Content type is overridden to application/json for message providers

[matdodgson]

Software versions

• OS: Ubuntu 22.04
• Consumer Pact library: Pact JS 9.18.1
• Provider Pact library: Pact JS 12.1.0
• Node Version: 18.17.0

Issue Checklist

Please confirm the following:

• I have upgraded to the latest
• I have the read the FAQs in the Readme
• I have triple checked, that there are no unhandled promises in my code and have read the section on intermittent test failures

Expected behaviour

That I can return an XML string from a message provider and be able to verify a pact from a message consumer that is also based on an XML string.

Actual behaviour

The content type on the provider is overridden to application/json so the verification always fails. See here:

pact-js/src/messageProviderPact.ts

Line 153 in ce5973c

res.header('Content-Type', 'application/json; charset=utf-8');

Additionally, from first glance it appears that MessageProviderPact assumes that message providers only return JSON. See here:

pact-js/src/messageProviderPact.ts

Line 123 in ce5973c

// Invoke the handler, and return the JSON response body

Steps to reproduce

• Create a consumer message contract where the content is XML (ie. not JSON).
• Create a message provider that returns an XML string
• Verify the message contract

[mefellows]

Thanks for raising.

I think one way to address it, is to set the content-type header in

pact-js/src/messageProviderPact.ts

Line 135 in ce5973c

res.header('PACT_MESSAGE_METADATA', metadata);

. It would have to extract the content type from either the metadata or we would need to find another way to explicitly pass this through.

We would also need to fix

pact-js/src/messageProviderPact.ts

Line 137 in ce5973c

return res.json(messageFromHandler.message);

which currently sends it as JSON, instead of whatever type it should be.