lisp/json.el

   1 ;;; json.el --- JavaScript Object Notation parser / generator
   2
   3 ;; Copyright (C) 2006-2016 Free Software Foundation, Inc.
   4
   5 ;; Author: Edward O'Connor <ted@oconnor.cx>
   6 ;; Version: 1.4
   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 ;; 2012-10-25 - Added pretty-printed reformatting -Ryan Crum (ryan@ryancrum.org)
  52
  53 ;;; Code:
  54
  55 (require 'map)
  56
  57 ;; Parameters
  58
  59 (defvar json-object-type 'alist
  60   "Type to convert JSON objects to.
  61 Must be one of `alist', `plist', or `hash-table'.  Consider let-binding
  62 this around your call to `json-read' instead of `setq'ing it.  Ordering
  63 is maintained for `alist' and `plist', but not for `hash-table'.")
  64
  65 (defvar json-array-type 'vector
  66   "Type to convert JSON arrays to.
  67 Must be one of `vector' or `list'.  Consider let-binding this around
  68 your call to `json-read' instead of `setq'ing it.")
  69
  70 (defvar json-key-type nil
  71   "Type to convert JSON keys to.
  72 Must be one of `string', `symbol', `keyword', or nil.
  73
  74 If nil, `json-read' will guess the type based on the value of
  75 `json-object-type':
  76
  77     If `json-object-type' is:   nil will be interpreted as:
  78       `hash-table'                `string'
  79       `alist'                     `symbol'
  80       `plist'                     `keyword'
  81
  82 Note that values other than `string' might behave strangely for
  83 Sufficiently Weird keys.  Consider let-binding this around your call to
  84 `json-read' instead of `setq'ing it.")
  85
  86 (defvar json-false :json-false
  87   "Value to use when reading JSON `false'.
  88 If this has the same value as `json-null', you might not be able to tell
  89 the difference between `false' and `null'.  Consider let-binding this
  90 around your call to `json-read' instead of `setq'ing it.")
  91
  92 (defvar json-null nil
  93   "Value to use when reading JSON `null'.
  94 If this has the same value as `json-false', you might not be able to
  95 tell the difference between `false' and `null'.  Consider let-binding
  96 this around your call to `json-read' instead of `setq'ing it.")
  97
  98 (defvar json-encoding-separator ","
  99   "Value to use as an element separator when encoding.")
 100
 101 (defvar json-encoding-default-indentation "  "
 102   "The default indentation level for encoding.
 103 Used only when `json-encoding-pretty-print' is non-nil.")
 104
 105 (defvar json--encoding-current-indentation "\n"
 106   "Internally used to keep track of the current indentation level of encoding.
 107 Used only when `json-encoding-pretty-print' is non-nil.")
 108
 109 (defvar json-encoding-pretty-print nil
 110   "If non-nil, then the output of `json-encode' will be pretty-printed.")
 111
 112 (defvar json-encoding-lisp-style-closings nil
 113   "If non-nil, ] and } closings will be formatted lisp-style,
 114 without indentation.")
 115
 116 (defvar json-encoding-object-sort-predicate nil
 117   "Sorting predicate for JSON object keys during encoding.
 118 If nil, no sorting is performed.  Else, JSON object keys are
 119 ordered by the specified sort predicate during encoding.  For
 120 instance, setting this to `string<' will have JSON object keys
 121 ordered alphabetically.")
 122
 123 (defvar json-pre-element-read-function nil
 124   "Function called (if non-nil) by `json-read-array' and
 125 `json-read-object' right before reading a JSON array or object,
 126 respectively.  The function is called with one argument, which is
 127 the current JSON key.")
 128
 129 (defvar json-post-element-read-function nil
 130   "Function called (if non-nil) by `json-read-array' and
 131 `json-read-object' right after reading a JSON array or object,
 132 respectively.")
 133
 134 \f
 135
 136 ;;; Utilities
 137
 138 (defun json-join (strings separator)
 139   "Join STRINGS with SEPARATOR."
 140   (mapconcat 'identity strings separator))
 141
 142 (defun json-alist-p (list)
 143   "Non-null if and only if LIST is an alist with simple keys."
 144   (while (consp list)
 145     (setq list (if (and (consp (car list))
 146                         (atom (caar list)))
 147                    (cdr list)
 148                  'not-alist)))
 149   (null list))
 150
 151 (defun json-plist-p (list)
 152   "Non-null if and only if LIST is a plist with keyword keys."
