www.delorie.com/gnu/docs/guile/guile_431.html   search  
 
Buy GNU books!


Guile Reference Manual

[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

38.11.3 Network Sockets and Communication

Socket ports can be created using socket and socketpair. The ports are initially unbuffered, to make reading and writing to the same port more reliable. A buffer can be added to the port using setvbuf, See section 38.2 Ports and File Descriptors.

The convention used for "host" vs "network" addresses is that addresses are always held in host order at the Scheme level. The procedures in this section automatically convert between host and network order when required. The arguments and return values are thus in host order.

Scheme Procedure: socket family style proto
C Function: scm_socket (family, style, proto)
Return a new socket port of the type specified by family, style and proto. All three parameters are integers. Supported values for family are AF_UNIX, AF_INET and AF_INET6. Typical values for style are SOCK_STREAM, SOCK_DGRAM and SOCK_RAW.

proto 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.

Scheme Procedure: socketpair family style proto
C Function: scm_socketpair (family, style, proto)
Return a pair of connected (but unnamed) socket ports of the type specified by family, style and proto. Many systems support only socket pairs of the AF_UNIX family. Zero is likely to be the only meaningful value for proto.

Scheme Procedure: getsockopt sock level optname
C Function: scm_getsockopt (sock, level, optname)
Return the value of a particular socket option for the socket port sock. 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.

Scheme Procedure: setsockopt sock level optname value
C Function: scm_setsockopt (sock, level, optname, value)
Set the value of a particular socket option for the socket port sock. 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.

Scheme Procedure: shutdown sock how
C Function: scm_shutdown (sock, how)
Sockets can be closed simply by using close-port. The shutdown procedure allows reception or transmission 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.

Scheme Procedure: connect sock fam address . args
C Function: scm_connect (sock, fam, address, args)
Initiate a connection from a socket using a specified address family to the address specified by address and possibly args. The format required for address and args 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 IPv4 host address and args must be a single integer port number.

For a socket of family AF_INET6, address must be an integer IPv6 host address and args may be up to three integers: port [flowinfo] [scope_id], where flowinfo and scope_id default to zero.

The return value is unspecified.

Scheme Procedure: bind sock fam address . args
C Function: scm_bind (sock, fam, address, args)
Assign an address to the socket port sock. 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 args 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 IPv4 address and args 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.

For a socket of family AF_INET6, address must be an integer IPv6 address and args may be up to three integers: port [flowinfo] [scope_id], where flowinfo and scope_id default to zero.

The return value is unspecified.

Scheme Procedure: listen sock backlog
C Function: scm_listen (sock, backlog)
Enable sock 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.

Scheme Procedure: accept sock
C Function: scm_accept (sock)
Accept a connection on a bound, listening socket. If there are no pending connections in the queue, wait 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.

sock 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.

Scheme Procedure: getsockname sock
C Function: scm_getsockname (sock)
Return the address of sock, 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.

Scheme Procedure: getpeername sock
C Function: scm_getpeername (sock)
Return the address that sock 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.

Scheme Procedure: recv! sock buf [flags]
C Function: scm_recv (sock, buf, flags)
Receive data from a socket port. sock 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.

Scheme Procedure: send sock message [flags]
C Function: scm_send (sock, message, flags)
Transmit the string message on a socket port sock. sock 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.

Scheme Procedure: recvfrom! sock str [flags [start [end]]]
C Function: scm_recvfrom (sock, str, flags, start, end)
Return data from the socket port sock and also information about where the data was received from. sock must already be bound to the address from which data is to be received. str, is a string into which the data will be written. The size of str 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 address will given as #f if not available, as is usually the case for stream sockets.

The start and end arguments specify a substring of str 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.

Scheme Procedure: sendto sock message fam address . args_and_flags
C Function: scm_sendto (sock, message, fam, address, args_and_flags)
Transmit the string message on the socket port sock. The destination address is specified using the fam, address and args_and_flags arguments, in a similar way to the connect procedure. args_and_flags contains the usual connection arguments optionally followed by a flags argument, which is a value or bitwise OR of MSG_OOB, MSG_PEEK, MSG_DONTROUTE etc.

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

The following functions can be used to convert short and long integers between "host" and "network" order. Although the procedures above do this automatically for addresses, the conversion will still need to be done when sending or receiving encoded integer data from the network.

Scheme Procedure: htons value
C Function: scm_htons (value)
Convert a 16 bit quantity from host to network byte ordering. value is packed into 2 bytes, which are then converted and returned as a new integer.

Scheme Procedure: ntohs value
C Function: scm_ntohs (value)
Convert a 16 bit quantity from network to host byte ordering. value is packed into 2 bytes, which are then converted and returned as a new integer.

Scheme Procedure: htonl value
C Function: scm_htonl (value)
Convert a 32 bit quantity from host to network byte ordering. value is packed into 4 bytes, which are then converted and returned as a new integer.

Scheme Procedure: ntohl value
C Function: scm_ntohl (value)
Convert a 32 bit quantity from network to host byte ordering. value is packed into 4 bytes, which are then converted and returned as a new integer.

These procedures are inconvenient to use at present, but consider:

 
(define write-network-long
  (lambda (value port)
    (let ((v (make-uniform-vector 1 1 0)))
      (uniform-vector-set! v 0 (htonl value))
      (uniform-vector-write v port))))

(define read-network-long
  (lambda (port)
    (let ((v (make-uniform-vector 1 1 0)))
      (uniform-vector-read! v port)
      (ntohl (uniform-vector-ref v 0)))))


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

  webmaster     delorie software   privacy  
  Copyright 2003   by The Free Software Foundation     Updated Jun 2003