lisp/json.el

   1 ;;; json.el --- JavaScript Object Notation parser / generator
   2
   3 ;; Copyright (C) 2006-2011 Free Software Foundation, Inc.
   4
   5 ;; Author: Edward O'Connor <ted@oconnor.cx>
   6 ;; Version: 1.3
   7 ;; Keywords: convenience
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software: you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation, either version 3 of the License, or
  14 ;; (at your option) any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25
  26 ;; This is a library for parsing and generating JSON (JavaScript Object
  27 ;; Notation).
  28
  29 ;; Learn all about JSON here: <URL:http://json.org/>.
  30
  31 ;; The user-serviceable entry points for the parser are the functions
  32 ;; `json-read' and `json-read-from-string'. The encoder has a single
  33 ;; entry point, `json-encode'.
  34
  35 ;; Since there are several natural representations of key-value pair
  36 ;; mappings in elisp (alist, plist, hash-table), `json-read' allows you
  37 ;; to specify which you'd prefer (see `json-object-type' and
  38 ;; `json-array-type').
  39
  40 ;; Similarly, since `false' and `null' are distinct in JSON, you can
  41 ;; distinguish them by binding `json-false' and `json-null' as desired.
  42
  43 ;;; History:
  44
  45 ;; 2006-03-11 - Initial version.
  46 ;; 2006-03-13 - Added JSON generation in addition to parsing. Various
  47 ;;              other cleanups, bugfixes, and improvements.
  48 ;; 2006-12-29 - XEmacs support, from Aidan Kehoe <kehoea@parhasard.net>.
  49 ;; 2008-02-21 - Installed in GNU Emacs.
  50 ;; 2011-10-17 - Patch `json-alist-p' and `json-plist-p' to avoid recursion -tzz
  51
  52 ;;; Code:
  53
  54 (eval-when-compile (require 'cl))
  55
  56 ;; Compatibility code
  57
  58 (defalias 'json-encode-char0 'encode-char)
  59 (defalias 'json-decode-char0 'decode-char)
  60
  61
  62 ;; Parameters
  63
  64 (defvar json-object-type 'alist
  65   "Type to convert JSON objects to.
  66 Must be one of `alist', `plist', or `hash-table'.  Consider let-binding
  67 this around your call to `json-read' instead of `setq'ing it.")
  68
  69 (defvar json-array-type 'vector
  70   "Type to convert JSON arrays to.
  71 Must be one of `vector' or `list'.  Consider let-binding this around
  72 your call to `json-read' instead of `setq'ing it.")
  73
  74 (defvar json-key-type nil
  75   "Type to convert JSON keys to.
  76 Must be one of `string', `symbol', `keyword', or nil.
  77
  78 If nil, `json-read' will guess the type based on the value of
  79 `json-object-type':
  80
  81     If `json-object-type' is:   nil will be interpreted as:
  82       `hash-table'                `string'
  83       `alist'                     `symbol'
  84       `plist'                     `keyword'
  85
  86 Note that values other than `string' might behave strangely for
  87 Sufficiently Weird keys.  Consider let-binding this around your call to
  88 `json-read' instead of `setq'ing it.")
  89
  90 (defvar json-false :json-false
  91   "Value to use when reading JSON `false'.
  92 If this has the same value as `json-null', you might not be able to tell
  93 the difference between `false' and `null'.  Consider let-binding this
  94 around your call to `json-read' instead of `setq'ing it.")
  95
  96 (defvar json-null nil
  97   "Value to use when reading JSON `null'.
  98 If this has the same value as `json-false', you might not be able to
  99 tell the difference between `false' and `null'.  Consider let-binding
 100 this around your call to `json-read' instead of `setq'ing it.")
 101
 102 \f
 103
 104 ;;; Utilities
 105
 106 (defun json-join (strings separator)
 107   "Join STRINGS with SEPARATOR."