 153   (while (consp list)
 154     (setq list (if (and (keywordp (car list))
 155                         (consp (cdr list)))
 156                    (cddr list)
 157                  'not-plist)))
 158   (null list))
 159
 160 (defun json--plist-reverse (plist)
 161   "Return a copy of PLIST in reverse order.
 162 Unlike `reverse', this keeps the property-value pairs intact."
 163   (let (res)
 164     (while plist
 165       (let ((prop (pop plist))
 166             (val (pop plist)))
 167         (push val res)
 168         (push prop res)))
 169     res))
 170
 171 (defun json--plist-to-alist (plist)
 172   "Return an alist of the property-value pairs in PLIST."
 173   (let (res)
 174     (while plist
 175       (let ((prop (pop plist))
 176             (val (pop plist)))
 177         (push (cons prop val) res)))
 178     (nreverse res)))
 179
 180 (defmacro json--with-indentation (body)
 181   `(let ((json--encoding-current-indentation
 182           (if json-encoding-pretty-print
 183               (concat json--encoding-current-indentation
 184                       json-encoding-default-indentation)
 185             "")))
 186      ,body))
 187
 188 ;; Reader utilities
 189
 190 (defsubst json-advance (&optional n)
 191   "Skip past the following N characters."
 192   (forward-char n))
 193
 194 (defsubst json-peek ()
 195   "Return the character at point."
 196   (let ((char (char-after (point))))
 197     (or char :json-eof)))
 198
 199 (defsubst json-pop ()
 200   "Advance past the character at point, returning it."
 201   (let ((char (json-peek)))
 202     (if (eq char :json-eof)
 203         (signal 'json-end-of-file nil)
 204       (json-advance)
 205       char)))
 206
 207 (defun json-skip-whitespace ()
 208   "Skip past the whitespace at point."
 209   (skip-chars-forward "\t\r\n\f\b "))
 210
 211 \f
 212
 213 ;; Error conditions
 214
 215 (define-error 'json-error "Unknown JSON error")
 216 (define-error 'json-readtable-error "JSON readtable error" 'json-error)
 217 (define-error 'json-unknown-keyword "Unrecognized keyword" 'json-error)
 218 (define-error 'json-number-format "Invalid number format" 'json-error)
 219 (define-error 'json-string-escape "Bad Unicode escape" 'json-error)
 220 (define-error 'json-string-format "Bad string format" 'json-error)
 221 (define-error 'json-key-format "Bad JSON object key" 'json-error)
 222 (define-error 'json-object-format "Bad JSON object" 'json-error)
 223 (define-error 'json-end-of-file "End of file while parsing JSON"
 224   '(end-of-file json-error))
 225
 226 \f
 227
 228 ;;; Paths
 229
 230 (defvar json--path '()
 231   "Used internally by `json-path-to-position' to keep track of
 232 the path during recursive calls to `json-read'.")
 233
 234 (defun json--record-path (key)
 235   "Record the KEY to the current JSON path.
 236 Used internally by `json-path-to-position'."
 237   (push (cons (point) key) json--path))
 238
 239 (defun json--check-position (position)
 240   "Check if the last parsed JSON structure passed POSITION.
 241 Used internally by `json-path-to-position'."
 242   (let ((start (caar json--path)))
 243     (when (< start position (+ (point) 1))
 244       (throw :json-path (list :path (nreverse (mapcar #'cdr json--path))
 245                               :match-start start
 246                               :match-end (point)))))
 247   (pop json--path))
 248
 249 (defun json-path-to-position (position &optional string)
 250   "Return the path to the JSON element at POSITION.
 251
 252 When STRING is provided, return the path to the position in the
 253 string, else to the position in the current buffer.
 254
 255 The return value is a property list with the following
 256 properties:
 257
 258 :path        -- A list of strings and numbers forming the path to
 259                 the JSON element at the given position.  Strings
 260                 denote object names, while numbers denote array
 261                 indexes.
 262
 263 :match-start -- Position where the matched JSON element begins.
 264
 265 :match-end   -- Position where the matched JSON element ends.
 266
 267 This can for instance be useful to determine the path to a JSON
 268 element in a deeply nested structure."
