Crate multihash_derive

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Expand description

A procedural macro for custom Multihash code tables.

This proc macro derives a custom Multihash code table from a list of hashers. It also generates a public type called Multihash which corresponds to the specified alloc_size.

The digests are stack allocated with a fixed size. That size needs to be big enough to hold any of the specified hash digests. This cannot be determined reliably on compile-time, hence it needs to set manually via the alloc_size attribute. Also you might want to set it to bigger sizes then necessarily needed for backwards/forward compatibility.

If you set #mh(alloc_size = …) to a too low value, you will get compiler errors. Please note the the sizes are checked only on a syntactic level and not on the type level. This means that digest need to have a size const generic, which is a valid usize, for example 32 or 64.

You can disable those compiler errors with setting the no_alloc_size_errors attribute. This can be useful if you e.g. have specified type aliases for your hash digests and you are sure you use the correct value for alloc_size.

When you want to define your own codetable, you should only depend on multihash-derive. It re-exports the multihash crate for you.

§Example

```ignore : proc-macro-crate does not work in docs, see https://github.com/bkchr/proc-macro-crate/issues/14 use multihash_derive::{Hasher, MultihashDigest};

struct FooHasher;

impl Hasher for FooHasher { // Implement hasher …

§fn update(&mut self, input: &u8) {

§

§}

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§fn finalize(&mut self) -> &u8 {

§&[]

§}

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§fn reset(&mut self) {

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§}

}

#[derive(Clone, Copy, Debug, Eq, MultihashDigest, PartialEq)] #[mh(alloc_size = 64)] pub enum Code { #[mh(code = 0x01, hasher = FooHasher)] Foo }

let hash = Code::Foo.digest(b“hello world!“);

println!(“{:02x?}”, hash);

Structs§

  • Error
    Opaque error struct for operations involving a Multihash.
  • Multihash
    A Multihash instance that only supports the basic functionality and no hashing.
  • UnsupportedCode
    The given code is not supported by this codetable.

Traits§

Derive Macros§