Create a socket library.

[ta0kira]

• Just TCP and named Unix sockets to start with. No creation of socket pairs (no fork support, anyway) or UDP yet.
• Both IPv6 and IPv4. Maybe no DNS to start with, since that requires choosing between IPv6 and IPv4 addresses.
• No setting of non-blocking flag yet, but read/write return should be able to indicate would-block vs. failure.
• Also need to decide if WriteAt should be the destination for reads, which would require making a copy of the data. The alternative is to dynamically allocate a new buffer each read.
• Should dup descriptor so that read and write block independently.
• Also needs reasonable listen semantics.

[ta0kira]

There should probably be some sort of SocketVisitor (etc.) to allow other categories to operate on the file descriptor.

@value interface SocketView {
  descriptor () -> (Int)
}

@value interface SocketVisitor {
  visitSocket ([SocketView&StreamSocket]) -> (#self)
}

@value interface StreamSocket {
  visit<#x>
    #x requires SocketVisitor
  (#x) -> (#x)
}

// ...

// some arbitrary socket implementation
define SomeSocket {
  refines SocketView

  @value Int fd

  visit (visitor) {
    return visitor.visitSocket(self)
  }
}

// ...

// uses the select system call to wait for input
define SocketSelect {
  refines SocketVisitor

  @value SearchTree<Int,StreamSocket> sockets

  add (socket) {
    return socket.visit<?>(self)
  }

  visitSocket (view) {
    \ sockets.set(view.descriptor(),view)
    return self
  }
}

// ...

SocketSelect select <- SocketSelect.new().add(socket1).add(socket2)
ReadAt<StreamSocket> ready <- select.wait()

---

There might also need to be a @type interface visitor, e.g., for the dup2 system call, which modifies global state rather than creating/changing a specific object.

[ta0kira]

Not sure if this is actually all that useful, since most socket use-cases are complex and have an existing C++ library that can be wrapped. For example, I wouldn't want to implement HTTP(S) in Zeolite; I'd just wrap cpp-httplib or something.

The POSIX socket API is also quite broad, so I think it would be too much effort to expose/test all of it. It might be useful to support AF_LOCAL sockets and (un)named pipes however, since you don't need to deal with addresses and ports.

[ta0kira]

I started working on pipe/exec support in https://github.com/ta0kira/zeolite-async. I'm not sure if I'll end up moving that to this repo.