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#lang scribble/manual
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@(require scribble/eval (for-label racket/base racket/class racket/file racket/dict racket/promise xenomorph))
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@(define my-eval (make-base-eval))
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@(my-eval `(require xenomorph))
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@title{Xenomorph: binary encoding & decoding}
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@author[(author+email "Matthew Butterick" "mb@mbtype.com")]
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@margin-note{This package is in development. I make no commitment to maintaining the public interface documented below.}
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@defmodule[xenomorph]
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Hands up: who likes working with binary formats?
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OK, just a few of you, in the back. You're free to go.
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As for everyone else: Xenomorph eases the pain of working with binary formats. Instead of laboriously counting bytes —
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@itemlist[#:style 'ordered
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@item{You describe a binary format declaratively by using smaller ingredients — e.g., integers, strings, lists, pointers, dicts, and perhaps other nested encodings. This is known as a @deftech{xenomorphic object}.}
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@item{This xenomorphic object can then be used as a binary encoder, allowing you to convert Racket values to binary and write them out to a file.}
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@item{But wait, there's more: once defined, this xenomorphic object can @emph{also} be used as a binary decoder, reading bytes and parsing them into Racket values.}
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]
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So one binary-format definition can be used for both input and output. Meanwhile, Xenomorph handles all the dull housekeeping of counting bytes (because somebody has to).
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This package is derived principally from Devon Govett's @link["https://github.com/devongovett/restructure"]{@tt{restructure}} library for Node.js. Thanks for doing the heavy lifting, dude.
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@section{Installation}
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At the command line:
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@verbatim{raco pkg install xenomorph}
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After that, you can update the package from the command line:
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@verbatim{raco pkg update xenomorph}
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Invoke the library in a source file by importing it in the usual way:
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@verbatim{(require xenomorph)}
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@;{
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@section{Quick tutorial}
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@examples[#:eval my-eval
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(define four-ints (+ArrayT uint8 4))
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(decode four-ints #"\1\2\3\4")
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(decode four-ints #"\1\2\3")
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(decode four-ints #"\1\2\3\4\5\6")
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(define op (open-output-string))
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(encode four-ints '(1 2 3 4) op)
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(get-output-bytes op)
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]
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}
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@section{The big picture}
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@subsection{Bytes and byte strings}
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Suppose we have a file on disk. What's in the file? Without knowing anything else, we can at least say the file contains a sequence of @deftech{bytes}. A @tech{byte} is the smallest unit of data storage. It's not, however, the smallest unit of information storage — that would be a @deftech{bit}. But when we read (or write) from disk (or other source, like memory), we work with bytes.
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A byte holds eight bits, so it can take on values between 0 and 255, inclusive. In Racket, a sequence of bytes is also known as a @deftech{byte string}. It prints as a series of values between quotation marks, prefixed with @litchar{#}:
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@racketblock[#"ABC"]
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Caution: though this looks similar to the ordinary string @racket["ABC"], we're better off thinking of it as a block of integers that are sometimes displayed as characters for convenience. For instance, the byte string above represents three bytes valued 65, 66, and 67. This byte string could also be written in hexadecimal like so:
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@(racketvalfont "#\"\\x41\\x42\\x43\"")
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Or octal like so:
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@(racketvalfont "#\"\\101\\102\\103\"")
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Both of these mean the same thing. (If you like, confirm this by trying them on the REPL.)
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We can also make an equivalent byte string with @racket[bytes]. As above, Racket doesn't care how we notate the values, as long as they're between 0 and 255:
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@examples[#:eval my-eval
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(bytes 65 66 67)
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(bytes (+ 31 34) (* 3 22) (- 100 33))
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(apply bytes (map char->integer '(#\A #\B #\C)))
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]
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Byte values between 32 and 127 are printed as characters. Other values are printed in octal:
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@examples[#:eval my-eval
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(bytes 65 66 67 154 206 255)
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]
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If you think this printing convention is a little weird, I agree. But that's how Racket does it.
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If we prefer to deal with lists of integers, we can always use @racket[bytes->list] and @racket[list->bytes]:
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@examples[#:eval my-eval
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(bytes->list #"ABC\232\316\377")
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(list->bytes '(65 66 67 154 206 255))
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]
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The key point: the @litchar{#"} prefix tells us we're looking at a byte string, not an ordinary string.
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@subsection{Binary formats}
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Back to files. Files are classified as being either @deftech{binary} or @deftech{text}. (A distinction observed by Racket functions such as @racket[write-to-file].) When we speak of binary vs. text, we're saying something about the internal structure of the byte sequence — what values those bytes represent. We'll call this internal structure the @deftech{binary format} of the file.
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@margin-note{This internal structure is also called an @emph{encoding}. Here, however, I avoid using that term as a synonym for @tech{binary format}, because I prefer to reserve it for when we talk about encoding and decoding as operations on data.}
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@;{
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@subsubsection{Text encodings}
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Text files are a just a particular subset of binary files that use a @deftech{text encoding} — that is, a binary encoding that stores human-readable characters.
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But since we all have experience with text files, let's use text encoding as a way of starting to understand what's happening under the hood with binary encodings.
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For example, ASCII is a familiar encoding that stores each character in seven bits, so it can describe 128 distinct characters. Because every ASCII code is less than 255, we can store ASCII text with one byte per character.