 269   (save-excursion
 270     (unless string
 271       (goto-char (point-min)))
 272     (let* ((json--path '())
 273            (json-pre-element-read-function #'json--record-path)
 274            (json-post-element-read-function
 275             (apply-partially #'json--check-position position))
 276            (path (catch :json-path
 277                    (if string
 278                        (json-read-from-string string)
 279                      (json-read)))))
 280       (when (plist-get path :path)
 281         path))))
 282
 283 ;;; Keywords
 284
 285 (defvar json-keywords '("true" "false" "null")
 286   "List of JSON keywords.")
 287
 288 ;; Keyword parsing
 289
 290 (defun json-read-keyword (keyword)
 291   "Read a JSON keyword at point.
 292 KEYWORD is the keyword expected."
 293   (unless (member keyword json-keywords)
 294     (signal 'json-unknown-keyword (list keyword)))
 295   (mapc (lambda (char)
 296           (unless (char-equal char (json-peek))
 297             (signal 'json-unknown-keyword
 298                     (list (save-excursion
 299                             (backward-word-strictly 1)
 300                             (thing-at-point 'word)))))
 301           (json-advance))
 302         keyword)
 303   (unless (looking-at "\\(\\s-\\|[],}]\\|$\\)")
 304     (signal 'json-unknown-keyword
 305             (list (save-excursion
 306                     (backward-word-strictly 1)
 307                     (thing-at-point 'word)))))
 308   (cond ((string-equal keyword "true") t)
 309         ((string-equal keyword "false") json-false)
 310         ((string-equal keyword "null") json-null)))
 311
 312 ;; Keyword encoding
 313
 314 (defun json-encode-keyword (keyword)
 315   "Encode KEYWORD as a JSON value."
 316   (cond ((eq keyword t)          "true")
 317         ((eq keyword json-false) "false")
 318         ((eq keyword json-null)  "null")))
 319
 320 ;;; Numbers
 321
 322 ;; Number parsing
 323
 324 (defun json-read-number (&optional sign)
 325  "Read the JSON number following point.
 326 The optional SIGN argument is for internal use.
 327
 328 N.B.: Only numbers which can fit in Emacs Lisp's native number
 329 representation will be parsed correctly."
 330  ;; If SIGN is non-nil, the number is explicitly signed.
 331  (let ((number-regexp
 332         "\\([0-9]+\\)?\\(\\.[0-9]+\\)?\\([Ee][+-]?[0-9]+\\)?"))
 333    (cond ((and (null sign) (char-equal (json-peek) ?-))
 334           (json-advance)
 335           (- (json-read-number t)))
 336          ((and (null sign) (char-equal (json-peek) ?+))
 337           (json-advance)
 338           (json-read-number t))
 339          ((and (looking-at number-regexp)
 340                (or (match-beginning 1)
 341                    (match-beginning 2)))
 342           (goto-char (match-end 0))
 343           (string-to-number (match-string 0)))
 344          (t (signal 'json-number-format (list (point)))))))
 345
 346 ;; Number encoding
 347
 348 (defun json-encode-number (number)
 349   "Return a JSON representation of NUMBER."
 350   (format "%s" number))
 351
 352 ;;; Strings
 353
 354 (defvar json-special-chars
 355   '((?\" . ?\")
 356     (?\\ . ?\\)
 357     (?b . ?\b)
 358     (?f . ?\f)
 359     (?n . ?\n)
 360     (?r . ?\r)
 361     (?t . ?\t))
 362   "Characters which are escaped in JSON, with their elisp counterparts.")
 363
 364 ;; String parsing
 365
 366 (defun json-read-escaped-char ()
 367   "Read the JSON string escaped character at point."
 368   ;; Skip over the '\'
 369   (json-advance)
 370   (let* ((char (json-pop))
 371          (special (assq char json-special-chars)))
 372     (cond
 373      (special (cdr special))
 374      ((not (eq char ?u)) char)
 375      ((looking-at "[0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f]")
 376       (let ((hex (match-string 0)))
 377         (json-advance 4)
 378         (string-to-number hex 16)))
 379      (t
 380       (signal 'json-string-escape (list (point)))))))
 381
 382 (defun json-read-string ()
 383   "Read the JSON string at point."
 384   (unless (char-equal (json-peek) ?\")
 385     (signal 'json-string-format (list "doesn't start with `\"'!")))
