;;; socks.el --- A Socks v5 Client for Emacs  -*- lexical-binding:t -*-

;; Copyright (C) 1996-2000, 2002, 2007-2024 Free Software Foundation,
;; Inc.

;; Author: William M. Perry <wmperry@gnu.org>
;;         Dave Love <fx@gnu.org>
;; Keywords: comm, firewalls

;; 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:

;; This is an implementation of the SOCKS v5 protocol as defined in
;; RFC 1928.

;; TODO
;; - Finish the redirection rules stuff
;; - Implement composition of servers.  Recursively evaluate the
;;   redirection rules and do SOCKS-over-HTTP and SOCKS-in-SOCKS

;;; Code:

(eval-when-compile (require 'cl-lib))

;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; ;;; Custom widgets
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; (eval-when-compile
;;   (require 'wid-edit))

;; (define-widget 'dynamic-choice 'menu-choice
;;   "A pretty simple dynamic dropdown list"
;;   :format "%[%t%]: %v"
;;   :tag "Network"
;;   :case-fold t
;;   :void '(item :format "invalid (%t)\n")
;;   :value-create 's5-widget-value-create
;;   :value-delete 'widget-children-value-delete
;;   :value-get 'widget-choice-value-get
;;   :value-inline 'widget-choice-value-inline
;;   :mouse-down-action 'widget-choice-mouse-down-action
;;   :action 'widget-choice-action
;;   :error "Make a choice"
;;   :validate 'widget-choice-validate
;;   :match 's5-dynamic-choice-match
;;   :match-inline 's5-dynamic-choice-match-inline)
;;
;; (defun s5-dynamic-choice-match (widget value)
;;   (let ((choices (funcall (widget-get widget :choice-function)))
;; 	current found)
;;     (while (and choices (not found))
;;       (setq current (car choices)
;; 	    choices (cdr choices)
;; 	    found (widget-apply current :match value)))
;;     found))
;;
;; (defun s5-dynamic-choice-match-inline (widget value)
;;   (let ((choices (funcall (widget-get widget :choice-function)))
;; 	current found)
;;     (while (and choices (not found))
;;       (setq current (car choices)
;; 	    choices (cdr choices)
;; 	    found (widget-match-inline current value)))
;;     found))
;;
;; (defun s5-widget-value-create (widget)
;;   (let ((choices (funcall (widget-get widget :choice-function)))
;; 	(value (widget-get widget :value)))
;;     (if (not value)
;; 	(widget-put widget :value (widget-value (car choices))))
;;     (widget-put widget :args choices)
;;     (widget-choice-value-create widget)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Customization support
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defgroup socks nil
  "SOCKS support."
  :version "22.2"
  :prefix "socks-"
  :group 'processes)

;; (defcustom socks-server-aliases nil
;;   "A list of server aliases for use in access control and filtering rules."
;;   :type '(repeat (list :format "%v"
;; 		       :value ("" "" 1080 5)
;; 		       (string :tag "Alias")
;; 		       (string :tag "Hostname/IP Address")
;; 		       (integer :tag "Port #")
;; 		       (choice :tag "SOCKS Version"
;; 			       (integer :tag "SOCKS v4" :value 4)
;; 			       (integer :tag "SOCKS v5" :value 5)))))
;;
;; (defcustom socks-network-aliases
;;   '(("Anywhere" (netmask "0.0.0.0" "0.0.0.0")))
;;   "A list of network aliases for use in subsequent rules."
;;   :type '(repeat (list :format "%v"
;; 		       :value (netmask "" "255.255.255.0")
;; 		       (string :tag "Alias")
;; 		       (radio-button-choice
;; 			:format "%v"
;; 			(list :tag  "IP address range"
;; 			      (const :format "" :value range)
;; 			      (string :tag "From")
;; 			      (string :tag "To"))
;; 			(list :tag  "IP address/netmask"
;; 			      (const :format "" :value netmask)
;; 			      (string :tag "IP Address")
;; 			      (string :tag "Netmask"))
;; 			(list :tag  "Domain Name"
;; 			      (const :format "" :value domain)
;; 			      (string :tag "Domain name"))
;; 			(list :tag  "Unique hostname/IP address"
;; 			      (const :format "" :value exact)
;; 			      (string :tag "Hostname/IP Address"))))))
;;
;; (defun s5-servers-filter ()
;;   (if socks-server-aliases
;;       (mapcar (lambda (x) (list 'const :tag (car x) :value (car x))) s5-server-aliases)
;;     '((const :tag "No aliases defined" :value nil))))
;;
;; (defun s5-network-aliases-filter ()
;;   (mapcar (lambda (x) (list 'const :tag (car x) :value (car x)))
;; 	  socks-network-aliases))
;;
;; (defcustom socks-redirection-rules
;;    nil
;;    "A list of redirection rules."
;;    :type '(repeat (list :format "%v"
;; 			:value ("Anywhere" nil)
;; 			(dynamic-choice :choice-function s5-network-aliases-filter
;; 					:tag "Destination network")
;; 			(radio-button-choice
;; 			 :tag "Connection type"
;; 			 (const :tag "Direct connection" :value nil)
;; 			 (dynamic-choice :format "%t: %[%v%]"
;; 					 :choice-function s5-servers-filter
;; 					 :tag "Proxy chain via")))))

