coap-handler

The coap-handler crate defines an interface between a [CoAP] server (that listens for requests on the network and parses the messages) and request handlers (that process the requests and creates responses from them).

The interface is generic over message formats by using the [coap-message] crate, which allows the handler to construct the response right into the send buffer prepared by the server implementation. By separating the request processing and the response phase, a server can be implemented even on network stacks that have only a single network buffer.

Convenience, example and reference implementations are available in the [coap-handler-implementations] crate.

Known shortcomings of the current interface are:

• No consideration for asynchronous processing.

• Handler mutability is a bit iffy -- there's no way yet for the server to express any promise about only running one handler at a time, thus handlers often hold shared references to a [RefCell] that is [borrow_mut()]'d (if no other code that can be concurrent with the CoAP server can have access to the T), or [try_borrow_mut()]'d (and errs back with a 5.03 Max-Age:0 response).

  Alternatives (where multiple handlers could be built based on a single mutable reference to their data) are being explored.

• Multiple responses (as, for example, in observations) are not supported.

The main item of this crate is the [Handler] trait. The [Reporting] trait can be implemented in addition to [Handler] to ease inclusion of the rendered resource in discovery, eg. through /.well-known/core as implemented in [coap-handler-implementations].

License: MIT OR Apache-2.0