From adb605716f2feda57a9ab5ea0d1d979e51ce8915 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jo=C3=A3o=20T=C3=A1vora?= <joaotavora@gmail.com>
Date: Wed, 14 Jan 2026 10:46:24 +0000
Subject: [PATCH] Jsonrpc: don't let remote endpoint requests go unanswered

Previously, 'quit' could cause remote endpoints to never get a
reply and thus sometimes hang.  Ensure we always reply.  Also,
give the application a chance to signal jsonrpc-error with the
served code=32000, meaning "no error".

* doc/lispref/text.texi (JSONRPC Overview): Rework section on
request dispatchers.

* lisp/jsonrpc.el (jsonrpc-connection-receive): Rework.
---
 doc/lispref/text.texi | 21 +++++++++++++++------
 lisp/jsonrpc.el       | 39 +++++++++++++++++++++++----------------
 2 files changed, 38 insertions(+), 22 deletions(-)

diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index d88fb99a6ed..a313480944b 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -6014,12 +6014,21 @@ must be a Lisp object that can be serialized as JSON (@pxref{Parsing
 JSON}).  The result is forwarded to the server as the JSONRPC
 @code{result} object.  A non-local return, achieved by calling the
 function @code{jsonrpc-error}, causes an error response to be sent to
-the server.  The details of the accompanying JSONRPC @code{error}
-object are filled out with whatever was passed to
-@code{jsonrpc-error}.  A non-local return triggered by an unexpected
-error of any other type also causes an error response to be sent
-(unless you have set @code{debug-on-error}, in which case this calls
-the Lisp debugger, @pxref{Error Debugging}).
+the server.  A non-local return triggered by an unexpected error of any
+other type also causes a response to be sent.  The debugger is never
+called (unless you have set @code{debug-on-error}, in which case the
+Lisp debugger may be called, @pxref{Error Debugging}).
+
+The details of the accompanying JSONRPC @code{error} object are filled
+out automatically (in the case of unexpected errors) or with whatever
+was passed to @code{jsonrpc-error} (in the case of explicit calls).
+
+Exceptionally, an explicit call to @code{jsonrpc-error} which sets
+@code{:code} to 32000 and @code{:data} to any JSON object has the
+meaning of ``no error'' and triggers a normal response to the remote
+endpoint with @code{result} being set to @code{:data}.  This is useful
+if the application wants to treat some non-local exits such as user
+quits as benign.
 
 @findex jsonrpc-convert-to-endpoint
 @findex jsonrpc-convert-from-endpoint
diff --git a/lisp/jsonrpc.el b/lisp/jsonrpc.el
index 0cd5097e5f0..74a59a04095 100644
--- a/lisp/jsonrpc.el
+++ b/lisp/jsonrpc.el
@@ -327,22 +327,29 @@ dispatcher in CONN."
               (and method id)
               (let* ((debug-on-error (and debug-on-error
                                           (not jsonrpc-inhibit-debug-on-error)))
-                     (reply
-                      (condition-case-unless-debug _ignore
-                          (condition-case oops
-                              `(:result ,(funcall rdispatcher conn (intern method)
-                                                  params))
-                            (jsonrpc-error
-                             `(:error
-                               (:code
-                                ,(or (alist-get 'jsonrpc-error-code (cdr oops))
-                                     -32603)
-                                :message ,(or (alist-get 'jsonrpc-error-message
-                                                         (cdr oops))
-                                              "Internal error")))))
-                        (error
-                         '(:error (:code -32603 :message "Internal error"))))))
-                (apply #'jsonrpc--reply conn id method reply)))
+                     reply)
+                (unwind-protect
+                    (setq
+                     reply
+                     (condition-case oops
+                         `(:result
+                           ,(funcall rdispatcher conn (intern method) params))
+                       (jsonrpc-error
+                        (let* ((data (cdr oops))
+                               (code (alist-get 'jsonrpc-error-code data))
+                               (msg (alist-get 'jsonrpc-error-message
+                                               (cdr oops))))
+                          (if (eq code 32000) ;; This means 'no error'
+                              (when-let* ((d (alist-get 'jsonrpc-error-data
+                                                        data)))
+                                `(:result ,d))
+                            `(:error
+                              (:code ,(or code -32603)
+                                     :message ,(or msg "Internal error"))))))))
+                  (unless reply
+                    (setq reply
+                          `(:error (:code -32603 :message "Internal error"))))
+                  (apply #'jsonrpc--reply conn id method reply))))
              (;; A remote notification
               method
               (funcall ndispatcher conn (intern method) params))