Question

I have a simple server-client model. In which Server sends some encrypted message to client. The client then uses the first few characters of the message to decide the processing. The problem is that these messages are getting buffered one after another hence I am loosing the all messages buffered after the first one. Is there a simple way to prevent buffering or tell the send function to flush.

Answer 1

Your client has to determine how many bytes should be read for it to process. The server will send one message after another, but the streaming socket allows the bytes to flow as if it is one long message. Your messages need some way to allow the client to know when one ends and the next one begins.

The easiest way to do that in a streaming socket is to prepend the message with the length of the message. So the client first reads the length, then the client reads that many bytes.

int send_message (int sock, const void *message, uint32_t len) {
    int r;
    uint32_t mlen = htonl(len);
    r = send(sock, &mlen, 4, 0);
    /* ...error checking... */
    r = send(sock, message, len, 0);
    /* ...error checking... */
    return ok ? len : error;
}

int recv_message (int sock, void *buf, uint32_t size) {
    int r;
    uint32_t mlen;
    r = recv(sock, &mlen, 4, 0);
    /* ...error checking... */
    mlen = ntohl(len);
    /* ...check buf is large enough... */
    r = recv(sock, buf, mlen, 0);
    /* ...error checking... */
    return ok ? mlen : error;
}