engine: drop fcU v4 from SSZ_CAPABILITIES until ELs ship target_gas_limit#6
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engine: drop fcU v4 from SSZ_CAPABILITIES until ELs ship target_gas_limit#6barnabasbusa wants to merge 1 commit into
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…imit PayloadAttributesV4 gained `target_gas_limit: uint64` in execution-apis PR #796 (commit a22fbd4, JSON spec) and we plumbed the field through in 0a1418b ("plumb target_gas_limit through PayloadAttributesV4 (alpha 8)"). The SSZ-encoding spec on PR #764 only just gained the matching container update on the `bbusa/ssz` branch, and EL implementations (nethermind glamsterdam-devnet-4 SSZ wire, geth) still decode PayloadAttributesV4 with the old 6-field layout. Our 8 extra trailing bytes shift the inner withdrawals offset and the EL replies `400 Malformed SSZ body` for every fcU at slot transition once Gloas is active. Workaround: stop advertising `POST /engine/v4/forkchoice` so fcU v4 falls back to JSON-RPC. JSON tolerates the unknown `targetGasLimit` field today, so the alpha-8 value still reaches the EL — it's just ignored for now. All other SSZ endpoints (newPayload, getPayload, fcU v1/v2/v3, blobs, etc.) stay advertised. Re-add the line once nethermind PR #11646 lands and a matching geth change ships.
🤖 qu0b-reviewerClean diff, well-scoped. No issues found. The PR drops Reviewed @ |
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Summary
POST /engine/v4/forkchoiceinSSZ_CAPABILITIESso engine_forkchoiceUpdatedV4 falls back to JSON-RPC for Gloas/Amsterdam.Engine API error 400: Malformed SSZ bodyon every fcU at slot transition once Gloas is active.Why
We added
target_gas_limit: uint64toPayloadAttributesV4SSZ container in 0a1418b ("plumb target_gas_limit through PayloadAttributesV4 (alpha 8)") to match execution-apis PR #796 (JSON spec landed as a22fbd4).But the SSZ-encoding spec on execution-apis PR #764 only just got the matching container change (commit 949d6a8 on
bbusa/ssz). EL implementations (nethermindglamsterdam-devnet-4, geth) still decodePayloadAttributesV4with the old 6-field layout — our 8 extra trailing bytes shift the inner withdrawals offset and the EL replies400 Malformed SSZ body.JSON-RPC tolerates unknown fields, so the alpha-8
targetGasLimitstill reaches the EL on the JSON path — it's just ignored for now until ELs ship support.How to undo
Re-add
\"POST /engine/v4/forkchoice\"toSSZ_CAPABILITIESonce:Test plan
Malformed SSZ bodytargetGasLimitstill appears in the JSON-RPC fcU body (already gated on the gloas fork epoch in node.py:1371)Engine SSZ transport negotiated: N endpointslog line)