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But if we want to use more than 128 distinct characters, we're stuck. That's why Racket instead uses the UTF-8 text encoding by default. UTF-8 uses between one and three bytes to encode each character, and can thus represent up to 1,112,064 distinct characters. We can see how this works by converting a string into an encoded byte sequence using @racket[string->bytes/utf-8]:
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@examples[#:eval my-eval
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(string->bytes/utf-8 "ABCD")
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(bytes->list (string->bytes/utf-8 "ABCD"))
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(string->bytes/utf-8 "ABÇ战")
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(bytes->list (string->bytes/utf-8 "ABÇ战"))
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]
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For ASCII-compatible characters, UTF-8 uses one byte for each character. Thus, the string @racket["ABCD"] is four bytes long in UTF-8.
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Now consider the string @racket["ABÇ战"], which has four characters, but the second two aren't ASCII-compatible. In UTF-8, it's encoded as seven bytes: the first two characters are one byte each, the @racket["Ç"] takes two bytes, and the @racket["战"] takes three.
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Moreover, for further simplicity, text files typically rely on a small set of pre-defined encodings, like ASCII or UTF-8 or Latin-1, so that those who write programs that manipulate text only have to support a smallish set of encodings.
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@subsubsection{Binary encodings}
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@subsubsection{In sum}
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Three corollaries follow:
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@itemlist[#:style 'ordered
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@item{A given sequence of bytes can mean different things, depending on what encoding we use.}
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@item{We can only make sense of a sequence of bytes if we know its encoding.}
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@item{A byte sequence does not describe its own encoding.}
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]
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For those familiar with programming-language lingo, an encoding somewhat resembles a @deftech{grammar}, which is a tool for describing the syntactic structure of a program. A grammar doesn't describe one particular program. Rather, it describes all possible programs that are consistent with the grammar, and therefore can be used to parse any particular one. Likewise for an encoding.
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@margin-note{Can a grammar work as a binary encoding? In limited cases, but not enough to be practical. Most grammars have to assume the target program is context free, meaning that the grammar rules apply the same way everywhere. By contrast, binary files are nonrecursive and contextual.}
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}
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@section{Main interface}
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@defproc[
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(xenomorphic?
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[x any/c])
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boolean?]{
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Whether @racket[x] is an object of type @racket[x:base%].
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}
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@defproc[
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(decode
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[xenomorphic-obj xenomorphic?]
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[byte-source (or/c bytes? input-port?) (current-input-port)]
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[#:parent parent (or/c xenomorphic? #false) #false]
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[arg any/c] ...)
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any/c]{
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Read bytes from @racket[byte-source] and convert them to a Racket value using @racket[xenomorphic-obj] as the decoder.
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}
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@defproc[
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(encode
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[xenomorphic-obj xenomorphic?]
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[val any/c]
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[byte-dest (or/c output-port? #false) (current-output-port)]
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[#:parent parent (or/c xenomorphic? #false) #false]
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[arg any/c] ...
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)
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(or/c void? bytes?)]{
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Convert @racket[val] to bytes using @racket[xenomorphic-obj] as the encoder.
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If @racket[byte-dest] is an @racket[output-port?], the bytes are written there and the return value is @racket[(void)]. If @racket[byte-dest] is @racket[#false], the encoded byte string is the return value.
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}
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@defproc[
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(size
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[xenomorphic-obj xenomorphic?]
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[val any/c #false]
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[#:parent parent (or/c xenomorphic? #false) #false]
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[arg any/c] ...)
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exact-nonnegative-integer?]{
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The length of the @tech{byte string} that @racket[val] would produce if it were encoded using @racket[encode].
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}
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@section{Core xenomorphic objects}
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These basic xenomorphic objects can be used on their own, or combined to make bigger xenomorphic objects.
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Note on naming: the main xenomorphix objects have an @litchar{x:} prefix to distinguish them from (and prevent name collisions with) the ordinary Racket thing (for instance, @racket[x:list] vs. @racket[list]). Other xenomorphic objects (like @racket[uint8]) don't have this prefix, because it seems unnecessary and therefore laborious.
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@defclass[x:base% object% ()]{
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When making your own xenomorphic objects, usually you'll want to stick together existing core objects, or inherit from one of those classes. Inheriting from @racket[x:base%] is also allowed, but you have to do all the heavy lifting.
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@defmethod[
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#:mode pubment
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(x:decode
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[input-port input-port?]
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[parent (or/c xenomorphic? #false)]
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[args any/c] ...)
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any/c]{
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Read bytes from @racket[input-port] and convert them into a Racket value. Called by @racket[decode].
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}
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@defmethod[
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(post-decode
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[val any/c])
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any/c]{
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Hook for post-processing on @racket[val] after it's returned by @racket[x:decode] but before it's returned by @racket[decode].
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}
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@defmethod[
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#:mode pubment
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(x:encode
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[val any/c]
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[output-port output-port?]
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[parent (or/c xenomorphic? #false)]
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[args any/c] ...)
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bytes?]{
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Convert a value into a @tech{byte string} which is written to @racket[output-port]. Called by @racket[encode].
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}
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@defmethod[
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(pre-encode
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[val any/c])
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any/c]{
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Hook for pre-processing on @racket[val] after it's passed to @racket[encode] but before it's passed to @racket[x:encode].
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}
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@defmethod[
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#:mode pubment
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(x:size
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[val any/c]
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[parent (or/c xenomorphic? #false)]
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[args any/c] ...)
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exact-nonnegative-integer?]{
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The length of the @tech{byte string} that @racket[val] would produce if it were encoded using @racket[x:encode]. Called by @racket[size].
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}
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}
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@subsection{Numbers}
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@defmodule[xenomorph/number]
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@defproc[
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(endian-value?
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[val any/c])
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boolean?]{
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Whether @racket[val] is either @racket['be] (representing big endian) or @racket['le] (representing little endian).
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}
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@defthing[system-endian endian-value?]{
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The endian value of the current system. Big endian is represented as @racket['be] and little endian as @racket['le]. This can be used as an argument for the @racket[x:number%] constructor.
