Crate scroll [−] [src]
Scroll
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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 scroll::{ctx, Pread}; let bytes: [u8; 4] = [0xde, 0xad, 0xbe, 0xef]; // we can use the Buffer type that scroll provides, or use it on regular byte slices (or anything that impl's `AsRef<[u8]>`) //let buffer = scroll::Buffer::new(bytes); let b = &bytes[..]; // reads a u32 out of `b` with Big Endian byte order, at offset 0 let i: u32 = b.pread_with(0, scroll::BE).unwrap(); // or a u16 - specify the type either on the variable or with the beloved turbofish let i2 = b.pread_with::<u16>(2, scroll::BE).unwrap(); // We can also skip the ctx by calling `pread`. // for the primitive numbers, this will default to the host machine endianness (technically it is whatever default `Ctx` the target type is impl'd for) let byte: u8 = b.pread(0).unwrap(); let i3: u32 = b.pread(0).unwrap(); // this will have the type `scroll::Error::BadOffset` because it tried to read beyond the bound let byte: scroll::Result<i64> = b.pread(0); // we can also get str and byte references from the underlying buffer/bytes using `pread_slice` let slice = b.pread_slice::<str>(0, 2).unwrap(); let byte_slice: &[u8] = b.pread_slice(0, 2).unwrap(); // here is an example of parsing a uleb128 custom datatype, which // uses the `ctx::DefaultCtx` let leb128_bytes: [u8; 5] = [0xde | 128, 0xad | 128, 0xbe | 128, 0xef | 128, 0x1]; // parses a uleb128 (variable length encoded integer) from the above bytes let uleb128: u64 = leb128_bytes.pread::<scroll::Uleb128>(0).unwrap().into(); assert_eq!(uleb128, 0x01def96deu64); // finally, we can also 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: &[u8] = b"hello_world\0more words"; let hello_world: &str = hello.pread(0).unwrap(); assert_eq!("hello_world", hello_world); // ... and this parses the string if its space separated! let spaces: &[u8] = b"hello world some junk"; let world: &str = spaces.pread_with(6, ctx::SPACE).unwrap(); assert_eq!("world", world);
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
/Gread
and/or Pwrite
/Gwrite
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 scroll::{self, ctx, Pread, BE}; struct Data<'a> { name: &'a str, id: u32, } // we could use a `(usize, endian::Scroll)` if we wanted #[derive(Debug, Clone, Copy, Default)] struct DataCtx { pub size: usize, pub endian: scroll::Endian } // note the lifetime specified here impl<'a> ctx::TryFromCtx<'a, (usize, DataCtx)> for Data<'a> { type Error = scroll::Error; // and the lifetime annotation on `&'a [u8]` here fn try_from_ctx (src: &'a [u8], (offset, DataCtx {size, endian}): (usize, DataCtx)) -> Result<Self, Self::Error> { let name = src.pread_slice::<str>(offset, size)?; let id = src.pread_with(offset+size, endian)?; Ok(Data { name: name, id: id }) } } let bytes = scroll::Buffer::new(b"UserName\x01\x02\x03\x04"); let data = bytes.pread_with::<Data>(0, DataCtx { size: 8, endian: BE }).unwrap(); assert_eq!(data.id, 0x01020304); assert_eq!(data.name.to_string(), "UserName".to_string());
Please see the Pread documentation examples
Modules
ctx |
Generic context-aware conversion traits, for automatic downstream extension of |
Structs
Buffer |
A byte buffer which is versed in both the Greater and Lesser arts |
Sleb128 |
An signed leb128 integer |
Uleb128 |
An unsigned leb128 integer |
Enums
Endian |
The endianness (byte order) of a stream of bytes |
Error |
A custom Scroll error |
Constants
BE |
Big Endian byte order context |
LE |
Little Endian byte order context |
LEB128 |
This context instructs the underlying |
NATIVE |
The machine's native byte order |
NETWORK |
Network byte order context |
Traits
Gread |
The Greater Read ( |
Gwrite |
The Greater Write ( |
Pread |
A very generic, contextual pread interface in Rust. Allows completely parallelized reads, as |
Pwrite |
Writes into |
TryOffsetWith |
Attempt to add an offset for a given |
Type Definitions
Leb128 |
A variable length integer parsing |
Result |