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

;; Copyright (C) 1996-2000, 2002, 2007-2021 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)
  ""
  :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 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)

;; 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"))

;; 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-match "\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)))))))
	  (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)
  (interactive)
  (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)
	(set-process-filter proc #'socks-filter)))
      proc)))

(defun socks-send-command (proc command atype address port)
  (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))))
	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 (eval-when-compile
			      (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)))
     ((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
		     (user-full-name)     ; username
		     "\0")))              ; terminate username
     ((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"
             (nth (or (process-get proc 'socks-reply) 1) socks-errors)))
    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 #'format "%c%c%c%c" 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))

(provide 'socks)

;;; socks.el ends here