Network sockets

Socket ports can be created using socket and socketpair. The ports are initially unbuffered, to makes reading and writing to the same port more reliable. Buffered ports can be obtained with duplicate-port, See section Ports and File Descriptors.

These procedures convert Internet addresses and port values between "host" order and "network" order as required. The arguments and return values should be in "host" order.

primitive: socket family style protocol

Returns a new socket port of the type specified by family, style and protocol. All three parameters are integers. Typical values for family are the values of AF_UNIX and AF_INET. Typical values for style are the values of SOCK_STREAM, SOCK_DGRAM and SOCK_RAW.

protocol can be obtained from a protocol name using getprotobyname. A value of zero specifies the default protocol, which is usually right.

A single socket port cannot by used for communication until it has been connected to another socket.

primitive: socketpair family style protocol

Returns a pair of connected (but unnamed) socket ports of the type specified by family, style and protocol. Many systems support only socket pairs of the AF_UNIX family. Zero is likely to be the only meaningful value for protocol.

primitive: getsockopt socket level optname

Returns the value of a particular socket option for the socket port socket. level is an integer code for type of option being requested, e.g., SOL_SOCKET for socket-level options. optname is an integer code for the option required and should be specified using one of the symbols SO_DEBUG, SO_REUSEADDR etc.

The returned value is typically an integer but SO_LINGER returns a pair of integers.

primitive: setsockopt socket level optname value

Sets the value of a particular socket option for the socket port socket. level is an integer code for type of option being set, e.g., SOL_SOCKET for socket-level options. optname is an integer code for the option to set and should be specified using one of the symbols SO_DEBUG, SO_REUSEADDR etc. value is the value to which the option should be set. For most options this must be an integer, but for SO_LINGER it must be a pair.

The return value is unspecified.

primitive: shutdown socket how

Sockets can be closed simply by using close-port. The shutdown procedure allows reception or tranmission on a connection to be shut down individually, according to the parameter how:

0

Stop receiving data for this socket. If further data arrives, reject it.

1

Stop trying to transmit data from this socket. Discard any data waiting to be sent. Stop looking for acknowledgement of data already sent; don't retransmit it if it is lost.

2

Stop both reception and transmission.

The return value is unspecified.

primitive: connect socket family address [arg ...]

Initiates a connection from socket to the address specified by address and possibly arg .... The format required for address and arg ... depends on the family of the socket.

For a socket of family AF_UNIX, only address is specified and must be a string with the filename where the socket is to be created.

For a socket of family AF_INET, address must be an integer Internet host address and arg ... must be a single integer port number.

The return value is unspecified.

primitive: bind socket family address arg ...

Assigns an address to the socket port socket. Generally this only needs to be done for server sockets, so they know where to look for incoming connections. A socket without an address will be assigned one automatically when it starts communicating.

The format of address and ARG ... depends on the family of the socket.

For a socket of family AF_UNIX, only address is specified and must be a string with the filename where the socket is to be created.

For a socket of family AF_INET, address must be an integer Internet host address and arg ... must be a single integer port number.

The values of the following variables can also be used for address:

Variable: INADDR_ANY

Allow connections from any address.

Variable: INADDR_LOOPBACK

The address of the local host using the loopback device.

Variable: INADDR_BROADCAST

The broadcast address on the local network.

Variable: INADDR_NONE

No address.

The return value is unspecified.

primitive: listen socket backlog

This procedure enables socket to accept connection requests. backlog is an integer specifying the maximum length of the queue for pending connections. If the queue fills, new clients will fail to connect until the server calls accept to accept a connection from the queue.

The return value is unspecified.

primitive: accept socket

Accepts a connection on a bound, listening socket socket. If there are no pending connections in the queue, it waits until one is available unless the non-blocking option has been set on the socket.

The return value is a pair in which the CAR is a new socket port for the connection and the CDR is an object with address information about the client which initiated the connection.

If the address is not available then the CDR will be an empty vector.

socket does not become part of the connection and will continue to accept new requests.

The following functions take a socket address object, as returned by accept and other procedures, and return a selected component.

sockaddr:fam

The socket family, typically equal to the value of AF_UNIX or AF_INET.

sockaddr:path

If the socket family is AF_UNIX, returns the path of the filename the socket is based on.

sockaddr:addr

If the socket family is AF_INET, returns the Internet host address.

sockaddr:port

If the socket family is AF_INET, returns the Internet port number.

primitive: getsockname socket

Returns the address of socket, in the same form as the object returned by accept. On many systems the address of a socket in the AF_FILE namespace cannot be read.

primitive: getpeername socket

Returns the address of the socket that the socket socket is connected to, in the same form as the object returned by accept. On many systems the address of a socket in the AF_FILE namespace cannot be read.

primitive: recv! socket buf [flags]

Receives data from the socket port socket. socket must already be bound to the address from which data is to be received. buf is a string into which the data will be written. The size of buf limits the amount of data which can be received: in the case of packet protocols, if a packet larger than this limit is encountered then some data will be irrevocably lost.

The optional flags argument is a value or bitwise OR of MSG_OOB, MSG_PEEK, MSG_DONTROUTE etc.

The value returned is the number of bytes read from the socket.

Note that the data is read directly from the socket file descriptor: any unread buffered port data is ignored.

primitive: send socket message [flags]

Transmits the string message on the socket port socket. socket must already be bound to a destination address. The value returned is the number of bytes transmitted -- it's possible for this to be less than the length of message if the socket is set to be non-blocking. The optional flags argument is a value or bitwise OR of MSG_OOB, MSG_PEEK, MSG_DONTROUTE etc.

Note that the data is written directly to the socket file descriptor: any unflushed buffered port data is ignored.

primitive: recvfrom! socket buf [flags] [start] [end]

Returns data from the socket port socket and also information about where the data was received from. socket must already be bound to the address from which data is to be received. buf, is a string into which the data will be written. The size of buf limits the amount of data which can be received: in the case of packet protocols, if a packet larger than this limit is encountered then some data will be irrevocably lost.

The optional flags argument is a value or bitwise OR of MSG_OOB, MSG_PEEK, MSG_DONTROUTE etc.

The value returned is a pair: the CAR is the number of bytes read from the socket and the CDR an address object in the same form as returned by accept.

The start and end arguments specify a substring of buf to which the data should be written.

Note that the data is read directly from the socket file descriptor: any unread buffered port data is ignored.

primitive: sendto socket message family address arg ... [flags]

Transmits the string message on the socket port socket. The destination address is specified using the family, address and arg arguments, in a similar way to the connect procedure. The value returned is the number of bytes transmitted -- it's possible for this to be less than the length of message if the socket is set to be non-blocking. The optional flags argument is a value or bitwise OR of MSG_OOB, MSG_PEEK, MSG_DONTROUTE etc.

Note that the data is written directly to the socket file descriptor: any unflushed buffered port data is ignored.

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