BSD Sockets#

accept#

int accept (int socket_id, struct sockaddr * addr, socklen_t * addr_len)

The argument socket_id is a socket that has been created with socket(), bound to an address with bind(), and is listening for connections after a listen().

The accept() system call extracts the first connection request on the queue of pending connections, creates a new socket, and allocates a new file descriptor for the socket.

If no pending connections are present on the queue, and the original socket is not marked as non-blocking, accept() blocks the caller until a connection is present. If the original socket is marked non-blocking and no pending connections are present on the queue, accept() returns an error. The accepted socket may not be used to accept more connections. The original socket socket_id remains open.

Returns

• These calls return -1 on error. If they succeed, they return a non-negative integer that is a descriptor for the accepted socket.

Note

• The accept() system call only supports blocking.

bind#

int bind (int socket_id, const struct sockaddr * addr, socklen_t addr_len)

The bind() system call assigns the local protocol address to a socket.

When a socket is created with socket() it exists in an address family space but has no protocol address assigned. The bind() system call requests that addr be assigned to the socket.

Returns

• The bind() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

connect#

int connect (int socket_id, const struct sockaddr * addr, socklen_t addr_len)

If socket_id is of type SOCK_DGRAM, connect() system call specifies the peer with which the socket is to be associated; If the socket is of type SOCK_STREAM, connect() system call attempts to make a connection to another socket.

The other socket is specified by addr, which is an address in the communications space of the socket. Each communications space interprets the addr argument in its own way. Generally, stream sockets may successfully connect() only once; datagram sockets may use connect() multiple times to change their association.

Returns

• The connect() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

Note

• Connecting to an invalid address, such as null address will result in EFAULT error.

getpeername#

int getpeername (int socket_id, struct sockaddr * name, socklen_t * name_len)

The getpeername() system call returns the name of the peer connected to socket socket_id.

The name is truncated if the buffer provided is too small.

Returns

• The getpeername() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

getsockname#

int getsockname (int socket_id, struct sockaddr * name, socklen_t * name_len)

The getsockname() system call returns the current name for the specified socket.

Returns

• The getsockname() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

getsockopt#

int getsockopt (int socket_id, int option_level, int option_name, void * option_value, socklen_t * option_length)

The getsockopt() system call manipulate the options associated with a socket.

Options may exist at multiple protocol levels; they are always present at the uppermost "socket" level. When manipulating socket options the level at which the option resides and the name of the option must be specified. To manipulate options at the socket level, level is specified as SOL_SOCKET. To manipulate options at any other level the protocol number of the appropriate protocol controlling the option is supplied. For example, to indicate that an option is to be interpreted by the TCP protocol, level should be set to the protocol number of TCP; For getsockopt() they identify a buffer in which the value for the requested option(s) are to be returned. The include file <sys/socket.h> contains definitions for socket level options. Options at other protocol levels vary in format and name. Most socket-level options utilize an int argument for option_value.

Returns

• Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

Note

• The following are the options, which are supported currently.

  • SO_RCVTIMEO

  • SO_KEEPALIVE

  • TCP_ULP

  • SO_MAX_RETRANSMISSION_TIMEOUT_VALUE

  • IP_TOS.

listen#

int listen (int socket_id, int backlog)

The listen() sysytem call listen for socket connections.

The listen() system call applies only to sockets of type SOCK_STREAM or SOCK_SEQPACKET.

• Pre-conditions:

  • To accept connections, a socket is first created with socket(), a willingness to accept incoming connections and a queue limit for incoming connections are specified with listen(), and then the connections are accepted with accept().

Returns

• The listen() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

recv#

ssize_t recv (int socket_id, void * buf, size_t buf_len, int flags)

The recv() function is normally used only on a connected socket.

recv() function Receive message(s) from a socket. The recv() return the length of the message on successful completion. If a message is too long to fit in the supplied buffer, excess bytes may be discarded depending on the type of socket the message is received from.

