;;; process-tests.el --- Testing the process facilities -*- lexical-binding: t -*-

;; Copyright (C) 2013-2020 Free Software Foundation, Inc.

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;;

;;; Code:

(require 'cl-lib)
(require 'ert)
(require 'puny)
(require 'rx)
(require 'subr-x)

;; Timeout in seconds; the test fails if the timeout is reached.
(defvar process-test-sentinel-wait-timeout 2.0)

;; Start a process that exits immediately.  Call WAIT-FUNCTION,
;; possibly multiple times, to wait for the process to complete.
(defun process-test-sentinel-wait-function-working-p (wait-function)
  (let ((proc (start-process "test" nil "bash" "-c" "exit 20"))
	(sentinel-called nil)
	(start-time (float-time)))
    (set-process-sentinel proc (lambda (_proc _msg)
				 (setq sentinel-called t)))
    (while (not (or sentinel-called
		    (> (- (float-time) start-time)
		       process-test-sentinel-wait-timeout)))
      (funcall wait-function))
    (cl-assert (eq (process-status proc) 'exit))
    (cl-assert (= (process-exit-status proc) 20))
    sentinel-called))

(ert-deftest process-test-sentinel-accept-process-output ()
  (skip-unless (executable-find "bash"))
  (with-timeout (60)
  (should (process-test-sentinel-wait-function-working-p
           #'accept-process-output))))

(ert-deftest process-test-sentinel-sit-for ()
  (skip-unless (executable-find "bash"))
  (with-timeout (60)
  (should
   (process-test-sentinel-wait-function-working-p (lambda () (sit-for 0.01 t))))))

(when (eq system-type 'windows-nt)
  (ert-deftest process-test-quoted-batfile ()
    "Check that Emacs hides CreateProcess deficiency (bug#18745)."
    (let (batfile)
      (unwind-protect
          (progn
            ;; CreateProcess will fail when both the bat file and 1st
            ;; argument are quoted, so include spaces in both of those
            ;; to force quoting.
            (setq batfile (make-temp-file "echo args" nil ".bat"))
            (with-temp-file batfile
              (insert "@echo arg1=%1, arg2=%2\n"))
            (with-temp-buffer
              (call-process batfile nil '(t t) t "x &y")
              (should (string= (buffer-string) "arg1=\"x &y\", arg2=\n")))
            (with-temp-buffer
              (call-process-shell-command
               (mapconcat #'shell-quote-argument (list batfile "x &y") " ")
               nil '(t t) t)
              (should (string= (buffer-string) "arg1=\"x &y\", arg2=\n"))))
        (when batfile (delete-file batfile))))))

(ert-deftest process-test-stderr-buffer ()
  (skip-unless (executable-find "bash"))
  (with-timeout (60)
  (let* ((stdout-buffer (generate-new-buffer "*stdout*"))
	 (stderr-buffer (generate-new-buffer "*stderr*"))
	 (proc (make-process :name "test"
			     :command (list "bash" "-c"
					    (concat "echo hello stdout!; "
						    "echo hello stderr! >&2; "
						    "exit 20"))
			     :buffer stdout-buffer
			     :stderr stderr-buffer))
	 (sentinel-called nil)
	 (start-time (float-time)))
    (set-process-sentinel proc (lambda (_proc _msg)
				 (setq sentinel-called t)))
    (while (not (or sentinel-called
		    (> (- (float-time) start-time)
		       process-test-sentinel-wait-timeout)))
      (accept-process-output))
    (cl-assert (eq (process-status proc) 'exit))
    (cl-assert (= (process-exit-status proc) 20))
    (should (with-current-buffer stdout-buffer
	      (goto-char (point-min))
	      (looking-at "hello stdout!")))
    (should (with-current-buffer stderr-buffer
	      (goto-char (point-min))
	      (looking-at "hello stderr!"))))))

