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Make MEV decoding less strict for Deneb encoded responses. #7045

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Merged
tersec merged 3 commits into from
Apr 2, 2025
Merged

Make MEV decoding less strict for Deneb encoded responses. #7045

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df0bb13
Disable strict requirement for `eth-consensus-version` header for Den…
cheatfate Apr 1, 2025
26043cc
Making it working with weird specification requirements, with `eth-co…
cheatfate Apr 2, 2025
55e479b
Address review comments.
cheatfate Apr 2, 2025
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23 changes: 12 additions & 11 deletions beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -3285,17 +3285,7 @@ proc decodeBytesJsonOrSsz*(
version: string
): Result[T, RestErrorMessage] =
var res {.noinit.}: T

let
typeFork = kind(typeof(res.data))
consensusFork = ConsensusFork.decodeString(version).valueOr:
return err(RestErrorMessage.init(Http400, UnableDecodeVersionError,
[version, $error]))
if typeFork != consensusFork:
return err(
RestErrorMessage.init(Http400, UnexpectedForkVersionError,
["eth-consensus-version", consensusFork.toString(),
typeFork.toString()]))
let typeFork = kind(typeof(res.data))

if contentType == ApplicationJsonMediaType:
res =
Expand All @@ -3321,6 +3311,17 @@ proc decodeBytesJsonOrSsz*(
typeFork.toString()]))
ok(res)
elif contentType == OctetStreamMediaType:
let consensusFork =
ConsensusFork.decodeString(version).valueOr:
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@tersec tersec Apr 2, 2025 •
edited
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version here comes from:

nimbus-eth2/beacon_chain/validators/beacon_validators.nim

Lines 649 to 687 in c00f35a

res = decodeBytesJsonOrSsz(
GetHeaderResponseDeneb, response.data, response.contentType,
response.headers.getString("eth-consensus-version"))
blindedHeader = res.valueOr:
return err(
"Unable to decode Deneb blinded header: " & $res.error &
" with HTTP status " & $response.status & ", Content-Type " &
$response.contentType & " and content " & $response.data)
elif EPH is electra_mev.BlindedExecutionPayloadAndBlobsBundle:
let
response = awaitWithTimeout(
payloadBuilderClient.getHeaderElectra(
slot, executionBlockHash, pubkey),
BUILDER_PROPOSAL_DELAY_TOLERANCE):
return err "Timeout obtaining Electra blinded header from builder"
res = decodeBytesJsonOrSsz(
GetHeaderResponseElectra, response.data, response.contentType,
response.headers.getString("eth-consensus-version"))
blindedHeader = res.valueOr:
return err(
"Unable to decode Electra blinded header: " & $res.error &
" with HTTP status " & $response.status & ", Content-Type " &
$response.contentType & " and content " & $response.data)
elif EPH is fulu_mev.BlindedExecutionPayloadAndBlobsBundle:
debugFuluComment "Because electra MEV isn't working yet, this is a placeholder copy"
let
response = awaitWithTimeout(
payloadBuilderClient.getHeaderFulu(
slot, executionBlockHash, pubkey),
BUILDER_PROPOSAL_DELAY_TOLERANCE):
return err "Timeout obtaining Fulu blinded header from builder"
res = decodeBytesJsonOrSsz(
GetHeaderResponseFulu, response.data, response.contentType,
response.headers.getString("eth-consensus-version"))

i.e. eth-consensus-version

Neither https://github.com/ethereum/builder-specs/blob/v0.5.0/apis/builder/header.yaml nor https://github.com/ethereum/builder-specs/blob/v0.5.0/apis/builder/blinded_blocks.yaml appears to require it even for SSZ mode, so it might compliantly be empty in/missing from the relay's REST response.

But, again, this isn't actually a real issue, because at any given callsite, there's only one valid fork, and it does not ever depend on eth-consensus-version, in no edge case.

nimbus-eth2/beacon_chain/validators/beacon_validators.nim

Lines 641 to 651 in c00f35a

when EPH is deneb_mev.BlindedExecutionPayloadAndBlobsBundle:
let
response = awaitWithTimeout(
payloadBuilderClient.getHeaderDeneb(
slot, executionBlockHash, pubkey),
BUILDER_PROPOSAL_DELAY_TOLERANCE):
return err "Timeout obtaining Deneb blinded header from builder"
res = decodeBytesJsonOrSsz(
GetHeaderResponseDeneb, response.data, response.contentType,
response.headers.getString("eth-consensus-version"))

can only happen when it's Deneb, and therefore the consensus version it's expecting must, always, be Deneb.

