Chez-simple-sockets is a package for Chez Scheme containing some procedures for everyday use of IPv4, IPv6 and unix domain SOCK_STREAM sockets. It does not purport to provide wide-ranging support for BSD sockets - just the procedures that users wanting to connect to remote hosts, or to run simple servers, might generally expect to use. It is mainly intended as a support library for chez-a-sync at https://github.com/ChrisVine/chez-a-sync.
The package has been designed to be thread-safe when blocking, so it can be used with installations of Chez Scheme with native thread support: it releases the garbage collector when blocking in C function calls (with appropriate protection for objects exported into C). It also avoids trying to provide scheme wrappers for C socket-related structs of a particular layout, because POSIX specifies the members that these structs must have and not their layout (accordingly, relevant structs are accessed at the C level and not the scheme level, which makes the code considerably more portable).
The package comes in two R6RS library files. The (simple-sockets basic) library file provides for making synchronous connections to remote and other hosts and for accepting synchronous connections from remote and other hosts, and has various additional utility procedures. The (simple-sockets a-sync) library file enables such connections to be handled asynchronously using the chez-a-sync library.
First, amend the Makefile as appropriate for the system in use, then run 'make' as user and 'make install' as root.
Assuming that the package has been installed in a library directory in which Chez Scheme can find library files, it can be imported into user code by importing it as (simple-sockets basic) and (simple-sockets a-sync). (simple-sockets a-sync) requires the chez-a-sync library; (simple-sockets basic) does not.
The (simple-sockets basic) library file offers the following procedures:
(connect-to-ipv4-host address service port)
This will connect to a remote IPv4 host. If 'port' is greater than 0, it is set as the port to which the connection will be made, otherwise this is deduced from the 'service' argument, which should be a string such as "html". The 'service' argument may be #f, in which case a port number greater than 0 must be given.
The 'address' argument should be a string which may be either the domain name of the server to which a connection is to be made or a dotted decimal address.
A &connect-condition exception will be raised if the connection attempt fails; applying connect-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
On success, this procedure returns the file descriptor of a connection socket. The file descriptor will be blocking.
(connect-to-ipv6-host address service port)
This will connect to a remote IPv6 host. If 'port' is greater than 0, it is set as the port to which the connection will be made, otherwise this is deduced from the 'service' argument, which should be a string such as "html". The 'service' argument may be #f, in which case a port number greater than 0 must be given.
The 'address' argument should be a string which may be either the domain name of the server to which a connection is to be made or a colonned IPv6 hex address.
A &connect-condition exception will be raised if the connection attempt fails; applying connect-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
On success, this procedure returns the file descriptor of a connection socket. The file descriptor will be blocking.
(connect-to-unix-host pathname)
This will connect to a unix domain host.
The 'pathname' argument should be a string comprising the filesystem name of the unix domain socket.
A &connect-condition exception will be raised if the connection attempt fails; applying connect-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
On success, this procedure returns the file descriptor of a connection socket. The file descriptor will be blocking.
(listen-on-ipv4-socket address port backlog)
This constructs a listening IPv4 server socket. 'address' may be a string or a boolean value. If it is a string, it must contain the address to bind the socket to in decimal dotted notation. Otherwise, if 'address' is boolean #t, the socket will bind on localhost, and if #f, it will bind on any interface. 'port' is the port to listen on. 'backlog' is the maximum number of queueing connections provided by the socket.
A &listen-condition exception will be raised if the making of a listening socket fails; applying listen-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
On success, this procedure returns the file descriptor of the server socket.
(listen-on-ipv6-socket address port backlog)
This constructs a listening IPv6 server socket. 'address' may be a string or a boolean value. If it is a string, it must contain the address to bind the socket to in colonned hex notation. Otherwise, if 'address' is boolean #t, the socket will bind on localhost, and if #f, it will bind on any interface. 'port' is the port to listen on. 'backlog' is the maximum number of queueing connections provided by the socket.
A &listen-condition exception will be raised if the making of a listening socket fails; applying listen-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
On success, this procedure returns the file descriptor of the server socket.
(listen-on-unix-socket pathname backlog [error-on-existing])
This constructs a listening unix domain server socket. 'pathname' is a string comprising the filesystem name of the unix domain socket. 'backlog' is the maximum number of queueing connections provided by the socket. The 'error-on-existing' argument is optional: it it is set #t, any existing or stale socket or other file by the name of 'pathname' will cause a &listen exception to arise when the unix domain socket is bound. If set #f, or the argument is not provided, then any prior existing socket will be deleted before binding.