(ert-deftest process-test-stderr-filter ()
  (skip-unless (executable-find "bash"))
  (with-timeout (60)
  (let* ((sentinel-called nil)
	 (stderr-sentinel-called nil)
	 (stdout-output nil)
	 (stderr-output nil)
	 (stdout-buffer (generate-new-buffer "*stdout*"))
	 (stderr-buffer (generate-new-buffer "*stderr*"))
	 (stderr-proc (make-pipe-process :name "stderr"
					 :buffer stderr-buffer))
	 (proc (make-process :name "test" :buffer stdout-buffer
			     :command (list "bash" "-c"
					    (concat "echo hello stdout!; "
						    "echo hello stderr! >&2; "
						    "exit 20"))
			     :stderr stderr-proc))
	 (start-time (float-time)))
    (set-process-filter proc (lambda (_proc input)
			       (push input stdout-output)))
    (set-process-sentinel proc (lambda (_proc _msg)
				 (setq sentinel-called t)))
    (set-process-filter stderr-proc (lambda (_proc input)
				      (push input stderr-output)))
    (set-process-sentinel stderr-proc (lambda (_proc _input)
					(setq stderr-sentinel-called t)))
    (while (not (or sentinel-called
		    (> (- (float-time) start-time)
		       process-test-sentinel-wait-timeout)))
      (accept-process-output))
    (cl-assert (eq (process-status proc) 'exit))
    (cl-assert (= (process-exit-status proc) 20))
    (should sentinel-called)
    (should (equal 1 (with-current-buffer stdout-buffer
		       (point-max))))
    (should (equal "hello stdout!\n"
		   (mapconcat #'identity (nreverse stdout-output) "")))
    (should stderr-sentinel-called)
    (should (equal 1 (with-current-buffer stderr-buffer
		       (point-max))))
    (should (equal "hello stderr!\n"
		   (mapconcat #'identity (nreverse stderr-output) ""))))))

(ert-deftest set-process-filter-t ()
  "Test setting process filter to t and back." ;; Bug#36591
  (with-timeout (60)
  (with-temp-buffer
    (let* ((print-level nil)
           (print-length nil)
           (proc (start-process
                  "test proc" (current-buffer)
                  (concat invocation-directory invocation-name)
                  "-Q" "--batch" "--eval"
                  (prin1-to-string
                   '(let ((s nil) (count 0))
                      (while (setq s (read-from-minibuffer
                                      (format "%d> " count)))
                        (princ s)
                        (princ "\n")
                        (setq count (1+ count))))))))
      (set-process-query-on-exit-flag proc nil)
      (send-string proc "one\n")
      (while (not (equal (buffer-substring
                          (line-beginning-position) (point-max))
                         "1> "))
        (accept-process-output proc))   ; Read "one".
      (should (equal (buffer-string) "0> one\n1> "))
      (set-process-filter proc t)       ; Stop reading from proc.
      (send-string proc "two\n")
      (should-not
       (accept-process-output proc 1))  ; Can't read "two" yet.
      (should (equal (buffer-string) "0> one\n1> "))
      (set-process-filter proc nil)     ; Resume reading from proc.
      (while (not (equal (buffer-substring
                          (line-beginning-position) (point-max))
                         "2> "))
        (accept-process-output proc))   ; Read "Two".
      (should (equal (buffer-string) "0> one\n1> two\n2> "))))))

(ert-deftest start-process-should-not-modify-arguments ()
  "`start-process' must not modify its arguments in-place."
  ;; See bug#21831.
  (with-timeout (60)
  (let* ((path (pcase system-type
                 ((or 'windows-nt 'ms-dos)
                  ;; Make sure the file name uses forward slashes.
                  ;; The original bug was that 'start-process' would
                  ;; convert forward slashes to backslashes.
                  (expand-file-name (executable-find "attrib.exe")))
                 (_ "/bin//sh")))
         (samepath (copy-sequence path)))
    ;; Make sure 'start-process' actually goes all the way and invokes
    ;; the program.
    (should (process-live-p (condition-case nil
                                (start-process "" nil path)
                              (error nil))))
    (should (equal path samepath)))))

