs([]Attr{Bool("sub2", true)})
			var wg sync.WaitGroup
			for i := 0; i < count; i++ {
				sub1Record := NewRecord(time.Time{}, LevelInfo, "hello from sub1", 0)
				sub1Record.AddAttrs(Int("i", i))
				sub2Record := NewRecord(time.Time{}, LevelInfo, "hello from sub2", 0)
				sub2Record.AddAttrs(Int("i", i))
				wg.Add(1)
				go func() {
					defer wg.Done()
					if err := sub1.Handle(ctx, sub1Record); err != nil {
						t.Error(err)
					}
					if err := sub2.Handle(ctx, sub2Record); err != nil {
						t.Error(err)
					}
				}()
			}
			wg.Wait()
			for i := 1; i <= 2; i++ {
				want := "hello from sub" + strconv.Itoa(i)
				n := strings.Count(buf.String(), want)
				if n != count {
					t.Fatalf("want %d occurrences of %q, got %d", count, want, n)
				}
			}
		})
	}
}

// Verify the common parts of TextHandler and JSONHandler.
func TestJSONAndTextHandlers(t *testing.T) {
	// remove all Attrs
	removeAll := func(_ []string, a Attr) Attr { return Attr{} }

	attrs := []Attr{String("a", "one"), Int("b", 2), Any("", nil)}
	preAttrs := []Attr{Int("pre", 3), String("x", "y")}

