Name: nt126004 Date: 11/29/2001


E:\work\bug>java -version
java version "1.4.0-beta3"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-beta3-b84)
Java HotSpot(TM) Client VM (build 1.4.0-beta3-b84, mixed mode)



When opening a HTTP-connection to a Web Server that supports keep-alive, the
Java client may throw a NullPointerException. This occurs, if the received content
length header does not meet the actual content length that was sent by the
server.

Scenario:
- client creates a HttpURLConnection object and gets the input stream
- the server answers the request
- for some reason, the server does not send as many bytes as it indicated in
the content-length header and closes the connection
- the client recognizes the end of the stream and tries to close the
KeepAliveStream
- this class performs skip operations, until as many bytes are received as
expected
- unfortunately, the underlying SocketInputStream cannot return more content,
instead it returns -1 (EOF)
- Exception

here is the stacktrace:

D:\development\mp\code\keepalive>java Client
sun.net.www.protocol.http.HttpURLConnection$HttpInputStream
123456789java.lang.NullPointerException
        at sun.net.www.http.KeepAliveStream.close(Unknown Source)
        at java.io.FilterInputStream.close(Unknown Source)
        at
sun.net.www.protocol.http.HttpURLConnection$HttpInputStream.close(Unk
nown Source)
        at java.io.BufferedInputStream.close(Unknown Source)
        at sun.nio.cs.StreamDecoder$CharsetSD.implClose(Unknown Source)
        at sun.nio.cs.StreamDecoder.close(Unknown Source)
        at java.io.InputStreamReader.close(Unknown Source)
        at Client.main(Client.java:32)

The following test code shows the problem.

Server.java:

import java.net.*;
import java.io.*;

public class Server
{
    public static void main(String[] args)
    {
        try
        {
            ServerSocket socket = new ServerSocket(8080);
            System.out.println("ServerSocket ready");

            Socket s = socket.accept();
            System.out.println("accepted");

            // read HTTP request from client
            DataInputStream din = new DataInputStream(s.getInputStream());
            while (true)
            {
                String line = din.readLine();
                System.out.println(line);
                if ((line == null) || line.trim().length() == 0)
                {
                    break;
                }
            }

            OutputStream out = s.getOutputStream();
            OutputStreamWriter ow = new OutputStreamWriter(out);

            ow.write("HTTP/1.0 200 OK\n");

            // Note: The client expects 10 bytes.
            ow.write("Content-Length: 10\n");
            ow.write("Content-Type: text/html\n");

            // Note: If this line is missing, everything works fine.
            ow.write("Connection: Keep-Alive\n");
            ow.write("\n");

            // Note: The (buggy) server only sends 9 bytes.
            ow.write("123456789");
            ow.flush();
            ow.close();

            System.out.println("Response sent");
        }
        catch (Exception ex)
        {
            ex.printStackTrace();
        }
    }
}

Client.java:

import java.net.*;
import java.io.*;

public class Client
{
    public static void main(String[] args)
    {
        HttpURLConnection con = null;
        InputStreamReader isr = null;

        try
        {
            // open connection
            con = (HttpURLConnection) new URL
("http://localhost:8080").openConnection();

            // get content
            InputStream in = con.getInputStream();
            System.out.println(in.getClass().getName());

            isr = new InputStreamReader(new BufferedInputStream(in));
            int i = 0;
            char cbuf[] = new char[1024];
            while (true)
            {
                i = isr.read(cbuf, 0, 1024);
                if (i <= 0) break;

                System.out.print(new String(cbuf, 0, i));
                System.out.flush();
            }
            
            isr.close();
            con.disconnect();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}

Of course, the behavior of the web server is not correct, but this may not hang
up the client!
(Review ID: 135870)
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