feat(slog): add slog.Handler adapter (#20)

* docs: add example programs for common usage patterns

Adds four focused examples in examples/ directory:
- basic: drop-in logger with web UI
- namespaces: namespace-based logging by component
- client: programmatic log client with filtering
- log-levels: all log levels and filtering

Fixes #7

* feat(slog): add slog.Handler adapter for log-socket

Implements log/slog.Handler that routes structured log records into the
log-socket broadcasting system. Supports namespaces, WithAttrs,
WithGroup, and configurable minimum level.

Also adds Broadcast() as a public entry point for adapter packages
that construct log.Entry values directly.

* chore: update to Go 1.26, resolve slog LogValuer values

go.mod

@@ -1,5 +1,5 @@
 module github.com/taigrr/log-socket/v2
 
-go 1.25.6
+go 1.26.0
 
 require github.com/gorilla/websocket v1.5.3

log/log.go

@@ -556,3 +556,37 @@ func fileInfo(skip int) string {
 	}
 	return fmt.Sprintf("%s:%d", file, line)
 }
+
+// Broadcast sends an [Entry] to all registered clients. This is the public
+// entry point used by adapter packages (such as the slog handler) that
+// construct entries themselves. The unexported level field is inferred from
+// [Entry.Level] when not already set.
+func Broadcast(e Entry) {
+	if e.level == 0 && e.Level != "" && e.Level != "TRACE" {
+		e.level = parseLevelString(e.Level)
+	}
+	createLog(e)
+}
+
+func parseLevelString(s string) Level {
+	switch s {
+	case "TRACE":
+		return LTrace
+	case "DEBUG":
+		return LDebug
+	case "INFO":
+		return LInfo
+	case "NOTICE":
+		return LNotice
+	case "WARN":
+		return LWarn
+	case "ERROR":
+		return LError
+	case "PANIC":
+		return LPanic
+	case "FATAL":
+		return LFatal
+	default:
+		return LInfo
+	}
+}

slog/handler.go

@@ -0,0 +1,165 @@
+// Package slog provides a [log/slog.Handler] that routes structured log
+// records into the log-socket broadcasting system, giving every slog-based
+// caller free WebSocket streaming and the browser viewer UI.
+package slog
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"runtime"
+	"strings"
+
+	"github.com/taigrr/log-socket/v2/log"
+)
+
+// Handler implements [slog.Handler] by converting each [slog.Record] into a
+// log-socket [log.Entry] and feeding it through the normal broadcast path.
+//
+// Attributes accumulated via [Handler.WithAttrs] are prepended to the log
+// message as key=value pairs. Groups set via [Handler.WithGroup] prefix
+// attribute keys with "group.".
+type Handler struct {
+	namespace string
+	level     slog.Level
+	attrs     []slog.Attr
+	groups    []string
+}
+
+// ensure interface compliance at compile time.
+var _ slog.Handler = (*Handler)(nil)
+
+// Option configures a [Handler].
+type Option func(*Handler)
+
+// WithNamespace sets the log-socket namespace for entries produced by this
+// handler.  If empty, [log.DefaultNamespace] is used.
+func WithNamespace(ns string) Option {
+	return func(h *Handler) {
+		h.namespace = ns
+	}
+}
+
+// WithLevel sets the minimum slog level the handler will accept.
+func WithLevel(l slog.Level) Option {
+	return func(h *Handler) {
+		h.level = l
+	}
+}
+
+// NewHandler returns a new [Handler] that writes to the log-socket broadcast
+// system.  Options may be used to set the namespace and minimum level.
+func NewHandler(opts ...Option) *Handler {
+	h := &Handler{
+		namespace: log.DefaultNamespace,
+		level:     slog.LevelDebug,
+	}
+	for _, o := range opts {
+		o(h)
+	}
+	return h
+}
+
+// Enabled reports whether the handler is configured to process records at
+// the given level.
+func (h *Handler) Enabled(_ context.Context, level slog.Level) bool {
+	return level >= h.level
+}
+
+// Handle converts r into a log-socket Entry and broadcasts it.
+func (h *Handler) Handle(_ context.Context, r slog.Record) error {
+	var b strings.Builder
+	b.WriteString(r.Message)
+
+	// Append pre-collected attrs.
+	for _, a := range h.attrs {
+		writeAttr(&b, h.groups, a)
+	}
+
+	// Append record-level attrs.
+	r.Attrs(func(a slog.Attr) bool {
+		writeAttr(&b, h.groups, a)
+		return true
+	})
+
+	file := "???"
+	if r.PC != 0 {
+		fs := runtime.CallersFrames([]uintptr{r.PC})
+		f, _ := fs.Next()
+		if f.File != "" {
+			short := f.File
+			if idx := strings.LastIndex(short, "/"); idx >= 0 {
+				short = short[idx+1:]
+			}
+			file = fmt.Sprintf("%s:%d", short, f.Line)
+		}
+	}
+
+	e := log.Entry{
+		Timestamp: r.Time,
+		Output:    b.String(),
+		File:      file,
+		Level:     slogLevelToString(r.Level),
+		Namespace: h.namespace,
+	}
+	log.Broadcast(e)
+	return nil
+}
+
+// WithAttrs returns a new Handler with the given attributes appended.
+func (h *Handler) WithAttrs(attrs []slog.Attr) slog.Handler {
+	h2 := h.clone()
+	h2.attrs = append(h2.attrs, attrs...)
+	return h2
+}
+
+// WithGroup returns a new Handler where subsequent attributes are nested
+// under the given group name.
+func (h *Handler) WithGroup(name string) slog.Handler {
+	if name == "" {
+		return h
+	}
+	h2 := h.clone()
+	h2.groups = append(h2.groups, name)
+	return h2
+}
+
+func (h *Handler) clone() *Handler {
+	h2 := &Handler{
+		namespace: h.namespace,
+		level:     h.level,
+		attrs:     make([]slog.Attr, len(h.attrs)),
+		groups:    make([]string, len(h.groups)),
+	}
+	copy(h2.attrs, h.attrs)
+	copy(h2.groups, h.groups)
+	return h2
+}
+
+func writeAttr(b *strings.Builder, groups []string, a slog.Attr) {
+	a.Value = a.Value.Resolve()
+	if a.Equal(slog.Attr{}) {
+		return
+	}
+	b.WriteByte(' ')
+	for _, g := range groups {
+		b.WriteString(g)
+		b.WriteByte('.')
+	}
+	b.WriteString(a.Key)
+	b.WriteByte('=')
+	b.WriteString(a.Value.String())
+}
+
+func slogLevelToString(l slog.Level) string {
+	switch {
+	case l >= slog.LevelError:
+		return "ERROR"
+	case l >= slog.LevelWarn:
+		return "WARN"
+	case l >= slog.LevelInfo:
+		return "INFO"
+	default:
+		return "DEBUG"
+	}
+}

