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codex/codex-rs/codex-api/src
T
jif baddb5e686 serialize websocket requests directly (#28323)
## Why

Responses WebSocket requests were encoded in two steps: first into a
full `serde_json::Value`, then again into the JSON string sent over the
socket.

That walks the full request twice and keeps an extra JSON tree alive.
These requests can contain the complete conversation history and tool
schemas, so the extra work grows with the request size.

## What changed

- serialize `ResponsesWsRequest` directly to the wire string
- pass that string through the existing WebSocket stream and send path
- keep the existing error mapping, tracing, send timeout, and telemetry
behavior
- compare the new wire JSON with the previous `to_value` payload in a
focused test

## Performance

I measured both paths in an optimized temporary test using a
6,324,180-byte request: 4 MiB of history plus 256 tools with 8 KiB
descriptions. Each path ran 100 times.

- previous `to_value` + `to_string`: 209 ms total, 2.09 ms per request
- direct `to_string`: 174 ms total, 1.74 ms per request
- difference: about 17% faster, or 0.35 ms per request

The direct path also removes one full temporary `serde_json::Value`
tree. For this mostly string-backed payload, that avoids roughly one
payload-sized copy plus the JSON node overhead. The exact memory saving
depends on the request shape.

The temporary benchmark was removed before committing.

## Validation

- `just test -p codex-api` — 125 passed
- `just fix -p codex-api`
baddb5e686 · 2026-06-15 18:33:35 +02:00
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