 386   ;; Skip over the '"'
 387   (json-advance)
 388   (let ((characters '())
 389         (char (json-peek)))
 390     (while (not (char-equal char ?\"))
 391       (push (if (char-equal char ?\\)
 392                 (json-read-escaped-char)
 393               (json-pop))
 394             characters)
 395       (setq char (json-peek)))
 396     ;; Skip over the '"'
 397     (json-advance)
 398     (if characters
 399         (apply 'string (nreverse characters))
 400       "")))
 401
 402 ;; String encoding
 403
 404 (defun json-encode-string (string)
 405   "Return a JSON representation of STRING."
 406   ;; Reimplement the meat of `replace-regexp-in-string', for
 407   ;; performance (bug#20154).
 408   (let ((l (length string))
 409         (start 0)
 410         res mb)
 411     ;; Only escape quotation mark, backslash and the control
 412     ;; characters U+0000 to U+001F (RFC 4627, ECMA-404).
 413     (while (setq mb (string-match "[\"\\[:cntrl:]]" string start))
 414       (let* ((c (aref string mb))
 415              (special (rassq c json-special-chars)))
 416         (push (substring string start mb) res)
 417         (push (if special
 418                   ;; Special JSON character (\n, \r, etc.).
 419                   (string ?\\ (car special))
 420                 ;; Fallback: UCS code point in \uNNNN form.
 421                 (format "\\u%04x" c))
 422               res)
 423         (setq start (1+ mb))))
 424     (push (substring string start l) res)
 425     (push "\"" res)
 426     (apply #'concat "\"" (nreverse res))))
 427
 428 (defun json-encode-key (object)
 429   "Return a JSON representation of OBJECT.
 430 If the resulting JSON object isn't a valid JSON object key,
 431 this signals `json-key-format'."
 432   (let ((encoded (json-encode object)))
 433     (unless (stringp (json-read-from-string encoded))
 434       (signal 'json-key-format (list object)))
 435     encoded))
 436
 437 ;;; JSON Objects
 438
 439 (defun json-new-object ()
 440   "Create a new Elisp object corresponding to a JSON object.
 441 Please see the documentation of `json-object-type'."
 442   (cond ((eq json-object-type 'hash-table)
 443          (make-hash-table :test 'equal))
 444         (t
 445          ())))
 446
 447 (defun json-add-to-object (object key value)
 448   "Add a new KEY -> VALUE association to OBJECT.
 449 Returns the updated object, which you should save, e.g.:
 450     (setq obj (json-add-to-object obj \"foo\" \"bar\"))
 451 Please see the documentation of `json-object-type' and `json-key-type'."
 452   (let ((json-key-type
 453          (if (eq json-key-type nil)
 454              (cdr (assq json-object-type '((hash-table . string)
 455                                            (alist . symbol)
 456                                            (plist . keyword))))
 457            json-key-type)))
 458     (setq key
 459           (cond ((eq json-key-type 'string)
 460                  key)
 461                 ((eq json-key-type 'symbol)
 462                  (intern key))
 463                 ((eq json-key-type 'keyword)
 464                  (intern (concat ":" key)))))
 465     (cond ((eq json-object-type 'hash-table)
 466            (puthash key value object)
 467            object)
 468           ((eq json-object-type 'alist)
 469            (cons (cons key value) object))
 470           ((eq json-object-type 'plist)
 471            (cons key (cons value object))))))
 472
 473 ;; JSON object parsing
 474
 475 (defun json-read-object ()
 476   "Read the JSON object at point."
 477   ;; Skip over the "{"
 478   (json-advance)
 479   (json-skip-whitespace)
 480   ;; read key/value pairs until "}"
 481   (let ((elements (json-new-object))
 482         key value)
 483     (while (not (char-equal (json-peek) ?}))
 484       (json-skip-whitespace)
 485       (setq key (json-read-string))
 486       (json-skip-whitespace)
 487       (if (char-equal (json-peek) ?:)
 488           (json-advance)
 489         (signal 'json-object-format (list ":" (json-peek))))
 490       (json-skip-whitespace)
 491       (when json-pre-element-read-function
 492         (funcall json-pre-element-read-function key))
 493       (setq value (json-read))
 494       (when json-post-element-read-function
 495         (funcall json-post-element-read-function))
 496       (setq elements (json-add-to-object elements key value))
 497       (json-skip-whitespace)
 498       (unless (char-equal (json-peek) ?})
 499         (if (char-equal (json-peek) ?,)
 500             (json-advance)
 501           (signal 'json-object-format (list "," (json-peek))))))
 502     ;; Skip over the "}"
 503     (json-advance)
 504     (pcase json-object-type
 505       (`alist (nreverse elements))
 506       (`plist (json--plist-reverse elements))
 507       (_ elements))))
 508
 509 ;; Hash table encoding
 510
 511 (defun json-encode-hash-table (hash-table)
 512   "Return a JSON representation of HASH-TABLE."
