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diff --git a/third_party/rust/scroll/README.md b/third_party/rust/scroll/README.md new file mode 100644 index 0000000000..717fe6a234 --- /dev/null +++ b/third_party/rust/scroll/README.md @@ -0,0 +1,193 @@ + [](https://travis-ci.org/m4b/scroll) +## Scroll - cast some magic + +```text + _______________ + ()==( (@==() + '______________'| + | | + | ἀρετή | + __)_____________| + ()==( (@==() + '--------------' + +``` + +### Documentation + +https://docs.rs/scroll + +### Usage + +Add to your `Cargo.toml` + +```toml, no_test +[dependencies] +scroll = "0.10" +``` + +### 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: + +```rust +use scroll::{ctx, Pread, LE}; + +fn main() -> Result<(), scroll::Error> { + let bytes: [u8; 4] = [0xde, 0xad, 0xbe, 0xef]; + + // reads a u32 out of `b` with the endianness of the host machine, at offset 0, turbofish-style + let number: u32 = bytes.pread::<u32>(0)?; + // ...or a byte, with type ascription on the binding. + let byte: u8 = bytes.pread(0)?; + + //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(0, scroll::BE)?; + // or a u16 - specify the type either on the variable or with the beloved turbofish + let be_number2 = bytes.pread_with::<u16>(2, scroll::BE)?; + + // 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: scroll::Result<i64> = bytes.pread(0); + + // 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: &[u8] = b"hello_world\0more words"; + let hello_world: &str = hello.pread(0)?; + assert_eq!("hello_world", hello_world); + + // ... and this parses the string if its space separated! + use scroll::ctx::*; + let spaces: &[u8] = b"hello world some junk"; + let world: &str = spaces.pread_with(6, StrCtx::Delimiter(SPACE))?; + assert_eq!("world", world); + Ok(()) +} +``` + +### Deriving `Pread` and `Pwrite` + +Scroll implements a custom derive that can provide `Pread` and `Pwrite` implementations for your structs. + +```rust +use scroll::{Pread, Pwrite, BE}; + +#[derive(Pread, Pwrite)] +struct Data { + one: u32, + two: u16, + three: u8, +} + +fn main() -> Result<(), scroll::Error> { + let bytes: [u8; 7] = [0xde, 0xad, 0xbe, 0xef, 0xfa, 0xce, 0xff]; + // Read a single `Data` at offset zero in big-endian byte order. + let data: Data = bytes.pread_with(0, BE)?; + assert_eq!(data.one, 0xdeadbeef); + assert_eq!(data.two, 0xface); + assert_eq!(data.three, 0xff); + + // Write it back to a buffer + let mut out: [u8; 7] = [0; 7]; + out.pwrite_with(data, 0, BE)?; + assert_eq!(bytes, out); + Ok(()) +} +``` + +This feature is **not** enabled by default, you must enable the `derive` feature in Cargo.toml to use it: + +```toml, no_test +[dependencies] +scroll = { version = "0.10", features = ["derive"] } +``` + +# `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: + +```rust +use std::io::Cursor; +use scroll::IOread; + +fn main() -> Result<(), scroll::Error> { + let bytes_ = [0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0xef,0xbe,0x00,0x00,]; + let mut bytes = Cursor::new(bytes_); + + // this will bump the cursor's Seek + let foo = bytes.ioread::<usize>()?; + // ..ditto + let bar = bytes.ioread::<u32>()?; + Ok(()) +} +``` + +Similarly, we can write to anything that implements `std::io::Write` quite naturally: + +```rust +use scroll::{IOwrite, LE, BE}; +use std::io::{Write, Cursor}; + +fn main() -> Result<(), scroll::Error> { + let mut bytes = [0x0u8; 10]; + let mut cursor = Cursor::new(&mut bytes[..]); + cursor.write_all(b"hello")?; + cursor.iowrite_with(0xdeadbeef as u32, BE)?; + assert_eq!(cursor.into_inner(), [0x68, 0x65, 0x6c, 0x6c, 0x6f, 0xde, 0xad, 0xbe, 0xef, 0x0]); + Ok(()) +} +``` + +# 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](trait.TryFromCtx.html) 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. + +```rust +use scroll::{ctx, Pread, BE, Endian}; + +struct Data<'a> { + name: &'a str, + id: u32, +} + +// note the lifetime specified here +impl<'a> ctx::TryFromCtx<'a, Endian> for Data<'a> { + type Error = scroll::Error; + // and the lifetime annotation on `&'a [u8]` here + fn try_from_ctx (src: &'a [u8], endian: Endian) + -> Result<(Self, usize), Self::Error> { + let offset = &mut 0; + let name = src.gread::<&str>(offset)?; + let id = src.gread_with(offset, endian)?; + Ok((Data { name: name, id: id }, *offset)) + } +} + +fn main() -> Result<(), scroll::Error> { + let bytes = b"UserName\x00\x01\x02\x03\x04"; + let data = bytes.pread_with::<Data>(0, BE)?; + assert_eq!(data.id, 0x01020304); + assert_eq!(data.name.to_string(), "UserName".to_string()); + Ok(()) +} +``` + +Please see the official documentation, or a simple [example](examples/data_ctx.rs) for more. + +# Contributing + +Any ideas, thoughts, or contributions are welcome! |