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typesetting/pitfall/restructure/decodestream.rkt

39 lines
1.7 KiB
Racket

#lang restructure/racket
(provide (all-defined-out))
#| approximates
https://github.com/mbutterick/restructure/blob/master/src/DecodeStream.coffee
|#
(define (read-bytes-exact count p)
(define bs (read-bytes count p))
(unless (and (bytes? bs) (= (bytes-length bs) count))
(raise-argument-error 'read-bytes-exact (format "byte string length ~a" count) bs))
bs)
(provide (rename-out [type-sizes TYPES]))
(define type-sizes (let-values ([(intkeys intvalues)
(for*/lists (intkeys intvalues)
([signed (in-list '(U ""))]
[size (in-list '(8 16 24 32))])
(values
(format "~aInt~a" signed size)
(/ size 8)))])
(for/hash ([key (in-list (append '(Float Double) intkeys))]
[value (in-list (append '(4 8) intvalues))]
#:when key
[endian '("" BE LE)])
(values (string->symbol (format "~a~a" key endian)) value))))
;; basically just a wrapper for a Racket port
;; but needs to start with a buffer so length can be found
(define-subclass object% (RDecodeStream [buffer #""])
(field [_port (if (bytes? buffer)
(open-input-bytes buffer)
(raise-argument-error 'RDecodeStream "bytes" buffer))])
(getter-field [pos (port-position _port)])
(getter-field [length (bytes-length buffer)])
(define/public (read count)
(read-bytes-exact count _port)))