 513   (if json-encoding-object-sort-predicate
 514       (json-encode-alist (map-into hash-table 'list))
 515     (format "{%s%s}"
 516             (json-join
 517              (let (r)
 518                (json--with-indentation
 519                 (maphash
 520                  (lambda (k v)
 521                    (push (format
 522                           (if json-encoding-pretty-print
 523                               "%s%s: %s"
 524                             "%s%s:%s")
 525                           json--encoding-current-indentation
 526                           (json-encode-key k)
 527                           (json-encode v))
 528                          r))
 529                  hash-table))
 530                r)
 531              json-encoding-separator)
 532             (if (or (not json-encoding-pretty-print)
 533                     json-encoding-lisp-style-closings)
 534                 ""
 535               json--encoding-current-indentation))))
 536
 537 ;; List encoding (including alists and plists)
 538
 539 (defun json-encode-alist (alist)
 540   "Return a JSON representation of ALIST."
 541   (when json-encoding-object-sort-predicate
 542     (setq alist
 543           (sort alist (lambda (a b)
 544                         (funcall json-encoding-object-sort-predicate
 545                                  (car a) (car b))))))
 546   (format "{%s%s}"
 547           (json-join
 548            (json--with-indentation
 549             (mapcar (lambda (cons)
 550                       (format (if json-encoding-pretty-print
 551                                   "%s%s: %s"
 552                                 "%s%s:%s")
 553                               json--encoding-current-indentation
 554                               (json-encode-key (car cons))
 555                               (json-encode (cdr cons))))
 556                     alist))
 557            json-encoding-separator)
 558           (if (or (not json-encoding-pretty-print)
 559                   json-encoding-lisp-style-closings)
 560               ""
 561             json--encoding-current-indentation)))
 562
 563 (defun json-encode-plist (plist)
 564   "Return a JSON representation of PLIST."
 565   (if json-encoding-object-sort-predicate
 566       (json-encode-alist (json--plist-to-alist plist))
 567     (let (result)
 568       (json--with-indentation
 569        (while plist
 570          (push (concat
 571                 json--encoding-current-indentation
 572                 (json-encode-key (car plist))
 573                 (if json-encoding-pretty-print
 574                     ": "
 575                   ":")
 576                 (json-encode (cadr plist)))
 577                result)
 578          (setq plist (cddr plist))))
 579       (concat "{"
 580               (json-join (nreverse result) json-encoding-separator)
 581               (if (and json-encoding-pretty-print
 582                        (not json-encoding-lisp-style-closings))
 583                   json--encoding-current-indentation
 584                 "")
 585               "}"))))
 586
 587 (defun json-encode-list (list)
 588   "Return a JSON representation of LIST.
 589 Tries to DWIM: simple lists become JSON arrays, while alists and plists
 590 become JSON objects."
 591   (cond ((null list)         "null")
 592         ((json-alist-p list) (json-encode-alist list))
 593         ((json-plist-p list) (json-encode-plist list))
 594         ((listp list)        (json-encode-array list))
 595         (t
 596          (signal 'json-error (list list)))))
 597
 598 ;;; Arrays
 599
 600 ;; Array parsing
 601
 602 (defun json-read-array ()
 603   "Read the JSON array at point."
 604   ;; Skip over the "["
 605   (json-advance)
 606   (json-skip-whitespace)
 607   ;; read values until "]"
 608   (let (elements)
 609     (while (not (char-equal (json-peek) ?\]))
 610       (json-skip-whitespace)
 611       (when json-pre-element-read-function
 612         (funcall json-pre-element-read-function (length elements)))
 613       (push (json-read) elements)
 614       (when json-post-element-read-function
 615         (funcall json-post-element-read-function))
 616       (json-skip-whitespace)
 617       (unless (char-equal (json-peek) ?\])
 618         (if (char-equal (json-peek) ?,)
 619             (json-advance)
 620           (signal 'json-error (list 'bleah)))))
 621     ;; Skip over the "]"
 622     (json-advance)
 623     (apply json-array-type (nreverse elements))))
 624
 625 ;; Array encoding
 626
 627 (defun json-encode-array (array)
 628   "Return a JSON representation of ARRAY."
