Enforce body size limits in protocol parsers

[wwbmmm]

What problem does this PR solve?

Issue Number: null

Problem Summary:

Some HTTP, memcache, and couchbase parsing paths did not consistently enforce
the global max_body_size setting. Non-progressive HTTP messages could buffer
more data than configured, while memcache and couchbase parsers could wait for
an oversized body declared in a response header.

What is changed and the side effects?

Changed:

• Track the accumulated body size of non-progressive HTTP messages and reject
  data before appending beyond max_body_size.
• Return HTTP 413 for oversized HTTP/1 requests and close the connection after
  writing the response.
• Reset only the oversized HTTP/2 stream with ENHANCE_YOUR_CALM.
• Reject oversized memcache and couchbase responses immediately after parsing
  their fixed-size headers.
• Add regression tests for fixed-length HTTP, chunked HTTP, memcache, and
  couchbase messages.

Side effects:

• Performance effects: Each non-progressive HTTP body block adds one
  overflow-safe size comparison and addition. Memcache and couchbase add one
  comparison per response. No additional scan, allocation, or copy is added.
• Breaking backward compatibility: Messages larger than max_body_size are
  now rejected as documented. Progressive HTTP reading remains unchanged so
  existing bounded-memory streaming transfers can exceed this setting.

Check List:

• The changes are compilable.
• Regression tests are included.
• The affected test suites pass.

[Copilot]

Pull request overview

This PR enforces the global max_body_size limit across several protocol parsers (HTTP/1, HTTP/2, memcache, couchbase) to prevent buffering or waiting on oversized message bodies, and adds regression coverage for the new enforcement paths.

Changes:

• Enforce max_body_size during non-progressive HTTP body parsing; return HTTP 413 for oversized HTTP/1 requests and reset oversized HTTP/2 streams with ENHANCE_YOUR_CALM.
• Reject oversized memcache and couchbase responses immediately after parsing their fixed-size headers.
• Add new unit tests covering fixed-length/chunked HTTP and oversized memcache/couchbase responses.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/brpc_memcache_unittest.cpp	Adds regression test ensuring oversized memcache responses are rejected before buffering the body.
test/brpc_http_rpc_protocol_unittest.cpp	Adds MaxBodySizeGuard and HTTP/1 tests verifying 413 behavior for oversized fixed-length and chunked bodies.
test/brpc_couchbase_unittest.cpp	Adds regression test ensuring oversized couchbase responses are rejected before buffering the body.
src/brpc/policy/memcache_binary_protocol.cpp	Enforces FLAGS_max_body_size against memcache total_body_length immediately after header parse.
src/brpc/policy/http2_rpc_protocol.cpp	Returns H2_ENHANCE_YOUR_CALM for oversized HTTP/2 stream bodies instead of a generic protocol error.
src/brpc/policy/http_rpc_protocol.cpp	Detects HttpMessage oversize condition and writes HTTP 413 (server-side) or returns TOO_BIG_DATA (client-side).
src/brpc/policy/couchbase_protocol.cpp	Enforces FLAGS_max_body_size against couchbase total_body_length immediately after header parse.
src/brpc/details/http_message.h	Adds body_too_large() and tracking fields to support non-progressive body size enforcement.
src/brpc/details/http_message.cpp	Tracks accumulated non-progressive body size and fails early when appending would exceed max_body_size.

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[chenBright]

LGTM