	for _, test := range []struct {
		name      string
		replace   func([]string, Attr) Attr
		addSource bool
		with      func(Handler) Handler
		preAttrs  []Attr
		attrs     []Attr
		wantText  string
		wantJSON  string
	}{
		{
			name:     "basic",
			attrs:    attrs,
			wantText: "time=2000-01-02T03:04:05.000Z level=INFO msg=message a=one b=2",
			wantJSON: `{"time":"2000-01-02T03:04:05Z","level":"INFO","msg":"message","a":"one","b":2}`,
		},
		{
			name:     "empty key",
			attrs:    append(slices.Clip(attrs), Any("", "v")),
			wantText: `time=2000-01-02T03:04:05.000Z level=INFO msg=message a=one b=2 ""=v`,
			wantJSON: `{"time":"2000-01-02T03:04:05Z","level":"INFO","msg":"message","a":"one","b":2,"":"v"}`,
		},
		{
			name:     "cap keys",
			replace:  upperCaseKey,
			attrs:    attrs,
			wantText: "TIME=2000-01-02T03:04:05.000Z LEVEL=INFO MSG=message A=one B=2",
			wantJSON: `{"TIME":"2000-01-02T03:04:05Z","LEVEL":"INFO","MSG":"message","A":"one","B":2}`,
		},
		{
			name:     "remove all",
			replace:  removeAll,
			attrs:    attrs,
			wantText: "",
			wantJSON: `{}`,
		},
		{
			name:     "preformatted",
			with:     func(h Handler) Handler { return h.WithAttrs(preAttrs) },
			preAttrs: preAttrs,
			attrs:    attrs,
			wantText: "time=2000-01-02T03:04:05.000Z level=INFO msg=message pre=3 x=y a=one b=2",
			wantJSON: `{"time":"2000-01-02T03:04:05Z","level":"INFO","msg":"message","pre":3,"x":"y","a":"one","b":2}`,
		},
		{
			name:     "preformatted cap keys",
			replace:  upperCaseKey,
			with:     func(h Handler) Handler { return h.WithAttrs(preAttrs) },
			preAttrs: preAttrs,
			attrs:    attrs,
			wantText: "TIME=2000-01-02T03:04:05.000Z LEVEL=INFO MSG=message PRE=3 X=y A=one B=2",
			wantJSON: `{"TIME":"2000-01-02T03:04:05Z","LEVEL":"INFO","MSG":"message","PRE":3,"X":"y","A":"one","B":2}`,
		},
		{
			name:     "preformatted remove all",
			replace:  removeAll,
			with:     func(h Handler) Handler { return h.WithAttrs(preAttrs) },
			preAttrs: preAttrs,
			attrs:    attrs,
			wantText: "",
			wantJSON: "{}",
		},
		{
			name:     "remove built-in",
			replace:  removeKeys(TimeKey, LevelKey, MessageKey),
			attrs:    attrs,
			wantText: "a=one b=2",
			wantJSON: `{"a":"one","b":2}`,
		},
		{
			name:     "preformatted remove built-in",
			replace:  removeKeys(TimeKey, LevelKey, MessageKey),
			with:     func(h Handler) Handler { return h.WithAttrs(preAttrs) },
			attrs:    attrs,
			wantText: "pre=3 x=y a=one b=2",
			wantJSON: `{"pre":3,"x":"y","a":"one","b":2}`,
		},
		{
			name:    "groups",
			replace: removeKeys(TimeKey, LevelKey), // to simplify the result
			attrs: []Attr{
				Int("a", 1),
				Group("g",
					Int("b", 2),
					Group("h", Int("c", 3)),
					Int("d", 4)),
				Int("e", 5),
			},
			wantText: "msg=message a=1 g.b=2 g.h.c=3 g.d=4 e=5",
			wantJSON: `{"msg":"message","a":1,"g":{"b":2,"h":{"c":3},"d":4},"e":5}`,
		},
		{
			name:     "empty group",
			replace:  removeKeys(TimeKey, LevelKey),
			attrs:    []Attr{Group("g"), Group("h", Int("a", 1))},
			wantText: "msg=message h.a=1",
			wantJSON: `{"msg":"message","h":{"a":1}}`,
		},
		{
			name:    "nested empty group",
			replace: removeKeys(TimeKey, LevelKey),
			attrs: []Attr{
				Group("g",
					Group("h",
						Group("i"), Group("j"))),
			},
			wantText: `msg=message`,
			wantJSON: `{"msg":"message"}`,
		},
		{
			name:    "nested non-empty group",
			replace: removeKeys(TimeKey, LevelKey),
			attrs: []Attr{
				Group("g",
					Group("h",
						Group("i"), Group("j", Int("a", 1)))),
			},
			wantText: `msg=message g.h.j.a=1`,
			wantJSON: `{"msg":"message","g":{"h":{"j":{"a":1}}}}`,
		},
		{
			name:    "escapes",
			replace: removeKeys(TimeKey, LevelKey),
			attrs: []Attr{
				String("a b", "x\t\n\000y"),
				Group(" b.c=\"\\x2E\t",
					String("d=e", "f.g\""),
					Int("m.d", 1)), // dot is not escaped
			},
			wantText: `msg=message "a b"="x\t\n\x00y" " b.c=\"\\x2E\t.d=e"="f.g\"" " b.c=\"\\x2E\t.m.d"=1`,
			wantJSON: `{"msg":"message","a b":"x\t\n\u0000y"," b.c=\"\\x2E\t":{"d=e":"f.g\"","m.d":1}}`,
		},
		{
			name:    "LogValuer",
			replace: removeKeys(TimeKey, LevelKey),
			attrs: []Attr{
				Int("a", 1),
				Any("name", logValueName{"Ren", "Hoek"}),
				Int("b", 2),
			},
			wantText: "msg=message a=1 name.first=Ren name.last=Hoek b=2",
			wantJSON: `{"msg":"message","a":1,"name":{"first":"Ren","last":"Hoek"},"b":2}`,
		},
		{
			// Test resolution when there is no ReplaceAttr function.
			name: "resolve",
			attrs: []Attr{
