Scroll - cast some magic
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Documentation
Usage
Add to your Cargo.toml
[]
= "0.7.0"
Overview
Scroll implements several traits for read/writing generic containers (byte buffers are currently implemented by default). Most familiar will likely be the Pread
trait, which at its basic takes an immutable reference to self, an immutable offset to read at, (and a parsing context, more on that later), and then returns the deserialized value.
Because self is immutable, all reads can be performed in parallel and hence are trivially parallelizable.
A simple example demonstrates its flexibility:
use ;
let bytes: = ;
// reads a u32 out of `b` with the endianness of the host machine, at offset 0, turbofish-style
let number: u32 = bytes..unwrap;
// ...or a byte, with type ascription on the binding.
let byte: u8 = bytes.pread.unwrap;
//If the type is known another way by the compiler, say reading into a struct field, we can omit the turbofish, and type ascription altogether!
// If we want, we can explicitly add a endianness to read with by calling `pread_with`.
// The following reads a u32 out of `b` with Big Endian byte order, at offset 0
let be_number: u32 = bytes.pread_with.unwrap;
// or a u16 - specify the type either on the variable or with the beloved turbofish
let be_number2 = bytes..unwrap;
// Scroll has core friendly errors (no allocation). This will have the type `scroll::Error::BadOffset` because it tried to read beyond the bound
let byte: Result = bytes.pread;
// Scroll is extensible: as long as the type implements `TryWithCtx`, then you can read your type out of the byte array!
// We can parse out custom datatypes, or types with lifetimes
// if they implement the conversion trait `TryFromCtx`; here we parse a C-style \0 delimited &str (safely)
let hello: & = b"hello_world\0more words";
let hello_world: &str = hello.pread.unwrap;
assert_eq!;
// ... and this parses the string if its space separated!
use *;
let spaces: & = b"hello world some junk";
let world: &str = spaces.pread_with.unwrap;
assert_eq!;
std::io
API
Scroll can also read/write simple types from a std::io::Read
or std::io::Write
implementor. The built-in numeric types are taken care of for you. If you want to read a custom type, you need to implement the FromCtx
(how to parse) and SizeWith
(how big the parsed thing will be) traits. You must compile with default features. For example:
use Cursor;
use IOread;
let bytes_ = ;
let mut bytes = new;
// this will bump the cursor's Seek
let foo = bytes..unwrap;
// ..ditto
let bar = bytes..unwrap;
Similarly, we can write to anything that implements std::io::Write
quite naturally:
use ;
use ;
let mut bytes = ;
let mut cursor = new;
cursor.write_all.unwrap;
cursor.iowrite_with.unwrap;
assert_eq!;
Advanced Uses
Scroll is designed to be highly configurable - it allows you to implement various context (Ctx
) sensitive traits, which then grants the implementor automatic uses of the Pread
and/or Pwrite
traits.
For example, suppose we have a datatype and we want to specify how to parse or serialize this datatype out of some arbitrary byte buffer. In order to do this, we need to provide a TryFromCtx impl for our datatype.
In particular, if we do this for the [u8]
target, using the convention (usize, YourCtx)
, you will automatically get access to
calling pread_with::<YourDatatype>
on arrays of bytes.
use ;
// note the lifetime specified here
let bytes = b"UserName\x00\x01\x02\x03\x04";
let data = bytes..unwrap;
assert_eq!;
assert_eq!;
Please see the official documentation, or a simple example for more.
Contributing
Any ideas, thoughts, or contributions are welcome!