Only receiving one byte from socket

Question

I coded a server program using python.

I'm trying to get a string but i got only a character! How can I receive a string?

def handleclient(connection):                                           
    while True:                             
        rec = connection.recv(200)
        if rec == "help": #when I put help in the client program, rec = 'h' and not to "help"
            connection.send("Help Menu!")


    connection.send(rec)
    connection.close()

def main():
   while True:
        connection, addr = sckobj.accept()   
        connection.send("Hello\n\r")
        connection.send("Message: ")   
        IpClient = addr[0]
        print 'Server was connected by :',IpClient


        thread.start_new(handleclient, (connection,))   

Answer 1

With TCP/IP connections your message can be fragmented. It might send one letter at a time, or it might send the whole lot at once - you can never be sure.

Your programs needs to be able to handle this fragmentation. Either use a fixed length packet (so you always read X bytes) or send the length of the data at the start of each packet. If you are only sending ASCII letters, you can also use a specific character (eg \n) to mark the end of transmission. In this case you would read until the message contains a \n.

recv(200) isn't guaranteed to receive 200 bytes - 200 is just the maximum.

This is an example of how your server could look:

rec = ""
while True:
    rec += connection.recv(1024)
    rec_end = rec.find('\n')
    if rec_end != -1:
        data = rec[:rec_end]

        # Do whatever you want with data here

        rec = rec[rec_end+1:]

Answer 2

My solve for stupid embarcadero C++ Builder

char RecvBuffer[4096];
boolean first_init_flag = true;
while(true)
{
    int bytesReceived;

    while(true)
    {
        ZeroMemory(RecvBuffer, 4096);
        bytesReceived = recv(clientSocket,(char*) &RecvBuffer, sizeof(RecvBuffer), 0);
        std::cout << "RecvBuffer: " << RecvBuffer << std::endl;
        std::cout << "bytesReceived: " << bytesReceived <<std ::endl;

        if (!std::strcmp(RecvBuffer, "\r\n"))
        {
            if (first_init_flag) {
                first_init_flag = !first_init_flag;
            }
            else
            {
                break;
            }
        }
    }


    if (bytesReceived == SOCKET_ERROR)
    {
        std::cout << "Client disconnected" << std::endl;
        break;
    }
    send(clientSocket, RecvBuffer, bytesReceived + 1, 0);
}

Firstly, you send \r\n or ENTER for escape concatenating handshake and first data sending