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Use this value carefully, however, as most binary formats are defined using one endian convention or the other (so that they can be exchanged among systems regardless of endianness).
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}
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@defclass[x:number% x:base% ()]{
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@defconstructor[
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([size exact-positive-integer?]
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[signed? boolean?]
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[endian endian-value?])]{
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Create class instance that represents a binary number format @racket[size] bytes long, either @racket[signed?] or not, with @racket[endian] byte ordering. The endian arugment can be @racket[system-endian].
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}
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}
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@subsubsection{Integers}
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@defclass[x:int% x:number% ()]{
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Base class for integer formats. Use @racket[x:int] to conveniently instantiate new integer formats.
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}
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@defproc[
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(x:int?
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[x any/c])
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boolean?]{
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Whether @racket[x] is an object of type @racket[x:int%].
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}
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@defproc[
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(x:int
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[size-arg (or/c exact-positive-integer? #false) #false]
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[#:size size-kw exact-positive-integer? 2]
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[#:signed signed boolean? #true]
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[#:endian endian endian-value? system-endian]
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[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
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[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
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[#:base-class base-class (λ (c) (subclass? c x:int%)) x:int%]
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)
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x:int?]{
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Generate an instance of @racket[x:int%] (or a subclass of @racket[x:int%]) with certain optional attributes.
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@racket[size-arg] or @racket[size-kw] (whichever is provided, though @racket[size-arg] takes precedence) controls the encoded size.
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@racket[signed] controls whether the integer is signed or unsigned.
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@racket[endian] controls the byte-ordering convention.
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@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
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@racket[base-class] controls the class used for instantiation of the new object.
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}
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@deftogether[
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(@defthing[int8 x:int?]
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@defthing[int16 x:int?]
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@defthing[int24 x:int?]
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@defthing[int32 x:int?]
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@defthing[uint8 x:int?]
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@defthing[uint16 x:int?]
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@defthing[uint24 x:int?]
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@defthing[uint32 x:int?])
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]{
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The common integer types, using @racket[system-endian] endianness. The @racket[u] prefix indicates unsigned. The numerical suffix indicates bit length.
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Use these carefully, however, as most binary formats are defined using one endian convention or the other (so that they can be exchanged among systems regardless of endianness).
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}
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@deftogether[
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(@defthing[int8be x:int?]
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@defthing[int16be x:int?]
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@defthing[int24be x:int?]
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@defthing[int32be x:int?]
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@defthing[uint8be x:int?]
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@defthing[uint16be x:int?]
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@defthing[uint24be x:int?]
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@defthing[uint32be x:int?])
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]{
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Big-endian versions of the common integer types. The @racket[u] prefix indicates unsigned. The numerical suffix indicates bit length.
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}
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@deftogether[
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(@defthing[int8le x:int?]
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@defthing[int16le x:int?]
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@defthing[int24le x:int?]
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@defthing[int32le x:int?]
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@defthing[uint8le x:int?]
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@defthing[uint16le x:int?]
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@defthing[uint24le x:int?]
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@defthing[uint32le x:int?])
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]{
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Little-endian versions of the common integer types. The @racket[u] prefix indicates unsigned. The numerical suffix indicates bit length.
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}
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@subsubsection{Floats}
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@defclass[x:float% x:number% ()]{
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Base class for floating-point number formats. By convention, all floats are signed. Use @racket[x:float] to conveniently instantiate new floating-point number formats.
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}
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@defproc[
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(x:float?
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[x any/c])
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boolean?]{
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Whether @racket[x] is an object of type @racket[x:float%].
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}
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@defproc[
|
|
|
(x:float
|
|
|
[size-arg (or/c exact-positive-integer? #false) #false]
|
|
|
[#:size size-kw exact-positive-integer? 2]
|
|
|
[#:endian endian endian-value? system-endian]
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:float%)) x:float%]
|
|
|
)
|
|
|
x:int?]{
|
|
|
Generate an instance of @racket[x:float%] (or a subclass of @racket[x:float%]) with certain optional attributes.
|
|
|
|
|
|
@racket[size-arg] or @racket[size-kw] (whichever is provided, though @racket[size-arg] takes precedence) controls the encoded size.
|
|
|
|
|
|
@racket[endian] controls the byte-ordering convention.
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
@deftogether[
|
|
|
(@defthing[float x:float?]
|
|
|
@defthing[floatbe x:float?]
|
|
|
@defthing[floatle x:float?])
|
|
|
]{
|
|
|
The common 32-bit floating-point types. They differ in byte-ordering convention: @racket[floatbe] uses big endian, @racket[floatle] uses little endian, @racket[float] uses @racket[system-endian].
|
|
|
}
|
|
|
|
|
|
@deftogether[
|
|
|
(@defthing[double x:float?]
|
|
|
@defthing[doublebe x:float?]
|
|
|
@defthing[doublele x:float?])
|
|
|
]{
|
|
|
The common 64-bit floating-point types. They differ in byte-ordering convention: @racket[doublebe] uses big endian, @racket[doublele] uses little endian, @racket[double] uses @racket[system-endian].
|
|
|
}
|
|
|
|
|
|
|
|
|
@subsubsection{Fixed-point numbers}
|
|
|
|
|
|
|
|
|
@defclass[x:fixed% x:int% ()]{
|
|
|
Base class for fixed-point number formats. Use @racket[x:fixed] to conveniently instantiate new fixed-point number formats.
|
|
|
|
|
|
@defconstructor[
|
|
|
([size exact-positive-integer?]
|
|
|
[signed? boolean?]
|
|
|
[endian endian-value?]
|
|
|
[fracbits exact-positive-integer?])]{
|
|
|
Create class instance that represents a fixed-point number format @racket[size] bytes long, either @racket[signed?] or not, with @racket[endian] byte ordering and @racket[fracbits] of precision.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:fixed?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:fixed%].