 108   (mapconcat 'identity strings separator))
 109
 110 (defun json-alist-p (list)
 111   "Non-null if and only if LIST is an alist."
 112   (while (consp list)
 113     (setq list (if (consp (car list))
 114                    (cdr list)
 115                  'not-alist)))
 116   (null list))
 117
 118 (defun json-plist-p (list)
 119   "Non-null if and only if LIST is a plist."
 120   (while (consp list)
 121     (setq list (if (and (keywordp (car list))
 122                         (consp (cdr list)))
 123                    (cddr list)
 124                  'not-plist)))
 125   (null list))
 126
 127 ;; Reader utilities
 128
 129 (defsubst json-advance (&optional n)
 130   "Skip past the following N characters."
 131   (forward-char n))
 132
 133 (defsubst json-peek ()
 134   "Return the character at point."
 135   (let ((char (char-after (point))))
 136     (or char :json-eof)))
 137
 138 (defsubst json-pop ()
 139   "Advance past the character at point, returning it."
 140   (let ((char (json-peek)))
 141     (if (eq char :json-eof)
 142         (signal 'end-of-file nil)
 143       (json-advance)
 144       char)))
 145
 146 (defun json-skip-whitespace ()
 147   "Skip past the whitespace at point."
 148   (skip-chars-forward "\t\r\n\f\b "))
 149
 150 \f
 151
 152 ;; Error conditions
 153
 154 (put 'json-error 'error-message "Unknown JSON error")
 155 (put 'json-error 'error-conditions '(json-error error))
 156
 157 (put 'json-readtable-error 'error-message "JSON readtable error")
 158 (put 'json-readtable-error 'error-conditions
 159      '(json-readtable-error json-error error))
 160
 161 (put 'json-unknown-keyword 'error-message "Unrecognized keyword")
 162 (put 'json-unknown-keyword 'error-conditions
 163      '(json-unknown-keyword json-error error))
 164
 165 (put 'json-number-format 'error-message "Invalid number format")
 166 (put 'json-number-format 'error-conditions
 167      '(json-number-format json-error error))
 168
 169 (put 'json-string-escape 'error-message "Bad unicode escape")
 170 (put 'json-string-escape 'error-conditions
 171      '(json-string-escape json-error error))
 172
 173 (put 'json-string-format 'error-message "Bad string format")
 174 (put 'json-string-format 'error-conditions
 175      '(json-string-format json-error error))
 176
 177 (put 'json-object-format 'error-message "Bad JSON object")
 178 (put 'json-object-format 'error-conditions
 179      '(json-object-format json-error error))
 180
 181 \f
 182
 183 ;;; Keywords
 184
 185 (defvar json-keywords '("true" "false" "null")
 186   "List of JSON keywords.")
 187
 188 ;; Keyword parsing
 189
 190 (defun json-read-keyword (keyword)
 191   "Read a JSON keyword at point.
 192 KEYWORD is the keyword expected."
 193   (unless (member keyword json-keywords)
 194     (signal 'json-unknown-keyword (list keyword)))
 195   (mapc (lambda (char)
 196           (unless (char-equal char (json-peek))
 197             (signal 'json-unknown-keyword
 198                     (list (save-excursion
 199                             (backward-word 1)
 200                             (thing-at-point 'word)))))
 201           (json-advance))
 202         keyword)
 203   (unless (looking-at "\\(\\s-\\|[],}]\\|$\\)")
 204     (signal 'json-unknown-keyword
 205             (list (save-excursion
 206                     (backward-word 1)
 207                     (thing-at-point 'word)))))
 208   (cond ((string-equal keyword "true") t)
 209         ((string-equal keyword "false") json-false)
 210         ((string-equal keyword "null") json-null)))
 211
 212 ;; Keyword encoding
 213
 214 (defun json-encode-keyword (keyword)
 215   "Encode KEYWORD as a JSON value."
