Accept/Support Custom Header Hasher from Parachain

[AurevoirXavier]

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• This is not a support question.

Description of bug

Some parachains use their own Hash type.

For instance, Hyperbridge defines a custom hash implementation (keccak256).

I discovered this while trying to match a Hyperbridge block with the Polkadot event’s parainclusion::CandidateIncluded.para_head field. Unfortunately, all the hash values were mismatched, making it impossible to index the Hyperbridge block based on the para_head value.

It seems that Polkadot assumes the use of blake2_256 for generating hashes, which may not align with Hyperbridge’s implementation.

Might relate to #5224?

Steps to reproduce

No response

[bkchr]

parainclusion::CandidateIncluded.para_head this is a field of a relay chain structure. That right now the hash matches most of the parachain header hashes is a coincidence, not done this way by design. There could be other chains which may insert different data to the head or just store a hash in para head. All of that is possible. These para_head hash is required by the internals of the relay chain and can not be changed.

For your request, the best is that you directly fetch all the heads and match them to the parachains. The paras::Heads will give you directly the mapping from ParaId to Head.

[AurevoirXavier]

That right now the hash matches most of the parachain header hashes is a coincidence, not done this way by design. There could be other chains which may insert different data to the head or just store a hash in para head.

Make sense.