(guile.info.gz) Network Sockets and Communication
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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',
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 `PF_UNIX', `PF_INET' and `PF_INET6'. Typical
values for STYLE are `SOCK_STREAM', `SOCK_DGRAM', `SOCK_RAW',
`SOCK_RDM' and `SOCK_SEQPACKET'.
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)))))
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