incompatibilities with big-endian target platforms / CPU architectures

[decathorpe]

I'm working on packaging this crate for Fedora Linux as a dependency of cargo-deny / cargo-audit. I noticed that tests fail on one of our officially supported architectures - the only big-endian architecture we support, s390x / IBM System Z.

From the output of cargo test --release (plus a few more distribution-specific flags):

...
test utils::test::canonicalizes_git_urls ... FAILED
test utils::test::matches_cargo ... FAILED
...
failures:
---- utils::test::canonicalizes_git_urls stdout ----
thread 'utils::test::canonicalizes_git_urls' panicked at src/utils.rs:298:9:
assertion `left == right` failed
  left: "git.luolix.top-016fae53232cc64d"
 right: "git.luolix.top-1b7079c2183ff52e"
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
---- utils::test::matches_cargo stdout ----
thread 'utils::test::matches_cargo' panicked at src/utils.rs:324:9:
assertion `left == right` failed
  left: ("registry/index/git.luolix.top-eae4ba8cbf2ce1c7", "https://github.com/rust-lang/crates.io-index")
 right: ("registry/index/git.luolix.top-1ecc6299db9ec823", "https://github.com/rust-lang/crates.io-index")
failures:
    utils::test::canonicalizes_git_urls
    utils::test::matches_cargo
test result: FAILED. 12 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s

From what I can tell, this is caused by this function:
https://github.com/EmbarkStudios/tame-index/blob/0.7.1/src/utils.rs#L18-L37

I think this chunk of code does not produce the same results on little-endian and big-endian architectures, and will produce results that are unexpectedly "shuffled" according to the different byte order:

    const CHARS: &[u8] = b"0123456789abcdef";

    for (i, &byte) in input.iter().enumerate() {
        let i = i * 2;
        output[i] = CHARS[(byte >> 4) as usize];
        output[i + 1] = CHARS[(byte & 0xf) as usize];
    }

[Jake-Shadle]

This is the same algorithm that cargo uses, is cargo not packaged for that target as well?

u64 hash -> bytes

https://github.com/rust-lang/cargo/blob/0871c0e2f4b6d4f95b7408fb8cef8ad3c9c8d834/src/cargo/util/hex.rs#L7

bytes -> string

https://github.com/KokaKiwi/rust-hex/blob/c333cf5128b6f5135d8f561b217f68e670275031/src/lib.rs#L106-L112

I can of course fix this so it is consistent for big endian targets, but AFAICT the directory will be different on big endian machines, according to cargo's own tests

https://github.com/rust-lang/cargo/blob/0871c0e2f4b6d4f95b7408fb8cef8ad3c9c8d834/src/cargo/core/source_id.rs#L930-L936

I think the best option is to to do the same as cargo and ignore the tests on big endian machines, the tests are just to verify we match cargo, if they pass on little endian they will also match on big endian.

[decathorpe]

Oh, of course, if cargo does the exact same thing, then the results will match (even if they are different depending on architecture endianness) ... thanks for the clarification and the "fix" :) 👍🏼