(ert-deftest make-process/noquery-stderr ()
  "Checks that Bug#30031 is fixed."
  (skip-unless (executable-find "sleep"))
  (with-timeout (60)
  (with-temp-buffer
    (let* ((previous-processes (process-list))
           (process (make-process :name "sleep"
                                  :command '("sleep" "1h")
                                  :noquery t
                                  :connection-type 'pipe
                                  :stderr (current-buffer))))
      (unwind-protect
          (let ((new-processes (cl-set-difference (process-list)
                                                  previous-processes
                                                  :test #'eq)))
            (should new-processes)
            (dolist (process new-processes)
              (should-not (process-query-on-exit-flag process))))
        (kill-process process))))))

;; Return t if OUTPUT could have been generated by merging the INPUTS somehow.
(defun process-tests--mixable (output &rest inputs)
  (while (and output (let ((ins inputs))
                       (while (and ins (not (eq (car (car ins)) (car output))))
                         (setq ins (cdr ins)))
                       (if ins
                           (setcar ins (cdr (car ins))))
                       ins))
    (setq output (cdr output)))
  (not (apply #'append output inputs)))

(ert-deftest make-process/mix-stderr ()
  "Check that `make-process' mixes the output streams if STDERR is nil."
  (skip-unless (executable-find "bash"))
  (with-timeout (60)
  ;; Frequent random (?) failures on hydra.nixos.org, with no process output.
  ;; Maybe this test should be tagged unstable?  See bug#31214.
  (skip-unless (not (getenv "EMACS_HYDRA_CI")))
  (with-temp-buffer
    (let ((process (make-process
                    :name "mix-stderr"
                    :command (list "bash" "-c"
                                   "echo stdout && echo stderr >&2")
                    :buffer (current-buffer)
                    :sentinel #'ignore
                    :noquery t
                    :connection-type 'pipe)))
      (while (or (accept-process-output process)
		 (process-live-p process)))
      (should (eq (process-status process) 'exit))
      (should (eq (process-exit-status process) 0))
      (should (process-tests--mixable (string-to-list (buffer-string))
                                      (string-to-list "stdout\n")
                                      (string-to-list "stderr\n")))))))

(ert-deftest make-process-w32-debug-spawn-error ()
  "Check that debugger runs on `make-process' failure (Bug#33016)."
  (skip-unless (eq system-type 'windows-nt))
  (with-timeout (60)
  (let* ((debug-on-error t)
         (have-called-debugger nil)
         (debugger (lambda (&rest _)
                     (setq have-called-debugger t)
                     ;; Allow entering the debugger later in the same
                     ;; test run, before going back to the command
                     ;; loop.
                     (setq internal-when-entered-debugger -1))))
    (should (eq :got-error ;; NOTE: `should-error' would inhibit debugger.
                (condition-case-unless-debug ()
                    ;; Emacs doesn't search for absolute filenames, so
                    ;; the error will be hit in the w32 process spawn
                    ;; code.
                    (make-process :name "test" :command '("c:/No-Such-Command"))
                  (error :got-error))))
    (should have-called-debugger))))

(ert-deftest make-process/file-handler/found ()
  "Check that the ‘:file-handler’ argument of ‘make-process’
works as expected if a file name handler is found."
  (with-timeout (60)
  (let ((file-handler-calls 0))
    (cl-flet ((file-handler
               (&rest args)
               (should (equal default-directory "test-handler:/dir/"))
               (should (equal args '(make-process :name "name"
                                                  :command ("/some/binary")
                                                  :file-handler t)))
               (cl-incf file-handler-calls)
               'fake-process))
      (let ((file-name-handler-alist (list (cons (rx bos "test-handler:")
                                                 #'file-handler)))
            (default-directory "test-handler:/dir/"))
        (should (eq (make-process :name "name"
                                  :command '("/some/binary")
                                  :file-handler t)
                    'fake-process))
        (should (= file-handler-calls 1)))))))

