codec: fix incorrect handling of invalid utf-8 in LinesCodec::decode_eof

tokio-util/src/codec/lines_codec.rs

@@ -169,14 +169,14 @@ impl Decoder for LinesCodec {
         Ok(match self.decode(buf)? {
             Some(frame) => Some(frame),
             None => {
+                self.next_index = 0;
                 // No terminating newline - return remaining data, if any
                 if buf.is_empty() || buf == &b"\r"[..] {
                     None
                 } else {
                     let line = buf.split_to(buf.len());
                     let line = without_carriage_return(&line);
                     let line = utf8(line)?;
-                    self.next_index = 0;
                     Some(line.to_string())
                 }
             }

tokio-util/tests/codecs.rs

@@ -62,6 +62,19 @@ fn lines_decoder() {
     assert_eq!(None, codec.decode_eof(buf).unwrap());
 }
 
+#[test]
+fn lines_decoder_invalid_utf8() {
+    let mut codec = LinesCodec::new();
+    let buf = &mut BytesMut::new();
+    buf.reserve(200);
+    buf.put_slice(b"line 1\xc3\x28");
+    assert_eq!(None, codec.decode(buf).unwrap());
+    assert!(codec.decode_eof(buf).is_err());
+    assert_eq!(None, codec.decode_eof(buf).unwrap());
+    buf.put_slice(b"line 22222222222222\n");
+    assert_eq!("line 22222222222222", codec.decode(buf).unwrap().unwrap());
+}
+
 #[test]
 fn lines_decoder_max_length() {
     const MAX_LENGTH: usize = 6;