 216   (cond ((eq keyword t)          "true")
 217         ((eq keyword json-false) "false")
 218         ((eq keyword json-null)  "null")))
 219
 220 ;;; Numbers
 221
 222 ;; Number parsing
 223
 224 (defun json-read-number (&optional sign)
 225  "Read the JSON number following point.
 226 The optional SIGN argument is for internal use.
 227
 228 N.B.: Only numbers which can fit in Emacs Lisp's native number
 229 representation will be parsed correctly."
 230  ;; If SIGN is non-nil, the number is explicitly signed.
 231  (let ((number-regexp
 232         "\\([0-9]+\\)?\\(\\.[0-9]+\\)?\\([Ee][+-]?[0-9]+\\)?"))
 233    (cond ((and (null sign) (char-equal (json-peek) ?-))
 234           (json-advance)
 235           (- (json-read-number t)))
 236          ((and (null sign) (char-equal (json-peek) ?+))
 237           (json-advance)
 238           (json-read-number t))
 239          ((and (looking-at number-regexp)
 240                (or (match-beginning 1)
 241                    (match-beginning 2)))
 242           (goto-char (match-end 0))
 243           (string-to-number (match-string 0)))
 244          (t (signal 'json-number-format (list (point)))))))
 245
 246 ;; Number encoding
 247
 248 (defun json-encode-number (number)
 249   "Return a JSON representation of NUMBER."
 250   (format "%s" number))
 251
 252 ;;; Strings
 253
 254 (defvar json-special-chars
 255   '((?\" . ?\")
 256     (?\\ . ?\\)
 257     (?/ . ?/)
 258     (?b . ?\b)
 259     (?f . ?\f)
 260     (?n . ?\n)
 261     (?r . ?\r)
 262     (?t . ?\t))
 263   "Characters which are escaped in JSON, with their elisp counterparts.")
 264
 265 ;; String parsing
 266
 267 (defun json-read-escaped-char ()
 268   "Read the JSON string escaped character at point."
 269   ;; Skip over the '\'
 270   (json-advance)
 271   (let* ((char (json-pop))
 272          (special (assq char json-special-chars)))
 273     (cond
 274      (special (cdr special))
 275      ((not (eq char ?u)) char)
 276      ((looking-at "[0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f]")
 277       (let ((hex (match-string 0)))
 278         (json-advance 4)
 279         (json-decode-char0 'ucs (string-to-number hex 16))))
 280      (t
 281       (signal 'json-string-escape (list (point)))))))
 282
 283 (defun json-read-string ()
 284   "Read the JSON string at point."
 285   (unless (char-equal (json-peek) ?\")
 286     (signal 'json-string-format (list "doesn't start with '\"'!")))
 287   ;; Skip over the '"'
 288   (json-advance)
 289   (let ((characters '())
 290         (char (json-peek)))
 291     (while (not (char-equal char ?\"))
 292       (push (if (char-equal char ?\\)
 293                 (json-read-escaped-char)
 294               (json-pop))
 295             characters)
 296       (setq char (json-peek)))
 297     ;; Skip over the '"'
 298     (json-advance)
 299     (if characters
 300         (apply 'string (nreverse characters))
 301       "")))
 302
 303 ;; String encoding
 304
 305 (defun json-encode-char (char)
 306   "Encode CHAR as a JSON string."
 307   (setq char (json-encode-char0 char 'ucs))
 308   (let ((control-char (car (rassoc char json-special-chars))))
 309     (cond
 310      ;; Special JSON character (\n, \r, etc.)
 311      (control-char
 312       (format "\\%c" control-char))
 313      ;; ASCIIish printable character
 314      ((and (> char 31) (< char 161))
 315       (format "%c" char))
 316      ;; Fallback: UCS code point in \uNNNN form
 317      (t
 318       (format "\\u%04x" char)))))
 319
 320 (defun json-encode-string (string)
 321   "Return a JSON representation of STRING."