Returns

• ssize_t.

Note

• The recv() system call doesn't support any flags.

recvfrom#

ssize_t recvfrom (int socket_id, void * buf, size_t buf_len, int flags, struct sockaddr * from_addr, socklen_t * from_addr_len)

The recvfrom() system calls are used to receive messages from a socket, and may be used to receive data on a socket whether or not it is connection-oriented.

If from_addr is not a null pointer and the socket is not connection-oriented, the source address of the message is filled in.

Returns

• ssize_t.

Note

• The recvfrom() system call doesn't support any flags.

send#

ssize_t send (int socket_id, const void * buf, size_t buf_len, int flags)

The send() system call is used to transmit one or more messages to another socket.

The send() function may be used only when the socket is in a connected state. If the socket is connection-mode, the protocol must support implied connect or the socket must be in a connected state before use. No indication of failure to deliver is implicit in a send(). Locally detected errors are indicated by a return value of -1. If no messages space is available at the socket to hold the message to be transmitted, then send() normally blocks, unless the socket has been placed in non-blocking I/O mode.

Returns

• The send() call return the number of octets sent. If an error occurred a value of -1 is returned.

Note

• Currently, send() system call supports only blocking. The send() system call doesn't guarantees the packets are transmitted to remote note, which are enqueued in the queue. The send() system call doesn't supports any flags. The send() system call can only send max of 1460 bytes incase of plain TCP, UDP. Whereas incase of TLS, the max buffer length is 1370.

sendto#

ssize_t sendto (int socket_id, const void * buf, size_t buf_len, int flags, const struct sockaddr * to_addr, socklen_t to_addr_len)

The sendto() system calls are used to transmit one or more messages to another socket.

The functions sendto() may be used at any time if the socket is connectionless-mode. If the socket is connection-mode, the protocol must support implied connect or the socket must be in a connected state before use. The address of the target is given by to with to_addr_len specifying its size. If the socket is in a connected state, the target address passed to sendto() is ignored. If the message is too long to pass atomically through the protocol, the error EMSGSIZE is returned, and the message is not transmitted.

Returns

• The sendto() call return the number of octets sent. If an error occurred a value of -1 is returned.

Note

• Due to firmware limitations, sendto() system call doesn't support any flags. The sendto() system call can only send max of 1460 bytes incase of plain TCP, UDP. Whereas incase of TLS, the max buffer length is 1370.

setsockopt#

int setsockopt (int socket_id, int option_level, int option_name, const void * option_value, socklen_t option_length)

The setsockopt() system call set options on sockets.

The setsockopt() system call manipulate the options associated with a socket. Options may exist at multiple protocol levels; they are always present at the uppermost "socket" level. When manipulating socket options the level at which the option resides and the name of the option must be specified. To manipulate options at the socket level, level is specified as SOL_SOCKET. To manipulate options at any other level the protocol number of the appropriate protocol controlling the option is supplied. For example, to indicate that an option is to be interpreted by the TCP protocol, level should be set to the protocol number of TCP; The option_value and option_length arguments are used to access option values for setsockopt(). The include file <sys/socket.h> contains definitions for socket level options. Options at other protocol levels vary in format and name.

Returns

• Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

Note

• The following are the options, which are supported currently.

  • SO_RCVTIMEO

  • SO_KEEPALIVE

  • TCP_ULP

  • SO_MAX_RETRANSMISSION_TIMEOUT_VALUE

  • IP_TOS.

close#

int close (int socket_id)

The close() system call deletes the file descriptor of the socket.

Returns

• The close() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

Note

• Calling close on server or first client socket would end up closing othet socket as well. Closing an non existing socket, error EBADF (Bad file descriptor) will be thrown.

socket#

int socket (int family, int type, int protocol)

The socket() system call creates an endpoint for communication and returns a descriptor.

Returns

• A -1 is returned if an error occurs, otherwise the return value is a descriptor referencing the socket.