 629   (if (and json-encoding-pretty-print
 630            (> (length array) 0))
 631       (concat
 632        (json--with-indentation
 633          (concat (format "[%s" json--encoding-current-indentation)
 634                  (json-join (mapcar 'json-encode array)
 635                             (format "%s%s"
 636                                     json-encoding-separator
 637                                     json--encoding-current-indentation))))
 638        (format "%s]"
 639                (if json-encoding-lisp-style-closings
 640                    ""
 641                  json--encoding-current-indentation)))
 642     (concat "["
 643             (mapconcat 'json-encode array json-encoding-separator)
 644             "]")))
 645
 646 \f
 647
 648 ;;; JSON reader.
 649
 650 (defvar json-readtable
 651   (let ((table
 652          '((?t json-read-keyword "true")
 653            (?f json-read-keyword "false")
 654            (?n json-read-keyword "null")
 655            (?{ json-read-object)
 656            (?\[ json-read-array)
 657            (?\" json-read-string))))
 658     (mapc (lambda (char)
 659             (push (list char 'json-read-number) table))
 660           '(?- ?+ ?. ?0 ?1 ?2 ?3 ?4 ?5 ?6 ?7 ?8 ?9))
 661     table)
 662   "Readtable for JSON reader.")
 663
 664 (defun json-read ()
 665   "Parse and return the JSON object following point.
 666 Advances point just past JSON object."
 667   (json-skip-whitespace)
 668   (let ((char (json-peek)))
 669     (if (not (eq char :json-eof))
 670         (let ((record (cdr (assq char json-readtable))))
 671           (if (functionp (car record))
 672               (apply (car record) (cdr record))
 673             (signal 'json-readtable-error record)))
 674       (signal 'json-end-of-file nil))))
 675
 676 ;; Syntactic sugar for the reader
 677
 678 (defun json-read-from-string (string)
 679   "Read the JSON object contained in STRING and return it."
 680   (with-temp-buffer
 681     (insert string)
 682     (goto-char (point-min))
 683     (json-read)))
 684
 685 (defun json-read-file (file)
 686   "Read the first JSON object contained in FILE and return it."
 687   (with-temp-buffer
 688     (insert-file-contents file)
 689     (goto-char (point-min))
 690     (json-read)))
 691
 692 \f
 693
 694 ;;; JSON encoder
 695
 696 (defun json-encode (object)
 697   "Return a JSON representation of OBJECT as a string."
 698   (cond ((memq object (list t json-null json-false))
 699          (json-encode-keyword object))
 700         ((stringp object)      (json-encode-string object))
 701         ((keywordp object)     (json-encode-string
 702                                 (substring (symbol-name object) 1)))
 703         ((symbolp object)      (json-encode-string
 704                                 (symbol-name object)))
 705         ((numberp object)      (json-encode-number object))
 706         ((arrayp object)       (json-encode-array object))
 707         ((hash-table-p object) (json-encode-hash-table object))
 708         ((listp object)        (json-encode-list object))
 709         (t                     (signal 'json-error (list object)))))
 710
 711 ;; Pretty printing
 712
 713 (defun json-pretty-print-buffer ()
 714   "Pretty-print current buffer."
 715   (interactive)
 716   (json-pretty-print (point-min) (point-max)))
 717
 718 (defun json-pretty-print (begin end)
 719   "Pretty-print selected region."
 720   (interactive "r")
 721   (atomic-change-group
 722     (let ((json-encoding-pretty-print t)
 723           ;; Ensure that ordering is maintained
 724           (json-object-type 'alist)
 725           (txt (delete-and-extract-region begin end)))
 726       (insert (json-encode (json-read-from-string txt))))))
 727
 728 (defun json-pretty-print-buffer-ordered ()
 729   "Pretty-print current buffer with object keys ordered."
 730   (interactive)
 731   (let ((json-encoding-object-sort-predicate 'string<))
 732     (json-pretty-print-buffer)))
 733
 734 (defun json-pretty-print-ordered (begin end)
 735   "Pretty-print the region with object keys ordered."
 736   (interactive "r")
 737   (let ((json-encoding-object-sort-predicate 'string<))
 738     (json-pretty-print begin end)))
 739
 740 (provide 'json)
 741
 742 ;;; json.el ends here