"read(byteBuf) = -1" Not Working

SOAP Web Service Tutorials - Herong's Tutorial Examples

∟Java Socket and HttpURLConnection for SOAP

∟"read(byteBuf) = -1" Not Working

This section provides a tutorial example of trying to use 'read(byteBuf) = -1' as the condition to stop reading the request on the server side. It will not work if the client keeps the connection open and waiting for the response.

I was not so happy about my socket server testing program, SocketRequestResponseServer.java, because it can only receive a request in a single read() statement with byte array of 10240 bytes. So I tried to read the request in a loop:

/* SocketServerTest.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.io.*;
import java.net.*;
public class SocketServerTest {
   public static void main(String[] args) {
      PrintStream out = System.out;

// Checking command line arguments
      if (args.length < 2) {
         out.println("Usage:");
         out.println(
            "java SocketServerTest inFile outFile");
         return;
      }
      String inFile = args[0];
      String outFile = args[1];

      try {
// Reading the response from a file
         File objFile = new File(inFile);
         int resLen = (int) objFile.length();
         byte[] resBytes = new byte[resLen];
         FileInputStream inStream = new FileInputStream(objFile);
         inStream.read(resBytes);
         inStream.close();

// Creating socket socket
         ServerSocket server = new ServerSocket(8888);
         out.println("Listening at 8888");
         Socket con = server.accept();
         out.println("Connection received from "
            +con.getInetAddress().toString());

// Receiving the request
         InputStream reqStream = con.getInputStream();
         FileOutputStream outStream = new FileOutputStream(outFile);
         byte[] byteBuf = new byte[1024];
         int reqLen = 0;
         int len = 0;
         while ((len=reqStream.read(byteBuf))>-1) {;
            reqLen += len;
            outStream.write(byteBuf,0,len);
            out.println("Bytes received: "+len);
         }
         outStream.close();

// Sending the response
         OutputStream resStream = con.getOutputStream();
         resStream.write(resBytes);
         resStream.close();

         reqStream.close();

// Output counts
         out.println("Request length: "+reqLen);
         out.println("Response length: "+resLen);
      } catch (Exception e) {
         e.printStackTrace();
      }
   }
}

The program code logic looks good. Let's run it in a command line window:

C:\herong>java SocketServerTest http_1_0_server.res server.req

Listening at 8888

Then run the socket client test program from another command line window:

C:\herong>java SocketRequestResponse localhost 8888 http_get.req client.res

Connecting to localhost at 8888

We have a problem here. The client program is hanging, and not able to receive the response from the server. If you look at the server window, you will see:

Connection received from /127.0.0.1
Bytes received: 18

The server is hanging too. It did receive the first 18 byte, which is the entire request. But the next len=reqStream.read(byteBuf) statement did not return -1 to signal end of the input stream. Why, because the client kept the connection open after sending the request and was waiting to receive response. There will be no end of the input stream as long as the connection is still open.

For now, I can press Ctrl-C to stop the server, and release the connect to client.

Takeaways:

It is impossible for the server to use read(byteBuf) = -1 as the indicator to stop reading the request, if the client keeps the connection and waits for response.
We need to find other ways to stop reading the request in a request-response socket communication.
If you are writing a HTTP server, you can inspect the request to pick up the Content-Length header line. If Content-Length does not exist, stop reading after a blank line, "\n\n", which is the end of header lines. If Content-Length does exist, stop reading after you received enough number of bytes specified in Content-Length,