Clarify safety invariants in SocketAddrArg.#1325
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sunfishcode merged 3 commits intomainfrom Feb 14, 2025
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In making another safety review of the `SocketAddrArg` code, I found it too subtle to have `MMsgHdr::new_with_addr` depending on knowing that `with_msghdr` happens to avoid using a temporary in the case `SocketAddrAny`. Change it to avoid doing this, add more comments, and change `with_msghdr`'s argument to a reference, to prevent it from being accidentally used in this way. And change `with_noaddr_msghdr` to `noaddr_msghdr` and make it just return a `msghdr`, because it never needs to construct any temporaries, so it avoids this issue. Also, make `SocketAddrArg::with_sockaddr` and `with_recv_msghdr` unsafe, as the provided function will need to contain an `unsafe` block which will need to be able to trust it's being called correctly. And add safety comments for the callers and impls of these functions and traits.
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In making another safety review of the
SocketAddrArgcode, I found it too subtle to haveMMsgHdr::new_with_addrdepending on knowing thatwith_msghdrhappens to avoid using a temporary in the caseSocketAddrAny. Change it to avoid doing this, add more comments, and changewith_msghdr's argument to a reference, to prevent it from being accidentally used in this way.And change
with_noaddr_msghdrtonoaddr_msghdrand make it just return amsghdr, because it never needs to construct any temporaries, so it avoids this issue.Also, make
SocketAddrArg::with_sockaddrandwith_recv_msghdrunsafe, as the provided function will need to contain anunsafeblock which will need to be able to trust it's being called correctly.And add safety comments for the callers and impls of these functions and traits.