fix(zapio): add carriage return support in Writer

zapio/writer.go

@@ -90,6 +90,24 @@ func (w *Writer) Write(bs []byte) (n int, err error) {
 // unconsumed bytes.
 func (w *Writer) writeLine(line []byte) (remaining []byte) {
 	idx := bytes.IndexByte(line, '\n')
+	crIdx := bytes.IndexByte(line, '\r')
+
+	if crIdx >= 0 && (idx < 0 || crIdx < idx) && (crIdx+1 == len(line) || line[crIdx+1] != '\n') {
+		w.buff.Reset()
+		return line[crIdx+1:]
+	}
+
+	// Handle \r\n sequences - these are line terminators that should log
+	if crIdx >= 0 && crIdx+1 < len(line) && line[crIdx+1] == '\n' {
+		if w.buff.Len() == 0 {
+			w.log(line[:crIdx])
+		} else {
+			w.buff.Write(line[:crIdx])
+			w.flush(true)
+		}
+		return line[crIdx+2:]
+	}
+
 	if idx < 0 {
 		// If there are no newlines, buffer the entire string.
 		w.buff.Write(line)
@@ -110,7 +128,7 @@ func (w *Writer) writeLine(line []byte) (remaining []byte) {
 
 	// Log empty messages in the middle of the stream so that we don't lose
 	// information when the user writes "foo\n\nbar".
-	w.flush(true /* allowEmpty */)
+	w.flush(true)
 
 	return remaining
 }
@@ -129,7 +147,7 @@ func (w *Writer) Sync() error {
 	// Don't allow empty messages on explicit Sync calls or on Close
 	// because we don't want an extraneous empty message at the end of the
 	// stream -- it's common for files to end with a newline.
-	w.flush(false /* allowEmpty */)
+	w.flush(false)
 	return nil
 }
 

zapio/writer_test.go

@@ -126,6 +126,51 @@ func TestWriter(t *testing.T) {
 				{Level: zap.InfoLevel, Message: ""},
 			},
 		},
+		{
+			desc: "carriage return newline sequence creates single line break",
+			writes: []string{
+				"foo\r\nbar\r\n",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.InfoLevel, Message: "foo"},
+				{Level: zap.InfoLevel, Message: "bar"},
+			},
+		},
+		{
+			desc: "mixed newlines and carriage returns",
+			writes: []string{
+				"foo\nbar\r\rbaz\r\nqux\n",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.InfoLevel, Message: "foo"},
+				{Level: zap.InfoLevel, Message: "baz"},
+				{Level: zap.InfoLevel, Message: "qux"},
+			},
+		},
+		{
+			desc: "carriage return with buffered content",
+			writes: []string{
+				"foo",
+				"ba",
+				"r\rqux",
+				"\n",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.InfoLevel, Message: "qux"},
+			},
+		},
+		{
+			desc: "carriage return newline with buffered content",
+			writes: []string{
+				"foo",
+				"ba",
+				"r\r\nqux\r\n",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.InfoLevel, Message: "foobar"},
+				{Level: zap.InfoLevel, Message: "qux"},
+			},
+		},
 	}
 
 	for _, tt := range tests {