Merge branch 'fix-serial-lingering-bytes' into combined

Author: matthijskooijman

arduino-core/src/processing/app/Serial.java

@@ -176,22 +176,41 @@ public synchronized void serialEvent(SerialPortEvent serialEvent) {
       try {
         byte[] buf = port.readBytes(serialEvent.getEventValue());
         int next = 0;
-        while(next < buf.length) {
-          while(next < buf.length && outToMessage.hasRemaining()) {
-            int spaceInIn = inFromSerial.remaining();
-            int copyNow = buf.length - next < spaceInIn ? buf.length - next : spaceInIn;
+        // This uses a CharsetDecoder to convert from bytes to UTF-8 in
+        // a streaming fashion (i.e. where characters might be split
+        // over multiple reads). This needs the data to be in a
+        // ByteBuffer (inFromSerial, which we also use to store leftover
+        // incomplete characters for the nexst run) and produces a
+        // CharBuffer (outToMessage), which we then convert to char[] to
+        // pass onwards.
+        // Note that these buffers switch from input to output mode
+        // using flip/compact/clear
+        while(next < buf.length || inFromSerial.position() > 0) {
+          do {
+            // This might be 0 when all data was already read from buf
+            // (but then there will be data in inFromSerial left to
+            // decode).
+            int copyNow = Math.min(buf.length - next, inFromSerial.remaining());
             inFromSerial.put(buf, next, copyNow);
             next += copyNow;
+
             inFromSerial.flip();
             bytesToStrings.decode(inFromSerial, outToMessage, false);
             inFromSerial.compact();
-          }
+
+            // When there are multi-byte characters, outToMessage might
+            // still have room, so add more bytes if we have any.
+          } while (next < buf.length && outToMessage.hasRemaining());
+
+          // If no output was produced, the input only contained
+          // incomplete characters, so we're done processing
+          if (outToMessage.position() == 0)
+            break;
+
           outToMessage.flip();
-          if(outToMessage.hasRemaining()) {
-            char[] chars = new char[outToMessage.remaining()];
-            outToMessage.get(chars);
-            message(chars, chars.length);
-          }
+          char[] chars = new char[outToMessage.remaining()];
+          outToMessage.get(chars);
+          message(chars, chars.length);
           outToMessage.clear();
         }
       } catch (SerialPortException e) {