Receiving wrong data on client side in socket communication

Question

I am working on a small project to determine the upload speed of network.I have created a small Server in C which calculates the upload speed based on 1 MB data being sent by the client to the time taken for so.

Here is my server Code in C:

void main(int argc, char** argv){

    int sock_desc = 0;
    int connfd = 0;
    int read_size = 0;
    int clntSock; 
    struct sockaddr_in serv_addr;
    struct sockaddr_in echoClntAddr; 
    int rc;
    char client_message[1048576];//1048576 //524288
    time_t start,end;
    double t;
    int temp;
    double Bandwidth;
    int result[1];


struct timeval  tv1, tv2;

    sock_desc = socket(AF_INET, SOCK_STREAM, 0); 

    if(sock_desc < 0 )
       dieWithError("Unable to open Socket\n");

    memset(&serv_addr,0,sizeof(serv_addr)); 

    serv_addr.sin_family = AF_INET ;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(7024);

    if(bind(sock_desc, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) 
       dieWithError("bind failed\n");


    if(listen(sock_desc,MAX_CONNECTIONS) < 0)
       dieWithError("listen failed\n");  

       clntSock = sizeof(struct sockaddr);
 bahar: 
       connfd = accept(sock_desc, (struct sockaddr *)&echoClntAddr,(socklen_t*)&clntSock);
       printf("Connection accepted\n");
   while(1){

          read_size = recv(connfd , client_message ,1, 0); 
          gettimeofday(&tv1, NULL);
          if(read_size < 1048576)
read_again:  temp = read_size;
             read_size = 0;
             read_size = recv(connfd , client_message+temp , (sizeof(client_message)-temp), 0); 
             read_size+=temp;
             printf("read size is %d\n",read_size);
             temp=0;

             if(read_size < 1048576)//524288
                goto read_again; 


         gettimeofday(&tv2, NULL); 


        t =  (double) (tv2.tv_usec - tv1.tv_usec) / 1000000 +
            (double) (tv2.tv_sec - tv1.tv_sec);

        read_size*=8;
        read_size/=1024;
          Bandwidth = read_size/t;
          result[0]= (int) Bandwidth;
        //  Bandwidth/=1024; 
          printf("Network Bandwidth is %d Kbps\n",result[0]);//Bandwidth);
          rc = send(connfd , result , 4, 0);//send Bandwidth to  client
          goto bahar;

           }

    }



    void dieWithError(char *errormsg){ 
         printf("%s", errormsg);    
    }

Here is my client code in Java:

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.Socket;

public class JavaSAmpleClient {

    public static void main(String[] args)throws IOException {
        int i;
        int arr[] = new int[10];
        byte bfr[] = new byte[1024*1024];
        for (i=0;i<1048576;i++)
            bfr[i] = (byte)i;

  Socket s1 = new Socket("127.0.0.1",7024);


        BufferedOutputStream bos = new BufferedOutputStream(s1.getOutputStream());
                    BufferedInputStream bos1 = new BufferedInputStream(s1.getInputStream());
                    bos.write(bfr);
                    i=  bos1.read();//read bandwidth returned by server
                    System.out.println(i);

    }

}

The problem being faced is that if I write the client program in C it is able to receive the upload speed correrctly.But in case of Java i am not getting correct results.

For Eg: In case of java client: If server sends the bandwidth as 4282279 the Java client receives it as 167.

In case of C client: If server sends the bandwidth as 4282279 the client receives it as 4282279.

I cannot do client programming in C because I need to run client application on android.

Answer 1

You have both a byte-order problem in your C sending code and a read() coding problem in your Java code.

1. You need to send the int in network byte order. Use result[0] = htonl(Bandwidth); for that in the C code.
2. You're reading one byte instead of a 4-byte integer. Wrap a DataInputStream around the BufferedInputStream , and call readInt() .