Detect nrepl+unix:socket.file configurations

"leiningen ... :socket nrepl.sock" reports the unix domain socket on
stdout like this:

  nREPL server listening on  nrepl+unix:nrepl.sock

Detect that in nrepl-server-filter and when found, set the
nrepl-endpoint to a suitable "local-unix-domain-socket" host-based
entry.

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### New features
 
+- [#3314](https://github.com/clojure-emacs/cider/issues/3314): Detect `nrepl+unix` sockets (say via `lein nrepl :headless :socket nrepl.sock`).
 - [#3262](https://github.com/clojure-emacs/cider/issues/3262): Add navigation functionality to `npfb` keys inside the data inspector's buffer.
 - [#3310](https://github.com/clojure-emacs/cider/issues/3310): Add ability to use custom coordinates in jack-in-dependecies
 

doc/modules/ROOT/pages/basics/up_and_running.adoc

@@ -280,10 +280,13 @@ CIDER's support for Unix sockets is considered experimental and its
 interface might change in future CIDER releases.
 
 When locally running nREPL servers, there is the option to listen on a
-socket file instead of opening a network port. This can have
-advantages in some use cases, e.g. when working with virtual networks
-(containers) where sharing a file socket can be vastly simpler than
-managing bridge networks and firewall setups.
+socket file instead of opening a network port.  As long as access to
+the parent directory of the socket is sufficiently protected, this is
+much more secure than the network port, since any local user can
+access the port-provided REPL.  It can also be be helpful in other
+cases, e.g. when working with virtual networks (containers) where
+sharing a file socket can be vastly simpler than managing bridge
+networks and firewall setups.
 
 After having started an nREPL server on a file socket, e.g. with the
 `clj` command (see https://nrepl.org/nrepl/usage/server.html for other
@@ -297,6 +300,12 @@ $ clj -R:nREPL -m nrepl.cmdline --socket nrepl.sock
 you can then connect CIDER by using the `local-unix-domain-socket`
 special hostname with `cider-connect`: kbd:[M-x] `cider-connect` kbd:[RET] `local-unix-domain-socket` kbd:[RET] `nrepl.sock` kbd:[RET].
 
+At the moment only with `leiningen`, commands like `cider-jack-in`
+will detect and use the unix domain socket if one is requested via the
+`:socket` argument.  This can be arranged by specifying a prefix
+argument to `cider-jack-in`, e.g. kbd:[C-u] kbd:[M-x] `cider-jack-in`,
+or by adjusting `cider-lein-parameters`.
+
 == What's Next?
 
 So, what to do next now that CIDER's ready for action? Here are a few ideas:

nrepl-client.el

@@ -1109,7 +1109,12 @@ been determined."
                (propertize cmd 'face 'font-lock-keyword-face))
       serv-proc)))
 
-(defconst nrepl-listening-address-regexp
+(defconst nrepl-listening-unix-address-regexp
+  (rx
+   (and "nREPL server listening on" (+ " ")
+        "nrepl+unix:" (group-n 1 (+ not-newline)))))
+
+(defconst nrepl-listening-inet-address-regexp
   (rx (or
        ;; standard
        (and "nREPL server started on port " (group-n 1 (+ (any "0-9"))))
@@ -1155,18 +1160,26 @@ up."
             (when-let* ((win (get-buffer-window)))
               (set-window-point win (point)))))
         ;; detect the port the server is listening on from its output
-        (when (and (null nrepl-endpoint)
-                   (string-match nrepl-listening-address-regexp output))
-          (let ((host (or (match-string 2 output)
-                          (file-remote-p default-directory 'host)
-                          "localhost"))
-                (port (string-to-number (match-string 1 output))))
-            (setq nrepl-endpoint (list :host host
-                                       :port port))
-            (message "[nREPL] server started on %s" port)
-            (cider--process-plist-put process :cider--nrepl-server-ready t)
-            (when nrepl-on-port-callback
-              (funcall nrepl-on-port-callback (process-buffer process)))))))))
+        (when (null nrepl-endpoint)
+          (let ((end (cond
+                      ((string-match nrepl-listening-unix-address-regexp output)
+                       (let ((path (match-string 1 output)))
+                         (message "[nREPL] server started on nrepl+unix:%s" path)
+                         (list :host "local-unix-domain-socket"
+                               :port path
+                               :socket-file path)))
+                      ((string-match nrepl-listening-inet-address-regexp output)
+                       (let ((host (or (match-string 2 output)
+                                       (file-remote-p default-directory 'host)
+                                       "localhost"))
+                             (port (string-to-number (match-string 1 output))))
+                         (message "[nREPL] server started on %s" port)
+                         (list :host host :port port))))))
+            (when end
+              (setq nrepl-endpoint end)
+              (cider--process-plist-put process :cider--nrepl-server-ready t)
+              (when nrepl-on-port-callback
+                (funcall nrepl-on-port-callback (process-buffer process))))))))))
 
 (defmacro emacs-bug-46284/when-27.1-windows-nt (&rest body)
   "Only evaluate BODY when Emacs bug #46284 has been detected."

test/nrepl-client-tests.el

@@ -114,29 +114,37 @@
 (describe "nrepl-parse-port"
   (it "standard"
       (let ((msg "nREPL server started on port 58882 on host kubernetes.docker.internal - nrepl://kubernetes.docker.internal:58882"))
-        (expect (string-match nrepl-listening-address-regexp msg)
+        (expect (string-match nrepl-listening-inet-address-regexp msg)
                 :not :to-be nil)
         (expect (match-string 1 msg)
                 :to-equal "58882")
         (expect (match-string 2 msg)
                 :to-be nil)))
   (it "babashka"
       (let ((msg "Started nREPL server at 127.0.0.1:1667"))
-        (expect (string-match nrepl-listening-address-regexp msg)
+        (expect (string-match nrepl-listening-inet-address-regexp msg)
                 :not :to-be nil)
         (expect (match-string 1 msg)
                 :to-equal "1667")
         (expect (match-string 2 msg)
                 :to-equal "127.0.0.1")))
     (it "shadow"
       (let ((msg "shadow-cljs - nREPL server started on port 50999"))
-        (expect (string-match nrepl-listening-address-regexp msg)
+        (expect (string-match nrepl-listening-inet-address-regexp msg)
                 :not :to-be nil)
         (expect (match-string 1 msg)
                 :to-equal "50999")
         (expect (match-string 2 msg)
                 :to-be nil))))
 
+(describe "nrepl-parse-sock"
+  (it "standard"
+      (let ((msg "nREPL server listening on  nrepl+unix:nrepl.sock"))
+        (expect (string-match nrepl-listening-unix-address-regexp msg)
+                :not :to-be nil)
+        (expect (match-string 1 msg)
+                :to-equal "nrepl.sock"))))
+
 (describe "nrepl-client-lifecycle"
   (it "start and stop nrepl client process"