Question

I use the following code (from Bluetooth Chat sample app) to read the incoming data and construct a string out of the bytes read. I want to read until this string has arrived <!MSG>. How to insert this condition with read() function?

The whole string looks like this <MSG><N>xxx<!N><V>yyy<!V><!MSG>. But the read() function does not read entire string at once. When I display the characters, I cannot see all the characters in the same line. It looks like:

Sender: <MS

Sender: G><N>xx

Sender: x<V

.

.

.

I display the characters on my phone (HTC Desire) and I send the data using windows hyperterminal.

How to make sure all the characters are displayed in a single line? I have tried using StringBuilder and StringBuffer instead of new String() but the problem is read() function does not read all the characters sent. The length of the input stream (bytes) is not equal to actual length of the string sent. The construction of string from the read bytes is happening alright.

Thank you for any suggestions and time spent on this. Also please feel free to suggest other mistakes or better way of doing below things, if any.

Cheers,

Madhu

public void run() {
        Log.i(TAG, "BEGIN mConnectedThread");
        //Writer writer = new StringWriter();
        byte[] buffer = new byte[1024];           
        int bytes;
        //String end = "<!MSG>";
        //byte compare = new Byte(Byte.parseByte(end));

        // Keep listening to the InputStream while connected
        while (true) {
            try {
                //boolean result = buffer.equals(compare);
                //while(true)   {
                    // Read from the InputStream
                    bytes = mmInStream.read(buffer);
                    //Reader reader = new BufferedReader(new InputStreamReader(mmInStream, "UTF-8"));
                    //int n;
                    //while ((bytes = reader.read(buffer)) != -1)   {   
                        //writer.write(buffer, 0, bytes);

                    //StringBuffer sb = new StringBuffer();                    
                    //sb = sb.append(buffer);

                    //String readMsg = writer.toString();
                    String readMsg = new String(buffer, 0, bytes);

                    //if (readMsg.endsWith(end))
                    // Send the obtained bytes to the UI Activity
                    mHandler.obtainMessage(BluetoothChat.MESSAGE_READ, bytes, -1, readMsg)
                            .sendToTarget();                        
                //}                    

            } catch (IOException e) {
                Log.e(TAG, "disconnected", e);
                connectionLost();
                break;
            }
        }
    }

Answer 1

The read function does not make any guarantee about the number of bytes it returns (it generally tries to return as many bytes from the stream as it can, without blocking). Therefore, you have to buffer the results, and keep them aside until you have your full message. Notice that you could receive something after the "<!MSG>" message, so you have to take care not to throw it away.

You can try something along these lines:

byte[] buffer = new byte[1024];
int bytes;
String end = "<!MSG>";
StringBuilder curMsg = new StringBuilder();

while (-1 != (bytes = mmInStream.read(buffer))) {
    curMsg.append(new String(buffer, 0, bytes, Charset.forName("UTF-8")));
    int endIdx = curMsg.indexOf(end);
    if (endIdx != -1) {
        String fullMessage = curMsg.substring(0, endIdx + end.length());
        curMsg.delete(0, endIdx + end.length());
        // Now send fullMessage
    }
}