Java Sockets - Hang on reading data from server

Question

I'm currently working on a little Client/Server task with using sockets. Sadly I the client hangs when it is supposed to read the "200 OK File Created" sent by the server. Is there anything i overlooked?

Client:

public HTTPClient(InetAddress adress, int portnumber, String filename) throws IOException {
    socket = new Socket(adress, portnumber);
    input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
    output = new PrintWriter(socket.getOutputStream());
    this.filename = filename;
}

public void sendPutRequest() throws IOException {
    output.println("PUT /" + filename + " HTTP/1.0");
    output.flush();
    File myFile = new File(this.filename);
    if (myFile.exists()) {
        for (String string : Files.readAllLines(myFile.toPath())) {
            output.println(string);
        }
        output.flush();
        String line;
        while ((line = input.readLine()) != null) {
            System.out.println(line);
        }
    } else {
        throw new IOException("File not found");
    }
}

Server:

  try (Socket client = this.socket.accept(); 
    BufferedReader in = new BufferedReader(
    new InputStreamReader(client.getInputStream()));
    PrintWriter out = new PrintWriter(client.getOutputStream())) {

    String lineIn = in.readLine();
    if (lineIn.contains("PUT")) {
        String filename = lineIn.split(" ")[1].substring(1);
        List<String> filedata = new ArrayList<>();
        String line;
        while ((line = in.readLine()) != null) {
            filedata.add(line);
            System.out.println(line);
        }
        writeToFile(filename, filedata);
        out.println("200 OK File Created");
        out.flush();
    }
}

it seems like no connection established. what's your `output` instance? — Haifeng Zhang, Mar 31 '16 at 18:17

score 1 · Accepted Answer · answered Mar 31 '16 at 18:22

1

Your server is reading from the connection until it is closed (only in such a case in.readLine()will return null).

However your client does not close the connection to the server. Therefore the server is stuck in the while loop.

Solution: You have to close the output stream after sending the request. Alternatively detect the end of the request on server side without waiting for the "end of stream" limit.

answered Mar 31 '16 at 18:22

Robert

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Note: Usually with HTTP the `Content-Length:` header will show how long the body is and where it ends. see: http://stackoverflow.com/questions/15991173/is-the-content-length-header-required-for-a-http-1-0-response for details. – ebyrob Mar 31 '16 at 18:27
If i would close the connection rightaway, I wouldn't be able to send the client an acknowledge afterwards or am I misunderstanding something? – Shinobu Mar 31 '16 at 18:36
Nevermind i got i now. I transfered the number of lines before doing any reading on the server side. Thank you for your help. – Shinobu Mar 31 '16 at 18:55
@ebyrob: We are talking about the code reading the request, not the response. AFAIR in HTTP the request end is indicated by two empty lines. – Robert Apr 01 '16 at 07:53

score 0 · Answer 2 · answered Mar 31 '16 at 18:23

In your server code:

            while ((line = in.readLine()) != null) {
                filedata.add(line);
                System.out.println(line);
            }
             writeToFile(filename, filedata); // getting to this line?

Your server is never getting to the writeToFile line, because the socket connection is still open, and it's still in the while loop. As a solution, use DataFetcher

Java Sockets - Hang on reading data from server

2 Answers2