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async: report a failed write on the io handle (ABI 0.26.0) - #27
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A write submitted without an awaiter gets no status of its own: its completion is a free_cb that takes the handle and the user pointer, nothing else. The consumer was left to infer the failure from the read side, where a peer that merely shut its write half down looks exactly like one that is gone. ZEND_ASYNC_IO_WRITE_FAILED is that report. The reactor sets it on the handle when a write completes with an error and never clears it, so a consumer can tell "this connection can no longer be written to" from "this peer has stopped sending". It says nothing about the read side.
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A write submitted without an awaiter gets no status of its own: its completion is a
free_cbtaking the handle and the user pointer, nothing else. The consumer was left to infer the failure from the read side — and there a peer that merely shut its write half down looks exactly like one that is gone.ZEND_ASYNC_IO_WRITE_FAILED(bit 7, the first free one) is that report. The reactor sets it on the handle when a write completes with an error and never clears it. It says nothing about the read side, which is the point: a half-closed peer keeps reading.Why the read side cannot stand in for it: the kernel hands
so_errorto whichever syscall asks first, and with a saturated outbound queue that is the write. Measured on bare sockets after an RST —write -> ECONNRESET,write -> EPIPE,read -> b'': the read behind the failing write returns a clean EOF and reports nothing.Consumers: php-async sets the flag (true-async/php-async, branch
write-failed-state-bit), and true-async/server reads it to keep a half-closed peer's response alive while still answering 499 to one that is gone (true-async/server#249). Both are guarded, so neither needs this to land first in order to build.ABI 0.25.0 → 0.26.0: additive, no signature or layout change.