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:fixed
|
|
|
[size-arg (or/c exact-positive-integer? #false) #false]
|
|
|
[#:size size-kw exact-positive-integer? 2]
|
|
|
[#:endian endian endian-value? system-endian]
|
|
|
[#:fracbits fracbits (or/c exact-positive-integer? #false) (/ (* _size 8) 2)]
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:fixed%)) x:fixed%]
|
|
|
)
|
|
|
x:int?]{
|
|
|
Generate an instance of @racket[x:fixed%] (or a subclass of @racket[x:fixed%]) with certain optional attributes.
|
|
|
|
|
|
@racket[size-arg] or @racket[size-kw] (whichever is provided, though @racket[size-arg] takes precedence) controls the encoded size. Defaults to @racket[2].
|
|
|
|
|
|
@racket[endian] controls the byte-ordering convention.
|
|
|
|
|
|
@racket[fracbits] controls the number of bits of precision. If no value or @racket[#false] is passed, defaults to @racket[(/ (* _size 8) 2)].
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
@deftogether[
|
|
|
(@defthing[fixed16 x:fixed?]
|
|
|
@defthing[fixed16be x:fixed?]
|
|
|
@defthing[fixed16le x:fixed?])
|
|
|
]{
|
|
|
The common 16-bit fixed-point number types with 2 bits of precision. They differ in byte-ordering convention: @racket[fixed16be] uses big endian, @racket[fixed16le] uses little endian, @racket[fixed16] uses @racket[system-endian].
|
|
|
}
|
|
|
|
|
|
@deftogether[
|
|
|
(@defthing[fixed32 x:fixed?]
|
|
|
@defthing[fixed32be x:fixed?]
|
|
|
@defthing[fixed32le x:fixed?])
|
|
|
]{
|
|
|
The common 32-bit fixed-point number types with 4 bits of precision. They differ in byte-ordering convention: @racket[fixed32be] uses big endian, @racket[fixed32le] uses little endian, @racket[fixed32] uses @racket[system-endian].
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
@subsection{Strings}
|
|
|
|
|
|
@defmodule[xenomorph/string]
|
|
|
|
|
|
Good old strings.
|
|
|
|
|
|
@defproc[
|
|
|
(supported-encoding?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] represents a supported encoding: either @racket['ascii] or @racket['utf8].
|
|
|
}
|
|
|
|
|
|
@defclass[x:string% x:base% ()]{
|
|
|
Base class for string formats. Use @racket[x:string] to conveniently instantiate new string formats.
|
|
|
|
|
|
@defconstructor[
|
|
|
([len length-resolvable?]
|
|
|
[encoding (or/c procedure? supported-encoding?)])]{
|
|
|
Create class instance that represents a string format of length @racket[len]. If @racket[len] is an integer, the string is fixed at that length, otherwise it can be any length.
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:decode
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
string?]{
|
|
|
Returns a @tech{string}.
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:encode
|
|
|
[val any/c]
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bytes?]{
|
|
|
Take a @racket[val], converts it to a string if needed, and encode it as a @tech{byte string}. If @racket[_len] is a @racket[xenomorphic?] object, the length is encoded at the beginning of the string using that object as the encoder.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:string?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:string%].
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:string
|
|
|
[len-arg (or/c length-resolvable? #false) #false]
|
|
|
[enc-arg (or/c procedure? supported-encoding? #false) #false]
|
|
|
[#:length len-kw (or/c length-resolvable? #false) #false]
|
|
|
[#:encoding enc-kw (or/c procedure? supported-encoding? #false) 'utf8]
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:string%)) x:string%]
|
|
|
)
|
|
|
x:string?]{
|
|
|
Generate an instance of @racket[x:string%] (or a subclass of @racket[x:string%]) with certain optional attributes.
|
|
|
|
|
|
@racket[len-arg] or @racket[len-kw] (whichever is provided, though @racket[len-arg] takes precedence) determines the length of the string. If this argument is an integer, the string is limited to that length. If it's another value, the string has variable length.
|
|
|
|
|
|
@racket[enc-arg] or @racket[enc-kw] (whichever is provided, though @racket[enc-arg] takes precedence) determines the encoding of the string. Default is @racket['utf8]. See also @racket[supported-encoding?].
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
@subsection{Symbols}
|
|
|
|
|
|
@defmodule[xenomorph/symbol]
|
|
|
|
|
|
Under the hood, just a wrapper around the @racket[x:string%] class.
|
|
|
|
|
|
@defclass[x:symbol% x:string% ()]{
|
|
|
Base class for symbol formats. Use @racket[x:symbol] to conveniently instantiate new symbol formats.
|
|
|
|
|
|
@defconstructor[
|
|
|
([len length-resolvable?]
|
|
|
[encoding (or/c procedure? supported-encoding?)])]{
|
|
|
Create class instance that represents a symbol format of length @racket[len]. If @racket[len] is an integer, the symbol is fixed at that length, otherwise it can be any length.
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:decode
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
symbol?]{
|
|
|
Returns a @tech{symbol}.
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:encode
|
|
|
[val any/c]
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bytes?]{
|
|
|
Take a @racket[val], converts it to a symbol if needed, and encode it as a @tech{byte string}. If @racket[_len] is a @racket[xenomorphic?] object, the length is encoded at the beginning of the symbol using that object as the encoder.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:symbol?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:symbol%].
