[Node Operator Question] Unexpected "parse error" from Proxyd for valid request

[chriswessels]

Issue Description

We are attempting to run Proxyd as a load balancer for RPC nodes as part of our open source project.

Proxyd v4.4.1 is throwing a parse error for this request:

curl -i -X POST -H 'X-Forwarded-For: 127.0.0.1'      -H "Content-Type: application/json"      --data '{"jsonrpc":"2.0","method":"eth_call","params":[{"data":"0xd8dfeb45","gas":"0x2faf080","to":"0xac957cddc645b791e3d0e34ffb29d87642c7ebb4"},{"blockHash":"0x17db678f3f91edbeb885cbd18069d029915a4f9fc3b880eecaad625dc3b2c801"}],"id":36318}'      proxyd:8545
HTTP/1.1 400 Bad Request
Content-Type: application/json
Vary: Origin
X-Proxyd-Cache-Status: MISS
Date: Fri, 27 Oct 2023 17:20:07 GMT
Content-Length: 77

{"jsonrpc":"2.0","error":{"code":-32700,"message":"parse error"},"id":36318}

However this request is successful directly against a node:

curl -i -X POST -H 'X-Forwarded-For: 127.0.0.1'      -H "Content-Type: application/json"      --data '{"jsonrpc":"2.0","method":"eth_call","params":[{"data":"0xd8dfeb45","gas":"0x2faf080","to":"0xac957cddc645b791e3d0e34ffb29d87642c7ebb4"},{"blockHash":"0x17db678f3f91edbeb885cbd18069d029915a4f9fc3b880eecaad625dc3b2c801"}],"id":36318}'      erigon-1-stateful-node:8545
HTTP/1.1 200 OK
Content-Type: application/json
Vary: Origin
Date: Fri, 27 Oct 2023 17:19:43 GMT
Content-Length: 107

{"jsonrpc":"2.0","id":36318,"result":"0x0000000000000000000000007da96a3891add058ada2e826306d812c638d87a7"}

The problem may be related to tag rewriting, as when removing the blockHash from the request, it succeeds.

Node Logs

No response

[felipe-op]

eth_call parameter 1 (starting at index 0) should be a string and not a map
ref: https://ethereum.org/en/developers/docs/apis/json-rpc/#eth_call

I think your request was supposed to be

'{"jsonrpc":"2.0","method":"eth_call","params":[{"data":"0xd8dfeb45","gas":"0x2faf080","to":"0xac957cddc645b791e3d0e34ffb29d87642c7ebb4"},"0x17db678f3f91edbeb885cbd18069d029915a4f9fc3b880eecaad625dc3b2c801"],"id":36318}'

as for the different error message, you are right - proxyd tag rewrite can't parse this request as it is expecting a string.. so the request is rejected before it get sent to the backend

[chriswessels]

Thank you for the quick response @felipe-op!

The {"blockHash": "0x..."} format for the parameter is defined in EIP 1898. Many workloads use this format.

[felipe-op]

Thank you, @chriswessels - I wasn't aware of this spec, but confirmed it is used by geth client.

I'll open an internal issue so we can add support to this format as well.

[chriswessels]

Thank you!

[felipe-op]

ethereum-optimism/optimism#7908