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.

Along with the interface, the crate provides some simple implementations, from the generic "4.04 Not Found" responder up to a handler that creates a [write] formatter for GET-only resources, and even provides [block-wise transfer] that. The [implementations::SimpleCBORWrapper] enables the easy creation of [serde_cbor] based resource implementations with GET, PUT and POST support in CBOR format. The HandlerBuilder implements crude static path based routing that may suffice for some applications, and is also useful to get started quickly.

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

License: LGPL-3.0