std: fix writeSplatHeaderLimit bug affecting chunked HTTP #25360
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The `writeSplatHeaderLimitFinish` logic correctly takes the limited prefix slice of the header, but fails to chop off excess in the data vector slices, causing a drain longer than the limit. I spotted this by accident, and found one usage in std, in the HTTP chunked encoding writer, and the issue ziglang#24944 that I speculate this commit will fix. I was able to partly reproduce it on Linux but only by disabling sendfile and some other weird kludges.
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This looks like a nice bug fix, but, unfortunately, this does not fix #24944 (see #24944 (comment)) |
squeek502
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Oct 5, 2025
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| // Test inspired by a bug in one of Io.Writer's write helpers. | ||
| // | ||
| // The fix doesn't touch the HTTP code, but the BodyWriter is | ||
| // from what I can tell the only affected code in std. | ||
| // | ||
| // Possibly the cause of https://github.com/ziglang/zig/issues/24944 | ||
| // wherein the `zig std` server on Windows, due to lack of sendfile, | ||
| // drains the streaming sources tarball by doing vector writes | ||
| // of file contents in the chunked body stream. |
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This type of information should go in the commit message rather than a comment. I'd say just remove the comment (without moving it to the commit message), since the fix in this PR doesn't actually affect the problem in #24944 (see my other comment)
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The
writeSplatHeaderLimitFinishlogic correctly takes the limited prefix slice of the header, but fails to chop off excess in the data vector slices, causing a drain longer than the limit.I spotted this by accident, and found one usage in std, in the HTTP chunked encoding writer, and the issue #24944 that I speculate this commit will fix. I was able to partly reproduce it on Linux but only by disabling sendfile and some other weird kludges.
First time hacking the Zig std. I verified tests failing and then passing with