bug#50008: 28.0.50; ERC sends empty lines with user input

["J.P." <jp@neverwas.me>]

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Tags: patch

Hi, this one may take some seeing to believe. For proof, set up a local
server or proxy (I can help with this) or fire up and tweak the
behavioral tests included with these bugs [1] or ask a network oper
friend to check their logs (they'll already know immediately if you
mention ERC).

BTW, the included unit tests may require a quick refresher on the
relevant portions of the codebase. Happy to make a mess of explaining
the specifics. Thanks.


[1] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=48598
    https://debbugs.gnu.org/cgi/bugreport.cgi?bug=49860


In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.30, cairo version 1.17.4)
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From 78314388e91aa263dfbaaf24528eac8ddd15e353 Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <jp@neverwas.me>
Date: Sun, 13 Jun 2021 02:15:55 -0700
Subject: [PATCH] Don't send empty lines for implicit targets in ERC

* erc.el (erc-send-input-line): Previously, any line typed into a
query or channel buffer without an explicit user-command
handler (meaning most lines), would be sent twice because a trailing
newline (linefeed) would be appended. This has been verified by
checking IRCd server logs. IRCds won't return an error upon receiving
an empty message, but they also won't forward them to channel
subscribers and DM pals.

* erc-tests.el: Add test for erc-process-input-line, which also
indirectly tests erc-send-input-line. It also tests the command
lookup and dispatch facility
---
 lisp/erc/erc.el            | 21 ++++++-------
 test/lisp/erc/erc-tests.el | 61 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 12 deletions(-)

diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index 73202016ba..733b0a4510 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -2791,20 +2791,17 @@ erc-message-type-member
   (let ((prop-val (erc-get-parsed-vector position)))
     (and prop-val (member (erc-response.command prop-val) list))))
 
-(defvar-local erc-send-input-line-function 'erc-send-input-line)
+(defvar-local erc-send-input-line-function 'erc-send-input-line
+  "Function for sending lines lacking a leading user command.
+When a line typed into a buffer contains an explicit command, like /msg,
+a corresponding handler (here, erc-cmd-MSG) is called.  But lines typed
+into a channel or query buffer already have an implicit target and
+command (PRIVMSG).  This function is called on such occasions and also
+for special purposes (see erc-dcc.el).")
 
 (defun erc-send-input-line (target line &optional force)
-  "Send LINE to TARGET.
-
-See also `erc-server-send'."
-  (setq line (format "PRIVMSG %s :%s"
-                     target
-                     ;; If the line is empty, we still want to
-                     ;; send it - i.e. an empty pasted line.
-                     (if (string= line "\n")
-                         " \n"
-                       line)))
-  (erc-server-send line force target))
+  "Send LINE to TARGET."
+  (erc-message "PRIVMSG" (concat target " " line) force))
 
 (defun erc-get-arglist (fun)
   "Return the argument list of a function without the parens."
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index d13397274a..e448a06db0 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -109,3 +109,64 @@ erc-ring-previous-command
         (should (looking-at "abc")))))
   (when noninteractive
     (kill-buffer "*#fake*")))
+
+;; The point of this test is to ensure output is handled identically
+;; regardless of whether a command handler is summoned.
+
+(ert-deftest erc-process-input-line ()
+  (let (erc-server-last-sent-time
+        erc-server-flood-queue
+        (orig-erc-cmd-MSG (symbol-function 'erc-cmd-MSG))
+        calls)
+    (with-temp-buffer
+      (cl-letf (((symbol-function 'erc-cmd-MSG)
+                 (lambda (line)
+                   (push line calls)
+                   (funcall orig-erc-cmd-MSG line)))
+                ((symbol-function 'erc-server-buffer)
+                 (lambda () (current-buffer)))
+                ((symbol-function 'erc-server-process-alive)
+                 (lambda () t))
+                ((symbol-function 'erc-server-send-queue)
+                 #'ignore)
+                ((symbol-function 'erc-default-target)
+                 (lambda () "" "#chan")))
+
+        (ert-info ("Dispatch to user command handler")
+
+          (ert-info ("Baseline")
+            (erc-process-input-line "/msg #chan hi\n")
+            (should (equal (pop calls) " #chan hi"))
+            (should (equal (pop erc-server-flood-queue)
+                           '("PRIVMSG #chan :hi\r\n" . utf-8))))
+
+          (ert-info ("Spaces preserved")
+            (erc-process-input-line "/msg #chan hi you\n")
+            (should (equal (pop calls) " #chan hi you"))
+            (should (equal (pop erc-server-flood-queue)
+                           '("PRIVMSG #chan :hi you\r\n" . utf-8))))
+
+          (ert-info ("Empty line honored")
+            (erc-process-input-line "/msg #chan\n")
+            (should (equal (pop calls) " #chan"))
+            (should (equal (pop erc-server-flood-queue)
+                           '("PRIVMSG #chan :\r\n" . utf-8)))))
+
+        (ert-info ("Implicit cmd via `erc-send-input-line-function'")
+
+          (ert-info ("Baseline")
+            (erc-process-input-line "hi")
+            (should (equal (pop erc-server-flood-queue)
+                           '("PRIVMSG #chan :hi\r\n" . utf-8))))
+
+          (ert-info ("Spaces preserved")
+            (erc-process-input-line "hi you")
+            (should (equal (pop erc-server-flood-queue)
+                           '("PRIVMSG #chan :hi you\r\n" . utf-8))))
+
+          (ert-info ("Empty line transmitted without injected-space kludge")
+            (erc-process-input-line "")
+            (should (equal (pop erc-server-flood-queue)
+                           '("PRIVMSG #chan :\r\n" . utf-8))))
+
+          (should-not calls))))))
-- 
2.31.1