Add support for unix sockets

[wews64]

resolve #30

[melekes]

👍

[melekes]

/cc @davebryson @tomtau

[davebryson]

@wews64 @melekes Thanks! looks good!
I have one suggestion. Why not just parse the address and simply select the appropriate listener versus duplicating code here:
https://github.com/tendermint/rust-abci/pull/47/files#diff-4ce93534efc34e923ce01e975eb7ed80R14

Example: if the address starts with unix use the UnixListener, otherwise use the tcp listener. The rest of the code stays the same and you can eliminate the whole serve_unix function

[wews64]

@davebryson
I can not remove duplicating code, because there different types of incoming connections std::os::unix::net::UnixStream and std::net::TcpStream. I can make common interface for both functions, something like pub fn serve<A>(app: A, addr: &str) -> io::Result<()>. But it, under the hood, will also call different handlers.

[tomtau]

@wews64 I'm not sure whether this works, but you could possibly pass in the listener as an argument, constructed based on the address type. Both UnixStream and TcpStream implement IntoIterator, so perhaps the listener argument could have a type like IntoIterator<Item=Result<S, E>> (where S is the stream, so something like S: Read + Write) and instead of:

for new_connection in listener.incoming() {
...

you could do:

for new_connection in listener.into_iter() {
...

[wews64]

@tomtau but on next step i'm must send specific type (UnixStream or TcpStream) in AbciStream::from.

[tomtau]

@wews64 just a correction -- when I wrote UnixStream and TcpStream, I meant UnixListener and TcpListener. For streams themselves, what if you constrain S more? Something like S: Read + Write + Into<AbciStream>?

[tomtau]

@wews64 there has been quite a lot of changes in the meantime (e.g. tokio was added), so will close this PR for the moment -- feel free to update your changes and open a new PR