Reading input from C socket client to Java socket server

Question

I have 2 socket clients and 2 socket servers, one of each in C and Java and all running on my local machine as processes.

They can all talk to each other successfully except the C socket and Java server. They connect successfully but when I type input into the C client, the enter key does not finish the message and send it to the Java server in the same manner it does when communicating with the C server.

Any insight would be greatly appreciated.

Java Server:

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

public class SimpleServer extends Thread
{
   private ServerSocket serverSocket;
   String clientmsg = "";

   public SimpleServer(int port) throws IOException
   {
      serverSocket = new ServerSocket(port);
      serverSocket.setSoTimeout(10000);
   }

    public void run()
    {
        while(true)
        {
            try
            {
                System.out.println("Waiting for client on port " + serverSocket.getLocalPort() + "...");
                Socket server = serverSocket.accept();
                System.out.println("Just connected to " + server.getRemoteSocketAddress());
                DataInputStream in = new DataInputStream(server.getInputStream());
                System.out.println(in.readUTF());
                DataOutputStream out = new DataOutputStream(server.getOutputStream());
                out.writeUTF("Thank you for connecting to "
                + server.getLocalSocketAddress() + "\nGoodbye!");
                server.close();
            }

            catch(SocketTimeoutException s)
            {
                System.out.println("Socket timed out!");
                break;
            }

            catch(IOException e)
            {
                e.printStackTrace();
                break;
            }
        }
    }
    public static void main(String [] args)
    {
        int port = Integer.parseInt(args[0]);
        try
        {
            Thread t = new SimpleServer(port);
            t.start();
        }

        catch(IOException e)
        {
            e.printStackTrace();
        }
    }
}

C client:

#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <netdb.h>

void error(char *msg) 
{
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[])
{
    int sockfd, portno;
    struct sockaddr_in serv_addr;
    struct hostent *server;
    int n;
    char buffer[256];

    if (argc < 3)
    {
        error("ERROR, no port provided");
    }

    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    if (sockfd < 0)
    {
        error("ERROR opening socket");
    }

    server = gethostbyname(argv[1]);

    if (server == NULL)
    {
        error("ERROR, host not found\n");
    }

    bzero((char *) &serv_addr, sizeof(serv_addr));
    portno = atoi(argv[2]);
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(portno);

    bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr, server->h_length);

    if (connect(sockfd,(struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
        error("ERROR connecting to server");
    }

    printf("Enter a message for the server: ");

    bzero(buffer,256);
    fgets(buffer,sizeof(buffer),stdin);
    n = write(sockfd,buffer,strlen(buffer));

    if (n < 0)
    {/
        error("ERROR writing to socket");
    }

    bzero(buffer,256);
    n = read(sockfd,buffer,255);

    if (n < 0)
    {
        error("ERROR reading from socket");
    }

    printf("%s\n", buffer);
    return 0;
}

Kavindu Dodanduwa · Accepted Answer · 2015-03-03 11:12:05Z

3

I would suggest to use BufferedReader and PrintWriter as follow,

BufferedReader in = new BufferedReader( new InputStreamReader(socket.getInputStream())); // Bufferreader from socket
PrintWriter out = new PrintWriter(socket.getOutputStream(), true); // printwriter from socket

You can simply use them as ,

in.readLine(); // read a line

out.println(); // write a line

So updated code would look like,

Socket server = serverSocket.accept();

System.out.println("Just connected to " + server.getRemoteSocketAddress());

BufferedReader in = new  BufferedReader( new InputStreamReader(socket.getInputStream()));

System.out.println(in.readline());

PrintWriter out = new PrintWriter(server.getOutputStream());

out.println("Thank you for connecting to ");

Additionally if i'm correct this approach would fulfill line terminal conditions for both Java and C.

edited Mar 3, 2015 at 11:12

answered Mar 3, 2015 at 10:57

Kavindu Dodanduwa

13.2k4 gold badges38 silver badges49 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

bbb Over a year ago

I tried this and I'm still encountering the same problem. Any suggestions as to how I could fix it?

ElderBug · Accepted Answer · 2015-03-03 10:37:09Z

0

From the readUTF() documentation :

First, two bytes are read and used to construct an unsigned 16-bit integer in exactly the manner of the readUnsignedShort method . This integer value is called the UTF length and specifies the number of additional bytes to be read.

In your C client, you are not sending these two bytes. Of course, this is also true for writeUTF().

answered Mar 3, 2015 at 10:37

ElderBug

6,16518 silver badges28 bronze badges

3 Comments

bbb Over a year ago

Okay thanks. What should I do fix this issue? Send 2 bytes in the C client or change the read method in the Java program? ReadUTF seems to be the only way to read a string

ElderBug Over a year ago

@Briscoooe The simplest would be to send the length. It is required anyway, no matter what you do, you must know when the string ends. strlen is enough to know the length, but note that the 2 bytes you must send are big endian.

bbb Over a year ago

Would you be able to give me some guidance in relation to how to implement this? Do you have any links for relative tutorials?

user207421 · Accepted Answer · 2015-03-03 10:51:50Z

0

Data to be read by readUTF() must be sent by writeUTF(), or something that can produce the same protoco:l: see the Javadoc. As your sender is C this is not practical, so you should use a different read API, for example readLine(), with suitable adjustment at the sender.

answered Mar 3, 2015 at 10:51

user207421

312k45 gold badges324 silver badges493 bronze badges

Collectives™ on Stack Overflow

Reading input from C socket client to Java socket server

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related