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File json.el

-;;; json.el --- JavaScript Object Notation parser / generator
-
-;; Copyright (C) 2006  Edward O'Connor <ted@oconnor.cx>
-
-;; Author: Edward O'Connor <ted@oconnor.cx>
-;; Keywords: convenience
-
-;; This file is NOT part of GNU Emacs.
-
-;; This 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 2, or (at your option) any later
-;; version.
-
-;; This file 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 Emacs; see the file COPYING, or type `C-h C-c'. If not,
-;; write to the Free Software Foundation at this address:
-
-;;   Free Software Foundation
-;;   51 Franklin Street, Fifth Floor
-;;   Boston, MA 02110-1301
-;;   USA
-
-;;; Commentary:
-
-;; This is a library for parsing and generating JSON (JavaScript Object
-;; Notation).
-
-;; Learn all about JSON here: <URL:http://json.org/>.
-
-;; The user-serviceable entry points for the parser are the functions
-;; `json-read' and `json-read-from-string'. The encoder has a single
-;; entry point, `json-encode'.
-
-;; Since there are several natural representations of key-value pair
-;; mappings in elisp (alist, plist, hash-table), `json-read' allows you
-;; to specify which you'd prefer (see `json-object-type' and
-;; `json-array-type').
-
-;; Similarly, since `false' and `null' are distinct in JSON, you can
-;; distinguish them by binding `json-false' and `json-null' as desired.
-
-;; The latest version of json.el can be found here:
-
-;;            <URL:http://edward.oconnor.cx/elisp/json.el>
-
-;;; History:
-
-;; 2006-03-11 - Initial version.
-;; 2006-03-13 - Added JSON generation in addition to parsing. Various
-;;              other cleanups, bugfixes, and improvements.
-
-;;; Code:
-
-(eval-when-compile (require 'cl))
-
-;; Parameters
-
-(defvar json-object-type 'alist
-  "Type to convert JSON objects to.
-Must be one of `alist', `plist', or `hash-table'. Consider let-binding
-this around your call to `json-read' instead of `setq'ing it.")
-
-(defvar json-array-type 'vector
-  "Type to convert JSON arrays to.
-Must be one of `vector' or `list'. Consider let-binding this around
-your call to `json-read' instead of `setq'ing it.")
-
-(defvar json-key-type nil
-  "Type to convert JSON keys to.
-Must be one of `string', `symbol', `keyword', or nil.
-
-If nil, `json-read' will guess the type based on the value of
-`json-object-type':
-
-    If `json-object-type' is:   nil will be interpreted as:
-      `hash-table'                `string'
-      `alist'                     `symbol'
-      `plist'                     `keyword'
-
-Note that values other than `string' might behave strangely for
-Sufficiently Weird keys. Consider let-binding this around your call to
-`json-read' instead of `setq'ing it.")
-
-(defvar json-false :json-false
-  "Value to use when reading JSON `false'.
-If this has the same value as `json-read-null-value', you might not be
-able to tell the difference between `false' and `null'. Consider let-
-binding this around your call to `json-read' instead of `setq'ing it.")
-
-(defvar json-null nil
-  "Value to use when reading JSON `null'.
-If this has the same value as `json-read-false-value', you might not be
-able to tell the difference between `false' and `null'. Consider let-
-binding this around your call to `json-read' instead of `setq'ing it.")
-
-
-
-;;; Utilities
-
-(defun json-join (strings separator)
-  "Join STRINGS with SEPARATOR."
-  (mapconcat 'identity strings separator))
-
-(defun json-alist-p (list)
-  "Non-null iff LIST is an alist."
-  (or (null list)
-      (and (consp (car list))
-           (json-alist-p (cdr list)))))
-
-(defun json-plist-p (list)
-  "Non-null iff LIST is a plist."
-  (or (null list)
-      (and (keywordp (car list))
-           (consp (cdr list))
-           (json-plist-p (cddr list)))))
-
-;; Reader utilities
-
-(defsubst json-advance (&optional n)
-  "Skip past the following N characters."
-  (unless n (setq n 1))
-  (let ((goal (+ (point) n)))
-    (goto-char goal)
-    (when (< (point) goal)
-      (signal 'end-of-file nil))))
-
-(defsubst json-peek ()
-  "Return the character at point."
-  (let ((char (char-after (point))))
-    (or char :json-eof)))
-
-(defsubst json-pop ()
-  "Advance past the character at point, returning it."
-  (let ((char (json-peek)))
-    (if (eq char :json-eof)
-        (signal 'end-of-file nil)
-      (json-advance)
-      char)))
-
-(defun json-skip-whitespace ()
-  "Skip past the whitespace at point."
