Move lisp/net/json.el to lisp/json.el.

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+;;; json.el --- JavaScript Object Notation parser / generator
+
+;; Copyright (C) 2006, 2007, 2008 Free Software Foundation, Inc.
+
+;; Author: Edward O'Connor <ted@oconnor.cx>
+;; Version: 1.2
+;; Keywords: convenience
+
+;; 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, 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; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 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.
+
+;;; History:
+
+;; 2006-03-11 - Initial version.
+;; 2006-03-13 - Added JSON generation in addition to parsing. Various
+;;              other cleanups, bugfixes, and improvements.
+;; 2006-12-29 - XEmacs support, from Aidan Kehoe <kehoea@parhasard.net>.
+;; 2008-02-21 - Installed in GNU Emacs.
+
+;;; Code:
+
+(eval-when-compile (require 'cl))
+(require 'thingatpt)
+
+;; Compatibility code
+
+(defalias 'json-encode-char0 'encode-char)
+(defalias 'json-decode-char0 'decode-char)
+
+
+;; 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-null', 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-false', 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.
+N.B.: Only numbers which can fit in Emacs Lisp's native number
+representation will be parsed correctly."
+  (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-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-contents 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