				Any("", &replace{Value{}}), // should be elided
				Any("name", logValueName{"Ren", "Hoek"}),
			},
			wantText: "time=2000-01-02T03:04:05.000Z level=INFO msg=message name.first=Ren name.last=Hoek",
			wantJSON: `{"time":"2000-01-02T03:04:05Z","level":"INFO","msg":"message","name":{"first":"Ren","last":"Hoek"}}`,
		},
		{
			name:     "with-group",
			replace:  removeKeys(TimeKey, LevelKey),
			with:     func(h Handler) Handler { return h.WithAttrs(preAttrs).WithGroup("s") },
			attrs:    attrs,
			wantText: "msg=message pre=3 x=y s.a=one s.b=2",
			wantJSON: `{"msg":"message","pre":3,"x":"y","s":{"a":"one","b":2}}`,
		},
		{
			name:    "preformatted with-groups",
			replace: removeKeys(TimeKey, LevelKey),
			with: func(h Handler) Handler {
				return h.WithAttrs([]Attr{Int("p1", 1)}).
					WithGroup("s1").
					WithAttrs([]Attr{Int("p2", 2)}).
					WithGroup("s2").
					WithAttrs([]Attr{Int("p3", 3)})
			},
			attrs:    attrs,
			wantText: "msg=message p1=1 s1.p2=2 s1.s2.p3=3 s1.s2.a=one s1.s2.b=2",
			wantJSON: `{"msg":"message","p1":1,"s1":{"p2":2,"s2":{"p3":3,"a":"one","b":2}}}`,
		},
		{
			name:    "two with-groups",
			replace: removeKeys(TimeKey, LevelKey),
			with: func(h Handler) Handler {
				return h.WithAttrs([]Attr{Int("p1", 1)}).
					WithGroup("s1").
					WithGroup("s2")
			},
			attrs:    attrs,
			wantText: "msg=message p1=1 s1.s2.a=one s1.s2.b=2",
			wantJSON: `{"msg":"message","p1":1,"s1":{"s2":{"a":"one","b":2}}}`,
		},
		{
			name:    "empty with-groups",
			replace: removeKeys(TimeKey, LevelKey),
			with: func(h Handler) Handler {
				return h.WithGroup("x").WithGroup("y")
			},
			wantText: "msg=message",
			wantJSON: `{"msg":"message"}`,
		},
		{
			name:    "empty with-groups, no non-empty attrs",
			replace: removeKeys(TimeKey, LevelKey),
			with: func(h Handler) Handler {
				return h.WithGroup("x").WithAttrs([]Attr{Group("g")}).WithGroup("y")
			},
			wantText: "msg=message",
			wantJSON: `{"msg":"message"}`,
		},
		{
			name:    "one empty with-group",
			replace: removeKeys(TimeKey, LevelKey),
			with: func(h Handler) Handler {
				return h.WithGroup("x").WithAttrs([]Attr{Int("a", 1)}).WithGroup("y")
			},
			attrs:    []Attr{Group("g", Group("h"))},
			wantText: "msg=message x.a=1",
			wantJSON: `{"msg":"message","x":{"a":1}}`,
		},
		{
			name:     "GroupValue as Attr value",
			replace:  removeKeys(TimeKey, LevelKey),
			attrs:    []Attr{{"v", AnyValue(IntValue(3))}},
			wantText: "msg=message v=3",
			wantJSON: `{"msg":"message","v":3}`,
		},
		{
			name:     "byte slice",
			replace:  removeKeys(TimeKey, LevelKey),
			attrs:    []Attr{Any("bs", []byte{1, 2, 3, 4})},
			wantText: `msg=message bs="\x01\x02\x03\x04"`,
			wantJSON: `{"msg":"message","bs":"AQIDBA=="}`,
		},
		{
			name:     "json.RawMessage",
			replace:  removeKeys(TimeKey, LevelKey),
			attrs:    []Attr{Any("bs", json.RawMessage([]byte("1234")))},
			wantText: `msg=message bs="1234"`,
			wantJSON: `{"msg":"message","bs":1234}`,
		},
		{
			name:    "inline group",
			replace: removeKeys(TimeKey, LevelKey),
			attrs: []Attr{
				Int("a", 1),
				Group("", Int("b", 2), Int("c", 3)),
				Int("d", 4),
			},
			wantText: `msg=message a=1 b=2 c=3 d=4`,
			wantJSON: `{"msg":"message","a":1,"b":2,"c":3,"d":4}`,
		},
		{
			name: "Source",
			replace: func(gs []string, a Attr) Attr {
				if a.Key == SourceKey {
					s := a.Value.Any().(*Source)
					s.File = filepath.Base(s.File)
					return Any(a.Key, s)
				}
				return removeKeys(TimeKey, LevelKey)(gs, a)
			},
			addSource: true,
			wantText:  `source=handler_test.go:$LINE msg=message`,
			wantJSON:  `{"source":{"function":"log/slog.TestJSONAndTextHandlers","file":"handler_test.go","line":$LINE},"msg":"message"}`,
		},
		{
			name: "replace built-in with group",
			replace: func(_ []string, a Attr) Attr {
				if a.Key == TimeKey {
					return Group(TimeKey, "mins", 3, "secs", 2)
				}
				if a.Key == LevelKey {
					return Attr{}
				}
				return a
			},
			wantText: `time.mins=3 time.secs=2 msg=message`,
			wantJSON: `{"time":{"mins":3,"secs":2},"msg":"message"}`,
		},
		{
			name:     "replace empty",
			replace:  func([]string, Attr) Attr { return Attr{} },
			attrs:    []Attr{Group("g", Int("a", 1))},
			wantText: "",
			wantJSON: `{}`,
		},
		{
			name: "replace empty 1",
			with: func(h Handler) Handler {
				return h.WithGroup("g").WithAttrs([]Attr{Int("a", 1)})
			},
			replace:  func([]string, Attr) Attr { return Attr{} },
