Good way to offer both LWCs and a REST API in the same code?

Question

We are building a product that will make use of multiple Lightning Web Components (LWCs), and some of those will make use of @AuraEnabled Apex methods. We also plan to provide an API that non-LWC UI can access. (In the past, we have provided such APIs by using @RestResource Apex classes receiving and sending JSON.)

Our present idea is to go ahead and build the @AuraEnabled Apex code methods/classes first, and then later wrap them in a single @RestResource Apex class that dispatches the requests according to the URL pattern to the relevant @AuraEnabled methods/classes. (I assume in this case the @AuraEnabled(cacheable=true) annotation will be ignored.)

Has anyone done this? Pros/cons?

Answer 1

Initial coding of the KISS solution:

global class Aura {

    // Call this from the REST API
    public static Object execute(String operation, String requestJson) {
        switch on operation {
            when 'op1' {
                return op1((Op1Params) JSON.deserialize(requestJson, Op1Params.class));
            }
            when 'op2' {
                return op2((Op2Params) JSON.deserialize(requestJson, Op2Params.class));
            }
            ...
        }
    }

    // Method used by LWC
    @AuraEnabled
    global static Result__c op1(Op1Params params) {
        ...
    }

    // Method used by LWC
    @AuraEnabled
    global static Result__c op2(Op2Params params) {
        ...
    }

    ...
}

and:

@RestResource(urlMapping = '/xyz/...')
global inherited sharing class Rest {

    ....

    @HttpPost
    global static void doPost() {

        Savepoint sp = Database.setSavepoint();
        try {
            dispatch(RestContext.request, RestContext.response);
        } catch (AuraHandledException e) {
            res.responseBody = Blob.valueOf(e.getMessage());
            res.statusCode = BAD_REQUEST;
            Database.rollback(sp);
        } catch (Exception e) {
            res.responseBody = Blob.valueOf(sanitizedMessage(e));
            res.statusCode = INTERNAL_SERVER_ERROR;
            Database.rollback(sp);
        }
    }

    private static void dispatch(RestRequest req, RestResponse res) {

        String[] parts = req.requestURI.split('\\/');
        String operation = parts.size() > 1 ? parts[1] : null;
        String requestJson = req.requestBody.toString();

        Object result = Aura.execute(operation, requestJson);

        res.responseBody = toJsonBlob(result);
        res.statusCode = OK;
    }
}