-  (while (looking-at "[\t\r\n\f\b ]")
-    (goto-char (match-end 0))))
-
-
-
-;; Error conditions
-
-(put 'json-error 'error-message "Unknown JSON error")
-(put 'json-error 'error-conditions '(json-error error))
-
-(put 'json-readtable-error 'error-message "JSON readtable error")
-(put 'json-readtable-error 'error-conditions
-     '(json-readtable-error json-error error))
-
-(put 'json-unknown-keyword 'error-message "Unrecognized keyword")
-(put 'json-unknown-keyword 'error-conditions
-     '(json-unknown-keyword json-error error))
-
-(put 'json-number-format 'error-message "Invalid number format")
-(put 'json-number-format 'error-conditions
-     '(json-number-format json-error error))
-
-(put 'json-string-escape 'error-message "Bad unicode escape")
-(put 'json-string-escape 'error-conditions
-     '(json-string-escape json-error error))
-
-(put 'json-string-format 'error-message "Bad string format")
-(put 'json-string-format 'error-conditions
-     '(json-string-format json-error error))
-
-(put 'json-object-format 'error-message "Bad JSON object")
-(put 'json-object-format 'error-conditions
-     '(json-object-format json-error error))
-
-
-
-;;; Keywords
-
-(defvar json-keywords '("true" "false" "null")
-  "List of JSON keywords.")
-
-;; Keyword parsing
-
-(defun json-read-keyword (keyword)
-  "Read a JSON keyword at point.
-KEYWORD is the keyword expected."
-  (unless (member keyword json-keywords)
-    (signal 'json-unknown-keyword (list keyword)))
-  (mapc (lambda (char)
-          (unless (char-equal char (json-peek))
-            (signal 'json-unknown-keyword
-                    (list (save-excursion
-                            (backward-word 1)
-                            (word-at-point)))))
-          (json-advance))
-        keyword)
-  (unless (looking-at "\\(\\s-\\|[],}]\\|$\\)")
-    (signal 'json-unknown-keyword
-            (list (save-excursion
-                    (backward-word 1)
-                    (word-at-point)))))
-  (cond ((string-equal keyword "true") t)
-        ((string-equal keyword "false") json-false)
-        ((string-equal keyword "null") json-null)))
-
-;; Keyword encoding
-
-(defun json-encode-keyword (keyword)
-  "Encode KEYWORD as a JSON value."
-  (cond ((eq keyword t)          "true")
-        ((eq keyword json-false) "false")
-        ((eq keyword json-null)  "null")))
-
-;;; Numbers
-
-;; Number parsing
-
-(defun json-read-number ()
-  "Read the JSON number following point."
-  (if (char-equal (json-peek) ?-)
-      (progn
-        (json-advance)
-        (- 0 (json-read-number)))
-    (if (looking-at "[0-9]+\\([.][0-9]+\\)?\\([eE][+-]?[0-9]+\\)?")
-        (progn
-          (goto-char (match-end 0))
-          (string-to-number (match-string 0)))
-      (signal 'json-number-format (list (point))))))
-
-;; Number encoding
-
-(defun json-encode-number (number)
-  "Return a JSON representation of NUMBER."
-  (format "%s" number))
-
-;;; Strings
-
-(defvar json-special-chars
-  '((?\" . ?\")
-    (?\\ . ?\\)
-    (?/ . ?/)
-    (?b . ?\b)
-    (?f . ?\f)
-    (?n . ?\n)
-    (?r . ?\r)
-    (?t . ?\t))
-  "Characters which are escaped in JSON, with their elisp counterparts.")
-
-;; String parsing
-
-(defun json-read-escaped-char ()
-  "Read the JSON string escaped character at point."
-  ;; Skip over the '\'
-  (json-advance)
-  (let* ((char (json-pop))
-         (special (assq char json-special-chars)))
-    (cond
-     (special (cdr special))
-     ((not (eq char ?u)) char)
-     ((looking-at "[0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f]")
-      (let ((hex (match-string 0)))
-        (json-advance 4)
-        (json-decode-char0 'ucs (string-to-number hex 16))))
-     (t
-      (signal 'json-string-escape (list (point)))))))
-
-(defun json-read-string ()
-  "Read the JSON string at point."
-  (unless (char-equal (json-peek) ?\")
-    (signal 'json-string-format (list "doesn't start with '\"'!")))
