Add support for TCP_NODELAY on network streams

* src/process.c (socket_options): add entry for TCP_NODELAY.
* lisp/emacs-lisp/bytecomp.el: add :nodelay to valid keywords
  for make-network-process compiler-macro.
* doc/lispref/processes.texi: document :nodelay keyword argument
  to set-network-process-option and make-network-process.

(Bug#74793)

3 files changed, 14 insertions, 2 deletions

diff --git a/doc/lispref/processes.texi b/doc/lispref/processes.texi
index 79ef959ae65..e0d71ac22b6 100644
--- a/doc/lispref/processes.texi
+++ b/doc/lispref/processes.texi
@@ -3090,6 +3090,13 @@ listening on that port.  If @var{reuseaddr-flag} is @code{nil}, there
 may be a period of time after the last use of that port (by any
 process on the host) where it is not possible to make a new server on
 that port.
+
+@item :nodelay @var{nodelay-flag}
+If @var{nodelay-flag} is non-@code{nil}, the @code{TCP_NODELAY} option
+is enabled on the socket.  This disables the Nagle algorithm, meaning
+that network segments are sent as soon as possible, even when they
+contain little data.  This reduces network latency on the network
+connection, but can lead to many small packets being sent.
 @end table
 
 @defun set-network-process-option process option value &optional no-error
diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index f058fc48cc7..07eb4690fce 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -6049,8 +6049,8 @@ and corresponding effects."
             :buffer :host :service :type :family :local :remote :coding
             :nowait :noquery :stop :filter :filter-multibyte :sentinel
             :log :plist :tls-parameters :server :broadcast :dontroute
-            :keepalive :linger :oobinline :priority :reuseaddr :bindtodevice
-            :use-external-socket)
+            :keepalive :linger :oobinline :priority :reuseaddr :nodelay
+            :bindtodevice :use-external-socket)
           '(:name :service))))
 
 (provide 'byte-compile)
diff --git a/src/process.c b/src/process.c
index b71ba3daf2d..cd1378f07ad 100644
--- a/src/process.c
+++ b/src/process.c
@@ -38,6 +38,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <sys/socket.h>
 #include <netdb.h>
 #include <netinet/in.h>
+#include <netinet/tcp.h>
 #include <arpa/inet.h>
 
 #else
@@ -2861,6 +2862,9 @@ static const struct socket_options {
 #ifdef SO_REUSEADDR
     { ":reuseaddr", SOL_SOCKET, SO_REUSEADDR, SOPT_BOOL, OPIX_REUSEADDR },
 #endif
+#ifdef TCP_NODELAY
+    { ":nodelay", IPPROTO_TCP, TCP_NODELAY, SOPT_BOOL, OPIX_MISC },
+#endif
     { 0, 0, 0, SOPT_UNKNOWN, OPIX_NONE }
   };
 
@@ -3899,6 +3903,7 @@ The following network options can be specified for this connection:
 :broadcast BOOL    -- Allow send and receive of datagram broadcasts.
 :dontroute BOOL    -- Only send to directly connected hosts.
 :keepalive BOOL    -- Send keep-alive messages on network stream.
+:nodelay BOOL      -- Set TCP_NODELAY on the network socket.
 :linger BOOL or TIMEOUT -- Send queued messages before closing.
 :oobinline BOOL    -- Place out-of-band data in receive data stream.
 :priority INT      -- Set protocol defined priority for sent packets.