 322   (format "\"%s\"" (mapconcat 'json-encode-char string "")))
 323
 324 ;;; JSON Objects
 325
 326 (defun json-new-object ()
 327   "Create a new Elisp object corresponding to a JSON object.
 328 Please see the documentation of `json-object-type'."
 329   (cond ((eq json-object-type 'hash-table)
 330          (make-hash-table :test 'equal))
 331         (t
 332          (list))))
 333
 334 (defun json-add-to-object (object key value)
 335   "Add a new KEY -> VALUE association to OBJECT.
 336 Returns the updated object, which you should save, e.g.:
 337     (setq obj (json-add-to-object obj \"foo\" \"bar\"))
 338 Please see the documentation of `json-object-type' and `json-key-type'."
 339   (let ((json-key-type
 340          (if (eq json-key-type nil)
 341              (cdr (assq json-object-type '((hash-table . string)
 342                                            (alist . symbol)
 343                                            (plist . keyword))))
 344            json-key-type)))
 345     (setq key
 346           (cond ((eq json-key-type 'string)
 347                  key)
 348                 ((eq json-key-type 'symbol)
 349                  (intern key))
 350                 ((eq json-key-type 'keyword)
 351                  (intern (concat ":" key)))))
 352     (cond ((eq json-object-type 'hash-table)
 353            (puthash key value object)
 354            object)
 355           ((eq json-object-type 'alist)
 356            (cons (cons key value) object))
 357           ((eq json-object-type 'plist)
 358            (cons key (cons value object))))))
 359
 360 ;; JSON object parsing
 361
 362 (defun json-read-object ()
 363   "Read the JSON object at point."
 364   ;; Skip over the "{"
 365   (json-advance)
 366   (json-skip-whitespace)
 367   ;; read key/value pairs until "}"
 368   (let ((elements (json-new-object))
 369         key value)
 370     (while (not (char-equal (json-peek) ?}))
 371       (json-skip-whitespace)
 372       (setq key (json-read-string))
 373       (json-skip-whitespace)
 374       (if (char-equal (json-peek) ?:)
 375           (json-advance)
 376         (signal 'json-object-format (list ":" (json-peek))))
 377       (setq value (json-read))
 378       (setq elements (json-add-to-object elements key value))
 379       (json-skip-whitespace)
 380       (unless (char-equal (json-peek) ?})
 381         (if (char-equal (json-peek) ?,)
 382             (json-advance)
 383           (signal 'json-object-format (list "," (json-peek))))))
 384     ;; Skip over the "}"
 385     (json-advance)
 386     elements))
 387
 388 ;; Hash table encoding
 389
 390 (defun json-encode-hash-table (hash-table)
 391   "Return a JSON representation of HASH-TABLE."
 392   (format "{%s}"
 393           (json-join
 394            (let (r)
 395              (maphash
 396               (lambda (k v)
 397                 (push (format "%s:%s"
 398                               (json-encode k)
 399                               (json-encode v))
 400                       r))
 401               hash-table)
 402              r)
 403            ", ")))
 404
 405 ;; List encoding (including alists and plists)
 406
 407 (defun json-encode-alist (alist)
 408   "Return a JSON representation of ALIST."
 409   (format "{%s}"
 410           (json-join (mapcar (lambda (cons)
 411                                (format "%s:%s"
 412                                        (json-encode (car cons))
 413                                        (json-encode (cdr cons))))
 414                              alist)
 415                      ", ")))
 416
 417 (defun json-encode-plist (plist)
 418   "Return a JSON representation of PLIST."
 419   (let (result)
 420     (while plist
 421       (push (concat (json-encode (car plist))
 422                     ":"
 423                     (json-encode (cadr plist)))
 424             result)
 425       (setq plist (cddr plist)))
 426     (concat "{" (json-join (nreverse result) ", ") "}")))
 427
 428 (defun json-encode-list (list)
 429   "Return a JSON representation of LIST.
