server.c

if (retSize == -2)
{
    if (send(client_sock, buf, BUF_SIZE, 0) == -1)
    {
        close_socket(client_sock);
        close_socket(sock);
        fprintf(stderr, "Error1 sending to client.\n");
        return EXIT_FAILURE;
    }
    printf("You have sent %d msg\n",   cntOfMsg);
    printf("The msg is:\n %s\n", buf);
    printf("------------\n");
}
else
{
    if (send(client_sock, ret, BUF_SIZE, 0) == -1)
    {
        close_socket(client_sock);
        close_socket(sock);
        fprintf(stderr, "Error2 sending to client.\n");
        return EXIT_FAILURE;
    }
    printf("You have sent %d msg\n",   cntOfMsg);
    printf("The msg is:\n %s\n", ret);
    printf("------------\n");
}

client.c

while ((bytes_received = recv(sock, buf, BUF_SIZE, 0)) > 1)
{
    buf[bytes_received] = '\0';
    printf("You have received %d msg\n",  cnt);
    fprintf(stdout, "Received:\n%s\n", buf);
    printf("-----------\n");
    memset(buf,0,sizeof(buf));
}

Part of the output is as shown below:

NOTICE:
output like "Can't write error_log" or "syntax error" have nothing to do with the problem.Your can believe the code I show is the only place where send or recv.

CodePudding user response：

TCP send can segment the data however it wants. If you send small buffers, TCP can group them and send them as a single packet after a timeout or a pending ack is received. If you send large buffers, TCP can break them into a series of smaller packets, favoring TCP segmentation over IP fragmentation.

TCP recv can theoretically return only 1 byte, even if you think there should be more data waiting.

When using TCP to send records, you need to use a record layer that prepends each record with its length (say, a 32-bit integer in big-endian order). The receiver must then accumulate a length (which could theoretically dribble in 1 byte at a time), and then accumulate the record content described by that length. The receiver ping-pongs between accumulating a length and accumulating record content.

In a line-oriented protocol, you could use a newline character to delineate record boundaries. It's really up to you to decide how to indicate boundaries within the TCP byte stream.

CodePudding user response：

On each recv(), you are just incrementing the cnt variable and printing, it doesn't represent the number of bytes received. Try printing the bytes_received instead.
In the same way, in the send() part, print the return value of send() call instead of cntOfMsg