dream/context

Request context for your application

Context holds per-request data that changes with every request—user authentication, session info, request IDs, etc. It’s passed to every middleware and controller.

The Default Context

Dream provides AppContext with just a request_id field. It’s fine for simple apps, but most applications will want their own context type.

Custom Context

Define your own context type to hold whatever per-request data you need:

pub type MyContext {
  MyContext(
    request_id: String,
    user: Option(User),
    session: Session,
    permissions: List(String),
  )
}

Then pass it to your server:

dream.new()
|> dream.context(MyContext(
     request_id: "",
     user: None,
     session: empty_session(),
     permissions: []
   ))
|> dream.services(my_services)
|> dream.router(my_router)
|> dream.listen(3000)

Enriching Context in Middleware

Middleware can update the context as requests flow through:

pub fn auth_middleware(request, context, services, next) {
  case extract_token(request) {
    Ok(token) -> {
      let user = verify_token(services.db, token)
      let new_context = MyContext(..context, user: Some(user))
      next(request, new_context, services)
    }
    Error(_) -> unauthorized_response()
  }
}

The type system ensures your controllers receive the right context type.

Types

AppContext

</>

Default context with just a request ID

Use this for simple applications or replace it with your own context type. Most real applications will want custom context for user data, sessions, etc.

pub type AppContext {
  AppContext(request_id: String)
}

Constructors

```
AppContext(request_id: String)
```

Values

new_context

</>

pub fn new_context(request_id: String) -> AppContext

Create a new AppContext

Helper for creating the default context. If you’re using a custom context, you’ll create it directly without this function.