A &listen-condition exception will be raised if the making of a listening socket fails; applying listen-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
On success, this procedure returns the file descriptor of the server socket.
(accept-ipv4-connection sock connection)
This procedure will accept incoming connections on a listening IPv4 socket. It will block until a connection is made.
'sock' is the file descriptor of the socket on which to accept connections, as returned by listen-on-ipv4-socket. 'connection' is a bytevector of size 4 to be passed to the procedure as an out parameter, in which the binary address of the connecting client will be placed in network byte order, or #f.
An &accept-condition exception will be raised if connection attempts fail; applying accept-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
If 'sock' is not a blocking descriptor, it will be made blocking by this procedure.
On success, this procedure returns the file descriptor for the connection socket. That file descriptor will be blocking.
(accept-ipv6-connection sock connection)
This procedure will accept incoming connections on a listening IPv6 socket. It will block until a connection is made.
'sock' is the file descriptor of the socket on which to accept connections, as returned by listen-on-ipv6-socket. 'connection' is a bytevector of size 16 to be passed to the procedure as an out parameter, in which the binary address of the connecting client will be placed in network byte order, or #f.
An &accept-condition exception will be raised if connection attempts fail; applying accept-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
If 'sock' is not a blocking descriptor, it will be made blocking by this procedure.
On success, this procedure returns the file descriptor for the connection socket. That file descriptor will be blocking.
(accept-unix-connection sock)
This procedure will accept incoming connections on a listening unix domain socket. It will block until a connection is made.
'sock' is the file descriptor of the socket on which to accept connections, as returned by listen-on-unix-socket.
An &accept-condition exception will be raised if connection attempts fail; applying accept-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
If 'sock' is not a blocking descriptor, it will be made blocking by this procedure.
On success, this procedure returns the file descriptor for the connection socket. That file descriptor will be blocking.
(ipv4-address->string addr)
This procedure takes a bytevector of size 4 containing an IPv4 address in network byte order, say as supplied as the 'connection' argument of accept-ipv4-connection, and returns a string with the address converted to decimal dotted format.
(ipv6-address->string addr)
This procedure takes a bytevector of size 16 containing an IPv6 address in network byte order, say as supplied as the 'connection' argument of accept-ipv6-connection, and returns a string with the address converted to fully uncompressed hex colonned upper case format.
(set-fd-non-blocking fd)
This procedure makes the file descriptor 'fd' non-blocking if it is not already non-blocking, otherwise this procedure does nothing. It returns #t if it succeeds (including if it does nothing because the descriptor is already non-blocking), otherwise #f.
(set-fd-blocking fd)
This procedure makes the file descriptor 'fd' blocking if it is not already blocking, otherwise this procedure does nothing. It returns #t if it succeeds (including if it does nothing because the descriptor is already blocking), otherwise #f.
(set-ignore-sigpipe)
It is almost always a mistake not to ignore or otherwise deal with SIGPIPE in programs using sockets. This procedure is a utility which if called will cause SIGPIPE to be ignored: instead any attempt to write to a socket which has been closed at the remote end will cause write/send to return with -1 and errno set to EPIPE. If something other than ignoring the signal is required, use Chez Scheme's register-signal-handler procedure.
This procedure returns #t if it succeeds, otherwise #f.
(connect-condition? cond)
This procedure returns #t if the condition object 'cond' is a &connection-condition object, otherwise #f.
(listen-condition? cond)
This procedure returns #t if the condition object 'cond' is a &listen-condition object, otherwise #f.
(accept-condition? cond)
This procedure returns #t if the condition object 'cond' is an &accept-condition object, otherwise #f.
(shutdown fd how)
This procedure shuts down a socket. 'fd' is the socket's file descriptor. 'how' is a symbol which can be 'rd, 'wr, or 'rdwr. This procedure returns #t on success and #f on failure.
(close-fd fd)
This closes a file descriptor. It returns #t on success and #f on failure. This procedure should only be used with file descriptors which are not owned by a port - otherwise apply the close-port procedure to the port.