 430 Tries to DWIM: simple lists become JSON arrays, while alists and plists
 431 become JSON objects."
 432   (cond ((null list)         "null")
 433         ((json-alist-p list) (json-encode-alist list))
 434         ((json-plist-p list) (json-encode-plist list))
 435         ((listp list)        (json-encode-array list))
 436         (t
 437          (signal 'json-error (list list)))))
 438
 439 ;;; Arrays
 440
 441 ;; Array parsing
 442
 443 (defun json-read-array ()
 444   "Read the JSON array at point."
 445   ;; Skip over the "["
 446   (json-advance)
 447   (json-skip-whitespace)
 448   ;; read values until "]"
 449   (let (elements)
 450     (while (not (char-equal (json-peek) ?\]))
 451       (push (json-read) elements)
 452       (json-skip-whitespace)
 453       (unless (char-equal (json-peek) ?\])
 454         (if (char-equal (json-peek) ?,)
 455             (json-advance)
 456           (signal 'json-error (list 'bleah)))))
 457     ;; Skip over the "]"
 458     (json-advance)
 459     (apply json-array-type (nreverse elements))))
 460
 461 ;; Array encoding
 462
 463 (defun json-encode-array (array)
 464   "Return a JSON representation of ARRAY."
 465   (concat "[" (mapconcat 'json-encode array ", ") "]"))
 466
 467 \f
 468
 469 ;;; JSON reader.
 470
 471 (defvar json-readtable
 472   (let ((table
 473          '((?t json-read-keyword "true")
 474            (?f json-read-keyword "false")
 475            (?n json-read-keyword "null")
 476            (?{ json-read-object)
 477            (?\[ json-read-array)
 478            (?\" json-read-string))))
 479     (mapc (lambda (char)
 480             (push (list char 'json-read-number) table))
 481           '(?- ?+ ?. ?0 ?1 ?2 ?3 ?4 ?5 ?6 ?7 ?8 ?9))
 482     table)
 483   "Readtable for JSON reader.")
 484
 485 (defun json-read ()
 486   "Parse and return the JSON object following point.
 487 Advances point just past JSON object."
 488   (json-skip-whitespace)
 489   (let ((char (json-peek)))
 490     (if (not (eq char :json-eof))
 491         (let ((record (cdr (assq char json-readtable))))
 492           (if (functionp (car record))
 493               (apply (car record) (cdr record))
 494             (signal 'json-readtable-error record)))
 495       (signal 'end-of-file nil))))
 496
 497 ;; Syntactic sugar for the reader
 498
 499 (defun json-read-from-string (string)
 500   "Read the JSON object contained in STRING and return it."
 501   (with-temp-buffer
 502     (insert string)
 503     (goto-char (point-min))
 504     (json-read)))
 505
 506 (defun json-read-file (file)
 507   "Read the first JSON object contained in FILE and return it."
 508   (with-temp-buffer
 509     (insert-file-contents file)
 510     (goto-char (point-min))
 511     (json-read)))
 512
 513 \f
 514
 515 ;;; JSON encoder
 516
 517 (defun json-encode (object)
 518   "Return a JSON representation of OBJECT as a string."
 519   (cond ((memq object (list t json-null json-false))
 520          (json-encode-keyword object))
 521         ((stringp object)      (json-encode-string object))
 522         ((keywordp object)     (json-encode-string
 523                                 (substring (symbol-name object) 1)))
 524         ((symbolp object)      (json-encode-string
 525                                 (symbol-name object)))
 526         ((numberp object)      (json-encode-number object))
 527         ((arrayp object)       (json-encode-array object))
 528         ((hash-table-p object) (json-encode-hash-table object))
 529         ((listp object)        (json-encode-list object))
 530         (t                     (signal 'json-error (list object)))))
 531
 532 (provide 'json)
 533
 534 ;;; json.el ends here