1 files changed, 296 insertions, 0 deletions
diff --git a/src/log/slog/logger.go b/src/log/slog/logger.go
new file mode 100644
index 0000000..a068085
--- /dev/null
+++ b/src/log/slog/logger.go
@@ -0,0 +1,296 @@
+// 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.
+
+package slog
+
+import (
+	"context"
+	"log"
+	loginternal "log/internal"
+	"log/slog/internal"
+	"runtime"
+	"sync/atomic"
+	"time"
+)
+
+var defaultLogger atomic.Value
+
+func init() {
+	defaultLogger.Store(New(newDefaultHandler(loginternal.DefaultOutput)))
+}
+
+// Default returns the default Logger.
+func Default() *Logger { return defaultLogger.Load().(*Logger) }
+
+// SetDefault makes l the default Logger.
+// After this call, output from the log package's default Logger
+// (as with [log.Print], etc.) will be logged at LevelInfo using l's Handler.
+func SetDefault(l *Logger) {
+	defaultLogger.Store(l)
+	// If the default's handler is a defaultHandler, then don't use a handleWriter,
+	// or we'll deadlock as they both try to acquire the log default mutex.
+	// The defaultHandler will use whatever the log default writer is currently
+	// set to, which is correct.
+	// This can occur with SetDefault(Default()).
+	// See TestSetDefault.
+	if _, ok := l.Handler().(*defaultHandler); !ok {
+		capturePC := log.Flags()&(log.Lshortfile|log.Llongfile) != 0
+		log.SetOutput(&handlerWriter{l.Handler(), LevelInfo, capturePC})
+		log.SetFlags(0) // we want just the log message, no time or location
+	}
+}
+
+// handlerWriter is an io.Writer that calls a Handler.
+// It is used to link the default log.Logger to the default slog.Logger.
+type handlerWriter struct {
+	h         Handler
+	level     Level
+	capturePC bool
+}
+
+func (w *handlerWriter) Write(buf []byte) (int, error) {
+	if !w.h.Enabled(context.Background(), w.level) {
+		return 0, nil
+	}
+	var pc uintptr
+	if !internal.IgnorePC && w.capturePC {
+		// skip [runtime.Callers, w.Write, Logger.Output, log.Print]
+		var pcs [1]uintptr
+		runtime.Callers(4, pcs[:])
+		pc = pcs[0]
+	}
+
+	// Remove final newline.
+	origLen := len(buf) // Report that the entire buf was written.
+	if len(buf) > 0 && buf[len(buf)-1] == '\n' {
+		buf = buf[:len(buf)-1]
+	}
+	r := NewRecord(time.Now(), w.level, string(buf), pc)
+	return origLen, w.h.Handle(context.Background(), r)
+}
+
+// A Logger records structured information about each call to its
+// Log, Debug, Info, Warn, and Error methods.
+// For each call, it creates a Record and passes it to a Handler.
+//
+// To create a new Logger, call [New] or a Logger method
+// that begins "With".
+type Logger struct {
+	handler Handler // for structured logging
+}
+
+func (l *Logger) clone() *Logger {
+	c := *l
+	return &c
+}
+
+// Handler returns l's Handler.
+func (l *Logger) Handler() Handler { return l.handler }
+
+// With returns a Logger that includes the given attributes
+// in each output operation. Arguments are converted to
+// attributes as if by [Logger.Log].
+func (l *Logger) With(args ...any) *Logger {
+	if len(args) == 0 {
+		return l
+	}
+	c := l.clone()
+	c.handler = l.handler.WithAttrs(argsToAttrSlice(args))
+	return c
+}
+
+// WithGroup returns a Logger that starts a group, if name is non-empty.
+// The keys of all attributes added to the Logger will be qualified by the given
+// name. (How that qualification happens depends on the [Handler.WithGroup]
+// method of the Logger's Handler.)
+//
+// If name is empty, WithGroup returns the receiver.
+func (l *Logger) WithGroup(name string) *Logger {
+	if name == "" {
+		return l
+	}
+	c := l.clone()
+	c.handler = l.handler.WithGroup(name)
+	return c
+
+}
+
+// New creates a new Logger with the given non-nil Handler.
+func New(h Handler) *Logger {
+	if h == nil {
+		panic("nil Handler")
+	}
+	return &Logger{handler: h}
+}
+
+// With calls Logger.With on the default logger.
+func With(args ...any) *Logger {
+	return Default().With(args...)
+}
+
+// Enabled reports whether l emits log records at the given context and level.
+func (l *Logger) Enabled(ctx context.Context, level Level) bool {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	return l.Handler().Enabled(ctx, level)
+}
+
+// NewLogLogger returns a new log.Logger such that each call to its Output method
+// dispatches a Record to the specified handler. The logger acts as a bridge from
+// the older log API to newer structured logging handlers.
+func NewLogLogger(h Handler, level Level) *log.Logger {
+	return log.New(&handlerWriter{h, level, true}, "", 0)
+}
+
+// Log emits a log record with the current time and the given level and message.
+// The Record's Attrs consist of the Logger's attributes followed by
+// the Attrs specified by args.
+//
+// The attribute arguments are processed as follows:
+//   - If an argument is an Attr, it is used as is.
+//   - If an argument is a string and this is not the last argument,
+//     the following argument is treated as the value and the two are combined
+//     into an Attr.