(write-bytevector port bv)
In chez scheme, ports can be constructed from file descriptors using the open-fd-input-port, open-fd-output-port and open-fd-input/output-port procedures. The last of those would be useful for sockets, except that chez scheme's port implementation has the unfortunate feature that a port opened and used for both reading and writing via the port's buffers must be seekable (that is to say, its underlying file descriptor must have a file position pointer). For ports representing non-seekable read/write file descriptors such as sockets, this means that with any port other than a non-buffered binary port, an exception will arise if attempting to write to the port using R6RS procedures after it has previously been read from, unless an intervening call is made to clear-input-port between the last read and the first next write.
As having buffering enabled on input ports is usually desirable, this procedure is designed to circumvent the problem mentioned above: it by-passes the port's output buffers entirely and sends the output to the underlying file descriptor directly. (This means that if the port has previously been used for writing using chez scheme's R6RS write procedures, the port must be flushed before this procedure is called; but the best thing with a socket is to carry out all writing to the socket port using this procedure or the write-string procedure, and all reading using R6RS read procedures, in which case all is good. This can be enforced by constructing the socket port with open-fd-input-port rather than open-fd-input/output-port.)
One remaining point to watch out for is that clear-input-port must normally be called before an input/output port representing a socket (that is, one which has been constructed with open-fd-input/output-port) is closed or otherwise flushed for output, otherwise the exception mentioned above might arise.
'port' can be a binary port or a textual port. However, this procedure will raise a &i/o-write-error exception if passed a port representing a regular file with a file position pointer.
This procedure will return #t if the write succeeded, or #f if a local error arose.
Do not use this procedure with a non-blocking socket: use chez-a-sync's await-put-bytevector! procedure instead.
(write-string port text)
See the documentation on the write-bytevector procedure for more information about this procedure. This procedure applies string->bytevector to 'text' using the transcoder associated with 'port', and then applies write-bytevector to the result. 'port' must be a textual port.
Do not use this procedure with a non-blocking socket: use chez-a-sync's await-put-string! procedure instead.
(get-errno)
This returns the current C errno value. Its main purpose is to be called after write-bytevector or write-string has returned #f in order to determine the source of the failure to write. For example, if errno is 32 then on BSDs and linux, EPIPE has arisen. Call this procedure immediately after the failure has arisen or its value may be superceded by a newer error.
Importing the (simple-sockets a-sync) library file requires chez-a-sync to be installed. It offers the following procedures:
(await-connect-to-ipv4-host! accept resume [loop] address service port)
This will connect asynchronously to a remote IPv4 host. If 'port' is greater than 0, it is set as the port to which the connection will be made, otherwise this is deduced from the 'service' argument, which should be a string such as "html". The 'service' argument may be #f, in which case a port number greater than 0 must be given.
The 'address' argument should be a string which may be either the domain name of the server to which a connection is to be made or a dotted decimal address.
The event loop will not be blocked by this procedure even if the connection is not immediately available, provided that the C getaddrinfo() function does not block. In addition this procedure only attempts to connect to the first address the resolver offers to it. These are important provisos which mean that this procedure should only be used where 'address' has a single network address which can be looked up from a local file such as /etc/hosts, or it is a string in IPv4 dotted decimal format. Otherwise call connect-to-ipv4-host via await-task-in-thread!, await-task-in-event-loop! or await-task-in-thread-pool!.
This procedure is intended to be called within a waitable procedure invoked by a-sync (which supplies the 'await' and 'resume' arguments). The 'loop' argument is optional: this procedure operates on the event loop passed in as an argument, or if none is passed (or #f is passed), on the default event loop.
A &connect-condition exception will be raised if the connection attempt fails; applying connect-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
On success, this procedure returns the file descriptor of a connection socket. The file descriptor will be set non-blocking.
(await-connect-to-ipv6-host! accept resume [loop] address service port)
This will connect asynchronously to a remote IPv6 host. If 'port' is greater than 0, it is set as the port to which the connection will be made, otherwise this is deduced from the 'service' argument, which should be a string such as "html". The 'service' argument may be #f, in which case a port number greater than 0 must be given.
The 'address' argument should be a string which may be either the domain name of the server to which a connection is to be made or a colonned IPv6 hex address.
The event loop will not be blocked by this procedure even if the connection is not immediately available, provided that the C getaddrinfo() function does not block. In addition this procedure only attempts to connect to the first address the resolver offers to it. These are important provisos which mean that this procedure should only be used where 'address' has a single network address which can be looked up from a local file such as /etc/hosts, or it is a string in IPv6 hex format. Otherwise call connect-to-ipv6-host via await-task-in-thread!, await-task-in-event-loop! or await-task-in-thread-pool!.
