log: allow external definition of log handling (#1561)

* poc

* linter: fix

---------

Co-authored-by: Ryan O'Hara-Reid <ryan.oharareid@thrasher.io>

log/custom_log_hooks.go

@@ -0,0 +1,17 @@
+package log
+
+// CustomLogHook is a function type for external log handling. It should return
+// true if the library's internal logging system should be bypassed, or false
+// if the library's internal logging system should be used.
+type CustomLogHook func(header, subLoggerName string, a ...any) (bypassLibraryLogSystem bool)
+
+var customLogHook CustomLogHook
+
+// SetCustomLogHook sets a custom log hook function that allows the complete
+// bypass of the library's internal logging system. This is useful for
+// implementing custom log handling.
+func SetCustomLogHook(h CustomLogHook) {
+	mu.Lock()
+	customLogHook = h
+	mu.Unlock()
+}

log/custom_log_hooks_test.go

@@ -0,0 +1,11 @@
+package log
+
+import "testing"
+
+func TestSetCustomLoghook(t *testing.T) {
+	t.Parallel()
+	logHook := func(_ string, _ string, _ ...interface{}) (bypassLibraryLogSystem bool) {
+		return false
+	}
+	SetCustomLogHook(logHook)
+}

log/loggers.go

@@ -264,12 +264,22 @@ func (l *fields) stage(header string, deferFunc deferral) {
 	logFieldsPool.Put(l)
 }
 
-// stageln stages a log event
+// stageln logs a message with the given header and arguments. It uses the
-func (l *fields) stageln(header string, a ...interface{}) {
+// custom log hook if set, otherwise falls back to the library's internal log
+// system.
+func (l *fields) stageln(header string, a ...any) {
+	if customLogHook != nil && customLogHook(header, l.name, a...) {
+		return
+	}
 	l.stage(header, func() string { return fmt.Sprint(a...) })
 }
 
-// stagef stages a log event
+// stagef logs a formatted message with the given header and arguments. It uses
-func (l *fields) stagef(header, format string, a ...interface{}) {
+// the custom log hook if set, otherwise falls back to the library's internal
+// log system.
+func (l *fields) stagef(header, format string, a ...any) {
+	if customLogHook != nil && customLogHook(header, l.name, fmt.Sprintf(format, a...)) {
+		return
+	}
 	l.stage(header, func() string { return fmt.Sprintf(format, a...) })
 }