Add new --timeout flag to emacsclient

* lib-src/emacsclient.c (DEFAULT_TIMEOUT): New constant.
(timeout): New static variable.
(longopts, shortopts, decode_options, print_help_and_exit): Add new
flag --timeout.
(set_socket_timeout, check_socket_timeout): New helper functions.
(main): Display a status message or exit after Emacs has not responded
for a while, depending on above new --timeout flag.  (Bug#50849)

* doc/emacs/misc.texi (emacsclient Options):
* doc/man/emacsclient.1: Document the above new option.
* etc/NEWS: Announce it.

1 files changed, 72 insertions, 3 deletions

diff --git a/lib-src/emacsclient.c b/lib-src/emacsclient.c
index 73c8e45a865..15acb4589a9 100644
--- a/lib-src/emacsclient.c
+++ b/lib-src/emacsclient.c
@@ -1,6 +1,6 @@
 /* Client process that communicates with GNU Emacs acting as server.
 
-Copyright (C) 1986-1987, 1994, 1999-2022 Free Software Foundation, Inc.
+Copyright (C) 1986-2022 Free Software Foundation, Inc.
 
 This file is part of GNU Emacs.
 
@@ -55,6 +55,8 @@ char *w32_getenv (const char *);
 # include <sys/socket.h>
 # include <sys/un.h>
 
+# define DEFAULT_TIMEOUT (30)
+
 # define SOCKETS_IN_FILE_SYSTEM
 
 # define INVALID_SOCKET (-1)
@@ -144,6 +146,9 @@ static char const *socket_name;
 /* If non-NULL, the filename of the authentication file.  */
 static char const *server_file;
 
+/* Seconds to wait before timing out (0 means wait forever).  */
+static uintmax_t timeout;
+
 /* If non-NULL, the tramp prefix emacs must use to find the files.  */
 static char const *tramp_prefix;
 
@@ -178,6 +183,7 @@ static struct option const longopts[] =
   { "server-file",      required_argument, NULL, 'f' },
   { "display",  required_argument, NULL, 'd' },
   { "parent-id", required_argument, NULL, 'p' },
+  { "timeout",  required_argument, NULL, 'w' },
   { "tramp",    required_argument, NULL, 'T' },
   { 0, 0, 0, 0 }
 };
@@ -185,7 +191,7 @@ static struct option const longopts[] =
 /* Short options, in the same order as the corresponding long options.
    There is no '-p' short option.  */
 static char const shortopts[] =
-  "nqueHVtca:F:"
+  "nqueHVtca:F:w:"
 #ifdef SOCKETS_IN_FILE_SYSTEM
   "s:"
 #endif
@@ -497,6 +503,7 @@ decode_options (int argc, char **argv)
       if (opt < 0)
         break;
 
+      char* endptr;
       switch (opt)
         {
         case 0:
@@ -530,6 +537,17 @@ decode_options (int argc, char **argv)
           nowait = true;
           break;
 
+        case 'w':
+          timeout = strtoumax (optarg, &endptr, 10);
+          if (timeout <= 0 ||
+              ((timeout == INTMAX_MAX || timeout == INTMAX_MIN)
+               && errno == ERANGE))
+            {
+              fprintf (stderr, "Invalid timeout: \"%s\"\n", optarg);
+              exit (EXIT_FAILURE);
+            }
+          break;
+
         case 'e':
           eval = true;
           break;
@@ -671,6 +689,7 @@ The following OPTIONS are accepted:\n\
                         Set the parameters of a new frame\n\
 -e, --eval              Evaluate the FILE arguments as ELisp expressions\n\
 -n, --no-wait           Don't wait for the server to return\n\
+-w, --timeout           Seconds to wait before timing out\n\
 -q, --quiet             Don't display messages on success\n\
 -u, --suppress-output   Don't display return values from the server\n\
 -d DISPLAY, --display=DISPLAY\n\
@@ -1870,6 +1889,33 @@ start_daemon_and_retry_set_socket (void)
   return emacs_socket;
 }
 
+static void
+set_socket_timeout (HSOCKET socket, int seconds)
+{
+#ifndef WINDOWSNT
+  struct timeval timeout;
+  timeout.tv_sec = seconds;
+  timeout.tv_usec = 0;
+  setsockopt (socket, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof timeout);
+#else
+  DWORD timeout = seconds * 1000;
+  setsockopt (socket, SOL_SOCKET, SO_RCVTIMEO, (char *) &timeout, sizeof timeout);
+#endif
+}
+
+static bool
+check_socket_timeout (int rl)
+{
+#ifndef WINDOWSNT
+  return (rl == -1)
+    && (errno == EAGAIN)
+    && (errno == EWOULDBLOCK);
+#else
+  return (rl == SOCKET_ERROR)
+    && (WSAGetLastError() == WSAETIMEDOUT);
+#endif
+}
+
 int
 main (int argc, char **argv)
 {
@@ -2086,19 +2132,42 @@ main (int argc, char **argv)
     }
   fflush (stdout);
 
+  set_socket_timeout (emacs_socket, timeout > 0 ? timeout : DEFAULT_TIMEOUT);
+  bool saw_response = false;
   /* Now, wait for an answer and print any messages.  */
   while (exit_status == EXIT_SUCCESS)
     {
+      bool retry = true;
+      bool msg_showed = quiet;
       do
         {
           act_on_signals (emacs_socket);
           rl = recv (emacs_socket, string, BUFSIZ, 0);
+          retry = check_socket_timeout (rl);
+          if (retry)
+            {
+              if (timeout > 0 && !saw_response)
+                {
+                  /* Don't retry if we were given a --timeout flag.  */
+                  fprintf (stderr, "\nServer not responding; timed out after %lu seconds",
+                           timeout);
+                  retry = false;
+                }
+              else if (!msg_showed)
+                {
+                  msg_showed = true;
+                  fprintf (stderr, "\nServer not responding; use Ctrl+C to break");
+                }
+            }
         }
-      while (rl < 0 && errno == EINTR);
+      while ((rl < 0 && errno == EINTR) || retry);
 
       if (rl <= 0)
         break;
 
+      if (msg_showed)
+        fprintf (stderr, "\nGot response from server");
+      saw_response = true;
       string[rl] = '\0';
 
       /* Loop over all NL-terminated messages.  */