log/slog: add LogLoggerLevel to enable setting level on the default logger

[gostls13.git] / src / log / slog / logger.go

diff --git a/src/log/slog/logger.go b/src/log/slog/logger.go
index fceafe0cbad87ff27864a9822b88f2802bec36b2..f03aeec295cb08ea71fb2958d03c09812a1a09e5 100644 (file)
--- a/src/log/slog/logger.go
+++ b/src/log/slog/logger.go
@@ -16,6 +16,36 @@ import (
 
 var defaultLogger atomic.Pointer[Logger]
 
+var logLoggerLevel LevelVar
+
+// SetLogLoggerLevel controls the level for the bridge to the [log] package.
+//
+// Before [SetDefault] is called, slog top-level logging functions call the default [log.Logger].
+// In that mode, SetLogLoggerLevel sets the minimum level for those calls.
+// By default, the minimum level is Info, so calls to [Debug]
+// (as well as top-level logging calls at lower levels)
+// will not be passed to the log.Logger. After calling
+//
+//     slog.SetLogLoggerLevel(slog.LevelDebug)
+//
+// calls to [Debug] will be passed to the log.Logger.
+//
+// After [SetDefault] is called, calls to the default [log.Logger] are passed to the
+// slog default handler. In that mode,
+// SetLogLoggerLevel sets the level at which those calls are logged.
+// That is, after calling
+//
+//     slog.SetLogLoggerLevel(slog.LevelDebug)
+//
+// A call to [log.Printf] will result in output at level [LevelDebug].
+//
+// SetLogLoggerLevel returns the previous value.
+func SetLogLoggerLevel(level Level) (oldLevel Level) {
+       oldLevel = logLoggerLevel.Level()
+       logLoggerLevel.Set(level)
+       return
+}
+
 func init() {
        defaultLogger.Store(New(newDefaultHandler(loginternal.DefaultOutput)))
 }
@@ -25,7 +55,8 @@ func Default() *Logger { return defaultLogger.Load() }
 
 // 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.
+// (as with [log.Print], etc.) will be logged using l's Handler,
+// at a level controlled by [SetLogLoggerLevel].
 func SetDefault(l *Logger) {
        defaultLogger.Store(l)
        // If the default's handler is a defaultHandler, then don't use a handleWriter,
@@ -36,7 +67,7 @@ func SetDefault(l *Logger) {
        // See TestSetDefault.
        if _, ok := l.Handler().(*defaultHandler); !ok {
                capturePC := log.Flags()&(log.Lshortfile|log.Llongfile) != 0
-               log.SetOutput(&handlerWriter{l.Handler(), LevelInfo, capturePC})
+               log.SetOutput(&handlerWriter{l.Handler(), &logLoggerLevel, capturePC})
                log.SetFlags(0) // we want just the log message, no time or location
        }
 }
@@ -45,12 +76,13 @@ func SetDefault(l *Logger) {
 // It is used to link the default log.Logger to the default slog.Logger.
 type handlerWriter struct {
        h         Handler
-       level     Level
+       level     Leveler
        capturePC bool
 }
 
 func (w *handlerWriter) Write(buf []byte) (int, error) {
-       if !w.h.Enabled(context.Background(), w.level) {
+       level := w.level.Level()
+       if !w.h.Enabled(context.Background(), level) {
                return 0, nil
        }
        var pc uintptr
@@ -66,7 +98,7 @@ func (w *handlerWriter) Write(buf []byte) (int, error) {
        if len(buf) > 0 && buf[len(buf)-1] == '\n' {
                buf = buf[:len(buf)-1]
        }
-       r := NewRecord(time.Now(), w.level, string(buf), pc)
+       r := NewRecord(time.Now(), level, string(buf), pc)
        return origLen, w.h.Handle(context.Background(), r)
 }