consume refused HEADERS block before RST_STREAM in h2

[ubeddulla]

What problem does this PR solve?

Issue Number: resolve N/A

Problem Summary:

When a HEADERS frame opens a stream past max_concurrent_streams, H2Context::OnHeaders returns RST_STREAM(REFUSED_STREAM) but never consumes that frame's header-block payload. REFUSED_STREAM is a stream error, so the connection stays open and ParseH2Message keeps parsing; the leftover header-block bytes are then read by ConsumeFrameHead as the next frame head, letting a peer smuggle frames past the h2 framing layer, and the HPACK decoder is left desynced because the refused block was never decoded. OnData and the client-side unknown-stream branch right below already drain the payload before returning a stream error; only the refused-stream path skipped it.

What is changed and the side effects?

Changed:

Decode and consume the refused stream's header block (sctx->OnHeaders) before deleting the context and returning REFUSED_STREAM, mirroring the two sibling paths. This keeps both the frame parser and the HPACK decoder in sync. Added a regression test in test/brpc_http_rpc_protocol_unittest.cpp that fails before the change (only the 9-byte frame head was consumed, leaving the header block to be misparsed) and passes after.

Side effects:

• Performance effects: one extra HPACK decode of a header block that is then discarded, only on refused streams.

• Breaking backward compatibility: none.

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

🟡 Changes recommended

The refused-stream path ignores header-decoding failures, potentially leaving framing and HPACK state desynchronized.

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Pull request overview

Fixes HTTP/2 refused-stream HEADERS handling and adds regression coverage.

Changes:

• Consume refused HEADERS payloads to preserve framing and HPACK state.
• Add a regression test for frame-buffer consumption.

File summaries

File	Summary
test/brpc_http_rpc_protocol_unittest.cpp	Adds refused-stream consumption regression coverage.
src/brpc/policy/http2_rpc_protocol.cpp	Handles refused HEADERS payloads before stream cleanup.

Review details

Suppressed comments (1)

src/brpc/policy/http2_rpc_protocol.cpp:665

• This also loses the continuation state for a fragmented header block. When END_HEADERS is absent, OnHeaders stores the partial block in sctx; deleting it here makes the required following CONTINUATION enter the server-side unknown-stream path and produce a connection PROTOCOL_ERROR/GOAWAY, even though REFUSED_STREAM is intended to leave the connection usable. Keep discard state for refused streams and decode/drain their CONTINUATION frames through END_HEADERS.

            sctx->OnHeaders(it, frame_head, frag_size, pad_length);
            delete sctx;

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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