(defcustom socks-server
  (list "Default server" "socks" 1080 5)
  "Socks server."
  :type '(list
	  (string :format "" :value "Default server")
	  (string :tag "Server")
	  (integer :tag "Port")
	  (radio-button-choice :tag "SOCKS Version"
			       :format "%t: %v"
			       (const :tag "SOCKS v4  " :format "%t" :value 4)
                               (const :tag "SOCKS v4a"  :format "%t" :value 4a)
			       (const :tag "SOCKS v5"   :format "%t" :value 5))))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Get down to the nitty gritty
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defconst socks-version 5)
(defvar socks-debug nil)

;; Common socks v5 commands
(defconst socks-connect-command 1)
(defconst socks-bind-command 2)
(defconst socks-udp-associate-command 3)

;; Miscellaneous other socks constants
(defconst socks-authentication-null 0)
(defconst socks-authentication-failure 255)

;; Extensions
(defconst socks-resolve-command #xf0)

;; Response codes
(defconst socks-response-success               0)
(defconst socks-response-general-failure       1)
(defconst socks-response-access-denied         2)
(defconst socks-response-network-unreachable   3)
(defconst socks-response-host-unreachable      4)
(defconst socks-response-connection-refused    5)
(defconst socks-response-ttl-expired           6)
(defconst socks-response-cmd-not-supported     7)
(defconst socks-response-address-not-supported 8)

(defvar socks-errors
  '("Succeeded"
    "General SOCKS server failure"
    "Connection not allowed by ruleset"
    "Network unreachable"
    "Host unreachable"
    "Connection refused"
    "Time-to-live expired"
    "Command not supported"
    "Address type not supported"))

(defconst socks--errors-4
  '("Granted"
    "Rejected or failed"
    "Cannot connect to identd on the client"
    "Client and identd report differing user IDs"))

;; The socks v5 address types
(defconst socks-address-type-v4   1)
(defconst socks-address-type-name 3)
(defconst socks-address-type-v6   4)

;; Base variables
(defvar socks-timeout 5)

;; Miscellaneous stuff for authentication
(defvar socks-authentication-methods nil)
(defvar socks-username (user-login-name))
(defvar socks-password nil)

(defun socks-register-authentication-method (id desc callback)
  (let ((old (assq id socks-authentication-methods)))
    (if old
	(setcdr old (cons desc callback))
      (setq socks-authentication-methods
	    (cons (cons id (cons desc callback))
		  socks-authentication-methods)))))

(defun socks-unregister-authentication-method (id)
  (let ((old (assq id socks-authentication-methods)))
    (if old
	(setq socks-authentication-methods
	      (delq old socks-authentication-methods)))))

(socks-register-authentication-method 0 "No authentication" 'identity)

(defun socks-build-auth-list ()
  (let ((num 0)
	(retval ""))
    (mapc
     (lambda (x)
       (if (fboundp (cdr (cdr x)))
           (setq retval (format "%s%c" retval (car x))
                 num (1+ num))))
     (reverse socks-authentication-methods))
    (format "%c%s" num retval)))

(defconst socks-state-waiting-for-auth 0)
(defconst socks-state-submethod-negotiation 1)
(defconst socks-state-authenticated 2)
(defconst socks-state-waiting 3)
(defconst socks-state-connected 4)

(defun socks-wait-for-state-change (proc cur-state)
  (while (and (= (process-get proc 'socks-state) cur-state)
	      (memq (process-status proc) '(run open)))
    (accept-process-output proc socks-timeout)))

