[![Actions][actions-badge]][actions-url] [![crates.io version][crates-scroll-badge]][crates-scroll] [actions-badge]: https://github.com/m4b/scroll/workflows/CI/badge.svg?branch=master [actions-url]: https://github.com/m4b/scroll/actions [crates-scroll-badge]: https://img.shields.io/crates/v/scroll.svg [crates-scroll]: https://crates.io/crates/scroll ## Scroll - cast some magic ```text _______________ ()==( (@==() '______________'| | | | ἀρετή | __)_____________| ()==( (@==() '--------------' ``` ### Documentation https://docs.rs/scroll ### Usage Add to your `Cargo.toml` ```toml, no_test [dependencies] scroll = "0.11" ``` ### 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::(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::(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 = 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::()?; // ..ditto let bar = bytes.ioread::()?; 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::` 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::(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!