Objects

What an object is

A module is a compiled .wasm file, with a header describing it. An object is one running instance of a module, declared in an image. In the tour, site.oth makes three of them: http, pages and files.

Two instances of the same module share code and nothing else. Each has its own memory and its own namespace.

Server and client at once

Every object is both a server and a client. It serves a tree of paths, and answers the requests made of them. It also has a view, the paths it has been given, and it makes requests of those.

Its header says both: what it serves, and what it needs in its view. The tour walks through HttpServer's header. Nothing else about an object is visible from outside: not its memory, not its functions, not the language it was written in.

No ambient access

An object has no files, no network, no clock and no randomness and so on.

Objects can only interact with other objects through the namespace. If it has a socket, it's because something put one in its view, and you can see where in the image. In the tour, that's the needs lines in static.oth: the socket and the console come from the environment, and are passed down from there as needed.

Single-threaded, sharing nothing

Objects share no memory. What passes between them is copied bytes.

Othismo currently runs as a single threaded message queue.

Protocols and traits

To enable code re-use and shared behaviors, Othismo supports protocols and traits.

A protocol describes the requests a single path takes:

## Something read whole.
protocol File { read -> */*, stat }

## A stream of bytes each way.
protocol Connection { watch -> application/octet-stream*, write application/octet-stream }

A trait describes the shape of a whole tree, in the same grammar as serves, and can use protocols for its paths:

## A listener, and the connections it accepts.
trait Listener {
  /                operator write text/plain
  /address         read -> text/plain
  /accept          watch -> text/plain*
  /{conn}/data     Connection
  /{conn}/remote   read -> text/plain
  /{conn}          remove
}

A trait can be used in two places. needs /net/tcp Listener says the object needs a whole Listener at /net/tcp. object StaticSite : FileTree says StaticSite serves a FileTree, alongside whatever else it serves.

Traits are names for shapes, not types to inherit from. HttpServer's console need is written out in its header rather than named as Console, and the real console still fits it.

This is also how stand-ins work. The runtime's console is a Console, and so is MemoryConsole, which touches nothing on the host. An image that needs a Console can be given either. That's how an image is tested.

The runtime's own traits, Console, Listener, Files, FileTree and the rest, are declared in its header, env.