DataInputStream stuck when initialized

user_16902311 0
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I have been trying to send a byte[] array across my client / server application using Sockets, DataInputStream and DataOutputStream, but on the server side, the program just gets stuck when I try to initialise the DataInputStream.

Here is the code on the client side (it works fine):

DataOutputStream datas = new DataOutputStream(connection.getOutputStream());
datas.flush();
byte[] send = identityKeyPair.serialize();
datas.write(send);
datas.flush();

Here is the code on the server side:

reader = new BufferedReader(new InputStreamReader(connection.getInputStream()) );

sender = new PrintWriter(connection.getOutputStream());


newUser = new BasicUserData();

System.out.println("New registration from: " + connection.getInetAddress());
System.out.println("Data:");

String un = reader.readLine();
newUser.USERNAME = un;
System.out.println(newUser.USERNAME);
String pw = reader.readLine();
newUser.PASSWORD = pw;
System.out.println(newUser.PASSWORD);

DataOutputStream dataout = new DataOutputStream(connection.getOutputStream());
System.out.println("Opened data output stream");
DataInputStream receiver = new DataInputStream(connection.getInputStream());
//It gets stuck here, and the program doesn't read anything further
receiver.read();
byte[] id = receiver.readAllBytes();
            
System.out.println("Opened data input stream");
inputstream sockets java
2 Answers

You are using both connection.getInputStream() and connection.getOutputStream() in two different ways. You should use one and only one way of reading from and writing to streams, don't mix multiple ways.

When you execute reader.readLine(), the BufferedReader called reader will read up-to 8192 characters from the input stream into its buffer, likely consuming all bytes your client has written. This means that when you construct your DataInputStream around that same input stream and try to read it, there is no data available to read, causing the receiver.read() to block waiting for data. That data is never received as your client has sent all its data, which is now buffered in reader.

In addition, unless your client has closed its output stream, InputStream.readAllBytes() will block indefinitely anyway, because it is only finished when the end-of-stream has been reached. And for socket communication, that only happens when the other side closed its output stream.

Change your code so there is only one way of writing data (though not relevant here), and one way of reading data. In addition, you should establish clearly how you need to read and write data in a protocol, so to avoid consuming too much data at the wrong point, and to know how much data you need to read when.

user_4668620

Of course it does nothing but wait as specified in the javadoc a call to DataInputStream#read() blocks the current thread until data can be read from the input stream.

Your reader = BufferedReader(...) uses the same underlying InputStream which means the all the data the client sent is most likely already consumed by the 'login' logic.

Since neither the client nor the server close their respective streams no EOF is emitted either which leads to the stream 'just dangling' around waiting for more data.

Unless your client sends more data the server will wait eternally.

There are two solutions for your issue. Either thread you application so that the 'await input' logic is in it's own thread or take a look at javas NIO package (more precisely Channels and Selectors)

user_81817500
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