Datagram Unix socket problem

This is a discussion on Datagram Unix socket problem within the C Programming forums, part of the General Programming Boards category; Server receives some string from the client and sends the same string as response with Code: bytes_no = recvfrom(sock_fd, buf, ...

  1. #1
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    Datagram Unix socket problem

    Server receives some string from the client and sends the same string as response with

    Code:
    bytes_no = recvfrom(sock_fd, buf, 100, 0, (struct sockaddr*)&client_addr, &addr_len    );
    buf[bytes_no] = '\0';
    printf("\nReceived '%s' with %d bytes.", buf, bytes_no);
    bytes_no = sendto(sock_fd, buf, strlen(buf) + 1, 0, (struct sockaddr*)&client_addr, sizeof(struct sockaddr));
    printf("\n%d sent", bytes_no);
    while client sends some string and receives the response with

    Code:
    printf("\nRequest:  ");
    scanf("%s", message);
    sendto(sock_fd, message, strlen(message) + 1, 0, (struct sockaddr*)&sock_addr, sizeof(struct sockaddr));
    memset(message, 0, 100);
    bytes_no = recvfrom(sock_fd, message, 100, 0, (struct sockaddr*)&sock_addr, &addr_len);
    printf("Received '%s' with %d bytes.", message, bytes_no);
    Problem comes when server with sendto() sends a response to the client. If socket is created as Internet socket, then everything works fine: server sends the response, client receives it and prints out. But, if the socket is created as Unis socket, then server does not send the response with sendto(); instead sendto() returns status -1. Why? (The code for both Unix and Internet sockets is same except in the part where different socket types are created.)
    Regards!

  2. #2
    Gawking at stupidity
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    Did you check errno to see what error it says it's having when it returns -1?
    If you understand what you're doing, you're not learning anything.

  3. #3
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    Put this declaration at the top of your code:

    Code:
    int errno;
    And after, check it's value after any (or almost any) libc function:

    Code:
    strerror (errno)
    Regards !

  4. #4
    Gawking at stupidity
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    What Ron means is actually:

    To use errno, make sure you #include <errno.h>

    And then you can do something like the following:
    Code:
    if(sendto(sock_fd, message, strlen(message) + 1, 0, (struct sockaddr*)&sock_addr, sizeof(struct sockaddr)) == -1)
      printf("CRAP! sendto() returned an error! Error is: %s\n", strerror(errno));
    There's no need to declare errno since it's declared in errno.h already.
    If you understand what you're doing, you're not learning anything.

  5. #5
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    Error is "Unknown error 1073831896". Any ideas what does it mean?

  6. #6
    Gawking at stupidity
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    Looks like you might be using winsock, in which case you need to use WSAGetLastError instead of errno.

    We don't just ask for the operating system for no reason
    If you understand what you're doing, you're not learning anything.

  7. #7
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    I'm using Linux. (No problem when using Internet sockets, only Unix)

  8. #8
    Gawking at stupidity
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    Let me see your error checking code. Are you only printing errno when an error occurs?
    If you understand what you're doing, you're not learning anything.

  9. #9
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    Code:
    if (bytes_no == -1)
        printf("\n%d, %s", errno, strerror(err));
    prints out
    22, Unknown error 1073831896.

  10. #10
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    Code:
    printf("\n%d, %s", errno, strerror(err));
    You're supposed to pass errno like I did, not err.

    At any rate, I have this in /usr/include/asm/errno.h:
    Code:
    #define EINVAL          22      /* Invalid argument */
    If you understand what you're doing, you're not learning anything.

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