fix error:debug_traceCall API returns not valid json format output

[marshalys]

try to fix debug_traceCall API returns not valid json format output when the tx execute is fail
#10376

[taratorio]

@marshalys can you please share your curl command that reproduces this issue?

[taratorio]

@marshalys can you also explain based on your investigation what exactly was attaching the "null" bit? my expectation was that it would only be "result":{"structLogs":[]},"error":{"code":-32000, ... - not clear what exactly appends the null after {"structLogs":[]}[].

[taratorio]

@marshalys can you please test your use case with PR #10383 instead? I think I found what appends the "null"

[marshalys]

@marshalys can you please share your curl command that reproduces this issue?

curl -H "Content-Type: application/json" -X POST --data '{"id":1,"jsonrpc":"2.0","method":"debug_traceCall","params":[{"from":"0xae2fc483527b8ef99eb5d9b44875f005ba1fae13","to":"0x6b75d8af000000e20b7a7ddf000ba900b4009a80","value":"0x16906ca2e71","gas":"0x2eaf9","gasPrice":"0x1175c375f","data":"0x57c7bbec68d12a0d1830360f8ec58fa599ba1b0e9b5fedbf9b6fdac17f958d2ee523a2206206994597c13d831ec70064","accessList":[],"type":"0x2"},"0x27a66641a0f38c81e961deeb142d54dc20ba64632f31ebc3c814057ed502c3e5",{}]}' 127.0.0.1:8545

[marshalys]

@marshalys can you please test your use case with PR #10383 instead? I think I found what appends the "null"

to check result has many case depend the api return value, result may be bool or string also.

[marshalys]

@marshalys can you also explain based on your investigation what exactly was attaching the "null" bit? my expectation was that it would only be "result":{"structLogs":[]},"error":{"code":-32000, ... - not clear what exactly appends the null after {"structLogs":[]}[].

if the api call failed, the result property is useless, I run the same api at geth, and the output of geth has no result property.

{"jsonrpc":"2.0","id":1,"error":{"code":-32000,"message":"tracing failed: max fee per gas less than block base fee ....

[taratorio]

@marshalys can you please test your use case with PR #10383 instead? I think I found what appends the "null"

to check result has many case depend the api return value, result may be bool or string also.

That's fine. I have other plans to make our json streaming guarantee correctness. Will work on implementing a stack-based Streamer around jsoniter.Stream that closes all pending json objects and fields upon errors. This way in case of errors we will always have generated correct json.

The PR I sent is aimed at simply fixing the issue you are reporting. Would appreciate you trying it out on your machine to verify it fixes the issue you raised please.

That is the direction I prefer to take for now.

[taratorio]

@marshalys can you also explain based on your investigation what exactly was attaching the "null" bit? my expectation was that it would only be "result":{"structLogs":[]},"error":{"code":-32000, ... - not clear what exactly appends the null after {"structLogs":[]}[].

if the api call failed, the result property is useless, I run the same api at geth, and the output of geth has no result property.

{"jsonrpc":"2.0","id":1,"error":{"code":-32000,"message":"tracing failed: max fee per gas less than block base fee ....

That is because as far as I know geth does not use JSON streaming.

Erigon uses json streaming.

If there is an error a client should ignore the result field. Only thing that matters for us is for that json to be valid. As I explained here I have a direction I would like to take for ensuring our json stream always produces valid json in case of errors.

[taratorio]

Managed to test #10383 which seems to have fixed the reported issue.

Closing in favour of:

• (short term) rpc/handler: do not append null to stream when json may be valid #10383
• (long term) implement stack based json stream that guarantees valid json in case of errors  #10389

@marshalys many thanks for your contribution and for reporting this issue 🙏

[marshalys]

Yes, I think your conside is good.
@taratorio Thank you for your incredibly quick response! 😊