Mercurial > core / lisp/lib/dat/json.lisp

 ;;; lib/dat/json.lisp --- JSON format
 
 ;; JSON parser generator
 
 ;; There are quite a few json libraries in the CL ecosystem. This
 ;; particular implementation is based on the JSON package here:
 ;; https://github.com/massung/json
 
 ;; It's object-based (like CL-JSON) instead of using a
 ;; parser-generator.
 
 ;;; Code:
 (in-package :dat/json)
 
 (defclass json-object ()
   ((members :initform nil
             :initarg :members
             :accessor json-object-members))
   (:documentation "An associative list of key/value pairs."))
 
 (defmethod print-object ((obj json-object) stream)
   "Output a JSON object to a stream in readable form."
   (print-unreadable-object (obj stream :type t)
     (let ((*print-level* 1))
       (json-encode obj stream))))
 
 (defun json-getf (object key &optional value)
   "Find an member's value in a JSON object."
   (let ((place (assoc key (json-object-members object) :test 'string=)))
     (if (null place)
         value
       (values (second place) t))))
 
 (defun json-setf (object key value)
   "Assign a value to a key in a JSON object."
   (let ((place (assoc key (json-object-members object) :test 'string=)))
     (prog1 value
       (if (null place)
           (let ((k (if (stringp key)
                        key
                      (princ-to-string key))))
             (push (list k value) (json-object-members object)))
         (rplacd place (list value))))))
 
 (defsetf json-getf json-setf)
 
 (defun json-decode (string &key (start 0) end)
   "Convert a JSON string into a Lisp object."
   (with-input-from-string (stream string :start start :end end)
     (values (json-read stream)
             (file-position stream))))
 
 (defmethod deserialize ((obj string) (format (eql :json)) &key (start 0) end)
   (declare (ignore format))
   (json-decode obj :start start :end end))
 
 (defun json-encode (value &optional stream)
   "Encodes a Lisp value into a stream."
   (json-write value stream))
 
 (defmethod serialize (obj (format (eql :json)) &key stream)
   (declare (ignore format))
   (if stream
       (json-encode obj stream)
       (with-output-to-string (s)
         (json-encode obj s)
         s)))
 
 (defun json-enable-reader-macro ()
   "Set the #{ dispatch macro character for reading JSON objects."
   (flet ((json-object-reader (stream char n)
            (declare (ignorable char n))
            (let ((xs (read-delimited-list #\} stream t)))
              (loop
                 for key = (pop xs)
                 for value = (pop xs)
 
                 ;; stop when nothing is left
                 unless (or xs key value)
                 return (make-instance 'json-object :members pairs)
 
                 ;; build associative list of key/value pairs
                 collect (list (princ-to-string key) value)
                 into pairs))))
     (set-dispatch-macro-character #\# #\{ #'json-object-reader)
     (set-macro-character #\} (get-macro-character #\) nil))))
 
 (defun json-read (stream &optional (eof-error-p t) eof-value)
   "Read a JSON object from a stream."
   (let ((c (peek-char t stream eof-error-p :eof)))
     (case c
       (:eof eof-value)
 
       ;; constants, objects, lists, and strings
       (#\t (json-read-true stream))
       (#\f (json-read-false stream))
       (#\n (json-read-null stream))
       (#\{ (json-read-object stream))
       (#\[ (json-read-list stream))
       (#\" (json-read-string stream))
       ;; must be a number
       (otherwise (json-read-number stream)))))
 
 (defun json-peek-char (stream expected &key skip-ws)
   "Peek at the next character or token and optionally error if unexpected."
   (declare (optimize (speed 3) (debug 0)))
   (when (equal (peek-char skip-ws stream) expected)
     (read-char stream)))
 
 (defun json-read-char (stream expected &key skip-ws)
   "Read the next, expected character in the stream."
   (declare (optimize (speed 3) (debug 0)))
   (if (json-peek-char stream expected :skip-ws skip-ws)
       t
     (error "JSON error: unexpected ~s" (read-char stream))))
 
 (defun json-read-true (stream)
   "Read true from a JSON stream."
   (json-read-char stream #\t :skip-ws t)
   (json-read-char stream #\r)
   (json-read-char stream #\u)
   (json-read-char stream #\e))
 
 (defun json-read-false (stream)
   "Read false from a JSON stream."
   (prog1 nil
     (json-read-char stream #\f :skip-ws t)
     (json-read-char stream #\a)
     (json-read-char stream #\l)
     (json-read-char stream #\s)
     (json-read-char stream #\e)))
 