(defun socks-filter (proc string)
  (let (state version desired-len)
    (or (process-get proc 'socks)
        (error "socks-filter called on non-SOCKS connection %S" proc))
    (setq state (process-get proc 'socks-state))
    (cond
     ((= state socks-state-waiting-for-auth)
      (cl-callf (lambda (s) (setq string (concat s string)))
          (process-get proc 'socks-scratch))
      (if (< (length string) 2)
	  nil				; We need to spin some more
	(process-put proc 'socks-authtype (aref string 1))
	(process-put proc 'socks-scratch (substring string 2 nil))
	(process-put proc 'socks-state socks-state-submethod-negotiation)))
     ((= state socks-state-submethod-negotiation)
      )
     ((= state socks-state-authenticated)
      )
     ((= state socks-state-waiting)
      (cl-callf (lambda (s) (setq string (concat s string)))
          (process-get proc 'socks-scratch))
      (setq version (process-get proc 'socks-server-protocol))
      (cond
       ((equal version 'http)
	(if (not (string-search "\r\n\r\n" string))
	    nil			; Need to spin some more
	  (process-put proc 'socks-state socks-state-connected)
	  (process-put proc 'socks-reply 0)
	  (process-put proc 'socks-response string)))
       ((equal version 4)
	(if (< (length string) 2)
	    nil			; Can't know how much to read yet
	  (setq desired-len
		(+ 4 ; address length
		   2 ; port
		   2 ; initial data
		   ))
	  (if (< (length string) desired-len)
	      nil			; need to spin some more
	    (let ((response (aref string 1)))
	      (if (= response 90)
		  (setq response 0))
	      (process-put proc 'socks-state socks-state-connected)
	      (process-put proc 'socks-reply response)
	      (process-put proc 'socks-response string)))))
       ((equal version 5)
	(if (< (length string) 4)
	    nil
	  (setq desired-len
		(+ 6			; Standard socks header
		   (pcase (aref string 3)
		     ((pred (= socks-address-type-v4)) 4)
		     ((pred (= socks-address-type-v6)) 16)
		     ((pred (= socks-address-type-name))
		      (if (< (length string) 5)
			  255
                        (+ 1 (aref string 4))))
                     (0 0))))
	  (if (< (length string) desired-len)
	      nil			; Need to spin some more
	    (process-put proc 'socks-state socks-state-connected)
	    (process-put proc 'socks-reply (aref string 1))
	    (process-put proc 'socks-response string))))))
     ((= state socks-state-connected)))))

;; FIXME this is a terrible idea.
;; It is not even compatible with the argument spec of open-network-stream
;; in 24.1.

(defvar socks-override-functions nil
  "If non-nil, overwrite `open-network-stream' function with SOCKSified version.")

(when socks-override-functions
  (advice-add 'open-network-stream :around #'socks--open-network-stream))

(defun socks-open-connection (server-info)
  (save-excursion
    (let ((proc
           (let ((socks-override-functions nil))
             (open-network-stream "socks"
				  nil
				  (nth 1 server-info)
				  (nth 2 server-info))))
	  (authtype nil)
	  version)

      ;; Initialize process and info about the process
      (set-process-filter proc #'socks-filter)
      (set-process-query-on-exit-flag proc nil)
      (process-put proc 'socks t)
      (process-put proc 'socks-state socks-state-waiting-for-auth)
      (process-put proc 'socks-authtype socks-authentication-failure)
      (process-put proc 'socks-server-protocol (nth 3 server-info))
      (process-put proc 'socks-server-name (nth 1 server-info))
      (setq version (nth 3 server-info))
      (cond
       ((equal version 'http)
	;; Don't really have to do any connection setup under http
	nil)
       ((equal version 4)
	;; Don't really have to do any connection setup under v4
	nil)
       ((equal version 5)
	;; Need to handle all the authentication crap under v5
	;; Send what we think we can handle for authentication types
	(process-send-string proc (format "%c%s" socks-version
					  (socks-build-auth-list)))

	;; Basically just do a select() until we change states.
	(socks-wait-for-state-change proc socks-state-waiting-for-auth)
	(setq authtype (process-get proc 'socks-authtype))
	(cond
	 ((= authtype socks-authentication-null)
	  (and socks-debug (message "No authentication necessary")))
	 ((= authtype socks-authentication-failure)
	  (error "No acceptable authentication methods found"))
	 (t
	  (let* ((auth-type (process-get proc 'socks-authtype))
		 (auth-handler (assoc auth-type socks-authentication-methods))
		 (auth-func (and auth-handler (cdr (cdr auth-handler))))
		 (auth-desc (and auth-handler (car (cdr auth-handler)))))
	    (set-process-filter proc nil)
	    (if (and auth-func (fboundp auth-func)
		     (funcall auth-func proc))
		nil			; We succeeded!
	      (delete-process proc)
	      (error "Failed to use auth method: %s (%d)"
		     (or auth-desc "Unknown") auth-type))
	    )
	  )
	 )
	(process-put proc 'socks-state socks-state-authenticated)
	(process-put proc 'socks-scratch "")
	(set-process-filter proc #'socks-filter)))
      proc)))

