Add :coding support to open-network-stream and open-gnutls-stream

* doc/lispref/processes.texi (Network): Describe :coding keyword support.

* doc/misc/emacs-gnutls.texi (Help For Developers): Describe :coding
keyword support.

* etc/NEWS: Announce change to open-network-stream and
open-gnutls-stream.

* lisp/net/gnutls.el (open-gnutls-stream): Add support for :coding, pass it
down to open-network-stream.

* lisp/net/network-stream.el (open-network-stream)
(network-stream-open-plain, network-stream-open-starttls): Add
support for :coding, pass it down to make-network-process.
(network-stream-open-shell): Add support-for :coding, use
set-process-coding-system to set it after process creation.

doc/lispref/processes.texi

@@ -2463,6 +2463,12 @@ that are mainly relevant to encrypted connections:
 @item :nowait @var{boolean}
 If non-@code{nil}, try to make an asynchronous connection.
 
+@item :coding @var{coding}
+Use this to set the coding systems used by the network process, in
+preference to binding @code{coding-system-for-read} or
+@code{coding-system-for-write}.  @xref{Network Processes} for
+details.
+
 @item :type @var{type}
 The type of connection.  Options are:
 

doc/misc/emacs-gnutls.texi

@@ -190,7 +190,7 @@ the connection process.
 
 The optional @var{parameters} argument is a list of keywords and
 values.  The only keywords which currently have any effect are
-@code{:client-certificate} and @code{:nowait}.
+@code{:client-certificate}, @code{:nowait}, and @code{:coding}.
 
 Passing @w{@code{:client certificate t}} triggers looking up of client
 certificates matching @var{host} and @var{service} using the

etc/NEWS

@@ -339,6 +339,15 @@ Emacs depended on the previous behavior; if you really want the
 process' coding-system to be nil, use 'set-process-coding-system'
 after the process has been created, or pass in ":coding '(nil nil)".
 
++++
+** 'open-network-stream' now accepts a :coding argument.
+This allows specifying the coding systems used by a network process
+for encoding and decoding without having to bind
+coding-system-for-{read,write} or call 'set-process-coding-system'.
+
++++
+** 'open-gnutls-stream' now also accepts a :coding argument.
+
 
 * Changes in Emacs 28.1 on Non-Free Operating Systems
 

lisp/net/gnutls.el

@@ -169,8 +169,9 @@ Third arg HOST is the name of the host to connect to, or its IP address.
 Fourth arg SERVICE is the name of the service desired, or an integer
 specifying a port number to connect to.
 Fifth arg PARAMETERS is an optional list of keyword/value pairs.
-Only :client-certificate and :nowait keywords are recognized, and
-have the same meaning as for `open-network-stream'.
+Only :client-certificate, :nowait, and :coding keywords are
+recognized, and have the same meaning as for
+`open-network-stream'.
 For historical reasons PARAMETERS can also be a symbol, which is
 interpreted the same as passing a list containing :nowait and the
 value of that symbol.
@@ -208,7 +209,8 @@ trust and key files, and priority string."
                               (gnutls-boot-parameters
                                :type 'gnutls-x509pki
                                :keylist keylist
-                               :hostname (puny-encode-domain host)))))))
+                               :hostname (puny-encode-domain host))))
+                   :coding (plist-get parameters :coding))))
     (if nowait
         process
       (gnutls-negotiate :process process

lisp/net/network-stream.el

@@ -113,6 +113,10 @@ values:
   `ssl'      -- Equivalent to `tls'.
   `shell'    -- A shell connection.
 
+:coding is a symbol or a cons used to specify the coding systems
+used to decode and encode the data which the process reads and
+writes.  See `make-network-process' for details.
+
 :return-list specifies this function's return value.
   If omitted or nil, return a process object.  A non-nil means to
   return (PROC . PROPS), where PROC is a process object and PROPS
@@ -189,7 +193,8 @@ gnutls-boot (as returned by `gnutls-boot-parameters')."
 			      :host (puny-encode-domain host) :service service
 			      :nowait (plist-get parameters :nowait)
                               :tls-parameters
-                              (plist-get parameters :tls-parameters))
+                              (plist-get parameters :tls-parameters)
+                              :coding (plist-get parameters :coding))
       (let ((work-buffer (or buffer
 			     (generate-new-buffer " *stream buffer*")))
 	    (fun (cond ((and (eq type 'plain)
@@ -249,7 +254,8 @@ gnutls-boot (as returned by `gnutls-boot-parameters')."
 	(stream (make-network-process :name name :buffer buffer
 				      :host (puny-encode-domain host)
                                       :service service
-				      :nowait (plist-get parameters :nowait))))
+				      :nowait (plist-get parameters :nowait)
+                                      :coding (plist-get parameters :coding))))
     (when (plist-get parameters :warn-unless-encrypted)
       (setq stream (nsm-verify-connection stream host service nil t)))
     (list stream
@@ -270,7 +276,8 @@ gnutls-boot (as returned by `gnutls-boot-parameters')."
 	 ;; Return (STREAM GREETING CAPABILITIES RESULTING-TYPE)
 	 (stream (make-network-process :name name :buffer buffer
 				       :host (puny-encode-domain host)
-                                       :service service))
+                                       :service service
+                                       :coding (plist-get parameters :coding)))
 	 (greeting (and (not (plist-get parameters :nogreeting))
 			(network-stream-get-response stream start eoc)))
 	 (capabilities (network-stream-command stream capability-command
@@ -350,7 +357,8 @@ gnutls-boot (as returned by `gnutls-boot-parameters')."
 	    (setq stream
 		  (make-network-process :name name :buffer buffer
 					:host (puny-encode-domain host)
-                                        :service service))
+                                        :service service
+                                        :coding (plist-get parameters :coding)))
 	    (network-stream-get-response stream start eoc)))
         (unless (process-live-p stream)
           (error "Unable to negotiate a TLS connection with %s/%s"
@@ -453,6 +461,7 @@ gnutls-boot (as returned by `gnutls-boot-parameters')."
   (let* ((capability-command (plist-get parameters :capability-command))
 	 (eoc 		     (plist-get parameters :end-of-command))
 	 (start (with-current-buffer buffer (point)))
+         (coding (plist-get parameters :coding))
 	 (stream (let ((process-connection-type nil))
 		   (start-process name buffer shell-file-name
 				  shell-command-switch
@@ -461,6 +470,13 @@ gnutls-boot (as returned by `gnutls-boot-parameters')."
 				   (format-spec-make
 				    ?s host
 				    ?p service))))))
+    (when coding (if (consp coding)
+                       (set-process-coding-system stream
+                                                  (car coding)
+                                                  (cdr coding))
+                     (set-process-coding-system stream
+                                                coding
+                                                coding)))
     (list stream
 	  (network-stream-get-response stream start eoc)
 	  (network-stream-command stream capability-command