libutil: treat EIO as EOF in readLine#15323
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Ericson2314 merged 1 commit intoNixOS:masterfrom Feb 23, 2026
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Reading from a pty master returns `EIO` once the slave side closes, however, `readLine` lets it propagate as an uncaught `SysError`, which causes spurious build failures in gvisor and similar sandboxed environments where pty teardown races differently. This commit catches `EIO` inside the read lambda and maps it to a zero-length read, reusing the existing EOF path.
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| try { | ||
| return read(fd, {reinterpret_cast<std::byte *>(&ch), 1}); | ||
| } catch (SystemError & e) { | ||
| // On pty masters, EIO signals that the slave side closed, | ||
| // which is semantically EOF. Map it to a zero-length read | ||
| // so the existing EOF path handles it. | ||
| if (e.is(std::errc::io_error)) | ||
| return 0; | ||
| throw; | ||
| } |
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Shouldn't we apply the same treatment to FdSource::readLine/readUnbuffered under a certain flag maybe? I don't think we want to keep the one-byte-at-a-time reading function for too long anyway.
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Motivation
Reading from a pty master returns
EIOonce the slave side closes, however,readLinelets it propagate as an uncaughtSysError, which causes spurious build failures in gvisor and similar sandboxed environments where pty teardown races differently. This commit catchesEIOinside the read lambda and maps it to a zero-length read, reusing the existing EOF path.Context
When pty support was first added in #2878, EIO was handled at the call site, but a later refactor moved reading to the generic
readLinewhich didn't carry the handling over, though muxable-pipe.cc still has it.Note that the test is skipped on macOS, because macOS returns EOF with 0 immediately and discards all buffered data (ref).
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