Report diff between expected and actual request body sent to a mock

It would be nice to be able to fail a test with a clear diff between the expected and actual request body sent to a mock.

Use case: I'm mocking a third-party XML-based API and want to verify that all requests to it contain the expected data. My mocks currently have a MethodExactMatcher, PathExactMatcher and BodyExactMatcher so they only respond when the exact expected API call is done. For example:

Mock::given(method(Post))
        .and(path(request_path))
        .and(body_string(expected_request_body))
        .respond_with(response_template)
        .mount(mock_server)
        .await;

The drawback of this approach is that when the actual request body contains a small error - the most common place for mistakes - a test fails with a 404 Not Found response because the BodyExactMatcher returns false. Those failures are a bit cumbersome to debug, having to enable debug logging so my code logs sent messages and rerun the test. It would be much nicer when a test failed with a clear diff between the expected and actual request body.

Is there a way to create such behavior with the current wiremock APIs? As far as I can see a custom matcher cannot report errors, and there's no way to add custom expectations either.

Start by reviewing BodyExactMatcher, MethodExactMatcher, and the mock failure path described in the issue, then check how custom matchers and expectations are exposed by the current wiremock APIs. Done means a mismatched request body produces a clear expected-versus-actual diff during test failure without requiring debug logging.