(ert-deftest make-process/file-handler/not-found ()
  "Check that the ‘:file-handler’ argument of ‘make-process’
works as expected if no file name handler is found."
  (with-timeout (60)
  (let ((file-name-handler-alist ())
        (default-directory invocation-directory)
        (program (expand-file-name invocation-name invocation-directory)))
    (should (processp (make-process :name "name"
                                    :command (list program "--version")
                                    :file-handler t))))))

(ert-deftest make-process/file-handler/disable ()
  "Check ‘make-process’ works as expected if it shouldn’t use the
file name handler."
  (with-timeout (60)
  (let ((file-name-handler-alist (list (cons (rx bos "test-handler:")
                                             #'process-tests--file-handler)))
        (default-directory "test-handler:/dir/")
        (program (expand-file-name invocation-name invocation-directory)))
    (should (processp (make-process :name "name"
                                    :command (list program "--version")))))))

(defun process-tests--file-handler (operation &rest _args)
  (cl-ecase operation
    (unhandled-file-name-directory "/")
    (make-process (ert-fail "file name handler called unexpectedly"))))

(put #'process-tests--file-handler 'operations
     '(unhandled-file-name-directory make-process))

(ert-deftest make-process/stop ()
  "Check that `make-process' doesn't accept a `:stop' key.
See Bug#30460."
  (with-timeout (60)
  (should-error
   (make-process :name "test"
                 :command (list (expand-file-name invocation-name
                                                  invocation-directory))
                 :stop t))))

;; All the following tests require working DNS, which appears not to
;; be the case for hydra.nixos.org, so disable them there for now.

(ert-deftest lookup-family-specification ()
  "network-lookup-address-info should only accept valid family symbols."
  (skip-unless (not (getenv "EMACS_HYDRA_CI")))
  (with-timeout (60)
  (should-error (network-lookup-address-info "google.com" 'both))
  (should (network-lookup-address-info "google.com" 'ipv4))
  (when (featurep 'make-network-process '(:family ipv6))
    (should (network-lookup-address-info "google.com" 'ipv6)))))

(ert-deftest lookup-unicode-domains ()
  "Unicode domains should fail"
  (skip-unless (not (getenv "EMACS_HYDRA_CI")))
  (with-timeout (60)
  (should-error (network-lookup-address-info "faß.de"))
  (should (network-lookup-address-info (puny-encode-domain "faß.de")))))

(ert-deftest unibyte-domain-name ()
  "Unibyte domain names should work"
  (skip-unless (not (getenv "EMACS_HYDRA_CI")))
  (with-timeout (60)
  (should (network-lookup-address-info (string-to-unibyte "google.com")))))

(ert-deftest lookup-google ()
  "Check that we can look up google IP addresses"
  (skip-unless (not (getenv "EMACS_HYDRA_CI")))
  (with-timeout (60)
  (let ((addresses-both (network-lookup-address-info "google.com"))
        (addresses-v4 (network-lookup-address-info "google.com" 'ipv4)))
    (should addresses-both)
    (should addresses-v4))
  (when (featurep 'make-network-process '(:family ipv6))
    (should (network-lookup-address-info "google.com" 'ipv6)))))

(ert-deftest non-existent-lookup-failure ()
  (skip-unless (not (getenv "EMACS_HYDRA_CI")))
  (with-timeout (60)
  "Check that looking up non-existent domain returns nil"
  (should (eq nil (network-lookup-address-info "emacs.invalid")))))

(defmacro process-tests--ignore-EMFILE (&rest body)
  "Evaluate BODY, ignoring EMFILE errors."
  (declare (indent 0) (debug t))
  (let ((err (make-symbol "err"))
        (message (make-symbol "message")))
    `(let ((,message (process-tests--EMFILE-message)))
       (condition-case ,err
           ,(macroexp-progn body)
         (file-error
          ;; If we couldn't determine the EMFILE message, just ignore
          ;; all `file-error' signals.
          (and ,message
               (not (string-equal (caddr ,err) ,message))
               (signal (car ,err) (cdr ,err))))))))

