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bc58e6e9ac
* Bound the multipart parser's buffer while it waits for a boundary FormDataParser accumulated the entire request body whenever the declared boundary never appeared in it. State 0 returned without erasing anything, so the buffer grew to the full payload (100 MB by default) and buf_find rescanned all of it on every 16 KB read. The cost grew with the square of the body size: 50 MB of '-' took 198 s of CPU on one core, and the buffer pinned the body in memory for the whole request. One unauthenticated request was enough, and the parser runs for any multipart request even when the handler never looks at the parsed result. State 0 now keeps only the last dash_boundary_crlf_.size() - 1 bytes while it waits, which bounds both the memory and the rescan without capping how long a preamble may be. The same 50 MB body now takes 0.14 s and the buffer stays at one read plus the boundary. A boundary split across reads still parses, which is whatde5a255(#2159) gave up this erase for. State 4 buffered without bound in the same way when a boundary was followed by neither CRLF nor "--". No further data can make such a body valid, so it now fails right away. That is only safe because the close-delimiter branch moves to a new state 5 that discards the epilogue: it used to stay in state 4, so an epilogue arriving in a later read fell into this same branch. An epilogue beginning with CRLF was then parsed as a new part and the request was rejected with 400, which state 5 fixes as well. Affected since v0.23.0, wherede5a255replaced the erase that had kept the buffer in check. * Skip buffering the multipart epilogue Once the close delimiter has been parsed the parser is in state 5 and discards whatever follows, but it still copied each epilogue read into the buffer before erasing it. Return before buffering so a large epilogue spread across several reads is dropped without being copied in at all. * Clean up the multipart parser tests and the state 4 branch Review follow-ups on top of the previous two commits, no behavior change. - Move the four new tests next to the rest of MultipartFormDataTest. They had landed in the middle of the RedirectTest block. - Use bind_to_any_port instead of the fixed PORT, as AGENTS.md requires for newly added servers. NoInitialBoundaryParsingIsNotQuadratic holds its port for a couple of seconds, which matters when the suite is run sharded. - Send "Connection: close" from expect_split_multipart_ok. The server kept the connection alive after answering, so the response drain idled until the client read timeout; both tests drop from about 3s to about 0.11s. - Drop the dead `dash_.size() > buf_size()` guard in state 4 and flatten the nested else. The check above it already guarantees two buffered bytes, and both CRLF and "--" are two bytes, so it can never fire. Removing it is what makes the new comment's claim readable straight off the code. * Rename the timing test's locals to avoid a Windows macro MSVC's <rpcndr.h>, pulled in by <windows.h>, defines `small` as `char`, so `auto small = ...` failed to compile on the Windows jobs. Same class of problem as the std::min / std::max collision.