nimbus-eth2/beacon_chain/validators/beacon_validators.nim

Lines 658 to 668 in c00f35a

elif EPH is electra_mev.BlindedExecutionPayloadAndBlobsBundle:
let
response = awaitWithTimeout(
payloadBuilderClient.getHeaderElectra(
slot, executionBlockHash, pubkey),
BUILDER_PROPOSAL_DELAY_TOLERANCE):
return err "Timeout obtaining Electra blinded header from builder"
res = decodeBytesJsonOrSsz(
GetHeaderResponseElectra, response.data, response.contentType,
response.headers.getString("eth-consensus-version"))

similarly with Electra

nimbus-eth2/beacon_chain/validators/beacon_validators.nim

Lines 675 to 687 in c00f35a

elif EPH is fulu_mev.BlindedExecutionPayloadAndBlobsBundle:
debugFuluComment "Because electra MEV isn't working yet, this is a placeholder copy"
let
response = awaitWithTimeout(
payloadBuilderClient.getHeaderFulu(
slot, executionBlockHash, pubkey),
BUILDER_PROPOSAL_DELAY_TOLERANCE):
return err "Timeout obtaining Fulu blinded header from builder"
res = decodeBytesJsonOrSsz(
GetHeaderResponseFulu, response.data, response.contentType,
response.headers.getString("eth-consensus-version"))

and with Fulu

This is all known at compile-time, statically; there's no need to use eth-consensus-version. There isn't never was any runtime detection of fork here.

If it's supplied, and it's incorrect, then, sure, can flag on that error, but otherwise its absence shouldn't matter at all.

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@cheatfate cheatfate Apr 2, 2025 •
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I would consider your opinion when specification will say exactly optional or not required, because right now it is:

The active consensus version to which the data belongs. Required in response so client can deserialize returned json or ssz data more effectively.

As you can see here present Required in response.
https://ethereum.github.io/builder-specs/#/Builder/getHeader

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@cheatfate cheatfate Apr 2, 2025

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One more proof to my opinion is present in original PR message ethereum/builder-specs#104

Adds Eth-Consensus-Version to responses, only required if response body is SSZ encoded but preferably should be added to all responses eventually.

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@tersec tersec Apr 2, 2025

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That phrasing appears to come in via https://ethereum.github.io/builder-specs/releases/v0.5.0/builder-oapi.json via https://github.com/ethereum/builder-specs/blob/1569fc45d43e3ed2bed94ec6788c3f8fa7d2a4b2/builder-oapi.yaml#L108-L112

  headers:
    Eth-Consensus-Version:
      $ref: "./beacon-apis/beacon-node-oapi.yaml#/components/headers/Eth-Consensus-Version"
      schema:
        $ref: "#/components/schemas/ConsensusVersion"

which in turn points to https://github.com/ethereum/beacon-APIs/blob/2b1d7b5ac4756881bd29e7adacc9b7032343d981/beacon-node-oapi.yaml#L482-L489

  headers:
    Eth-Consensus-Version:
      description: |
        The active consensus version to which the data belongs. Required in response so client can deserialize returned json or ssz data 
        more effectively.
      required: true
      schema:
        $ref: '#/components/schemas/ConsensusVersion'

That's descriptive/explanatory phrasing from another non-builder API spec in a human-readable description field only, which sort of leaks its way into the website description (not the spec proper).

Meanwhile the builder-API spec itself is clear on this:
https://github.com/ethereum/builder-specs/blob/c7b0abad0d0b995915cde8d2e5ebcd650de5b163/apis/builder/header.yaml#L35-L41

  responses:
    "200":
      description: Success response.
      headers:
        Eth-Consensus-Version:
          $ref: "../../builder-oapi.yaml#/components/headers/Eth-Consensus-Version"
          required: false

and https://github.com/ethereum/builder-specs/blob/c7b0abad0d0b995915cde8d2e5ebcd650de5b163/apis/builder/blinded_blocks.yaml#L49-L55

  responses:
    "200":
      description: Success response.
      headers:
        Eth-Consensus-Version:
          $ref: "../../beacon-apis/beacon-node-oapi.yaml#/components/headers/Eth-Consensus-Version"
          required: false

The "required" is flavor text, and doesn't even .... necessarily mean it's required, per se. It's vague and handwavy enough even without the contradictory evidence from the builder API itself it's be questionable.

I can say, X is required for Y to happen, and it's a conditional requirement: if one wants Y to be true, X must be true, a kind of logical implication operator.

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@tersec tersec Apr 2, 2025

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One more proof to my opinion is present in original PR message ethereum/builder-specs#104

Adds Eth-Consensus-Version to responses, only required if response body is SSZ encoded but preferably should be added to all responses eventually.

That speaks to intent of the PR creator, yes. Not what the spec actually says.

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sorry for that, I have opened a PR to clarify / formalize this on the spec ethereum/builder-specs#118

return err(RestErrorMessage.init(Http400, UnableDecodeVersionError,
[version, $error]))
if typeFork != consensusFork:
return err(
RestErrorMessage.init(
Http400, UnexpectedForkVersionError,
["eth-consensus-version", consensusFork.toString(),
typeFork.toString()]))

ok(T(
version: newJString(typeFork.toString()),
data:
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