2 stable releases
1.1.0 | Aug 8, 2023 |
---|---|
1.0.0 | Apr 6, 2023 |
#1668 in Encoding
470 downloads per month
Used in 6 crates
(2 directly)
38KB
754 lines
compact-encoding
A series of compact encoding schemes in Rust for building small and fast parsers and serializers. Binary compatible with the original Javascript compact-encoding library.
License
MIT OR Apache-2.0
lib.rs
:
Series of compact encoding schemes for building small and fast parsers and serializers
Binary compatible with the original Javascript compact-encoding library.
Usage
Basic
Using only the types implemented here (replace unwrap()
with proper
handling of [EncodingError]):
use compact_encoding::{CompactEncoding, State};
// Start with an empty state
let mut enc_state = State::new();
let number = 41_u32;
let str = "hi".to_string();
// Use preencode to figure out how big a buffer is needed
enc_state.preencode(&number).unwrap();
enc_state.preencode(&str).unwrap();
// Create buffer of pre-encoded size
let mut buffer = enc_state.create_buffer();
assert_eq!(buffer.len(), 1 + 1 + 2);
// Then actually encode the values
enc_state.encode(&number, &mut buffer).unwrap();
enc_state.encode(&str, &mut buffer).unwrap();
assert_eq!(buffer.to_vec(), vec![41_u8, 2_u8, b'h', b'i']);
// On the decoding end, create a state from byte buffer
let mut dec_state = State::from_buffer(&buffer);
let number_dec: u32 = dec_state.decode(&buffer).unwrap();
let str_dec: String = dec_state.decode(&buffer).unwrap();
assert_eq!(number_dec, number);
assert_eq!(str_dec, str);
Custom
If you want to encode your own structs directly, you can do that
by implementing [CompactEncoding] yourself (replace unwrap()
with proper
handling of [EncodingError]):
use compact_encoding::{CompactEncoding, EncodingError, State};
#[derive(Debug, PartialEq)]
struct MyStruct {
my_flag_1: bool,
my_flag_2: bool,
my_values: Vec<[u8; 32]>,
}
impl CompactEncoding<MyStruct> for State {
fn preencode(&mut self, value: &MyStruct) -> Result<usize, EncodingError> {
self.add_end(1)?; // flags
if !value.my_values.is_empty() {
self.preencode(&value.my_values)?;
}
Ok(self.end())
}
fn encode(&mut self, value: &MyStruct, buffer: &mut [u8]) -> Result<usize, EncodingError> {
let mut flags: u8 = 0;
if value.my_flag_1 {
flags |= 1;
}
if value.my_flag_2 {
flags |= 2;
}
if !value.my_values.is_empty() {
flags |= 4;
}
self.encode(&flags, buffer)?;
if !value.my_values.is_empty() {
self.encode(&value.my_values, buffer)?;
}
Ok(self.start())
}
fn decode(&mut self, buffer: &[u8]) -> Result<MyStruct, EncodingError> {
let flags: u8 = self.decode(buffer)?;
let my_flag_1: bool = flags & 1 != 0;
let my_flag_2: bool = flags & 2 != 0;
let my_values: Vec<[u8; 32]> = if flags & 4 != 0 {
self.decode(buffer)?
} else {
vec![]
};
Ok(MyStruct {
my_flag_1,
my_flag_2,
my_values
})
}
}
// Test values
let empty = MyStruct {
my_flag_1: false,
my_flag_2: true,
my_values: vec![]
};
let non_empty = MyStruct {
my_flag_1: true,
my_flag_2: false,
my_values: vec![[1; 32], [2; 32]]
};
// Start with an empty state
let mut enc_state = State::new();
enc_state.preencode(&empty).unwrap();
enc_state.preencode(&non_empty).unwrap();
let mut buffer = enc_state.create_buffer();
// With the above use of a flags byte, the empty value encodes to only one byte
assert_eq!(buffer.len(), 1 + 1 + 1 + 2 * 32);
// Then actually encode the values
enc_state.encode(&empty, &mut buffer).unwrap();
enc_state.encode(&non_empty, &mut buffer).unwrap();
// On the decoding end, create a state from byte buffer
let mut dec_state = State::from_buffer(&buffer);
// And decode directly to your own struct
let empty_dec: MyStruct = dec_state.decode(&buffer).unwrap();
let non_empty_dec: MyStruct = dec_state.decode(&buffer).unwrap();
assert_eq!(empty_dec, empty);
assert_eq!(non_empty_dec, non_empty);
NB: This only works if you don't export your struct out of your crate.
If you export the struct, orphan rule will require you to
implement a wrapper for [State], e.g. struct MyState(State);
and implement
[CompactEncoding] for the wrapper struct instead.