#derive #data #segment #memory

macro segsource-derive

Derive implementations for segsource. You should use segsource instead.

2 unstable releases

0.2.0 Jul 11, 2021
0.1.0 Jul 6, 2021

#191 in #data

Used in segsource

MIT license



Segsource is a crate designed to assist in reading data. Although is specifically designed with binary (u8) data, it is not limited to this.


Segsource is designed to easily and efficiently allow the reading of data without using much memory. It does this by having two basic concepts: [Source]s, which own the data and [Segment]s which allow access the data.

Each [Segment] is a thread-safe struct that retains minimal basic information such as the position of an internal cursor (expressed via the [Segment::current_offset] method), a reference to this data, etcetera.

Feature Flags

The following features are available for segsource:

  1. async which adds support for various async operations using tokio.
  2. derive which includes several macros for creating structs from [Segment]s.
  3. mmap which adds support for memory mapped files.
  4. std which adds support for file and I/O operations.
  5. with_bytes which adds support for using the bytes crate.

Of these, only derive and std are enabled by default.

Why segsource?

There are various other crates out there in a similar vein to segsource, and in your use case, some of them might be a better idea. I'll go through a few of the other options and let you decide for yourself:

  • bytes: segsource actually offers native support for bytes crate via the appropriately named bytes feature. While bytes is great, it does have its limitations, the two biggest ones being the most read operations require it to be mutable and that there's no way to go "back". Segsource solves both of these cases.

  • binread: Not a replacement for segsource as a whole, but for the derivations provided via the derive feature. As of this writing, binread is more feature rich than segsource's derives (and since [Segment]s extend std::io::Seek and std::io::Read, they will work with binread]. Unfortunately, this again requires the passed in

  • bitvec: You may have noticed that you can essentially do simple memory emulation with segsource (e.g. you can have an initial offset, you work in offsets, etcetera). Simple, being the keyword here. bitvec` is not simple nor can it be given its scope.

  • std: You could use various items from the standard library, such as a Vec or an io::Cursor, but all of these have limitations (e.g. a Vec can't have an initial offset and a can only move relative to its current position).


Documentation is on my TODO list...


Instead of indexes, segsource use offsets. Depending on your use case, these will probably end up being the same. However, you can specify an initial offset that will essentially change the index from zero to whatever the initial_offset is.

For example:

let test_data = [0x00, 0x01, 0x02, 0x03, 0x04, 0x05];
let source = SourceOfYourChoice::from_u8_slice_with_offset(&test_data, 100, Endidness::Big).
let segment = source.all().unwrap();
assert_eq!(segment.u8_at(100).unwrap(), 0);


One thing you may have noticed is that we had to unwrap the value each time. This is because methods first check to make an offset is valid. For example:

assert!(matches!(segment.u8_at(99), Err(Error::OffsetTooSmall { offset :99 })));

License: MIT


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