Wasmtime GitHub notifications bot (Sep 25 2026 at 20:40): Wasmtime GitHub notifications bot (Sep 25 2026 at 20:40):xia-chao opened PR #14429 from xia-chao:fix-write-permit to bytecodealliance:main:
check-write gives the guest a number of bytes it may write next, and the interface says writing more than that traps. On stdout and on files it doesn't: I take a permit of 1048576, write 104857600 bytes in one call, get Ok back, and every byte arrives. TCP streams already trap and write-zeroes already checks in the same shared host function, so the check goes there and covers stdio, files and pipes at once - for TCP only the message text changes.
Wasmtime GitHub notifications bot (Sep 25 2026 at 20:40):xia-chao requested dicej for a review on PR #14429.
Wasmtime GitHub notifications bot (Sep 25 2026 at 20:40):xia-chao requested wasmtime-wasi-reviewers for a review on PR #14429.
Wasmtime GitHub notifications bot (Sep 25 2026 at 20:40):xia-chao requested wasmtime-core-reviewers for a review on PR #14429.
Wasmtime GitHub notifications bot (Sep 25 2026 at 20:45):xia-chao edited PR #14429:
The shared output-stream write host function doesn't check the permit that check-write returned. wasi:io says a write with more bytes than the permit has to trap, and today it returns Ok instead - after a permit of 1048576, a 104857600 byte write goes through on stdout and on files. The check isn't missing everywhere: TCP output streams enforce it, and write-zeroes checks in that same shared function, so I added it there and stdio, files and pipes are covered at once. TCP streams already trapped, and for them only the message text changes.
Wasmtime GitHub notifications bot (Sep 25 2026 at 20:47):xia-chao edited PR #14429:
The shared output-stream write host function doesn't check the permit that check-write returned. wasi:io says a write with more bytes than the permit has to trap, and today it returns Ok instead - after a permit of 1048576, a 104857600 byte write goes through on stdout and on files.
The check isn't missing everywhere: TCP output streams enforce it, and write-zeroes checks in that same shared function, so I added it there and stdio, files and pipes are covered at once. TCP streams already trapped, and for them only the message text changes.
Wasmtime GitHub notifications bot (Sep 25 2026 at 20:49):xia-chao edited PR #14429:
The shared output-stream write host function doesn't check the permit that check-write returned. wasi:io says a write with more bytes than the permit has to trap, and today it returns Ok instead.
after a permit of 1048576, a 104857600 byte write goes through on stdout and on files.
The check isn't missing everywhere: TCP output streams enforce it, and write-zeroes checks in that same shared function, so I added it there and stdio, files and pipes are covered at once. TCP streams already trapped, and for them only the message text changes.
Wasmtime GitHub notifications bot (Sep 25 2026 at 20:50):xia-chao edited PR #14429:
The shared output-stream write host function doesn't check the permit that check-write returned. wasi:io says a write with more bytes than the permit has to trap, and today it returns Ok instead.
after a permit of 1048576, a 104857600 byte write goes through on stdout and on files.
The check isn't missing everywhere: TCP output streams enforce it, and write-zeroes checks in that same shared function.
so I added it there and stdio, files and pipes are covered at once. TCP streams already trapped, and for them only the message text changes.
Wasmtime GitHub notifications bot (Sep 25 2026 at 21:07):xia-chao updated PR #14429.
Wasmtime GitHub notifications bot (Sep 25 2026 at 21:11):xia-chao edited PR #14429:
The stdio and file output streams don't enforce the permit their own check_write reports. StdioOutputStream hands back 1 MiB and then writes any size it is given, so a 100 MiB write returns Ok; FileOutputStream checks that check-write came first, not the size. Every other output stream already traps on an over-permit write. I added the missing check to those two, so no existing trap message changes.
Wasmtime GitHub notifications bot (Sep 25 2026 at 21:11):xia-chao edited PR #14429:
The stdio and file output streams don't enforce the permit their own check_write reports. StdioOutputStream hands back 1 MiB and then writes any size it is given, so a 100 MiB write returns Ok; FileOutputStream checks that check-write came first, not the size. Every other output stream already traps on an over-permit write.
I added the missing check to those two, so no existing trap message changes.
Wasmtime GitHub notifications bot (Sep 25 2026 at 22:44):github-actions[bot] added the label wasi on PR #14429.
Wasmtime GitHub notifications bot (Sep 28 2026 at 13:42)::thumbs_up: dicej submitted PR review:
Thanks, @xia-chao!
Wasmtime GitHub notifications bot (Sep 28 2026 at 13:42):dicej added PR #14429 wasi:io: enforce the check-write permit in output-stream::write to the merge queue.
Wasmtime GitHub notifications bot (Sep 28 2026 at 14:09)::check: dicej merged PR #14429.
Wasmtime GitHub notifications bot (Sep 28 2026 at 14:09):dicej removed PR #14429 wasi:io: enforce the check-write permit in output-stream::write from the merge queue.
Last updated: Oct 11 2026 at 04:10 UTC