			attrs:    []Attr{Group("h", Int("b", 2))},
			wantText: "",
			wantJSON: `{}`,
		},
		{
			name: "replace empty 2",
			with: func(h Handler) Handler {
				return h.WithGroup("g").WithAttrs([]Attr{Int("a", 1)}).WithGroup("h").WithAttrs([]Attr{Int("b", 2)})
			},
			replace:  func([]string, Attr) Attr { return Attr{} },
			attrs:    []Attr{Group("i", Int("c", 3))},
			wantText: "",
			wantJSON: `{}`,
		},
		{
			name:     "replace empty 3",
			with:     func(h Handler) Handler { return h.WithGroup("g") },
			replace:  func([]string, Attr) Attr { return Attr{} },
			attrs:    []Attr{Int("a", 1)},
			wantText: "",
			wantJSON: `{}`,
		},
		{
			name: "replace empty inline",
			with: func(h Handler) Handler {
				return h.WithGroup("g").WithAttrs([]Attr{Int("a", 1)}).WithGroup("h").WithAttrs([]Attr{Int("b", 2)})
			},
			replace:  func([]string, Attr) Attr { return Attr{} },
			attrs:    []Attr{Group("", Int("c", 3))},
			wantText: "",
			wantJSON: `{}`,
		},
		{
			name: "replace partial empty attrs 1",
			with: func(h Handler) Handler {
				return h.WithGroup("g").WithAttrs([]Attr{Int("a", 1)}).WithGroup("h").WithAttrs([]Attr{Int("b", 2)})
			},
			replace: func(groups []string, attr Attr) Attr {
				return removeKeys(TimeKey, LevelKey, MessageKey, "a")(groups, attr)
			},
			attrs:    []Attr{Group("i", Int("c", 3))},
			wantText: "g.h.b=2 g.h.i.c=3",
			wantJSON: `{"g":{"h":{"b":2,"i":{"c":3}}}}`,
		},
		{
			name: "replace partial empty attrs 2",
			with: func(h Handler) Handler {
				return h.WithGroup("g").WithAttrs([]Attr{Int("a", 1)}).WithAttrs([]Attr{Int("n", 4)}).WithGroup("h").WithAttrs([]Attr{Int("b", 2)})
			},
			replace: func(groups []string, attr Attr) Attr {
				return removeKeys(TimeKey, LevelKey, MessageKey, "a", "b")(groups, attr)
			},
			attrs:    []Attr{Group("i", Int("c", 3))},
			wantText: "g.n=4 g.h.i.c=3",
			wantJSON: `{"g":{"n":4,"h":{"i":{"c":3}}}}`,
		},
		{
			name: "replace partial empty attrs 3",
			with: func(h Handler) Handler {
				return h.WithGroup("g").WithAttrs([]Attr{Int("x", 0)}).WithAttrs([]Attr{Int("a", 1)}).WithAttrs([]Attr{Int("n", 4)}).WithGroup("h").WithAttrs([]Attr{Int("b", 2)})
			},
			replace: func(groups []string, attr Attr) Attr {
				return removeKeys(TimeKey, LevelKey, MessageKey, "a", "c")(groups, attr)
			},
			attrs:    []Attr{Group("i", Int("c", 3))},
			wantText: "g.x=0 g.n=4 g.h.b=2",
			wantJSON: `{"g":{"x":0,"n":4,"h":{"b":2}}}`,
		},
		{
			name: "replace resolved group",
			replace: func(groups []string, a Attr) Attr {
				if a.Value.Kind() == KindGroup {
					return Attr{"bad", IntValue(1)}
				}
				return removeKeys(TimeKey, LevelKey, MessageKey)(groups, a)
			},
			attrs:    []Attr{Any("name", logValueName{"Perry", "Platypus"})},
			wantText: "name.first=Perry name.last=Platypus",
			wantJSON: `{"name":{"first":"Perry","last":"Platypus"}}`,
		},
		{
			name:    "group and key (or both) needs quoting",
			replace: removeKeys(TimeKey, LevelKey),
			attrs: []Attr{
				Group("prefix",
					String(" needs quoting ", "v"), String("NotNeedsQuoting", "v"),
				),
				Group("prefix needs quoting",
					String(" needs quoting ", "v"), String("NotNeedsQuoting", "v"),
				),
			},
			wantText: `msg=message "prefix. needs quoting "=v prefix.NotNeedsQuoting=v "prefix needs quoting. needs quoting "=v "prefix needs quoting.NotNeedsQuoting"=v`,
			wantJSON: `{"msg":"message","prefix":{" needs quoting ":"v","NotNeedsQuoting":"v"},"prefix needs quoting":{" needs quoting ":"v","NotNeedsQuoting":"v"}}`,
		},
	} {
		r := NewRecord(testTime, LevelInfo, "message", callerPC(2))
		source := r.Source()
		if source == nil {
			t.Fatal("source is nil")
		}
		line := strconv.Itoa(source.Line)
		r.AddAttrs(test.attrs...)
		var buf bytes.Buffer
		opts := HandlerOptions{ReplaceAttr: test.replace, AddSource: test.addSource}
		t.Run(test.name, func(t *testing.T) {
			for _, handler := range []struct {
				name string
				h    Handler
				want string
			}{
				{"text", NewTextHandler(&buf, &opts), test.wantText},
				{"json", NewJSONHandler(&buf, &opts), test.wantJSON},
			} {
				t.Run(handler.name, func(t *testing.T) {
					h := handler.h
					if test.with != nil {
						h = test.with(h)
					}
					buf.Reset()
					if err := h.Handle(nil, r); err != nil {
						t.Fatal(err)
					}
					want := strings.ReplaceAll(handler.want, "$LINE", line)
					got := strings.TrimSuffix(buf.String(), "\n")
					if got != want {
						t.Errorf("\ngot  %s\nwant %s\n", got, want)
					}
				})
			}
		})
	}
}

