Write Windows line breaks on Windows; tee to stdout

cmd/syncthing/monitor.go

@@ -22,10 +22,13 @@ import (
 	"os/exec"
 	"os/signal"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"sync"
 	"syscall"
 	"time"
+
+	"github.com/syncthing/syncthing/internal/osutil"
 )
 
 var (
@@ -45,16 +48,29 @@ func monitorMain() {
 	l.SetPrefix("[monitor] ")
 
 	var err error
-	var dst io.Writer
+	var dst io.Writer = os.Stdout
 
-	if logFile == "" {
-		dst = os.Stdout
-	} else {
-		dst, err = os.Create(logFile)
+	if logFile != "" {
+		var fileDst io.Writer
+
+		fileDst, err = os.Create(logFile)
 		if err != nil {
 			l.Fatalln("log file:", err)
 		}
-		l.Infof(`Log output directed to file "%s"`, logFile)
+
+		if runtime.GOOS == "windows" {
+			// Translate line breaks to Windows standard
+			fileDst = osutil.ReplacingWriter{
+				Writer: fileDst,
+				From:   '\n',
+				To:     []byte{'\r', '\n'},
+			}
+		}
+
+		// Log to both stdout and file.
+		dst = io.MultiWriter(dst, fileDst)
+
+		l.Infof(`Log output saved to file "%s"`, logFile)
 	}
 
 	args := os.Args

internal/osutil/replacingwriter.go

@@ -0,0 +1,57 @@
+// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation, either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+// more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>.
+
+package osutil
+
+import (
+	"bytes"
+	"io"
+)
+
+type ReplacingWriter struct {
+	Writer io.Writer
+	From   byte
+	To     []byte
+}
+
+func (w ReplacingWriter) Write(bs []byte) (int, error) {
+	var n, written int
+	var err error
+
+	newlineIdx := bytes.IndexByte(bs, w.From)
+	for newlineIdx >= 0 {
+		n, err = w.Writer.Write(bs[:newlineIdx])
+		written += n
+		if err != nil {
+			break
+		}
+		if len(w.To) > 0 {
+			n, err := w.Writer.Write(w.To)
+			if n == len(w.To) {
+				written++
+			}
+			if err != nil {
+				break
+			}
+		}
+		bs = bs[newlineIdx+1:]
+		newlineIdx = bytes.IndexByte(bs, w.From)
+	}
+
+	n, err = w.Writer.Write(bs)
+	written += n
+
+	return written, err
+}

internal/osutil/replacingwriter_test.go

@@ -0,0 +1,53 @@
+// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation, either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+// more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>.
+
+package osutil
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+)
+
+var testcases = []struct {
+	from byte
+	to   []byte
+	a, b string
+}{
+	{'\n', []byte{'\r', '\n'}, "", ""},
+	{'\n', []byte{'\r', '\n'}, "foo", "foo"},
+	{'\n', []byte{'\r', '\n'}, "foo\n", "foo\r\n"},
+	{'\n', []byte{'\r', '\n'}, "foo\nbar", "foo\r\nbar"},
+	{'\n', []byte{'\r', '\n'}, "foo\nbar\nbaz", "foo\r\nbar\r\nbaz"},
+	{'\n', []byte{'\r', '\n'}, "\nbar", "\r\nbar"},
+	{'o', []byte{'x', 'l', 'r'}, "\nfoo", "\nfxlrxlr"},
+	{'o', nil, "\nfoo", "\nf"},
+	{'f', []byte{}, "\nfoo", "\noo"},
+}
+
+func TestReplacingWriter(t *testing.T) {
+	for _, tc := range testcases {
+		var buf bytes.Buffer
+		w := ReplacingWriter{
+			Writer: &buf,
+			From:   tc.from,
+			To:     tc.to,
+		}
+		fmt.Fprint(w, tc.a)
+		if buf.String() != tc.b {
+			t.Errorf("%q != %q", buf.String(), tc.b)
+		}
+	}
+}