The per-call SERVER span ended inside `handleCall()`, so the JSON-RPC
response write happened after the span closed. For large responses like
`engine_getBlobsV*`, that write time was missing from traces.
- Extend the SERVER span past `writeJSON`.
- For batches, add a top-level `jsonrpc.batch` SERVER span (with `rpc.batch.size`) covering the whole batch including `callBuffer.write`.
- Add `rpc.writeJSON` span around the non-batch response write.
- Add `rpc.writeJSONBatch` span around the batch response write.
- Add `rpc.httpWrite` span around the actual HTTP write, separating JSON encoding from network write.
- Add additional telemetry helpers.
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Co-authored-by: Felix Lange <fjl@twurst.com>
The endSpan closure accepted error by value, meaning deferred calls like
defer spanEnd(err) captured the error at defer-time (always nil), not at
function-return time. This meant errors were never recorded on spans.
- Changed endSpan to accept *error
- Updated all call sites in rpc/handler.go to pass error pointers, and
adjusted handleCall to avoid propagating child-span errors to the parent
- Added TestTracingHTTPErrorRecording to verify that errors from RPC
methods are properly recorded on the rpc.runMethod span
Add Open Telemetry tracing inside the RPC server to help attribute runtime costs within `handler.handleCall()`. In particular, it allows us to distinguish time spent decoding arguments, invoking methods via reflection, and actually executing the method and constructing/encoding JSON responses.
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Co-authored-by: lightclient <lightclient@protonmail.com>