-  ;; Skip over the '"'
-  (json-advance)
-  (let ((characters '())
-        (char (json-peek)))
-    (while (not (char-equal char ?\"))
-      (push (if (char-equal char ?\\)
-                (json-read-escaped-char)
-              (json-pop))
-            characters)
-      (setq char (json-peek)))
-    ;; Skip over the '"'
-    (json-advance)
-    (if characters
-        (apply 'string (nreverse characters))
-      "")))
-
-;; String encoding
-
-(defun json-unicode-setup ()
-  "Determine what Unicode code-point support this emacs has. "
-  (if (and (fboundp 'encode-char) (fboundp 'decode-char))
-      (progn
-        (defalias 'json-encode-char0 'encode-char)
-        (defalias 'json-decode-char0 'decode-char))
-    (defun json-decode-char0 (quote-ucs code &optional restriction) 
-      (assert (eq quote-ucs 'ucs) t
-              "Sorry, decode-char doesn't yet support anything but the UCS.  ")
-      (assert (< code 255) t
-              "Sorry, no support for Unicode code points above 255")
-      (if (fboundp 'decode-coding-string)
-          (car (append (decode-coding-string (format "%c" code)
-                                             'iso-8859-1) nil))
-        (int-to-char code)))
-    (defun json-encode-char0 (char quote-ucs &optional restriction)
-      (assert (eq quote-ucs 'ucs) t
-              "Sorry, encode-char doesn't yet support anything but the UCS.  ")
-      (assert (if (featurep 'mule) 
-                  (memq (char-charset char) '(ascii latin-iso8859-1 control-1))
-                t) t
-              "Sorry, no support for Unicode code points above 255")
-      (if (fboundp 'encode-coding-string)
-          (car (append (encode-coding-string (format "%c" char)
-                                             'iso-8859-1) nil))
-        (char-to-int char)))))
-
-(json-unicode-setup)
-
-(unless (featurep 'un-define)
-  (eval-after-load "un-define" '(progn (load "mucs") (json-unicode-setup))))
-
-(defun json-encode-char (char)
-  "Encode CHAR as a JSON string."
-  (setq char (json-encode-char0 char 'ucs))
-  (let ((control-char (car (rassoc char json-special-chars))))
-    (cond
-     ;; Special JSON character (\n, \r, etc.)
-     (control-char
-      (format "\\%c" control-char))
-     ;; ASCIIish printable character
-     ((and (> char 31) (< char 161))
-      (format "%c" char))
-     ;; Fallback: UCS code point in \uNNNN form
-     (t
-      (format "\\u%04x" char)))))
-
-(defun json-encode-string (string)
-  "Return a JSON representation of STRING."
-  (format "\"%s\"" (mapconcat 'json-encode-char string "")))
-
-;;; JSON Objects
-
-(defun json-new-object ()
-  "Create a new Elisp object corresponding to a JSON object.
-Please see the documentation of `json-object-type'."
-  (cond ((eq json-object-type 'hash-table)
-         (make-hash-table :test 'equal))
-        (t
-         (list))))
-
-(defun json-add-to-object (object key value)
-  "Add a new KEY -> VALUE association to OBJECT.
-Returns the updated object, which you should save, e.g.:
-    (setq obj (json-add-to-object obj \"foo\" \"bar\"))
-Please see the documentation of `json-object-type' and `json-key-type'."
-  (let ((json-key-type
-         (if (eq json-key-type nil)
-             (cdr (assq json-object-type '((hash-table . string)
-                                           (alist . symbol)
-                                           (plist . keyword))))
-           json-key-type)))
-    (setq key
-          (cond ((eq json-key-type 'string)
-                 key)
-                ((eq json-key-type 'symbol)
-                 (intern key))
-                ((eq json-key-type 'keyword)
-                 (intern (concat ":" key)))))
-    (cond ((eq json-object-type 'hash-table)
-           (puthash key value object)
-           object)
-          ((eq json-object-type 'alist)
-           (cons (cons key value) object))
-          ((eq json-object-type 'plist)
-           (cons key (cons value object))))))
-
-;; JSON object parsing
-
-(defun json-read-object ()
-  "Read the JSON object at point."
-  ;; Skip over the "{"
-  (json-advance)
-  (json-skip-whitespace)
-  ;; read key/value pairs until "}"
-  (let ((elements (json-new-object))
-        key value)
-    (while (not (char-equal (json-peek) ?}))
-      (json-skip-whitespace)
-      (setq key (json-read-string))
-      (json-skip-whitespace)
-      (if (char-equal (json-peek) ?:)
-          (json-advance)
-        (signal 'json-object-format (list ":" (json-peek))))
-      (setq value (json-read))
-      (setq elements (json-add-to-object elements key value))
-      (json-skip-whitespace)
-      (unless (char-equal (json-peek) ?})
-        (if (char-equal (json-peek) ?,)
-            (json-advance)
-          (signal 'json-object-format (list "," (json-peek))))))
-    ;; Skip over the "}"
-    (json-advance)
-    elements))
-
-;; Hash table encoding
-
-(defun json-encode-hash-table (hash-table)
-  "Return a JSON representation of HASH-TABLE."