slog/handler_test.go

@@ -0,0 +1,118 @@
+package slog
+
+import (
+	"context"
+	"log/slog"
+	"testing"
+	"time"
+
+	"github.com/taigrr/log-socket/v2/log"
+)
+
+// getWithTimeout reads from a log client with a timeout to avoid hanging tests.
+func getWithTimeout(c *log.Client, timeout time.Duration) (log.Entry, bool) {
+	ch := make(chan log.Entry, 1)
+	go func() { ch <- c.Get() }()
+	select {
+	case e := <-ch:
+		return e, true
+	case <-time.After(timeout):
+		return log.Entry{}, false
+	}
+}
+
+func TestHandler_Enabled(t *testing.T) {
+	h := NewHandler(WithLevel(slog.LevelWarn))
+	if h.Enabled(context.Background(), slog.LevelInfo) {
+		t.Error("expected Info to be disabled when min level is Warn")
+	}
+	if !h.Enabled(context.Background(), slog.LevelWarn) {
+		t.Error("expected Warn to be enabled")
+	}
+	if !h.Enabled(context.Background(), slog.LevelError) {
+		t.Error("expected Error to be enabled")
+	}
+}
+
+func TestHandler_Handle(t *testing.T) {
+	c := log.CreateClient()
+	defer c.Destroy()
+	c.SetLogLevel(log.LTrace)
+
+	h := NewHandler(WithNamespace("test-ns"))
+	logger := slog.New(h)
+
+	logger.Info("hello world", "key", "value")
+
+	e, ok := getWithTimeout(c, time.Second)
+	if !ok {
+		t.Fatal("timed out waiting for log entry")
+	}
+	if e.Namespace != "test-ns" {
+		t.Errorf("namespace = %q, want %q", e.Namespace, "test-ns")
+	}
+	if e.Level != "INFO" {
+		t.Errorf("level = %q, want INFO", e.Level)
+	}
+	if e.Output == "" {
+		t.Error("output should not be empty")
+	}
+}
+
+func TestHandler_WithAttrs(t *testing.T) {
+	c := log.CreateClient()
+	defer c.Destroy()
+	c.SetLogLevel(log.LTrace)
+
+	h := NewHandler()
+	h2 := h.WithAttrs([]slog.Attr{slog.String("service", "api")})
+	logger := slog.New(h2)
+
+	logger.Info("request")
+
+	e, ok := getWithTimeout(c, time.Second)
+	if !ok {
+		t.Fatal("timed out")
+	}
+	if e.Output != "request service=api" {
+		t.Errorf("output = %q, want %q", e.Output, "request service=api")
+	}
+}
+
+func TestHandler_WithGroup(t *testing.T) {
+	c := log.CreateClient()
+	defer c.Destroy()
+	c.SetLogLevel(log.LTrace)
+
+	h := NewHandler()
+	h2 := h.WithGroup("http").WithAttrs([]slog.Attr{slog.Int("status", 200)})
+	logger := slog.New(h2)
+
+	logger.Info("done")
+
+	e, ok := getWithTimeout(c, time.Second)
+	if !ok {
+		t.Fatal("timed out")
+	}
+	if e.Output != "done http.status=200" {
+		t.Errorf("output = %q, want %q", e.Output, "done http.status=200")
+	}
+}
+
+func TestSlogLevelMapping(t *testing.T) {
+	tests := []struct {
+		level slog.Level
+		want  string
+	}{
+		{slog.LevelDebug, "DEBUG"},
+		{slog.LevelInfo, "INFO"},
+		{slog.LevelWarn, "WARN"},
+		{slog.LevelError, "ERROR"},
+	}
+	for _, tt := range tests {
+		got := slogLevelToString(tt.level)
+		if got != tt.want {
+			t.Errorf("slogLevelToString(%v) = %q, want %q", tt.level, got, tt.want)
+		}
+	}
+}