Custom headers containing commas are incorrectly split (pact-js#1058)

[mefellows]

Summary

The parse_header function in pact_models/src/headers.rs incorrectly splits all unknown headers by comma. Custom headers containing JSON or other comma-separated data are broken into invalid fragments, causing verification failures.

Reproduction

Branch with reproduction tests: repro/issue-header-comma-split

Root Cause

In pact_models/src/headers.rs:30-33 - the logic is inverted:

• Current: Split everything except known single-value headers
• Should be: Split only known multi-value headers

Suggested Fix

Use MULTI_VALUE_HEADERS allowlist instead of SINGLE_VALUE_HEADERS blocklist, following the JVM implementation.

Related

• Downstream: Header is parsed incorrectly pact-js#1058
• multi-valued headers are incorrectly verified #300
• Pact-JVM fix: pact-foundation/pact-jvm@8c5b0b1

[YOU54F]

Should we allow for an escape hatch for users to specify their own multi value headers or to extend the supported list? or does that become problematic, in case a consumer has specified an additional value which the provider isn’t aware of.

[mefellows]

OK so update on this - the fix didn't work. The issue is actually upstream of it (or at least, another issue is upstream of it - because the repro did show the bug at the lowest level).

The chain of calls is this:

• pactffi_with_header_v2
• from_integration_json_v2
  • This attempts to parse the value into JSON (expecting a matcher, generator etc.)
  • It IS JSON, but isn't a matcher
  • It doesn't see a matcher, so instead extracts the value key
  • The log entry pact_ffi::mock_server::handles: Configuring a normal value using the 'value' attribute shows this
  • There is no value, so it treats the value as "" (pact_ffi::mock_server::handles: parsed header value: Left(""))
  • Fail: Mismatches: [HeaderMismatch { key: "x-special-header", expected: "", actual: "{\"id\":\"asd-asdasd-sd\",\"additionalInfo\":\"some additional string\"}", mismatch: "Mismatch with header 'x-special-header': Expected '{\"id\":\"asd-asdasd-sd\",\"additionalInfo\":\"some additional string\"}' to be equal to ''" }]

I then decided to cheat by passing in { "value": {"id":"asd-asdasd-sd","additionalInfo":"some additional string"} }, however it fails as it reorders the keys :)

Mismatch with header 'x-special-header': Expected '{"id":"asd-asdasd-sd","additionalInfo":"some additional string"}' to be equal to '{"additionalInfo":"some additional string","id":"asd-asdasd-sd"}'

Need to think about how to do this safely 🤔 .