From 01a2aa830b73028aecf1f7dae7dadba7467a3144 Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <jp@neverwas.me>
Date: Wed, 8 Mar 2023 06:14:36 -0800
Subject: [PATCH 1/1] Add conditional erc-server-reconnect-function

* lisp/erc/erc-backend.el (erc--server-reconnect-timer,
erc-server-delayed-check-reconnect): Add possible alternate value for
option `erc-server-reconnect-function' that only attempts to reconnect
after hearing back from the server.  Also add helper variable.
---
 lisp/erc/erc-backend.el | 56 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/lisp/erc/erc-backend.el b/lisp/erc/erc-backend.el
index 567443f5329..d289df98bab 100644
--- a/lisp/erc/erc-backend.el
+++ b/lisp/erc/erc-backend.el
@@ -744,6 +744,62 @@ erc-server-delayed-reconnect
     (with-current-buffer buffer
       (erc-server-reconnect))))
 
+(defvar-local erc--server-reconnect-timeout nil)
+
+(defun erc-server-delayed-check-reconnect (buffer)
+  "Wait for internet connectivity before trying to reconnect.
+BUFFER is the server buffer for the current connection."
+  ;; This may appear to hang for a good while at various places
+  ;; because it calls wait_reading_process_output a bunch.  It does at
+  ;; least sometimes print "Waiting for socket from ..." or similar.
+  (with-current-buffer buffer
+    (setq erc--server-reconnect-timeout
+          (min 300 (* (or erc--server-reconnect-timeout
+                          erc-server-reconnect-timeout)
+                      2)))
+    (let ((reschedule
+           (lambda (proc)
+             (let ((erc-server-reconnect-timeout
+                    erc--server-reconnect-timeout))
+               (with-current-buffer buffer
+                 (delete-process proc)
+                 (erc-display-message nil 'error buffer "Nobody home...")
+                 (erc-schedule-reconnect buffer 0))))))
+      (condition-case _
+          (let ((proc (funcall erc-session-connector
+                               "*erc-connectivity-check" nil
+                               erc-session-server erc-session-port
+                               :nowait t))
+                tls-check)
+            (when (and (not (eq erc-session-connector
+                                #'erc-open-network-stream))
+                       (process-contact proc :tls-parameters))
+              (setq tls-check
+                    (run-at-time
+                     1 1 (lambda (proc)
+                           (unless (eq 'connect (process-status proc))
+                             (cancel-timer tls-check))
+                           (when (eq 'failed (process-status proc))
+                             (funcall reschedule proc)))
+                     proc)))
+            (set-process-filter
+             proc (lambda (proc _)
+                    (delete-process proc)
+                    (with-current-buffer buffer
+                      (setq erc--server-reconnect-timeout nil))
+                    (run-at-time nil nil #'erc-server-delayed-reconnect
+                                 buffer)))
+            (set-process-sentinel
+             proc (lambda (cproc event)
+                    (with-current-buffer buffer
+                      (pcase event
+                        ("open\n"
+                         (run-at-time nil nil #'send-string
+                                      cproc "PING *connect-check*\r\n"))
+                        ("connection broken by remote peer\n"
+                         (funcall reschedule cproc)))))))
+        (file-error (funcall reschedule nil))))))
+
 (defun erc-server-filter-function (process string)
   "The process filter for the ERC server."
   (with-current-buffer (process-buffer process)
-- 
2.39.2