+//   - Otherwise, the argument is treated as a value with key "!BADKEY".
+func (l *Logger) Log(ctx context.Context, level Level, msg string, args ...any) {
+	l.log(ctx, level, msg, args...)
+}
+
+// LogAttrs is a more efficient version of [Logger.Log] that accepts only Attrs.
+func (l *Logger) LogAttrs(ctx context.Context, level Level, msg string, attrs ...Attr) {
+	l.logAttrs(ctx, level, msg, attrs...)
+}
+
+// Debug logs at LevelDebug.
+func (l *Logger) Debug(msg string, args ...any) {
+	l.log(context.Background(), LevelDebug, msg, args...)
+}
+
+// DebugContext logs at LevelDebug with the given context.
+func (l *Logger) DebugContext(ctx context.Context, msg string, args ...any) {
+	l.log(ctx, LevelDebug, msg, args...)
+}
+
+// Info logs at LevelInfo.
+func (l *Logger) Info(msg string, args ...any) {
+	l.log(context.Background(), LevelInfo, msg, args...)
+}
+
+// InfoContext logs at LevelInfo with the given context.
+func (l *Logger) InfoContext(ctx context.Context, msg string, args ...any) {
+	l.log(ctx, LevelInfo, msg, args...)
+}
+
+// Warn logs at LevelWarn.
+func (l *Logger) Warn(msg string, args ...any) {
+	l.log(context.Background(), LevelWarn, msg, args...)
+}
+
+// WarnContext logs at LevelWarn with the given context.
+func (l *Logger) WarnContext(ctx context.Context, msg string, args ...any) {
+	l.log(ctx, LevelWarn, msg, args...)
+}
+
+// Error logs at LevelError.
+func (l *Logger) Error(msg string, args ...any) {
+	l.log(context.Background(), LevelError, msg, args...)
+}
+
+// ErrorContext logs at LevelError with the given context.
+func (l *Logger) ErrorContext(ctx context.Context, msg string, args ...any) {
+	l.log(ctx, LevelError, msg, args...)
+}
+
+// log is the low-level logging method for methods that take ...any.
+// It must always be called directly by an exported logging method
+// or function, because it uses a fixed call depth to obtain the pc.
+func (l *Logger) log(ctx context.Context, level Level, msg string, args ...any) {
+	if !l.Enabled(ctx, level) {
+		return
+	}
+	var pc uintptr
+	if !internal.IgnorePC {
+		var pcs [1]uintptr
+		// skip [runtime.Callers, this function, this function's caller]
+		runtime.Callers(3, pcs[:])
+		pc = pcs[0]
+	}
+	r := NewRecord(time.Now(), level, msg, pc)
+	r.Add(args...)
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	_ = l.Handler().Handle(ctx, r)
+}
+
+// logAttrs is like [Logger.log], but for methods that take ...Attr.
+func (l *Logger) logAttrs(ctx context.Context, level Level, msg string, attrs ...Attr) {
+	if !l.Enabled(ctx, level) {
+		return
+	}
+	var pc uintptr
+	if !internal.IgnorePC {
+		var pcs [1]uintptr
+		// skip [runtime.Callers, this function, this function's caller]
+		runtime.Callers(3, pcs[:])
+		pc = pcs[0]
+	}
+	r := NewRecord(time.Now(), level, msg, pc)
+	r.AddAttrs(attrs...)
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	_ = l.Handler().Handle(ctx, r)
+}
+
+// Debug calls Logger.Debug on the default logger.
+func Debug(msg string, args ...any) {
+	Default().log(context.Background(), LevelDebug, msg, args...)
+}
+
+// DebugContext calls Logger.DebugContext on the default logger.
+func DebugContext(ctx context.Context, msg string, args ...any) {
+	Default().log(ctx, LevelDebug, msg, args...)
+}
+
+// Info calls Logger.Info on the default logger.
+func Info(msg string, args ...any) {
+	Default().log(context.Background(), LevelInfo, msg, args...)
+}
+
+// InfoContext calls Logger.InfoContext on the default logger.
+func InfoContext(ctx context.Context, msg string, args ...any) {
+	Default().log(ctx, LevelInfo, msg, args...)
+}
+
+// Warn calls Logger.Warn on the default logger.
+func Warn(msg string, args ...any) {
+	Default().log(context.Background(), LevelWarn, msg, args...)
+}
+
+// WarnContext calls Logger.WarnContext on the default logger.
+func WarnContext(ctx context.Context, msg string, args ...any) {
+	Default().log(ctx, LevelWarn, msg, args...)
+}
+
+// Error calls Logger.Error on the default logger.
+func Error(msg string, args ...any) {
+	Default().log(context.Background(), LevelError, msg, args...)
+}
+
+// ErrorContext calls Logger.ErrorContext on the default logger.
+func ErrorContext(ctx context.Context, msg string, args ...any) {
+	Default().log(ctx, LevelError, msg, args...)
+}
+
+// Log calls Logger.Log on the default logger.
+func Log(ctx context.Context, level Level, msg string, args ...any) {
+	Default().log(ctx, level, msg, args...)
+}
+
+// LogAttrs calls Logger.LogAttrs on the default logger.
+func LogAttrs(ctx context.Context, level Level, msg string, attrs ...Attr) {
+	Default().logAttrs(ctx, level, msg, attrs...)
+}