 (defun json-read-null (stream)
   "Read null from a JSON stream."
   (prog1 nil
     (json-read-char stream #\n :skip-ws t)
     (json-read-char stream #\u)
     (json-read-char stream #\l)
     (json-read-char stream #\l)))
 
 (defun json-read-number (stream)
   "Read a number from a JSON stream."
   (declare (optimize (speed 3) (debug 0)))
   (let ((s (with-output-to-string (s)
              (when (equal (peek-char t stream) #\-)
                (write-char (read-char stream) s))
 
              ;; read base-10 digits, fraction, and exponent
              (labels ((read-digits ()
                         (let ((c (read-char stream)))
                           (unless (digit-char-p c)
                             (error "JSON error: unexpected ~s" c))
 
                           ;; write the digits
                           (loop
                              (write-char c s)
 
                              ;; next digit, test for eof
                              (unless (setf c (read-char stream nil))
                                (return))
 
                              ;; ensure digit
                              (unless (digit-char-p c)
                                (return (unread-char c stream))))))
 
                       ;; fractional component
                       (read-fraction ()
                         (when (equal (peek-char nil stream nil) #\.)
                           (write-char (read-char stream) s)
                           (read-digits)))
 
                       ;; exponent
                       (read-exponent ()
                         (when (equalp (peek-char nil stream nil) #\e)
                           (write-char (read-char stream) s)
 
                           ;; optional sign
                           (case (peek-char nil stream)
                             (#\- (write-char (read-char stream) s))
                             (#\+ (write-char (read-char stream) s)))
 
                           ;; exponent
                           (read-digits))))
 
                ;; read each component; numbers beginning with 0 are a special case
                (if (equalp (peek-char nil stream) #\0)
                    (write-char (read-char stream) s)
                  (read-digits))
                (read-fraction)
                (read-exponent)))))
     (prog1
       (read-from-string s))))
 
 (defun json-read-string (stream)
   "Read a string from a JSON stream."
   (declare (optimize (speed 3) (debug 0)))
 
   ;; read the expected quote
   (json-read-char stream #\" :skip-ws t)
 
   ;; read into an output buffer
   (with-output-to-string (s)
     (loop
        for c = (read-char stream)
 
        ;; stop at closing quote
        until (char= c #\")
 
        ;; write character to output
        do (if (char/= c #\\)
               (write-char c s)
             (let ((c (case (read-char stream)
                        (#\n #\newline)
                        (#\t #\tab)
                        (#\f #\formfeed)
                        (#\b #\backspace)
                        (#\r #\return)
 
                        ;; read unicode character
                        (#\u (let ((x1 (digit-char-p (read-char stream) 16))
                                   (x2 (digit-char-p (read-char stream) 16))
                                   (x3 (digit-char-p (read-char stream) 16))
                                   (x4 (digit-char-p (read-char stream) 16)))
                               (code-char (logior (ash x1 12)
                                                  (ash x2  8)
                                                  (ash x3  4)
                                                  (ash x4  0)))))
 
                        ;; verbatim character
                        (otherwise c))))
               (write-char c s))))))
 
 (defun json-read-list (stream)
   "Read a list of JSON values."
   (declare (optimize (speed 3) (debug 0)))
 
   ;; read the expected open bracket
   (json-read-char stream #\[ :skip-ws t)
 
   ;; check for an empty list
   (if (json-peek-char stream #\] :skip-ws t)
       nil
     (loop
        for x = (json-read stream)
        collect x
        into xs
 
        ;; check for another element
        while (json-peek-char stream #\, :skip-ws t)
 
        ;; return the final list
        finally (return (prog1 xs
                          (json-read-char stream #\] :skip-ws t))))))
 
 (defun json-read-object (stream)
   "Read an associative list of key/value pairs into a JSON object."
   (declare (optimize (speed 3) (debug 0)))
 
   ;; read the expected open brace
   (json-read-char stream #\{ :skip-ws t)
 
   ;; check for an empty object
   (if (json-peek-char stream #\} :skip-ws t)
       (make-instance 'json-object)
     (loop
        for key = (json-read-string stream)
        for value = (progn
                      (json-read-char stream #\: :skip-ws t)
                      (json-read stream))
 
        ;; build the associative list of members
        collect (list key value)
        into xs
 
        ;; check for another element
        while (json-peek-char stream #\, :skip-ws t)
 
        ;; return the final list
        finally (return (prog1 (make-instance 'json-object :members xs)
                          (json-read-char stream #\} :skip-ws t))))))
 
