feat(engine): add experimental REST/SSZ /new-payload-with-witness endpoint - #24617
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This PR introduces an experimental
POST /new-payload-with-witnessREST endpoint to Reth, as a complement to the existingengine_newPayloadV5JSON-RPC method.The current approach to witness retrieval requires two separate operations,
engine_newPayloadanddebug_executionWitness, both of which use JSON serialization. For large witnesses, JSON encoding introduces roughly 2× size overhead, making the process slow and bandwidth-intensive.This endpoint combines both operations into a single HTTP call using SSZ serialization, dramatically improving performance:
Benchmarked against a 500 MB witness, a worst-case, constructible block.
It is also important to note that there are ongoing discussions around introducing SSZ + HTTP to the Engine API more broadly, replacing JSON-RPC entirely, including proposals to combine "new-payload" execution and witness retrieval into a single operation. Once these discussions mature, we can standardize around a unified approach. However, this is a significant architectural change and will likely take time to reach consensus.
Engine: add Rest-SSZ spec
ethereum/execution-apis#793
Add SSZ to Engine API
ethereum/execution-apis#764
Proposal: opt-in witness retrieval via flag on existing engine methods
ethereum/execution-apis#799