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|
#lang racket/base
#| Roughly based on the PLaneT package by Dave Herman,
Originally released under MIT license.
|#
;; ----------------------------------------------------------------------------
;; Customization
;; The default translation for a JSON `null' value
(provide json-null)
(define json-null (make-parameter 'null))
;; ----------------------------------------------------------------------------
;; Predicate
(provide jsexpr?)
(define (jsexpr? x #:null [jsnull (json-null)])
(let loop ([x x])
(or (exact-integer? x)
(inexact-real? x)
(boolean? x)
(string? x)
(eq? x jsnull)
(and (list? x) (andmap loop x))
(and (hash? x) (for/and ([(k v) (in-hash x)])
(and (symbol? k) (loop v)))))))
;; ----------------------------------------------------------------------------
;; Generation: Racket -> JSON
(provide write-json)
(define (write-json x [o (current-output-port)]
#:null [jsnull (json-null)] #:encode [enc 'control])
(define (escape m)
(define ch (string-ref m 0))
(define r
(assoc ch '([#\backspace . "\\b"] [#\newline . "\\n"] [#\return . "\\r"]
[#\page . "\\f"] [#\tab . "\\t"]
[#\\ . "\\\\"] [#\" . "\\\""])))
(define (u-esc n)
(define str (number->string n 16))
(define pad (case (string-length str)
[(1) "000"] [(2) "00"] [(3) "0"] [else ""]))
(string-append "\\u" pad str))
(if r
(cdr r)
(let ([n (char->integer ch)])
(if (n . < . #x10000)
(u-esc n)
;; use the (utf-16 surrogate pair) double \u-encoding
(let ([n (- n #x10000)])
(string-append (u-esc (+ #xD800 (arithmetic-shift n -10)))
(u-esc (+ #xDC00 (bitwise-and n #x3FF)))))))))
(define rx-to-encode
(case enc
[(control) #rx"[\0-\37\\\"\177]"]
[(all) #rx"[\0-\37\\\"\177-\U10FFFF]"]
[else (raise-type-error 'write-json "encoding symbol" enc)]))
(define (write-json-string str)
(write-bytes #"\"" o)
(write-string (regexp-replace* rx-to-encode str escape) o)
(write-bytes #"\"" o))
(let loop ([x x])
(cond [(or (exact-integer? x) (inexact-real? x)) (write x o)]
[(eq? x #f) (write-bytes #"false" o)]
[(eq? x #t) (write-bytes #"true" o)]
[(eq? x jsnull) (write-bytes #"null" o)]
[(string? x) (write-json-string x)]
[(list? x)
(write-bytes #"[" o)
(when (pair? x)
(loop (car x))
(for ([x (in-list (cdr x))]) (write-bytes #"," o) (loop x)))
(write-bytes #"]" o)]
[(hash? x)
(write-bytes #"{" o)
(define first? #t)
(for ([(k v) (in-hash x)])
(unless (symbol? k)
(raise-type-error 'write-json "bad JSON key value" k))
(if first? (set! first? #f) (write-bytes #"," o))
(write (symbol->string k) o) ; no `printf' => proper escapes
(write-bytes #":" o)
(loop v))
(write-bytes #"}" o)]
[else (raise-type-error 'write-json "bad JSON value" x)]))
(void))
;; ----------------------------------------------------------------------------
;; Parsing: JSON -> Racket
(require syntax/readerr)
(provide read-json)
(define (read-json [i (current-input-port)] #:null [jsnull (json-null)])
;; Follows the specification (eg, at json.org) -- no extensions.
;;
(define (err fmt . args)
(define-values [l c p] (port-next-location i))
(raise-read-error (format "read-json: ~a" (apply format fmt args))
(object-name i) l c p #f))
(define (skip-whitespace) (regexp-match? #px#"^\\s*" i))
;;
;; Reading a string *could* have been nearly trivial using the racket
;; reader, except that it won't handle a "\/"...
