connmgr: add ability to send large outbound request headers#48368
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clintjedwards
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Jun 16, 2026
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Following #48365, this PR implements support for large outbound request headers.
Currently,
http1::client::Request::prepare_headerserializes its inputs (method, URI, headers) to a buffer and returns aRequestHeaderinstance. Then the async methodRequestHeader::sendwrites the buffer to the socket. This PR reworks things such thatprepare_headerborrows its inputs without doing any serialization, keeping them in theRequestHeaderinstance, and then thesendmethod writes the inputs directly to the socket, with resumption for partial writes.The resulting API is essentially the same except callers have to ensure the inputs live until
sendcompletes, so some variables are moved around near call sites to achieve this.Note: moving variables around in order to extend their lifetimes caused the async task sizes to increase beyond our latest thresholds. I'll see about optimizing the sizes afterwards, but if nothing can be done I think it's fine.
The underlying
http1::protocol::ClientRequest::send_headerfunction, like many of our low level I/O functions, is synchronous and operates on aWriteimplementation. In order to operate on anAsyncWriteimplementation from within an async function, we use a pattern involving two convenience wrappers,StdWriteWrapperandAsyncOperation.StdWriteWrapperimplementsWriteon anything that implementsAsyncWrite. With it, an async socket object can be passed tosend_header.AsyncOperationis then used to wrap the call and present it as a future that can be awaited.Below is a manual test of ~20kb headers proxied from pushpin to nginx, using an 8kb block size in pushpin.
Before:
Logs:
After: