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38 lines
1.2 KiB
Racket
38 lines
1.2 KiB
Racket
#lang racket/base
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(require racket/class racket/match "base.rkt" "util.rkt" "number.rkt")
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(provide (all-defined-out))
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#|
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approximates
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https://github.com/mbutterick/restructure/blob/master/src/Buffer.coffee
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|#
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(define x:buffer%
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(class xenobase%
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(super-new)
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(init-field [(@len len)])
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(unless (length-resolvable? @len)
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(raise-argument-error 'x:buffer "resolvable length" @len))
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(define/augment (decode port parent)
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(read-bytes (resolve-length @len port parent)))
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(define/augment (encode buf port [parent #f])
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(unless (bytes? buf)
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(raise-argument-error 'x:buffer-encode "bytes" buf))
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(when (x:int? @len)
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(send @len encode (bytes-length buf) port))
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(write-bytes buf port))
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(define/augment (size [val #f] [parent #f])
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(match val
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[(? bytes?) (bytes-length val)]
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[(== #false) (resolve-length @len val parent)]
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[_ (raise-argument-error 'x:buffer-size "bytes or #f" val)]))))
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(define (x:buffer [len-arg #f]
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#:length [len-kwarg #f]
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#:pre-encode [pre-proc #f]
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#:post-decode [post-proc #f])
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(define len (or len-arg len-kwarg #xffff))
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(new (generate-subclass x:buffer% pre-proc post-proc) [len len])) |