(define (read-string)
(let loop ([l* '()])
;; note: use a string regexp to extract utf-8-able text
(define m (cdr (or (regexp-try-match #rx"^([^\"\\]*)(\"|\\\\(.))" i)
(err "unterminated string"))))
(define l (if ((bytes-length (car m)) . > . 0) (cons (car m) l*) l*))
(define esc (caddr m))
(cond
[(not esc) (bytes->string/utf-8 (apply bytes-append (reverse l)))]
[(assoc esc '([#"b" . #"\b"] [#"n" . #"\n"] [#"r" . #"\r"]
[#"f" . #"\f"] [#"t" . #"\t"]
[#"\\" . #"\\"] [#"\"" . #"\""] [#"/" . #"/"]))
=> (λ (m) (loop (cons (cdr m) l)))]
[(equal? esc #"u")
(let* ([e (or (regexp-try-match #px#"^[a-fA-F0-9]{4}" i)
(err "bad string \\u escape"))]
[e (string->number (bytes->string/utf-8 (car e)) 16)])
(define e*
(if (<= #xD800 e #xDFFF)
;; it's the first part of a UTF-16 surrogate pair
(let* ([e2 (or (regexp-try-match #px#"^\\\\u([a-fA-F0-9]{4})" i)
(err "bad string \\u escape, ~a"
"missing second half of a UTF16 pair"))]
[e2 (string->number (bytes->string/utf-8 (cadr e2)) 16)])
(if (<= #xDC00 e2 #xDFFF)
(+ (arithmetic-shift (- e #xD800) 10) (- e2 #xDC00) #x10000)
(err "bad string \\u escape, ~a"
"bad second half of a UTF16 pair")))
e)) ; single \u escape
(loop (cons (string->bytes/utf-8 (string (integer->char e*))) l)))]
[else (err "bad string escape: \"~a\"" esc)])))
;;
(define (read-list what end-rx read-one)
(skip-whitespace)
(if (regexp-try-match end-rx i)
'()
(let loop ([l (list (read-one))])
(skip-whitespace)
(cond [(regexp-try-match end-rx i) (reverse l)]
[(regexp-try-match #rx#"^," i) (loop (cons (read-one) l))]
[else (err "error while parsing a json ~a" what)]))))
;;
(define (read-hash)
(define (read-pair)
(define k (read-json))
(unless (string? k) (err "non-string value used for json object key"))
(skip-whitespace)
(unless (regexp-try-match #rx#"^:" i)
(err "error while parsing a json object pair"))
(list (string->symbol k) (read-json)))
(apply hasheq (apply append (read-list 'object #rx#"^}" read-pair))))
;;
(define (read-json [top? #f])
(skip-whitespace)
(cond
[(and top? (eof-object? (peek-char i))) eof]
[(regexp-try-match #px#"^true\\b" i) #t]
[(regexp-try-match #px#"^false\\b" i) #f]
[(regexp-try-match #px#"^null\\b" i) jsnull]
[(regexp-try-match
#rx#"^-?(?:0|[1-9][0-9]*)(?:\\.[0-9]+)?(?:[eE][+-]?[0-9]+)?" i)
=> (λ (bs) (string->number (bytes->string/utf-8 (car bs))))]
[(regexp-try-match #rx#"^[\"[{]" i)
=> (λ (m)
(let ([m (car m)])
(cond [(equal? m #"\"") (read-string)]
[(equal? m #"[") (read-list 'array #rx#"^\\]" read-json)]
[(equal? m #"{") (read-hash)])))]
[else (err "bad input")]))
;;
(read-json #t))
;; ----------------------------------------------------------------------------
;; Convenience functions
(provide jsexpr->string jsexpr->bytes)
(define (jsexpr->string x #:null [jsnull (json-null)] #:encode [enc 'control])
(define o (open-output-string))
(write-json x o #:null jsnull #:encode enc)
(get-output-string o))
(define (jsexpr->bytes x #:null [jsnull (json-null)] #:encode [enc 'control])
(define o (open-output-bytes))
(write-json x o #:null jsnull #:encode enc)
(get-output-bytes o))
(provide string->jsexpr bytes->jsexpr)
(define (string->jsexpr str #:null [jsnull (json-null)])
(unless (string? str) (raise-type-error 'string->jsexpr "string" str))
(read-json (open-input-string str) #:null jsnull))
(define (bytes->jsexpr str #:null [jsnull (json-null)])
(unless (bytes? str) (raise-type-error 'bytes->jsexpr "bytes" str))
(read-json (open-input-bytes str) #:null jsnull))
|