// removeKeys returns a function suitable for HandlerOptions.ReplaceAttr
// that removes all Attrs with the given keys.
func removeKeys(keys ...string) func([]string, Attr) Attr {
	return func(_ []string, a Attr) Attr {
		for _, k := range keys {
			if a.Key == k {
				return Attr{}
			}
		}
		return a
	}
}

func upperCaseKey(_ []string, a Attr) Attr {
	a.Key = strings.ToUpper(a.Key)
	return a
}

type logValueName struct {
	first, last string
}

func (n logValueName) LogValue() Value {
	return GroupValue(
		String("first", n.first),
		String("last", n.last))
}

func TestHandlerEnabled(t *testing.T) {
	levelVar := func(l Level) *LevelVar {
		var al LevelVar
		al.Set(l)
		return &al
	}

	for _, test := range []struct {
		leveler Leveler
		want    bool
	}{
		{nil, true},
		{LevelWarn, false},
		{&LevelVar{}, true}, // defaults to Info
		{levelVar(LevelWarn), false},
		{LevelDebug, true},
		{levelVar(LevelDebug), true},
	} {
		h := &commonHandler{opts: HandlerOptions{Level: test.leveler}}
		got := h.enabled(LevelInfo)
		if got != test.want {
			t.Errorf("%v: got %t, want %t", test.leveler, got, test.want)
		}
	}
}

func TestJSONAndTextHandlersWithUnavailableSource(t *testing.T) {
	// Verify that a nil source does not cause a panic.
	// and that the source is empty.
	var buf bytes.Buffer
	opts := &HandlerOptions{
		ReplaceAttr: removeKeys(LevelKey),
		AddSource:   true,
	}

	for _, test := range []struct {
		name string
		h    Handler
		want string
	}{
		{"text", NewTextHandler(&buf, opts), "msg=message"},
		{"json", NewJSONHandler(&buf, opts), `{"msg":"message"}`},
	} {
		t.Run(test.name, func(t *testing.T) {
			buf.Reset()
			r := NewRecord(time.Time{}, LevelInfo, "message", 0)
			err := test.h.Handle(t.Context(), r)
			if err != nil {
				t.Fatal(err)
			}

			want := strings.TrimSpace(test.want)
			got := strings.TrimSpace(buf.String())
			if got != want {
				t.Errorf("\ngot  %s\nwant %s", got, want)
			}
		})
	}
}

func TestSecondWith(t *testing.T) {
	// Verify that a second call to Logger.With does not corrupt
	// the original.
	var buf bytes.Buffer
	h := NewTextHandler(&buf, &HandlerOptions{ReplaceAttr: removeKeys(TimeKey)})
	logger := New(h).With(
		String("app", "playground"),
		String("role", "tester"),
		Int("data_version", 2),
	)
	appLogger := logger.With("type", "log") // this becomes type=met
	_ = logger.With("type", "metric")
	appLogger.Info("foo")
	got := strings.TrimSpace(buf.String())
	want := `level=INFO msg=foo app=playground role=tester data_version=2 type=log`
	if got != want {
		t.Errorf("\ngot  %s\nwant %s", got, want)
	}
}