This procedure is intended to be called within a waitable procedure invoked by a-sync (which supplies the 'await' and 'resume' arguments). The 'loop' argument is optional: this procedure operates on the event loop passed in as an argument, or if none is passed (or #f is passed), on the default event loop.
A &connect-condition exception will be raised if the connection attempt fails; applying connect-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
On success, this procedure returns the file descriptor of a connection socket. The file descriptor will be set non-blocking.
(await-connect-to-unix-host! accept resume [loop] pathname)
This will connect asynchronously to a unix domain host.
The 'pathname' argument should be a string comprising the filesystem name of the unix domain socket.
The event loop will not be blocked by this procedure even if the connection is not immediately available.
This procedure is intended to be called within a waitable procedure invoked by a-sync (which supplies the 'await' and 'resume' arguments). The 'loop' argument is optional: this procedure operates on the event loop passed in as an argument, or if none is passed (or #f is passed), on the default event loop.
A &connect-condition exception will be raised if the connection attempt fails; applying connect-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
On success, this procedure returns the file descriptor of a connection socket. The file descriptor will be set non-blocking.
(await-accept-ipv4-connection! await resume [loop] sock connection)
This procedure will accept incoming connections on a listening IPv4 socket asynchronously.
'sock' is the file descriptor of the socket on which to accept connections, as returned by listen-on-ipv4-socket. 'connection' is a bytevector of size 4 to be passed to the procedure as an out parameter, in which the binary address of the connecting client will be placed in network byte order, or #f.
This procedure will only return when a connection has been accepted. However, the event loop will not be blocked by this procedure while waiting. This procedure is intended to be called within a waitable procedure invoked by a-sync (which supplies the 'await' and 'resume' arguments). The 'loop' argument is optional: this procedure operates on the event loop passed in as an argument, or if none is passed (or #f is passed), on the default event loop.
An &accept-condition exception will be raised if connection attempts fail; applying accept-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
If 'sock' is not a non-blocking descriptor, it will be made non-blocking by this procedure.
On success, this procedure returns the file descriptor for the connection socket. That file descriptor will be set non-blocking.
This procedure will not call 'await' if a connection is immediately available to be accepted without waiting: instead, after accepting the connection this procedure would return straight away without invoking the event loop.
(await-accept-ipv6-connection! await resume [loop] sock connection)
This procedure will accept incoming connections on a listening IPv6 socket.
'sock' is the file descriptor of the socket on which to accept connections, as returned by listen-on-ipv6-socket. 'connection' is a bytevector of size 16 to be passed to the procedure as an out parameter, in which the binary address of the connecting client will be placed in network byte order, or #f.
This procedure will only return when a connection has been accepted. However, the event loop will not be blocked by this procedure while waiting. This procedure is intended to be called within a waitable procedure invoked by a-sync (which supplies the 'await' and 'resume' arguments). The 'loop' argument is optional: this procedure operates on the event loop passed in as an argument, or if none is passed (or #f is passed), on the default event loop.
An &accept-condition exception will be raised if connection attempts fail; applying accept-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
If 'sock' is not a non-blocking descriptor, it will be made non-blocking by this procedure.
On success, this procedure returns the file descriptor for the connection socket. That file descriptor will be set non-blocking.
This procedure will not call 'await' if a connection is immediately available to be accepted without waiting: instead, after accepting the connection this procedure would return straight away without invoking the event loop.
(await-accept-unix-connection! await resume [loop] sock)
This procedure will accept incoming connections on a listening unix domain socket asynchronously.
'sock' is the file descriptor of the socket on which to accept connections, as returned by listen-on-unix-socket.
This procedure will only return when a connection has been accepted. However, the event loop will not be blocked by this procedure while waiting. This procedure is intended to be called within a waitable procedure invoked by a-sync (which supplies the 'await' and 'resume' arguments). The 'loop' argument is optional: this procedure operates on the event loop passed in as an argument, or if none is passed (or #f is passed), on the default event loop.
An &accept-condition exception will be raised if connection attempts fail; applying accept-condition? to the raised condition object will return #t. The raised condition object includes an irritants condition providing the errno number concerned.
If 'sock' is not a non-blocking descriptor, it will be made non-blocking by this procedure.
On success, this procedure returns the file descriptor for the connection socket. That file descriptor will be set non-blocking.
This procedure will not call 'await' if a connection is immediately available to be accepted without waiting: instead, after accepting the connection this procedure would return straight away without invoking the event loop.