(defmacro process-tests--with-buffers (var &rest body)
  "Bind VAR to nil and evaluate BODY.
Afterwards, kill all buffers in the list VAR.  BODY should add
some buffer objects to VAR."
  (declare (indent 1) (debug (symbolp body)))
  (cl-check-type var symbol)
  `(let ((,var nil))
     (unwind-protect
         ,(macroexp-progn body)
       (mapc #'kill-buffer ,var))))

(defmacro process-tests--with-processes (var &rest body)
  "Bind VAR to nil and evaluate BODY.
Afterwards, delete all processes in the list VAR.  BODY should
add some process objects to VAR."
  (declare (indent 1) (debug (symbolp body)))
  (cl-check-type var symbol)
  `(let ((,var nil))
     (unwind-protect
         ,(macroexp-progn body)
       (mapc #'delete-process ,var))))

(defmacro process-tests--with-many-pipes (&rest body)
  "Generate lots of pipe processes.
Try to generate pipe processes until we are close to the
FD_SETSIZE limit.  Within BODY, only a small number of file
descriptors should still be available."
  (declare (indent 0) (debug t))
  (let ((process (make-symbol "process"))
        (processes (make-symbol "processes"))
        (buffer (make-symbol "buffer"))
        (buffers (make-symbol "buffers"))
        ;; FD_SETSIZE is typically 1024 on Unix-like systems.  On
        ;; MS-Windows we artificially limit FD_SETSIZE to 64, see the
        ;; commentary in w32proc.c.
        (fd-setsize (if (eq system-type 'windows-nt) 64 1024)))
    `(process-tests--with-buffers ,buffers
       (process-tests--with-processes ,processes
         ;; First, allocate enough pipes to definitely exceed the
         ;; FD_SETSIZE limit.
         (cl-loop for i from 1 to ,(1+ fd-setsize)
                  for ,buffer = (generate-new-buffer
                                 (format " *pipe %d*" i))
                  do (push ,buffer ,buffers)
                  for ,process = (process-tests--ignore-EMFILE
                                   (make-pipe-process
                                    :name (format "pipe %d" i)
                                    :buffer ,buffer
                                    :coding 'no-conversion
                                    :noquery t))
                  while ,process
                  do (push ,process ,processes))
         (unless (cddr ,processes)
           (ert-fail "Couldn't allocate enough pipes"))
         ;; Delete two pipes to test more edge cases.
         (delete-process (pop ,processes))
         (delete-process (pop ,processes))
         ,@body))))

(defmacro process-tests--with-temp-file (var &rest body)
  "Bind VAR to the name of a new regular file and evaluate BODY.
Afterwards, delete the file."
  (declare (indent 1) (debug (symbolp body)))
  (cl-check-type var symbol)
  (let ((file (make-symbol "file")))
    `(let ((,file (make-temp-file "emacs-test-")))
       (unwind-protect
           (let ((,var ,file))
             ,@body)
         (delete-file ,file)))))

(defmacro process-tests--with-temp-directory (var &rest body)
  "Bind VAR to the name of a new directory and evaluate BODY.
Afterwards, delete the directory."
  (declare (indent 1) (debug (symbolp body)))
  (cl-check-type var symbol)
  (let ((dir (make-symbol "dir")))
    `(let ((,dir (make-temp-file "emacs-test-" :dir)))
       (unwind-protect
           (let ((,var ,dir))
             ,@body)
         (delete-directory ,dir :recursive)))))

;; Tests for FD_SETSIZE overflow (Bug#24325).  The following tests
;; generate lots of process objects of the various kinds.  Running the
;; tests with assertions enabled should not result in any crashes due
;; to file descriptor set overflow.  These tests first generate lots
;; of unused pipe processes to fill up the file descriptor space.
;; Then, they create a few instances of the process type under test.

