Service Stack

Types implementing the Service trait may be the one actually providing the Result directly or indirectly. They might also contain as one of its properties another Service that somehow produces a Result instead. The exact mode of operation is freely defined by the Service implementation.

An easy example of this is a Timeout service which contains any other Service but will return a timeout 'error' in case that service took more then the defined deadline to produce a result. A service such as Timeout is referred to as a Layer and is usually created using an implementation of the Layer trait, as defined in https://github.com/plabayo/rama/blob/main/rama-core/src/layer/mod.rs.

You can nest Services as deep as you want and some can even contain multiple ones that are either all helping in producing a response for the given request or where it branches of and calls on of the wrapped services depending on some defined conditions. All is possible. The contract is simple, the implementation is yours.

As such a topology such as the following is easily possible, where each node in the graph is a service:

What might not be clear on the graph, but what is important to understand, is that a response can be produced at any layer of such a service stack. While ideally it is produced by a leaf service, there will be scenarios where this is not the case.

In the case of the example above it will be the Timeout layer Service to return an Error early in case the inner Service::serve call takes longer then expanded as defined by its Duration property.