(defun socks-send-command (proc command atype address port)
  "Send COMMAND to SOCKS service PROC for proxying ADDRESS and PORT.
When ATYPE indicates an IP, param ADDRESS must be given as raw bytes."
  (let ((addr (cond
	       ((or (= atype socks-address-type-v4)
		    (= atype socks-address-type-v6))
		address)
	       ((= atype socks-address-type-name)
		(format "%c%s" (length address) address))
	       (t
		(error "Unknown address type: %d" atype))))
        trailing
	request version)
    (or (process-get proc 'socks)
        (error "socks-send-command called on non-SOCKS connection %S" proc))
    (process-put proc 'socks-state socks-state-waiting)
    (setq version (process-get proc 'socks-server-protocol))
    (cond
     ((equal version 'http)
      (setq request (format (concat
			     "CONNECT %s:%d HTTP/1.0\r\n"
			     "User-Agent: Emacs/SOCKS v1.0\r\n"
			     "\r\n")
			    (cond
			     ((equal atype socks-address-type-name) address)
			     (t
			      (error "Unsupported address type for HTTP: %d" atype)))
			    port)))
     ((and (eq version '4a)
           (setf addr "\0\0\0\1"
                 trailing (concat address "\0")
                 version 4 ; become version 4
                 (process-get proc 'socks-server-protocol) 4)
           nil)) ; fall through
     ((equal version 4)
      (setq request (concat
		     (unibyte-string
		      version             ; version
		      command             ; command
		      (ash port -8)       ; port, high byte
		      (logand port #xff)) ; port, low byte
		     addr                 ; address
                     socks-username       ; username
                     "\0"                 ; terminate username
                     trailing)))          ; optional host to look up
     ((equal version 5)
      (setq request (concat
		     (unibyte-string
		      version		; version
		      command		; command
		      0			; reserved
		      atype)		; address type
		     addr		; address
		     (unibyte-string
                      (ash port -8)          ; port, high byte
		      (logand port #xff))))) ; port, low byte
     (t
      (error "Unknown protocol version: %d" version)))
    (process-send-string proc request)
    (socks-wait-for-state-change proc socks-state-waiting)
    (process-status proc)
    (if (= (or (process-get proc 'socks-reply) 1) socks-response-success)
	nil				; Sweet sweet success!
      (delete-process proc)
      (error "SOCKS: %s"
             (let ((err (process-get proc 'socks-reply)))
               (if (eql version 5)
                   (nth (or err 1) socks-errors)
                 ;; The defined error codes for v4 range from
                 ;; 90-93, but we store them in a simple list.
                 (nth (pcase err (90 0) (92 2) (93 3) (_ 1))
                      socks--errors-4)))))
    proc))


;; Replacement functions for open-network-stream, etc.
(defvar socks-noproxy nil
  "List of regexps matching hosts that we should not socksify connections to.")

(defun socks-find-route (host _service)
  (let ((route socks-server)
	(noproxy socks-noproxy))
    (while noproxy
      (if (eq ?! (aref (car noproxy) 0))
	  (if (string-match (substring (car noproxy) 1) host)
	      (setq noproxy nil))
	(if (string-match (car noproxy) host)
	    (setq route nil
		  noproxy nil)))
      (setq noproxy (cdr noproxy)))
    route))

(defvar socks-services-file "/etc/services")
(defvar socks-tcp-services (make-hash-table :size 13 :test 'equal))
(defvar socks-udp-services (make-hash-table :size 13 :test 'equal))

