Add SSZ response to HTTP API endpoints

[PoulavBhowmick03]

Issue Addressed

Closes #8892

Proposed Changes

Adds SSZ response support to several endpoints for Beacon API spec compliance.

• GET /eth/v1/beacon/states/{state_id}/pending_consolidations
• GET /eth/v1/beacon/states/{state_id}/pending_deposits
• GET /eth/v1/beacon/states/{state_id}/pending_partial_withdrawals
• GET /eth/v2/validator/aggregate_attestation
• GET /eth/v1/validator/attestation_data
• POST /eth/v1/beacon/states/{state_id}/validator_identities

[eserilev]

Thanks for working on this. Can you write tests for the ssz routes? There's examples in the codebase for other ssz routes we test that you can use as an example

[PoulavBhowmick03]

Thanks for working on this. Can you write tests for the ssz routes? There's examples in the codebase for other ssz routes we test that you can use as an example

Sure! Doing so

[chong-he]

CI is failing, can you address it @PoulavBhowmick03? Thanks

Edit: looks like it is due to an update in cargo sort that causes it to fail. please ignore it.

[chong-he]

I have tested the endpoints and they are working.

I think we should also add the SSZ-equivalent test for: test_get_validator_attestation_data and test_beacon_states_validator_identities as well. Would be great to have those tests

[PoulavBhowmick03]

@chong-he do take a look again! thanks

[chong-he]

Thanks for the changes, I can see the tests are added, but I got another comment as below. I am sorry for another back-and-forth as I should have identified this and commented in the last review but I didn't realize this back then.

[chong-he]

CI is failing

You can run the test locally: cargo test -p http_api --release test_name to be sure that it is happy

[chong-he]

I just did a very minor rearrange for the function post_bytes_opt_accept_header so that all the post_with_timeout_* are together.

This PR looks great now. Thanks for sticking on it.

[chong-he]

merge conflict if you have time to resolve, that will be great @PoulavBhowmick03

[PoulavBhowmick03]

merge conflict if you have time to resolve, that will be great @PoulavBhowmick03

Fixed the merge conflicts!

[mergify]

Some required checks have failed. Could you please take a look @PoulavBhowmick03? 🙏

[chong-he]

Some more conflicts to resolve @PoulavBhowmick03

[mergify]

Hi @PoulavBhowmick03, this pull request has been closed automatically due to 30 days of inactivity. If you’d like to continue working on it, feel free to reopen at any time.

[mergify]

Queued — the merge queue status continues in this comment ↓.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-08-14 01:19 UTC · Rule: default · triggered by @chong-he with the merge queue checkbox
• ✅ Checks passed · on draft merge queue: checking unstable (4bae7c9) and #8907 together #9809
• ✅ Merged — 2026-08-14 01:50 UTC · at 65089cd99481a86b5a485b3ddd416fe0e07beab9 · squash

This pull request spent 30 minutes 51 seconds in the queue, including 29 minutes 19 seconds running CI.

Required conditions to merge

• check-success=local-testnet-success
• check-success=test-suite-success
• github-review-approved [🛡 GitHub branch protection]
  • Add SSZ response to HTTP API endpoints #8907