(ert-deftest process-tests/fd-setsize-no-crash/make-process ()
  "Check that Emacs doesn't crash when trying to use more than
FD_SETSIZE file descriptors (Bug#24325)."
  (with-timeout (60 (ert-fail "Test timed out"))
    (let ((sleep (executable-find "sleep")))
      (skip-unless sleep)
      (dolist (conn-type '(pipe pty))
        (ert-info ((format "Connection type `%s'" conn-type))
          (process-tests--with-many-pipes
            (process-tests--with-processes processes
              ;; Start processes until we exhaust the file descriptor
              ;; set size.  We assume that each process requires at
              ;; least one file descriptor.
              (dotimes (i 10)
                (let ((process
                       ;; Failure to allocate more file descriptors
                       ;; should signal `file-error', but not crash.
                       ;; Since we don't know the exact limit, we
                       ;; ignore `file-error'.
                       (process-tests--ignore-EMFILE
                         (make-process :name (format "test %d" i)
                                       :command (list sleep "5")
                                       :connection-type conn-type
                                       :coding 'no-conversion
                                       :noquery t))))
                  (when process (push process processes))))
              ;; We should have managed to start at least one process.
              (should processes)
              (dolist (process processes)
                (while (accept-process-output process))
                (should (eq (process-status process) 'exit))
                (should (eql (process-exit-status process) 0))))))))))

(ert-deftest process-tests/fd-setsize-no-crash/make-pipe-process ()
  "Check that Emacs doesn't crash when trying to use more than
FD_SETSIZE file descriptors (Bug#24325)."
  (with-timeout (60 (ert-fail "Test timed out"))
    (process-tests--with-many-pipes
      (process-tests--with-buffers buffers
        (process-tests--with-processes processes
          ;; Start processes until we exhaust the file descriptor set
          ;; size.  We assume that each process requires at least one
          ;; file descriptor.
          (dotimes (i 10)
            (let ((buffer (generate-new-buffer (format " *%d*" i))))
              (push buffer buffers)
              (let ((process
                     ;; Failure to allocate more file descriptors
                     ;; should signal `file-error', but not crash.
                     ;; Since we don't know the exact limit, we ignore
                     ;; `file-error'.
                     (process-tests--ignore-EMFILE
                       (make-pipe-process :name (format "test %d" i)
                                          :buffer buffer
                                          :coding 'no-conversion
                                          :noquery t))))
                (when process (push process processes)))))
          ;; We should have managed to start at least one process.
          (should processes))))))

(ert-deftest process-tests/fd-setsize-no-crash/make-network-process ()
  "Check that Emacs doesn't crash when trying to use more than
FD_SETSIZE file descriptors (Bug#24325)."
  (skip-unless (featurep 'make-network-process '(:server t)))
  (skip-unless (featurep 'make-network-process '(:family local)))
  (with-timeout (60 (ert-fail "Test timed out"))
    (process-tests--with-temp-directory directory
      (process-tests--with-processes processes
        (let* ((num-clients 10)
               (socket-name (expand-file-name "socket" directory))
               ;; Run a UNIX server to connect to.
               (server (make-network-process :name "server"
                                             :server num-clients
                                             :buffer nil
                                             :service socket-name
                                             :family 'local
                                             :coding 'no-conversion
                                             :noquery t)))
          (push server processes)
          (process-tests--with-many-pipes
            ;; Start processes until we exhaust the file descriptor
            ;; set size.  We assume that each process requires at
            ;; least one file descriptor.
            (dotimes (i num-clients)
              (let ((client
                     ;; Failure to allocate more file descriptors
                     ;; should signal `file-error', but not crash.
                     ;; Since we don't know the exact limit, we ignore
                     ;; `file-error'.
                     (process-tests--ignore-EMFILE
                       (make-network-process
                        :name (format "client %d" i)
                        :service socket-name
                        :family 'local
                        :coding 'no-conversion
                        :noquery t))))
                (when client (push client processes))))
            ;; We should have managed to start at least one process.
            (should processes)))))))