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:symbol
|
|
|
[len-arg (or/c length-resolvable? #false) #false]
|
|
|
[enc-arg (or/c procedure? supported-encoding? #false) #false]
|
|
|
[#:length len-kw (or/c length-resolvable? #false) #false]
|
|
|
[#:encoding enc-kw (or/c procedure? supported-encoding? #false) 'utf8]
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:symbol%)) x:symbol%]
|
|
|
)
|
|
|
x:symbol?]{
|
|
|
Generate an instance of @racket[x:symbol%] (or a subclass of @racket[x:symbol%]) with certain optional attributes.
|
|
|
|
|
|
@racket[len-arg] or @racket[len-kw] (whichever is provided, though @racket[len-arg] takes precedence) determines the length of the symbol. If this argument is an integer, the symbol is limited to that length. If it's another value, the symbol has variable length.
|
|
|
|
|
|
@racket[enc-arg] or @racket[enc-kw] (whichever is provided, though @racket[enc-arg] takes precedence) determines the encoding of the string. Default is @racket['utf8]. See also @racket[supported-encoding?].
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
|
|
|
@subsection{Lists}
|
|
|
|
|
|
@defmodule[xenomorph/list]
|
|
|
|
|
|
Lists in Xenomorph have a @emph{type} and maybe a @emph{length}. Every element in the list must have the same type. The list can have a specific length, but it doesn't need to (in which case the length is encoded as part of the data).
|
|
|
|
|
|
If you want to store heterogeneous item types in a single Xenomorph list, you can wrap them in @secref{Pointers} so they have a uniform type.
|
|
|
|
|
|
@defclass[x:list% x:base% ()]{
|
|
|
Base class for list formats. Use @racket[x:list] to conveniently instantiate new list formats.
|
|
|
|
|
|
@defconstructor[
|
|
|
([type xenomorphic?]
|
|
|
[len length-resolvable?]
|
|
|
[count-bytes? boolean?])]{
|
|
|
Create class instance that represents a list format with elements of type @racket[type]. If @racket[len] is an integer, the list is fixed at that length, otherwise it can be any length.
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:decode
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
list?]{
|
|
|
Returns a @tech{list} of values whose length is @racket[_len] and where each value is @racket[_type].
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:encode
|
|
|
[seq sequence?]
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bytes?]{
|
|
|
Take a @tech{sequence} @racket[seq] and encode it as a @tech{byte string}.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:list?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:list%].
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:list
|
|
|
[type-arg (or/c xenomorphic? #false) #false]
|
|
|
[len-arg (or/c length-resolvable? #false) #false]
|
|
|
[#:type type-kw (or/c xenomorphic? #false) #false]
|
|
|
[#:length len-kw (or/c length-resolvable? #false) #false]
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:list%)) x:list%]
|
|
|
)
|
|
|
x:list?]{
|
|
|
Generate an instance of @racket[x:list%] (or a subclass of @racket[x:list%]) with certain optional attributes.
|
|
|
|
|
|
@racket[type-arg] or @racket[type-kw] (whichever is provided, though @racket[type-arg] takes precedence) determines the type of the elements in the list.
|
|
|
|
|
|
@racket[len-arg] or @racket[len-kw] (whichever is provided, though @racket[len-arg] takes precedence) determines the length of the list. This can be an ordinary integer, but it can also be any value that is @racket[length-resolvable?].
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
|
|
|
@subsection{Streams}
|
|
|
|
|
|
@defmodule[xenomorph/stream]
|
|
|
|
|
|
Under the hood, just a wrapper around the @racket[x:list%] class that produces a stream rather than a list.
|
|
|
|
|
|
The distinguishing feature of a @tech{stream} is that the evaluation is lazy: elements are only decoded as they are requested (and then they are cached for subsequent use). Therefore, a Xenomorph stream is a good choice when you don't want to incur the costs of decoding every element immediately (as you will when you use @secref{Lists}).
|
|
|
|
|
|
@defclass[x:stream% x:list% ()]{
|
|
|
Base class for stream formats. Use @racket[x:stream] to conveniently instantiate new stream formats.
|
|
|
|
|
|
@defconstructor[
|
|
|
([type xenomorphic?]
|
|
|
[len length-resolvable?]
|
|
|
[count-bytes? boolean?])]{
|
|
|
Create class instance that represents a stream format with elements of type @racket[type]. If @racket[len] is an integer, the stream is fixed at that length, otherwise it can be any length.
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:decode
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
stream?]{
|
|
|
Returns a @tech{stream} of values whose length is @racket[_len] and where each value is @racket[_type].
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:encode
|
|
|
[seq sequence?]
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bytes?]{
|
|
|
Take a @tech{sequence} @racket[seq] and encode it as a @tech{byte string}.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:stream?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:stream%].
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:stream
|
|
|
[type-arg (or/c xenomorphic? #false) #false]
|
|
|
[len-arg (or/c length-resolvable? #false) #false]
|
|
|
[#:type type-kw (or/c xenomorphic? #false) #false]
|
|
|
[#:length len-kw (or/c length-resolvable? #false) #false]
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:stream%)) x:stream%]
|
|
|
)
|
|
|
x:stream?]{
|
|
|
Generate an instance of @racket[x:stream%] (or a subclass of @racket[x:stream%]) with certain optional attributes.
|
|
|
|
|
|
@racket[type-arg] or @racket[type-kw] (whichever is provided, though @racket[type-arg] takes precedence) determines the type of the elements in the list.
|
|
|
|
|
|
@racket[len-arg] or @racket[len-kw] (whichever is provided, though @racket[len-arg] takes precedence) determines the length of the list. This can be an ordinary integer, but it can also be any value that is @racket[length-resolvable?].