(defun socks-parse-services ()
  (if (not (and (file-exists-p socks-services-file)
		(file-readable-p socks-services-file)))
      (error "Could not find services file: %s" socks-services-file))
  (clrhash socks-tcp-services)
  (clrhash socks-udp-services)
  (with-current-buffer (get-buffer-create " *socks-tmp*")
    (erase-buffer)
    (insert-file-contents socks-services-file)
    ;; Nuke comments
    (goto-char (point-min))
    (while (re-search-forward "#.*" nil t)
      (replace-match ""))
    ;; Nuke empty lines
    (goto-char (point-min))
    (while (re-search-forward "^[ \t\n]+" nil t)
      (replace-match ""))
    ;; Now find all the lines
    (goto-char (point-min))
    (let (name port type)
      (while (re-search-forward "^\\([^ \t]+\\)[ \t]+\\([0-9]+\\)/\\([a-z]+\\)"
				nil t)
	(setq name (downcase (match-string 1))
	      port (string-to-number (match-string 2))
	      type (downcase (match-string 3)))
	(puthash name port (if (equal type "udp")
			       socks-udp-services
			     socks-tcp-services))))))

(defun socks-find-services-entry (service &optional udp)
  "Return the port # associated with SERVICE."
  (if (= (hash-table-count socks-tcp-services) 0)
      (socks-parse-services))
  (gethash (downcase service)
	      (if udp socks-udp-services socks-tcp-services)))

(defun socks-open-network-stream (name buffer host service)
  (let ((socks-override-functions t))
    (socks--open-network-stream
     (lambda (&rest args)
       (let ((socks-override-functions nil))
         (apply #'open-network-stream args)))
     name buffer host service)))

(defun socks--open-network-stream (orig-fun name buffer host service &rest params)
  (let ((route (and socks-override-functions
                    (socks-find-route host service))))
    (if (not route)
	(apply orig-fun name buffer host service params)
      ;; FIXME: Obey `params'!
      (let* ((proc (socks-open-connection route))
	     (version (process-get proc 'socks-server-protocol))
             (atype
              (cond
               ((equal version 4)
	        (setq host (socks-nslookup-host host))
	        (if (not (listp host))
	            (error "Could not get IP address for: %s" host))
		(setq host (apply #'unibyte-string host))
                socks-address-type-v4)
               (t
                socks-address-type-name))))
        (socks-send-command proc
			    socks-connect-command
			    atype
			    host
			    (if (stringp service)
			        (or
			         (socks-find-services-entry service)
			         (error "Unknown service: %s" service))
			      service))
        (process-put proc 'socks-buffer buffer)
        (process-put proc 'socks-host host)
        (process-put proc 'socks-service service)
        (set-process-filter proc nil)
        (set-process-buffer proc (if buffer (get-buffer-create buffer)))
        proc))))

;; Authentication modules go here

;; Basic username/password authentication, ala RFC 1929
(socks-register-authentication-method 2 "Username/Password"
				      'socks-username/password-auth)

(defconst socks-username/password-auth-version 1)

(defun socks-username/password-auth-filter (proc str)
  (or (process-get proc 'socks)
      (error "socks-filter called on non-SOCKS connection %S" proc))
  (cl-callf (lambda (s) (concat s str))
      (process-get proc 'socks-scratch))
  (if (< (length (process-get proc 'socks-scratch)) 2)
      nil
    (process-put proc 'socks-password-auth-status
                 (aref (process-get proc 'socks-scratch) 1))
    (process-put proc 'socks-state socks-state-authenticated)))

(defun socks-username/password-auth (proc)
  (let ((state (process-get proc 'socks-state)))
    (if (not socks-password)
	(setq socks-password (read-passwd
			      (format "Password for %s@%s: "
				      socks-username
				      (process-get proc 'socks-server-name)))))
    (process-put proc 'socks-scratch "")
    (set-process-filter proc #'socks-username/password-auth-filter)
    (process-send-string proc
			 (format "%c%c%s%c%s"
				 socks-username/password-auth-version
				 (length socks-username)
				 socks-username
				 (length socks-password)
				 socks-password))
    (socks-wait-for-state-change proc state)
    (= (process-get proc 'socks-password-auth-status) 0)))


;; More advanced GSS/API stuff, not yet implemented - volunteers?
;; (socks-register-authentication-method 1 "GSS/API" 'socks-gssapi-auth)

(defun socks-gssapi-auth (_proc)
  nil)


;; CHAP stuff
;; (socks-register-authentication-method 3 "CHAP" 'socks-chap-auth)
(defun socks-chap-auth (_proc)
  nil)


;; CRAM stuff
;; (socks-register-authentication-method 5 "CRAM" 'socks-cram-auth)
(defun socks-cram-auth (_proc)
  nil)


(defcustom socks-nslookup-program "nslookup"
  "If non-nil then a string naming the nslookup program."
  :type '(choice (const :tag "None" :value nil) string))