-  (format "{%s}"
-          (json-join
-           (let (r)
-             (maphash
-              (lambda (k v)
-                (push (format "%s:%s"
-                              (json-encode k)
-                              (json-encode v))
-                      r))
-              hash-table)
-             r)
-           ", ")))
-
-;; List encoding (including alists and plists)
-
-(defun json-encode-alist (alist)
-  "Return a JSON representation of ALIST."
-  (format "{%s}"
-          (json-join (mapcar (lambda (cons)
-                               (format "%s:%s"
-                                       (json-encode (car cons))
-                                       (json-encode (cdr cons))))
-                             alist)
-                     ", ")))
-
-(defun json-encode-plist (plist)
-  "Return a JSON representation of PLIST."
-  (let (result)
-    (while plist
-      (push (concat (json-encode (car plist))
-                    ":"
-                    (json-encode (cadr plist)))
-            result)
-      (setq plist (cddr plist)))
-    (concat "{" (json-join (nreverse result) ", ") "}")))
-
-(defun json-encode-list (list)
-  "Return a JSON representation of LIST.
-Tries to DWIM: simple lists become JSON arrays, while alists and plists
-become JSON objects."
-  (cond ((null list)         "null")
-        ((json-alist-p list) (json-encode-alist list))
-        ((json-plist-p list) (json-encode-plist list))
-        ((listp list)        (json-encode-array list))
-        (t
-         (signal 'json-error (list list)))))
-
-;;; Arrays
-
-;; Array parsing
-
-(defun json-read-array ()
-  "Read the JSON array at point."
-  ;; Skip over the "["
-  (json-advance)
-  (json-skip-whitespace)
-  ;; read values until "]"
-  (let (elements)
-    (while (not (char-equal (json-peek) ?\]))
-      (push (json-read) elements)
-      (json-skip-whitespace)
-      (unless (char-equal (json-peek) ?\])
-        (if (char-equal (json-peek) ?,)
-            (json-advance)
-          (signal 'json-error (list 'bleah)))))
-    ;; Skip over the "]"
-    (json-advance)
-    (apply json-array-type (nreverse elements))))
-
-;; Array encoding
-
-(defun json-encode-array (array)
-  "Return a JSON representation of ARRAY."
-  (concat "[" (mapconcat 'json-encode array ", ") "]"))
-
-
-
-;;; JSON reader.
-
-(defvar json-readtable
-  (let ((table
-         '((?t json-read-keyword "true")
-           (?f json-read-keyword "false")
-           (?n json-read-keyword "null")
-           (?{ json-read-object)
-           (?\[ json-read-array)
-           (?\" json-read-string))))
-    (mapc (lambda (char)
-            (push (list char 'json-read-number) table))
-          '(?- ?0 ?1 ?2 ?3 ?4 ?5 ?6 ?7 ?8 ?9))
-    table)
-  "Readtable for JSON reader.")
-
-(defun json-read ()
-  "Parse and return the JSON object following point.
-Advances point just past JSON object."
-  (json-skip-whitespace)
-  (let ((char (json-peek)))
-    (if (not (eq char :json-eof))
-        (let ((record (cdr (assq char json-readtable))))
-          (if (functionp (car record))
-              (apply (car record) (cdr record))
-            (signal 'json-readtable-error record)))
-      (signal 'end-of-file nil))))
-
-;; Syntactic sugar for the reader
-
-(defun json-read-from-string (string)
-  "Read the JSON object contained in STRING and return it."
-  (with-temp-buffer
-    (insert string)
-    (goto-char (point-min))
-    (json-read)))
-
-(defun json-read-file (file)
-  "Read the first JSON object contained in FILE and return it."
-  (with-temp-buffer
-    (insert-file file)
-    (goto-char (point-min))
-    (json-read)))
-
-
-
-;;; JSON encoder
-
-(defun json-encode (object)
-  "Return a JSON representation of OBJECT as a string."
-  (cond ((memq object (list t json-null json-false))
-         (json-encode-keyword object))
-        ((stringp object)      (json-encode-string object))
-        ((keywordp object)     (json-encode-string
-                                (substring (symbol-name object) 1)))
-        ((symbolp object)      (json-encode-string
-                                (symbol-name object)))
-        ((numberp object)      (json-encode-number object))
-        ((arrayp object)       (json-encode-array object))
-        ((hash-table-p object) (json-encode-hash-table object))
-        ((listp object)        (json-encode-list object))
-        (t                     (signal 'json-error (list object)))))
-
-(provide 'json)
-;;; json.el ends here