Support for unix sockets

[cmkarlsson]

It would be great if glisten can support unix sockets and abstract unix sockets.

Erlang supports this by passing the option {ip, {local, Path}} to gen_tcp:listen where Path is either a file system path, or an abstract unix sockets where the Path starts with null byte (<<0,path:utf8>>).

I have implemented a prototype in glisten where this is implemented. The prototype makes a couple of different modifications to achieve this:

1. Extending IpAddress to also represent a UnixSocketAddress
2. modifying bind to see if the incoming interface starts with "/" or "@" (which is the convention to deal with unix sockets, however we can change this to use something other than bind, like: fn bind_unix_socket(handler, path: String) -> Handler instead
3. Modifying the type of sockname from #(Dynamic, Int) to Dynamic as the underlying erlang code might return {Hostname :: binary(), Port :: int()} | {local, Path :: binary()}. Then this dynamic is decoded into either #(ipv4|ipv6, port) or #(path, 0).

From my point of view the biggest problem with the prototype is that it piggy-backs on some naming conventions like IpAddress and the return type from sockname which might not be ideal.

Would it be OK if I do the PR with what I currently have and we can take discussion from there?

[rawhat]

Hey, thanks for your interest in this! I have a local branch attempting to address this exact issue, but wasn't super thrilled with the API I came up with.

If you want to open a PR, I'd be more than happy to look at it!

[rawhat]

For reference, this was the original ask: rawhat/mist#48

[ollie-dot-earth]

Hey, thanks for your interest in this! I have a local branch attempting to address this exact issue, but wasn't super thrilled with the API I came up with.

Whats the status on this?
Asking for Unix socket support PR in mug, which uses glisten for tests.

[rawhat]

Sorry I've been super busy and haven't prioritized this. Lemme think a little bit more about what I had (might need to start over since I didn't like it lol). But hopefully can report back here soon.

[jtdowney]

I took a stab at implementing Unix socket support. Here's the API I landed on:

API

// Filesystem socket
glisten.new(on_init, loop)
|> glisten.start_unix("/tmp/myapp.sock")

// Abstract socket (Linux only)
glisten.new(on_init, loop)
|> glisten.start_unix("@myapp")

The @ prefix for abstract sockets follows the common convention (socat, systemd, etc.) and gets converted to a null-byte prefix internally.

Design decisions

• Separate start_unix() instead of overloading bind()/start() - Unix sockets don't have ports, so trying to unify them with the existing start(port) signature felt awkward. A separate method makes the intent clear and avoids confusion.

• New ServerInfo type - Since get_server_info() previously returned port/IP info that doesn't exist for Unix sockets, it now returns a sum type:

pub type ServerInfo {
  TcpServerInfo(port: Int, ip_address: IpAddress)
  UnixServerInfo(path: String)
}

• Like @cmkarlsson suggested, modifying the type of sockname from #(Dynamic, Int) to Dynamic as the underlying erlang code might return {Hostname :: binary(), Port :: int()} | {local, Path :: binary()}.