1 [![Build Status](https://travis-ci.org/m4b/scroll.svg?branch=master)](https://travis-ci.org/m4b/scroll)
2 ## Scroll - cast some magic
18 https://docs.rs/scroll
22 Add to your `Cargo.toml`
31 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.
33 Because self is immutable, _**all** reads can be performed in parallel_ and hence are trivially parallelizable.
35 A simple example demonstrates its flexibility:
38 use scroll::{ctx, Pread, LE};
40 fn main() -> Result<(), scroll::Error> {
41 let bytes: [u8; 4] = [0xde, 0xad, 0xbe, 0xef];
43 // reads a u32 out of `b` with the endianness of the host machine, at offset 0, turbofish-style
44 let number: u32 = bytes.pread::<u32>(0)?;
45 // ...or a byte, with type ascription on the binding.
46 let byte: u8 = bytes.pread(0)?;
48 //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!
50 // If we want, we can explicitly add a endianness to read with by calling `pread_with`.
51 // The following reads a u32 out of `b` with Big Endian byte order, at offset 0
52 let be_number: u32 = bytes.pread_with(0, scroll::BE)?;
53 // or a u16 - specify the type either on the variable or with the beloved turbofish
54 let be_number2 = bytes.pread_with::<u16>(2, scroll::BE)?;
56 // Scroll has core friendly errors (no allocation). This will have the type `scroll::Error::BadOffset` because it tried to read beyond the bound
57 let byte: scroll::Result<i64> = bytes.pread(0);
59 // Scroll is extensible: as long as the type implements `TryWithCtx`, then you can read your type out of the byte array!
61 // We can parse out custom datatypes, or types with lifetimes
62 // if they implement the conversion trait `TryFromCtx`; here we parse a C-style \0 delimited &str (safely)
63 let hello: &[u8] = b"hello_world\0more words";
64 let hello_world: &str = hello.pread(0)?;
65 assert_eq!("hello_world", hello_world);
67 // ... and this parses the string if its space separated!
69 let spaces: &[u8] = b"hello world some junk";
70 let world: &str = spaces.pread_with(6, StrCtx::Delimiter(SPACE))?;
71 assert_eq!("world", world);
76 ### Deriving `Pread` and `Pwrite`
78 Scroll implements a custom derive that can provide `Pread` and `Pwrite` implementations for your structs.
81 use scroll::{Pread, Pwrite, BE};
83 #[derive(Pread, Pwrite)]
90 fn main() -> Result<(), scroll::Error> {
91 let bytes: [u8; 7] = [0xde, 0xad, 0xbe, 0xef, 0xfa, 0xce, 0xff];
92 // Read a single `Data` at offset zero in big-endian byte order.
93 let data: Data = bytes.pread_with(0, BE)?;
94 assert_eq!(data.one, 0xdeadbeef);
95 assert_eq!(data.two, 0xface);
96 assert_eq!(data.three, 0xff);
98 // Write it back to a buffer
99 let mut out: [u8; 7] = [0; 7];
100 out.pwrite_with(data, 0, BE)?;
101 assert_eq!(bytes, out);
106 This feature is **not** enabled by default, you must enable the `derive` feature in Cargo.toml to use it:
110 scroll = { version = "0.10", features = ["derive"] }
115 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:
121 fn main() -> Result<(), scroll::Error> {
122 let bytes_ = [0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0xef,0xbe,0x00,0x00,];
123 let mut bytes = Cursor::new(bytes_);
125 // this will bump the cursor's Seek
126 let foo = bytes.ioread::<usize>()?;
128 let bar = bytes.ioread::<u32>()?;
133 Similarly, we can write to anything that implements `std::io::Write` quite naturally:
136 use scroll::{IOwrite, LE, BE};
137 use std::io::{Write, Cursor};
139 fn main() -> Result<(), scroll::Error> {
140 let mut bytes = [0x0u8; 10];
141 let mut cursor = Cursor::new(&mut bytes[..]);
142 cursor.write_all(b"hello")?;
143 cursor.iowrite_with(0xdeadbeef as u32, BE)?;
144 assert_eq!(cursor.into_inner(), [0x68, 0x65, 0x6c, 0x6c, 0x6f, 0xde, 0xad, 0xbe, 0xef, 0x0]);
151 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.
153 For example, suppose we have a datatype and we want to specify how to parse or serialize this datatype out of some arbitrary
154 byte buffer. In order to do this, we need to provide a [TryFromCtx](trait.TryFromCtx.html) impl for our datatype.
156 In particular, if we do this for the `[u8]` target, using the convention `(usize, YourCtx)`, you will automatically get access to
157 calling `pread_with::<YourDatatype>` on arrays of bytes.
160 use scroll::{ctx, Pread, BE, Endian};
167 // note the lifetime specified here
168 impl<'a> ctx::TryFromCtx<'a, Endian> for Data<'a> {
169 type Error = scroll::Error;
170 // and the lifetime annotation on `&'a [u8]` here
171 fn try_from_ctx (src: &'a [u8], endian: Endian)
172 -> Result<(Self, usize), Self::Error> {
174 let name = src.gread::<&str>(offset)?;
175 let id = src.gread_with(offset, endian)?;
176 Ok((Data { name: name, id: id }, *offset))
180 fn main() -> Result<(), scroll::Error> {
181 let bytes = b"UserName\x00\x01\x02\x03\x04";
182 let data = bytes.pread_with::<Data>(0, BE)?;
183 assert_eq!(data.id, 0x01020304);
184 assert_eq!(data.name.to_string(), "UserName".to_string());
189 Please see the official documentation, or a simple [example](examples/data_ctx.rs) for more.
193 Any ideas, thoughts, or contributions are welcome!