 (defmethod json-write ((value (eql t)) &optional stream)
   "Encode the true value."
   (declare (ignore value))
   (format stream "~<true~>"))
 
 (defmethod json-write ((value (eql nil)) &optional stream)
   "Encode the null constant."
   (declare (ignore value))
   (format stream "~<null~>"))
 
 (defmethod json-write ((value symbol) &optional stream)
   "Encode a symbol to a stream."
   (json-write (symbol-name value) stream))
 
 (defmethod json-write ((value number) &optional stream)
   "Encode a number to a stream."
   (format stream "~<~a~>" value))
 
 (defmethod json-write ((value ratio) &optional stream)
   "Encode a ratio to a stream."
   (format stream "~<~a~>" (float value)))
 
 (defmethod json-write ((value string) &optional stream)
   "Encode a string as a stream."
   (flet ((encode-char (c)
            (cond
             ((char= c #\\) "\\\\")
             ((char= c #\") "\\\"")
             ((char= c #\newline) "\\n")
             ((char= c #\tab) "\\t")
             ((char= c #\formfeed) "\\f")
             ((char= c #\backspace) "\\b")
             ((char= c #\return) "\\r")
             ((char> c #\~)
              (format nil "\\u~16,4,'0r" (char-code c)))
             (t
              (string c)))))
     (format stream "~<\"~{~a~}\"~>" (map 'list #'encode-char value))))
 
 (defmethod json-write ((value pathname) &optional stream)
   "Encode a pathname as a stream."
   (json-write (namestring value) stream))
 
 (defmethod json-write ((value vector) &optional stream)
   "Encode an array to a stream."
   (let ((*print-pretty* t)
         (*print-length* nil)
         (*print-lines* nil)
         (*print-right-margin* 72))
     (pprint-logical-block (stream nil :prefix "[" :suffix "]")
       (when (plusp (length value))
         (json-write (aref value 0)))
       (loop
          for i from 1 below (length value)
          do (progn
               (write-char #\, stream)
               (pprint-newline :fill)
               (pprint-indent :block 0)
               (json-write (aref value i) stream))))))
 
 (defmethod json-write ((value list) &optional stream)
   "Encode a list to a stream."
   (let ((*print-pretty* t)
         (*print-length* nil)
         (*print-lines* nil)
         (*print-right-margin* 72))
     (pprint-logical-block (stream value :prefix "[" :suffix "]")
       (pprint-exit-if-list-exhausted)
       (loop
          (json-write (pprint-pop) stream)
          (pprint-exit-if-list-exhausted)
          (write-char #\, stream)
          (pprint-newline :fill)
          (pprint-indent :block 0)))))
 
 (defmethod json-write ((value hash-table) &optional stream)
   "Encode a hash-table to a stream."
   (let ((*print-pretty* t)
         (*print-length* nil)
         (*print-lines* nil)
         (*print-right-margin* 72))
     (let ((keys (loop for key being each hash-keys in value collect key)))
       (pprint-logical-block (stream keys :prefix "{" :suffix "}")
         (pprint-exit-if-list-exhausted)
         (loop
            (let ((key (pprint-pop)))
              (if (not (stringp key))
                  (progn
                    (warn "~s is not a valid JSON key; skipping...~%" key)
                    (pprint-exit-if-list-exhausted))
                (progn
                  (json-write key stream)
                  (write-char #\: stream)
                  (json-write (gethash key value) stream)
                  (pprint-exit-if-list-exhausted)
                  (write-char #\, stream)
                  (pprint-newline :mandatory)
                  (pprint-indent :current 0)))))))))
 
 (defmethod json-write ((value json-object) &optional stream)
   "Encode a JSON object with an associative list of members to a stream."
   (let ((*print-pretty* t)
         (*print-length* nil)
         (*print-lines* nil)
         (*print-right-margin* 72))
     (pprint-logical-block (stream (json-object-members value)
                                   :prefix "{"
                                   :suffix "}")
       (pprint-exit-if-list-exhausted)
       (loop
          (let ((kv-pair (pprint-pop)))
            (destructuring-bind (k v)
                kv-pair
              (if (not (stringp k))
                  (progn
                    (warn "~s is not a valid JSON key; skipping...~%" k)
                    (pprint-exit-if-list-exhausted))
                (progn
                  (json-write k stream)
                  (write-char #\: stream)
                  (json-write v stream)
                  (pprint-exit-if-list-exhausted)
                  (write-char #\, stream)
                  (pprint-newline :mandatory)
                  (pprint-indent :current 0)))))))))