Explanations of Network Functions

Network Functions

Winstock Byte-ordering Functions

TERM

EXPLANATION

htonl

Converts from host to network byte-order for a 32-bit (long) quantity .

htons

Converts from host to network byte-order for a 16-bit (short) quantity .

ntohl

Converts from network to host byte-order for a 32-bit (long) quantity .

ntohs

Converts from network to host byte-order for a 16-bit (short) quantity .

TERM

EXPLANATION

sendto

Transmits data to a host address specified in a socket address structure, using a simple message buffer.

recvfrom

Recieves data from a socker and optionally records the network address of the sending host, using a simple message buffer.

Select Functions

The select function performs synchronous I/O multiplexing by monoitoring the status of multiple sockets.

TERM

EXPLANATION

FD_ZERO

Initialises a set of socket handles.

FD_SET

Adds a socket handle to a set.

FD_ISSET

Returns a non-sero value (true) if the socket handle is set and zero (false) if the socket handle is not set.

FD_CLR

Removes a socket handle from a set.

SOCKET FUNCTIONS

The following tables are from my notes on using socket functions on a UNIX system. An example of how each socket function was used is given underneath the main equation.

FUNCTION

EXPLANATION

socket_handle = socket(protocol_family, socket_type, protocol);

fd = (AF_INET, SOCK_STREAM, 0);

Creates a socket

result = bind (socket_handle, local_socket_address, address_length);

result = (fd, (struct sockaddr*)&addr, sizeof(addr));

Associates a local address (combination of host address and protocol port) with a socket.

result = listen(socket_handle, queue_length);

result = (fd, 5);

Listen for incoming service requests, acknowledges them and places them into a queue of given length.

result = select(number_of_sockets, readable_sockets, writeable_sockets, error_sockets, max_time);

result = select(MaxFds, &setReadTest, &setWriteTest, &setErrorTest, &time_out);

result = accept(socket_handle, socket_address, address_length);

result = accept(fd, (struct sockaddr*)&addr, &addlen);

Accepts function lets the server accept connections from a client program. When a request arrives at the specified socket, the socket implementation fills the socket address structure with the address of the client that requested the connection.

FUNCTION

EXPLANATION

return_value = sendto(socket_handle, message_buffer, buffer_length, special_flags, socket_address_structure, address_structure_length);

return_value = sendto(fd, icmp, 8, 0, (struct sockaddr*) &addr, sizeof(addr));

Function sendto is used on an unconnected socket. Remote host information is stored in the socket-data structure, pointed to in the fifth parameter in the sendto function.

return_value = recvfrom(socket_handle, message_buffer, buffer_length, special_flags, socket_address_structure, address_structure_length));

return_value = recvfrom(fd, recbuff, sizeoff(recvbuff), 0, (struct sockaddr*) &addr, &addrlen);

Retrieves data from a protocol port and on an unconnected socket (SOCK_DGRAM), and extracts from the datagram header the network address of the host that sent the datagram. The recvfrom function copies the network address of the host that sent the datagram into the socket address structure pointed to in the fifth parameter.

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BOOKS

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