(defun socks-nslookup-host (host)
  "Attempt to resolve the given HOSTNAME using nslookup if possible."
  (interactive "sHost:  ")
  (if socks-nslookup-program
      (let ((proc (start-process " *nslookup*" " *nslookup*"
				 socks-nslookup-program host))
	    (res host))
	(set-process-query-on-exit-flag proc nil)
	(with-current-buffer (process-buffer proc)
	  (while (progn
		   (accept-process-output proc)
		   (memq (process-status proc) '(run open))))
	  (goto-char (point-min))
	  (if (re-search-forward "Name:.*\nAddress\\(es\\)?: *\\([0-9.]+\\)$" nil t)
	      (progn
		(setq res (buffer-substring (match-beginning 2)
					    (match-end 2))
		      res (mapcar #'string-to-number
				  (split-string res "\\.")))))
	  (kill-buffer (current-buffer)))
	res)
    host))

(defun socks--extract-resolve-response (proc)
  "Parse response for PROC and maybe return destination IP address."
  (when-let ((response (process-get proc 'socks-response)))
    (pcase (process-get proc 'socks-server-protocol)
      (4 ; https://www.openssh.com/txt/socks4a.protocol
       ;; In the latest Tor version (0.4.8.12 in Sept 2024), a query
       ;; that normally returns an IPv6 address gives a 91 error.
       (and-let* (((zerop (process-get proc 'socks-reply)))
                  ((eq (aref response 1) 90)) ; #x5a request granted
                  (a (substring response 4)) ; ignore port for now
                  ((not (string-empty-p a)))
                  ((not (string= a "\0\0\0\0"))))
         a))
      (5 ; https://tools.ietf.org/html/rfc1928
       (cl-assert (eq 5 (aref response 0)) t)
       (pcase (aref response 3) ; ATYP
         (1 (and-let* ((a (substring response 4 8))
                       ((not (string= a "\0\0\0\0")))
                       a)))
         ;; No reason to support RESOLVE_PTR [F1] extension, right?
         (3 (let ((len (1- (aref response 4))))
              (substring response 5 (+ 5 len))))
         (4 (socks--convert-address (substring response 4 20))))))))

(defun socks--convert-address (input)
  "Unpack pairs of bytes into 2-byte words."
  ;; This is a poor man's version of:
  ;;
  ;;   (let ((spec (bindat-type (words vec 8 uint 16))))
  ;;     (bindat-get-field (bindat-unpack spec input) 'words))
  ;;
  (cl-assert (arrayp input))
  (cl-assert (= (length input) 16))
  (let ((result (make-vector 8 0))
        (i -1))
    (while-let (((< (cl-incf i) 8))
                (j (* i 2))
                (hi (aref input j))
                (lo (aref input (1+ j))))
      (aset result i (logior (ash hi 8) lo)))
    result))

(declare-function puny-encode-domain "puny" (domain))

;; This is a hash table containing the most recent lookups.  It's
;; cleared every 5 minutes, which is obviously dumb.
;; FIXME use some kind of LRU instead.
(defvar socks--tor-resolve-cache nil)

(defun socks-tor-resolve (name &optional _family _flags)
  "Return list with a single IPv4 address for domain NAME.

See `make-network-process' for the format of the return value.  Note
that this function exists for novelty purposes only."
  (unless (string-match (rx bot (+ ascii) eot) name)
    (require 'puny)
    (setq name (puny-encode-domain name)))
  (if socks--tor-resolve-cache
      (when (time-less-p (car socks--tor-resolve-cache) (current-time))
        (clrhash (cdr socks--tor-resolve-cache)))
    (setq socks--tor-resolve-cache (cons (time-add (* 60 5) (current-time))
                                         (make-hash-table :test #'equal))))
  (with-memoization (gethash name (cdr socks--tor-resolve-cache))
    (condition-case err
        (if-let ((socks-password (or socks-password ""))
                 (route (socks-find-route name nil))
                 (proc (socks-send-command (socks-open-connection route)
                                           socks-resolve-command
                                           socks-address-type-name
                                           name
                                           0))
                 (ip (prog1 (socks--extract-resolve-response proc)
                       (delete-process proc))))
            (list (vconcat ip [0]))
          (error "Failed to resolve %s" name))
      (error
       (unless (member (cadr err) '("SOCKS: Host unreachable"
                                    "SOCKS: Rejected or failed"))
         (signal (car err) (cdr err)))))))

(provide 'socks)

;;; socks.el ends here