Implement safe sendmsg/recvmsg abstractions

[teisenbe]

Supports SCM_CREDENTIALS and SCM_RIGHTS control messages

Resolves #4 and resolves #5

[elmarco]

thank you!

[sfackler]

This isn't necessary - it's only needed when linking to third party stuff.

[sfackler]

Thanks for doing this! I left some comments here and there. Also, this'll need to be put behind a feature since these are Linux-only APIs I believe.

I'm not totally sure what the API for sendmsg and recvmsg should look like, but it seems like we can do better than a raw c_int of flags.

[teisenbe]

I think all of the flags are potentially applicable and usable with this API. If you want, I can replace the c_int with a struct of bools to make it a bit more friendly? Can also take it out completely, but I think the options flags provides and the data it returns are genuinely useful. Will probably work to address comments today

[sfackler]

Oh yeah, the options flags are definitely useful, I'd just prefer something more structured than a raw c_int. A struct with bool setters/getters seems reasonable to me.

[teisenbe]

Take a look at the latest version of the pull request. Replaced it with the struct as requested

[geofft]

I just saw this -- I have a PR for a pure-Rust implementation of this (just SCM_RIGHTS, but SCM_CREDENTIALS would be easy to add) in nix-rust/nix#179 (now nix-rust/nix#197). We should potentially make sure our APIs are in sync, and maybe it makes sense to share implementation, too.

[sfackler]

path doesn't appear to be a parameter here anymore.

[teisenbe]

Finally got around to addressing the comments

[maghoff]

struct ucred now exists in libc, from version 0.2.3: rust-lang/libc@4920c7e :)