The basic function for creating network connections and network servers is make-network-process. It can do either of those jobs, depending on the arguments you give it.
This function creates a network connection or server and returns the process object that represents it. The arguments args are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value nil, except for :coding, :filter-multibyte, and :reuseaddr. Here are the meaningful keywords (those corresponding to network options are listed in the following section):
Use the string name as the process name. It is modified if necessary to make it unique.
Specify the communication type. A value of nil specifies a stream connection (the default); datagram specifies a datagram connection; seqpacket specifies a sequenced packet stream connection. Both connections and servers can be of these types.
If server-flag is non-nil, create a server. Otherwise, create a connection. For a stream type server, server-flag may be an integer, which then specifies the length of the queue of pending connections to the server. The default queue length is 5.
Specify the host to connect to. host should be a host name or Internet address, as a string, or the symbol local to specify the local host. If you specify host for a server, it must specify a valid address for the local host, and only clients connecting to that address will be accepted. When using local, by default IPv4 will be used, specify a family of ipv6 to override this. To listen on all interfaces, specify an address of ‘"0.0.0.0"’ for IPv4 or ‘"::"’ for IPv6. Note that on some operating systems, listening on ‘"::"’ will also listen on IPv4, so attempting to then listen separately on IPv4 will result in EADDRINUSE errors (‘"Address already in use"’).
service specifies a port number to connect to; or, for a server, the port number to listen on. It should be a service name like ‘"https"’ that translates to a port number, or an integer like ‘443’ or an integer string like ‘"443"’ that specifies the port number directly. For a server, it can also be t, which means to let the system select an unused port number.
family specifies the address (and protocol) family for communication. nil means determine the proper address family automatically for the given host and service. local specifies a Unix socket, in which case host is ignored. ipv4 and ipv6 specify to use IPv4 and IPv6, respectively.
If use-external-socket is non-nil use any sockets passed to Emacs on invocation instead of allocating one. This is used by the Emacs server code to allow on-demand socket activation. If Emacs wasn’t passed a socket, this option is silently ignored.
For a server process, local-address is the address to listen on. It overrides family, host and service, so you might as well not specify them.
For a connection, remote-address is the address to connect to. It overrides family, host and service, so you might as well not specify them.
For a datagram server, remote-address specifies the initial setting of the remote datagram address.
The format of local-address or remote-address depends on the address family:
[a b c d p] corresponding to numeric IPv4 address a.b.c.d and port number p. [a b c d e f
g h p] corresponding to numeric IPv6 address a:b:c:d:e:f:g:h and port number p. (f . av), where f is the family number and av is a vector specifying the socket address using one element per address data byte. Do not rely on this format in portable code, as it may depend on implementation defined constants, data sizes, and data structure alignment. If bool is non-nil for a stream connection, return without waiting for the connection to complete. When the connection succeeds or fails, Emacs will call the sentinel function, with a second argument matching "open" (if successful) or "failed". The default is to block, so that make-network-process does not return until the connection has succeeded or failed.
If you’re setting up an asynchronous TLS connection, you have to also provide the :tls-parameters parameter (see below).
Depending on the capabilities of Emacs, how asynchronous :nowait is may vary. The three elements that may (or may not) be done asynchronously are domain name resolution, socket setup, and (for TLS connections) TLS negotiation.
Many functions that interact with process objects, (for instance, process-datagram-address) rely on them at least having a socket before they can return a useful value. These functions will block until the socket has achieved the desired status. The recommended way of interacting with asynchronous sockets is to place a sentinel on the process, and not try to interact with it before it has changed status to ‘"run"’. That way, none of these functions will block.
When opening a TLS connection, this should be where the first element is the TLS type (which should either be gnutls-x509pki or gnutls-anon, and the remaining elements should form a keyword list acceptable for gnutls-boot. (This keyword list can be obtained from the gnutls-boot-parameters function.) The TLS connection will then be negotiated after completing the connection to the host.
If stopped is non-nil, start the network connection or server in the stopped state.
Use buffer as the process buffer.
Use coding as the coding system for this process. To specify different coding systems for decoding data from the connection and for encoding data sent to it, specify (decoding .
encoding) for coding.
If you don’t specify this keyword at all, the default is to determine the coding systems from the data.
Initialize the process query flag to query-flag. See Query Before Exit.
Initialize the process filter to filter.
If multibyte is non-nil, strings given to the process filter are multibyte, otherwise they are unibyte. The default is t.
Initialize the process sentinel to sentinel.
Initialize the log function of a server process to log. The log function is called each time the server accepts a network connection from a client. The arguments passed to the log function are server, connection, and message; where server is the server process, connection is the new process for the connection, and message is a string describing what has happened.
Initialize the process plist to plist.
The original argument list, modified with the actual connection information, is available via the process-contact function.
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Licensed under the GNU GPL license.
https://www.gnu.org/software/emacs/manual/html_node/elisp/Network-Processes.html