(ert-deftest process-tests/fd-setsize-no-crash/make-serial-process ()
  "Check that Emacs doesn't crash when trying to use more than
FD_SETSIZE file descriptors (Bug#24325)."
  (with-timeout (60 (ert-fail "Test timed out"))
    (skip-unless (file-executable-p shell-file-name))
    (skip-unless (executable-find "tty"))
    (skip-unless (executable-find "sleep"))
    ;; `process-tests--new-pty' probably only works with GNU Bash.
    (skip-unless (string-equal
                  (file-name-nondirectory shell-file-name) "bash"))
    (process-tests--with-processes processes
      ;; In order to use `make-serial-process', we need to create some
      ;; pseudoterminals.  The easiest way to do that is to start a
      ;; normal process using the `pty' connection type.  We need to
      ;; ensure that the terminal stays around while we connect to it.
      ;; Create the host processes before the dummy pipes so we have a
      ;; high chance of succeeding here.
      (let ((tty-names ()))
        (dotimes (_ 10)
          (cl-destructuring-bind
              (host tty-name) (process-tests--new-pty)
            (should (processp host))
            (push host processes)
            (should tty-name)
            (should (file-exists-p tty-name))
            (push tty-name tty-names)))
        (process-tests--with-many-pipes
          (process-tests--with-processes processes
            (process-tests--with-buffers buffers
              (dolist (tty-name tty-names)
                (let ((buffer (generate-new-buffer
                               (format " *%s*" tty-name))))
                  (push buffer buffers)
                  ;; Failure to allocate more file descriptors should
                  ;; signal `file-error', but not crash.  Since we
                  ;; don't know the exact limit, we ignore
                  ;; `file-error'.
                  (let ((process (process-tests--ignore-EMFILE
                                   (make-serial-process
                                    :name (format "test %s" tty-name)
                                    :port tty-name
                                    :speed 9600
                                    :buffer buffer
                                    :coding 'no-conversion
                                    :noquery t))))
                    (when process (push process processes))))))
            ;; We should have managed to start at least one process.
            (should processes)))))))

(defvar process-tests--EMFILE-message :unknown
  "Cached result of the function `process-tests--EMFILE-message'.")

(defun process-tests--EMFILE-message ()
  "Return the error message for the EMFILE POSIX error.
Return nil if that can't be determined."
  (when (eq process-tests--EMFILE-message :unknown)
    (setq process-tests--EMFILE-message
          (with-temp-buffer
            (when (eql (call-process "errno" nil t nil "EMFILE") 0)
              (goto-char (point-min))
              (when (looking-at (rx "EMFILE" (+ blank) (+ digit)
                                    (+ blank) (group (+ nonl))))
                (match-string-no-properties 1))))))
  process-tests--EMFILE-message)

(defun process-tests--new-pty ()
  "Allocate a new pseudoterminal.
Return a list (PROCESS TTY-NAME)."
  ;; The command below will typically only work with GNU Bash.
  (should (string-equal (file-name-nondirectory shell-file-name)
                        "bash"))
  (process-tests--with-temp-file temp-file
    (should-not (file-remote-p temp-file))
    (let* ((command (list shell-file-name shell-command-switch
                          (format "tty > %s && sleep 60"
                                  (shell-quote-argument
                                   (file-name-unquote temp-file)))))
           (process (make-process :name "tty host"
                                  :command command
                                  :buffer nil
                                  :coding 'utf-8-unix
                                  :connection-type 'pty
                                  :noquery t))
           (tty-name nil)
           (coding-system-for-read 'utf-8-unix)
           (coding-system-for-write 'utf-8-unix))
      ;; Wait until TTY name has arrived.
      (with-timeout (2 (message "Timed out waiting for TTY name"))
        (while (and (process-live-p process) (not tty-name))
          (sleep-for 0.1)
          (when-let ((attributes (file-attributes temp-file)))
            (when (cl-plusp (file-attribute-size attributes))
              (with-temp-buffer
                (insert-file-contents temp-file)
                (goto-char (point-max))
                ;; `tty' has printed a trailing newline.
                (skip-chars-backward "\n")
                (unless (bobp)
                  (setq tty-name (buffer-substring-no-properties
                                  (point-min) (point)))))))))
      (list process tty-name))))

(provide 'process-tests)
;;; process-tests.el ends here