Clarify message-related FFI

[JP-Ellis]

Summary

We need to clarify how the Foreign Function Interface (FFI) should be used in relation to message interactions. Currently, there is confusion regarding the purpose and distinction between the following elements:

• PactHandle vs MessagePactHandle
• InteractionHandle vs MessageHandle

Motivation

Recent contributions to Pact Python have added support for message pacts using the FFI library, which has been greatly appreciated. However, this has also highlighted some ambiguities in how best to use the FFI for message interactions. Clarifying these distinctions will improve usability and reduce confusion for developers.

Proposed Solution

The goal is to deprecate MessagePactHandle in favor of PactHandle, and MessageHandle in favor of InteractionHandle. Where overlapping functionality exists, a simple deprecation notice will be sufficient initially.

In cases where functionality exclusive to MessagePactHandle or MessageHandle needs to be incorporated into their respective replacements (PactHandle or InteractionHandle), those features should be added before deprecation.

Tasks

• feat(ffi): add with_metadata #439

• to identify

• Document how FFI should be used when verifying message pacts

  Once the FFI is disambiguated, there is still a need for a clear description as to how messages should be verified by the upstream languages. This is needed because the transport mechanism (e.g., queuing system) is abstracted away and the upstream language needs to handle that.

[YOU54F]

this confused me when trying to create a repro with a v4 pact so clarification is certainly welcome

https://github.com/pact-foundation/pact-reference/pull/437/files#diff-d6fdf640e7952e605d5a425978e18d3aa2606501c1b9743426f76dc5989178daR1458

[YOU54F]

if that deeplink doesnt work
this is the test

pact-reference/rust/pact_ffi/tests/tests.rs

Line 1458 in 37bc38f

// Issue - Should we be able to set version of message pact, and write to file containing v4 interactions