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
@subsection{Vectors}
|
|
|
|
|
|
@defmodule[xenomorph/vector]
|
|
|
|
|
|
Under the hood, just a wrapper around the @racket[x:list%] class that decodes to a vector rather than a list.
|
|
|
|
|
|
|
|
|
@defclass[x:vector% x:list% ()]{
|
|
|
Base class for vector formats. Use @racket[x:vector] to conveniently instantiate new vector formats.
|
|
|
|
|
|
@defconstructor[
|
|
|
([type xenomorphic?]
|
|
|
[len length-resolvable?]
|
|
|
[count-bytes? boolean?])]{
|
|
|
Create class instance that represents a vector format with elements of type @racket[type]. If @racket[len] is an integer, the vector is fixed at that length, otherwise it can be any length.
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:decode
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
vector?]{
|
|
|
Returns a @tech{vector} of values whose length is @racket[_len] and where each value is @racket[_type].
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:encode
|
|
|
[seq sequence?]
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bytes?]{
|
|
|
Take a @tech{sequence} @racket[seq] and encode it as a @tech{byte string}.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:vector?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:vector%].
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:vector
|
|
|
[type-arg (or/c xenomorphic? #false) #false]
|
|
|
[len-arg (or/c length-resolvable? #false) #false]
|
|
|
[#:type type-kw (or/c xenomorphic? #false) #false]
|
|
|
[#:length len-kw (or/c length-resolvable? #false) #false]
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:vector%)) x:vector%]
|
|
|
)
|
|
|
x:vector?]{
|
|
|
Generate an instance of @racket[x:vector%] (or a subclass of @racket[x:vector%]) with certain optional attributes.
|
|
|
|
|
|
@racket[type-arg] or @racket[type-kw] (whichever is provided, though @racket[type-arg] takes precedence) determines the type of the elements in the list.
|
|
|
|
|
|
@racket[len-arg] or @racket[len-kw] (whichever is provided, though @racket[len-arg] takes precedence) determines the length of the list. This can be an ordinary integer, but it can also be any value that is @racket[length-resolvable?].
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
|
|
|
@subsection{Dicts}
|
|
|
|
|
|
@defmodule[xenomorph/dict]
|
|
|
|
|
|
A @deftech{dict} is a store of keys and values. The analogy to a Racket @racket[dict?] is intentional, but in Xenomorph a dict must also be @emph{ordered}, because a binary encoding doesn't make sense if it happens in a different order every time. The more precise analogy would be to an @tech{association list} — a thing that has both dict-like and list-like qualities — but this would be a laborious name.
|
|
|
|
|
|
@defclass[x:dict% x:base% ()]{
|
|
|
Base class for dict formats. Use @racket[x:dict] to conveniently instantiate new dict formats.
|
|
|
|
|
|
@defconstructor[
|
|
|
([fields dict?])]{
|
|
|
Create class instance that represents a dict format with @racket[fields] as a dictionary holding the key–value pairs that define the dict format. Each key must be a @racket[symbol?] and each value must be a @racket[xenomorphic?] type.
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:decode
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
hash-eq?]{
|
|
|
Returns a @racket[hasheq] whose keys are the same as the keys in @racket[_fields].
|
|
|
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:encode
|
|
|
[kvs dict?]
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bytes?]{
|
|
|
Take the keys and values in @racket[kvs] and encode them as a @tech{byte string}.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:dict?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:dict%].
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:dict
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:dict%)) x:dict%]
|
|
|
[dict (listof (pairof symbol? xenomorphic?))] ...
|
|
|
[key symbol?] [val-type xenomorphic?] ... ...
|
|
|
)
|
|
|
x:dict?]{
|
|
|
Generate an instance of @racket[x:dict%] (or a subclass of @racket[x:dict%]) with certain optional attributes.
|
|
|
|
|
|
The rest arguments determine the keys and value types of the dict. These arguments can either be alternating keys and value-type arguments (similar to the calling pattern for @racket[hasheq]) or @tech{association lists}.
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
@subsection{Versioned dicts}
|
|
|
|
|
|
@defmodule[xenomorph/versioned-dict]
|
|
|
|
|
|
|
|
|
The versioned dict is a format derived from @racket[x:dict%] that contains multiple possible dict encodings. It also carries a version field to select among them. This version is stored with the encoded data, of course, so on decode, the correct version will be chosen.
|
|
|
|
|
|
|
|
|
@defproc[
|
|
|
(version-type?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] can be used as the version type of a versioned dict. Valid types are @racket[integer?], @racket[procedure?], @racket[xenomorphic?], or @racket[symbol?].
|
|
|
}
|
|
|
|
|
|
|
|
|
@defclass[x:versioned-dict% x:dict% ()]{
|
|
|
Base class for versioned dict formats. Use @racket[x:versioned-dict] to conveniently instantiate new dict formats.
|
|
|
|
|
|
@defconstructor[
|
|
|
([type version-type?]
|
|
|
[versions dict?]
|
|
|
[fields #false])]{
|
|
|
Create class instance that represents a versioned dict format with @racket[type] as the encoded type of the version value, and @racket[versions] as a dictionary holding the key–value pairs that define the versioned dict. Each key of @racket[versions] must be a value consistent with @racket[type], and each value must either be a @racket[dict?] or @racket[x:dict?].
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:decode
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
hash-eq?]{
|
|
|
Returns a @racket[hasheq] whose keys are the same as the keys in @racket[_fields].
|
|
|
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:encode
|
|
|
[kvs dict?]
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bytes?]{
|
|
|
Take the keys and values in @racket[kvs] and encode them as a @tech{byte string}.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:versioned-dict?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:versioned-dict%].
