lib/mlog: implement io.Writer and add function ErrorWriter

The ErrorWriter will return the internal default MultiLogger.
A call to Write() on returned io.Writer will forward it to all registered
error writers.

A Write method on MultiLogger write the b to all error writers.
It will always return the length of b without an error.

2 files changed, 19 insertions, 0 deletions

diff --git a/lib/mlog/mlog.go b/lib/mlog/mlog.go
index 6626c048..db474730 100644
--- a/lib/mlog/mlog.go
+++ b/lib/mlog/mlog.go
@@ -31,6 +31,7 @@
 package mlog
 
 import (
+	"io"
 	"os"
 )
 
@@ -142,3 +143,12 @@ func UnregisterErrorWriter(name string) {
 func UnregisterOutputWriter(name string) {
 	defaultMLog.UnregisterOutputWriter(name)
 }
+
+//
+// ErrorWriter return the internal default MultiLogger.
+// A call to Write() on returned io.Writer will forward it to all registered
+// error writers.
+//
+func ErrorWriter() io.Writer {
+	return defaultMLog
+}
diff --git a/lib/mlog/multi_logger.go b/lib/mlog/multi_logger.go
index 14ed0ee3..5c7f35d0 100644
--- a/lib/mlog/multi_logger.go
+++ b/lib/mlog/multi_logger.go
@@ -200,6 +200,15 @@ func (mlog *MultiLogger) UnregisterOutputWriter(name string) {
 	delete(mlog.outs, name)
 }
 
+//
+// Write write the b to all error writers.
+// It will always return the length of b without an error.
+//
+func (mlog *MultiLogger) Write(b []byte) (n int, err error) {
+	mlog.qerr <- libbytes.Copy(b)
+	return len(b), nil
+}
+
 func (mlog *MultiLogger) processErrorQueue() {
 	var err error
 	for {