Implement safe API for ripemd160

[austinabell]

This could have use cases, so we should support this interface. Unlike the APIs that exist within the SDK for other hash functions, an array of 20 bytes should be returned ([u8; 20]), since it is guaranteed this is always the length and fixed.

API should look roughly like:

pub fn ripemd(value: &[u8]) -> [u8; 20] {
 // ...
}

and live in near_sdk::env

[austinabell]

This will be made very easy after #646 comes in

[itegulov]

@austinabell While trying to implement a safe API call for RIPEMD-160 (based on top of #646 as per your last comment), I encountered this error:

  = note: /usr/bin/ld: /home/itegulov/Work/near/near-sdk-rs/target/debug/deps/near_sdk-56b2f12843352185.c0qiw6jpquo2vdz.rcgu.o: in function `near_sdk::environment::env::ripemd160_hash':
          /home/itegulov/Work/near/near-sdk-rs/near-sdk/src/environment/env.rs:294: undefined reference to `ripemd160'
          collect2: error: ld returned 1 exit status
          
  = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)

At first, I thought this was because of the old nearcore crate (as ripemd160 seems to have been introduced fairly recently) so I tried rebasing on top of #639. Unfortunately the issue did not go away and I am not sure what I am doing wrong... Maybe I need to re-generate something? My branch is here: https://github.com/near/near-sdk-rs/tree/safe-api-ripemd-160

[itegulov]

Nevermind, just took a look at literally the next issue in the list (#631) and instantly realized what went wrong 🤦 I was missing a mocked implementation of ripemd160...

[austinabell]

My apologies, forgot to link to that PR! You only need this for mocked implementation and you are trying to write a unit test