func TestReplaceAttrGroups(t *testing.T) {
	// Verify that ReplaceAttr is called with the correct groups.
	type ga struct {
		groups string
		key    string
		val    string
	}

	var got []ga

	h := NewTextHandler(io.Discard, &HandlerOptions{ReplaceAttr: func(gs []string, a Attr) Attr {
		v := a.Value.String()
		if a.Key == TimeKey {
			v = "<now>"
		}
		got = append(got, ga{strings.Join(gs, ","), a.Key, v})
		return a
	}})
	New(h).
		With(Int("a", 1)).
		WithGroup("g1").
		With(Int("b", 2)).
		WithGroup("g2").
		With(
			Int("c", 3),
			Group("g3", Int("d", 4)),
			Int("e", 5)).
		Info("m",
			Int("f", 6),
			Group("g4", Int("h", 7)),
			Int("i", 8))

	want := []ga{
		{"", "a", "1"},
		{"g1", "b", "2"},
		{"g1,g2", "c", "3"},
		{"g1,g2,g3", "d", "4"},
		{"g1,g2", "e", "5"},
		{"", "time", "<now>"},
		{"", "level", "INFO"},
		{"", "msg", "m"},
		{"g1,g2", "f", "6"},
		{"g1,g2,g4", "h", "7"},
		{"g1,g2", "i", "8"},
	}
	if !slices.Equal(got, want) {
		t.Errorf("\ngot  %v\nwant %v", got, want)
	}
}

const rfc3339Millis = "2006-01-02T15:04:05.000Z07:00"

func TestWriteTimeRFC3339(t *testing.T) {
	for _, tm := range []time.Time{
		time.Date(2000, 1, 2, 3, 4, 5, 0, time.UTC),
		time.Date(2000, 1, 2, 3, 4, 5, 400, time.Local),
		time.Date(2000, 11, 12, 3, 4, 500, 5e7, time.UTC),
	} {
		got := string(appendRFC3339Millis(nil, tm))
		want := tm.Format(rfc3339Millis)
		if got != want {
			t.Errorf("got %s, want %s", got, want)
		}
	}
}

func BenchmarkWriteTime(b *testing.B) {
	tm := time.Date(2022, 3, 4, 5, 6, 7, 823456789, time.Local)
	b.ResetTimer()
	var buf []byte
	for i := 0; i < b.N; i++ {
		buf = appendRFC3339Millis(buf[:0], tm)
	}
}

func TestDiscardHandler(t *testing.T) {
	ctx := context.Background()
	stdout, stderr := os.Stdout, os.Stderr
	os.Stdout, os.Stderr = nil, nil // panic on write
	t.Cleanup(func() {
		os.Stdout, os.Stderr = stdout, stderr
	})

	// Just ensure nothing panics during normal usage
	l := New(DiscardHandler)
	l.Info("msg", "a", 1, "b", 2)
	l.Debug("bg", Int("a", 1), "b", 2)
	l.Warn("w", Duration("dur", 3*time.Second))
	l.Error("bad", "a", 1)
	l.Log(ctx, LevelWarn+1, "w", Int("a", 1), String("b", "two"))
	l.LogAttrs(ctx, LevelInfo+1, "a b c", Int("a", 1), String("b", "two"))
	l.Info("info", "a", []Attr{Int("i", 1)})
	l.Info("info", "a", GroupValue(Int("i", 1)))
}

func BenchmarkAppendKey(b *testing.B) {
	for _, size := range []int{5, 10, 30, 50, 100} {
		for _, quoting := range []string{"no_quoting", "pre_quoting", "key_quoting", "both_quoting"} {
			b.Run(fmt.Sprintf("%s_prefix_size_%d", quoting, size), func(b *testing.B) {
				var (
					hs     = NewJSONHandler(io.Discard, nil).newHandleState(buffer.New(), false, "")
					prefix = bytes.Repeat([]byte("x"), size)
					key    = "key"
				)

				if quoting == "pre_quoting" || quoting == "both_quoting" {
					prefix[0] = '"'
				}
				if quoting == "key_quoting" || quoting == "both_quoting" {
					key = "ke\""
				}

				hs.prefix = (*buffer.Buffer)(&prefix)

				for b.Loop() {
					hs.appendKey(key)
					hs.buf.Reset()
				}
			})
		}
	}
}