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:versioned-dict
|
|
|
[type-arg (or/c version-type? #false)]
|
|
|
[versions-arg (or/c dict? #false)]
|
|
|
[#:type type-kw (or/c version-type? #false)]
|
|
|
[#:versions versions-kw (or/c dict? #false)]
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:versioned-dict%)) x:versioned-dict%]
|
|
|
)
|
|
|
x:versioned-dict?]{
|
|
|
Generate an instance of @racket[x:versioned-dict%] (or a subclass of @racket[x:versioned-dict%]) with certain optional attributes.
|
|
|
|
|
|
@racket[type-arg] or @racket[type-kw] (whichever is provided, though @racket[type-arg] takes precedence) determines the type of the version value that is used to select from among available dicts.
|
|
|
|
|
|
@racket[versions-arg] or @racket[versions-kw] (whichever is provided, though @racket[versions-arg] takes precedence) is a dictionary holding the key–value pairs that define the versioned dict. Each key of @racket[versions] must be a value consistent with @racket[type], and each value must either be a @racket[dict?] or @racket[x:dict?].
|
|
|
|
|
|
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
|
|
|
@subsection{Pointers}
|
|
|
|
|
|
@defmodule[xenomorph/pointer]
|
|
|
|
|
|
A pointer can be thought of as a meta-object that can wrap any of the other binary formats here. It doesn't change how they work: they still take the same inputs (on @racket[encode]) and produce the same values (on @racket[decode]).
|
|
|
|
|
|
What it does change is the underlying housekeeping, by creating a layer of indirection around the data.
|
|
|
|
|
|
On @racket[encode], instead of storing the raw data at a certain point in the byte stream, it creates a reference — that is, a @deftech{pointer} — to that data at another location, and then puts the data at that location.
|
|
|
|
|
|
On @racket[decode], the process is reversed: the pointer is dereferenced to discover the true location of the data, the data is read from that location, and then the decode proceeds as usual.
|
|
|
|
|
|
Under the hood, this housekeeping is fiddly and annoying. But good news! It's already been done. Please do something worthwhile with the hours of your life that have been returned to you.
|
|
|
|
|
|
Pointers can be useful for making data types of different sizes behave as if they were the same size. For instance, @secref{Lists} require all elements to have the same encoded size. What if you want to put different data types in the list? Wrap each item in a pointer, and you can make a list of pointers (because they have consistent size) that reference different kinds of data.
|
|
|
|
|
|
|
|
|
|
|
|
@defclass[x:pointer% x:base% ()]{
|
|
|
Base class for pointer formats. Use @racket[x:pointer] to conveniently instantiate new pointer formats.
|
|
|
|
|
|
@defproc[
|
|
|
(pointer-relative-value?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] can be used as a value for the @racket[_pointer-relative-to] field of @racket[x:pointer%]. Valid choices are @racket['(local immediate parent global)].
|
|
|
}
|
|
|
|
|
|
@defconstructor[
|
|
|
([ptr-type x:int?]
|
|
|
[dest-type (or/c xenomorphic? 'void)]
|
|
|
[pointer-relative-to pointer-relative-value?]
|
|
|
[allow-null? boolean?]
|
|
|
[null-value any/c]
|
|
|
[pointer-lazy? boolean?])]{
|
|
|
Create class instance that represents a pointer format. See @racket[x:pointer] for a description of the fields.
|
|
|
|
|
|
|
|
|
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:decode
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
pointer?]{
|
|
|
Returns a @tech{pointer} of values whose length is @racket[_len] and where each value is @racket[_type].
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:encode
|
|
|
[seq sequence?]
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bytes?]{
|
|
|
Take a @tech{sequence} @racket[seq] and encode it as a @tech{byte string}.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:pointer?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:pointer%].
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:pointer
|
|
|
[ptr-type-arg (or/c x:int? #false) #false]
|
|
|
[dest-type-arg (or/c xenomorphic? 'void #false) #false]
|
|
|
[#:type ptr-type-kw (or/c x:int? #false) uint32]
|
|
|
[#:dest-type dest-type-kw (or/c xenomorphic? 'void #false) uint8]
|
|
|
[#:relative-to pointer-relative-to pointer-relative-value? 'local]
|
|
|
[#:allow-null allow-null? boolean? #true]
|
|
|
[#:null null-value any/c 0]
|
|
|
[#:lazy pointer-lazy? boolean? #false]
|
|
|
[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
|
|
|
[#:base-class base-class (λ (c) (subclass? c x:pointer%)) x:pointer%]
|
|
|
)
|
|
|
x:pointer?]{
|
|
|
Generate an instance of @racket[x:pointer%] (or a subclass of @racket[x:pointer%]) with certain optional attributes.
|
|
|
|
|
|
@racket[ptr-dest-type-arg] or @racket[ptr-type-kw] (whichever is provided, though @racket[ptr-dest-type-arg] takes precedence) controls the type of the pointer value itself, which must be an @racket[x:int?]). Default is @racket[uint32].
|
|
|
|
|
|
@racket[dest-type-arg] or @racket[dest-type-kw] (whichever is provided, though @racket[dest-type-arg] takes precedence) controls the type of the thing being pointed at, which must be a @racket[xenomorphic?] object or the symbol @racket['void] to indicate a void pointer. Default is @racket[uint8].
|
|
|
|
|
|
|
|
|
@racket[pointer-relative-to] controls the style of pointer, which must be one of @racket['(local immediate parent global)]. Default is @racket['local].
|
|
|
|
|
|
@racket[allow-null?] controls whether the pointer can take on null values, and @racket[null-value] controls what that value is. Defaults are @racket[#true] and @racket[0], respectively.
|
|
|
|
|
|
@racket[pointer-lazy?] controls whether the pointer is decoded immediately. If @racket[pointer-lazy?] is @racket[#true], then the decoding of the pointer is wrapped in a @tech{promise} that can later be evaluated with @racket[force]. Default is @racket[#false].
|
|
|
|
|
|
@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
|
|
|
|
|
|
@racket[base-class] controls the class used for instantiation of the new object.
