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POSending buffered images between Java client and Twisted Python socket server
 

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  1. POSending buffered images between Java client and Twisted Python socket server
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    <p>I have a server-side function that draws an image with the Python Imaging Library. The Java client requests an image, which is returned via socket and converted to a BufferedImage. </p> <p>I prefix the data with the size of the image to be sent, followed by a CR. I then read this number of bytes from the socket input stream and attempt to use ImageIO to convert to a BufferedImage. </p> <p>In abbreviated code for the client:</p> <pre class="lang-java prettyprint-override"><code>public String writeAndReadSocket(String request) { // Write text to the socket BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); bufferedWriter.write(request); bufferedWriter.flush(); // Read text from the socket BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream())); // Read the prefixed size int size = Integer.parseInt(bufferedReader.readLine()); // Get that many bytes from the stream char[] buf = new char[size]; bufferedReader.read(buf, 0, size); return new String(buf); } public BufferedImage stringToBufferedImage(String imageBytes) { return ImageIO.read(new ByteArrayInputStream(s.getBytes())); } </code></pre> <p>and the server:</p> <pre class="lang-py prettyprint-override"><code># Twisted server code here # The analog of the following method is called with the proper client # request and the result is written to the socket. def worker_thread(): img = draw_function() buf = StringIO.StringIO() img.save(buf, format="PNG") img_string = buf.getvalue() return "%i\r%s" % (sys.getsizeof(img_string), img_string) </code></pre> <p>This works for sending and receiving Strings, but image conversion (usually) fails. <strong>I'm trying to understand why the images are not being read properly.</strong> My best guess is that the client is not reading the proper number of bytes, but I honestly don't know why that would be the case.</p> <p><strong>Side notes:</strong></p> <ul> <li>I realize that the char[]-to-String-to-bytes-to-BufferedImage Java logic is roundabout, but reading the bytestream directly produces the same errors.</li> <li>I have a version of this working where the client socket isn't persistent, ie. the request is processed and the connection is dropped. That version works fine, as I don't need to care about the image size, but I want to learn <em>why</em> the proposed approach doesn't work.</li> </ul>
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    1. USPattimusPrime
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      1. VTUpMod
    1. COIt is usually a very bad idea to convert binary into text (so many things that can go wrong) Why don't you just send out the binary data over to your server?
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    2. COYou're definitely right. I work in a chemistry lab, and we historically neglect anything that doesn't directly translate to papers. I'm trying to fix that, but I'm not exactly an experienced coder.
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      1. USPattimusPrime
 

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