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
@subsection{Bitfields}
|
|
|
|
|
|
@defmodule[xenomorph/bitfield]
|
|
|
|
|
|
A @deftech{bitfield} is a compact encoding for Boolean values, where each bit of an integer indicates @racket[#true] or @racket[#false] (depending on whether its value is @racket[1] or @racket[0]).
|
|
|
|
|
|
@defclass[x:bitfield% x:base% ()]{
|
|
|
Base class for bitfield formats. Use @racket[x:bitfield] to conveniently instantiate new bitfield formats.
|
|
|
|
|
|
@defproc[
|
|
|
(bitfield-relative-value?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] can be used as a value for the @racket[_bitfield-relative-to] field of @racket[x:bitfield%]. Valid choices are @racket['(local immediate parent global)].
|
|
|
}
|
|
|
|
|
|
@defconstructor[
|
|
|
([offset-type xenomorphic?]
|
|
|
[type x:int?]
|
|
|
[bitfield-relative-to bitfield-relative-value?]
|
|
|
[allow-null? boolean?]
|
|
|
[null-value any/c]
|
|
|
[bitfield-lazy? boolean?])]{
|
|
|
Create class instance that represents a bitfield format. See @racket[x:bitfield] for a description of the fields.
|
|
|
|
|
|
|
|
|
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:decode
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bitfield?]{
|
|
|
Returns a @tech{bitfield} of values whose length is @racket[_len] and where each value is @racket[_type].
|
|
|
}
|
|
|
|
|
|
@defmethod[
|
|
|
#:mode extend
|
|
|
(x:encode
|
|
|
[seq sequence?]
|
|
|
[input-port input-port?]
|
|
|
[parent (or/c xenomorphic? #false)])
|
|
|
bytes?]{
|
|
|
Take a @tech{sequence} @racket[seq] and encode it as a @tech{byte string}.
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
@defproc[
|
|
|
(x:bitfield?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is an object of type @racket[x:bitfield%].
|
|
|
}
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@defproc[
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(x:bitfield
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[ptr-type-arg (or/c xenomorphic? #false) #false]
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[type-arg (or/c x:int? 'void #false) #false]
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[#:type ptr-type-kw (or/c xenomorphic? #false) uint8]
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[#:type type-kw (or/c x:int? 'void #false) uint32]
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[#:relative-to bitfield-relative-to bitfield-relative-value? 'local]
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[#:allow-null allow-null? boolean? #true]
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[#:null null-value any/c 0]
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[#:lazy bitfield-lazy? boolean? #false]
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[#:pre-encode pre-encode-proc (or/c (any/c . -> . any/c) #false) #false]
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[#:post-decode post-decode-proc (or/c (any/c . -> . any/c) #false) #false]
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[#:base-class base-class (λ (c) (subclass? c x:bitfield%)) x:bitfield%]
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)
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x:bitfield?]{
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Generate an instance of @racket[x:bitfield%] (or a subclass of @racket[x:bitfield%]) with certain optional attributes.
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@racket[ptr-type-arg] or @racket[ptr-type-kw] (whichever is provided, though @racket[ptr-type-arg] takes precedence) controls the type of the thing being pointed at. Default is @racket[uint8].
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@racket[type-arg] or @racket[type-kw] (whichever is provided, though @racket[type-arg] takes precedence) controls the type of the bitfield value itself, which must be either an @racket[x:int?] or the symbol @racket['void] to indicate a void bitfield). Default is @racket[uint32].
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@racket[bitfield-relative-to] controls the style of bitfield, which must be one of @racket['(local immediate parent global)]. Default is @racket['local].
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@racket[allow-null?] controls whether the bitfield can take on null values, and @racket[null-value] controls what that value is. Defaults are @racket[#true] and @racket[0], respectively.
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@racket[bitfield-lazy?] controls whether the bitfield is decoded immediately. If @racket[bitfield-lazy?] is @racket[#true], then the decoding of the bitfield is wrapped in a @tech{promise} that can later be evaluated with @racket[force]. Default is @racket[#false].
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@racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decodeing procedures, respectively.
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@racket[base-class] controls the class used for instantiation of the new object.
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}
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@subsection{Enumerations}
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|
@defmodule[xenomorph/enum]
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|
@subsection{Optional}
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|
|
|
@defmodule[xenomorph/optional]
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|
@subsection{Reserved}
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|
|
@defmodule[xenomorph/reserved]
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|
@subsection{Utilities}
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|
|
|
|
@defmodule[xenomorph/util]
|
|
|
|
|
|
@defproc[
|
|
|
(length-resolvable?
|
|
|
[x any/c])
|
|
|
boolean?]{
|
|
|
Whether @racket[x] is something that can be used as a length argument with @racket[xenomorphic?] objects that have length. For instance, an @racket[x:list] or @racket[x:stream].
|
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|
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|
The following values are deemed to be resolvable: any @racket[exact-nonnegative-integer?], any @racket[procedure?] that returns a @racket[exact-nonnegative-integer?], or an @racket[x:int?].
|
|
|
}
|
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|
@section{License & source code}
|
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|
|
|
This module is licensed under the MIT license.
|
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|
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|
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|
Source repository at @link["http://github.com/mbutterick/xenomorph"]{http://github.com/mbutterick/xenomorph}. Suggestions & corrections welcome.
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