fix: pin rustls to a single crypto provider preventing panics

[surpher]

disclaimer: The following PR description was prepared with help of Claude AI.

Before accepting these suggested changes, verify it doesn't break other libpact_ffi users.

Problem

Starting a TLS mock server panics and then aborts the host process. rustls cannot pick a crypto provider because both of its backend features are enabled:

thread '<unnamed>' panicked at rustls-0.23.43/src/crypto/mod.rs:249:14:
Could not automatically determine the process-level CryptoProvider from Rustls crate features.
Call CryptoProvider::install_default() before this point to select a provider manually, or make
sure exactly one of the 'aws-lc-rs' and 'ring' features is enabled.

The panic then poisons a lock inside pact_ffi, and the next pactffi_free_pact_handle unwraps the PoisonError from a context that cannot unwind, which turns a recoverable error into a hard abort:

thread '<unnamed>' panicked at pact_ffi/src/mock_server/handles.rs:3271:41:
called `Result::unwrap()` on an `Err` value: PoisonError { .. }
thread caused non-unwinding panic. aborting.

For an FFI consumer this is fatal rather than merely a failed test: the whole test host dies, taking unrelated tests with it. It reproduces through the FFI on libpact_ffi-v0.5.5 (and v0.5.4) on aarch64-apple-darwin via pactffi_create_mock_server_for_transport with an HTTPS transport, and equally via pactffi_get_tls_ca_certificate.

Root cause

Both providers get enabled by feature unification, because the workspace straddles two reqwest majors that default to different backends:

Crate	reqwest	Feature requested	Provider it forces
pact_matching, pact_models	0.12.28	rustls-tls-native-roots	__rustls-ring → ring
pact_ffi, pact_verifier, pact_consumer	0.13	rustls	__rustls-aws-lc-rs → aws-lc-rs

pact_mock_server 2.2.4 — which implements the TLS mock server — also depends on rustls, tokio-rustls and hyper-rustls with ring directly. Cargo unions all of it, so rustls ends up with both:

# cargo tree --edges no-dev --format "{f}" -p rustls
rustls v0.23.43 :: aws-lc-rs,aws_lc_rs,log,logging,ring,std,tls12

In reqwest 0.13, the rustls feature hard-wires the backend, whereas rustls-no-provider is the same feature set minus the forced backend:

rustls             = ["__rustls-aws-lc-rs", "dep:rustls-platform-verifier", "__rustls"]
rustls-no-provider = [                      "dep:rustls-platform-verifier", "__rustls"]

Change

Switch the three reqwest 0.13 dependencies from rustls to rustls-no-provider, leaving ring — already required by pact_mock_server — as the single provider:

• pact_ffi/Cargo.toml
• pact_verifier/Cargo.toml
• pact_consumer/Cargo.toml

Because the two features differ only in the forced backend, rustls-platform-verifier stays enabled and certificate verification behaviour is unchanged.

Result:

# cargo tree --edges no-dev --format "{f}" -p rustls
rustls v0.23.43 :: log,logging,ring,std,tls12

aws-lc disappears from the pact_ffi dependency graph entirely, which also drops the aws-lc-sys C build. Cargo.lock loses exactly two dependency edges (aws-lc-rs from quinn, quinn from reqwest); no packages are added or removed.

Verification

Built pact_ffi for aarch64-apple-darwin, aarch64-apple-ios and aarch64-apple-ios-sim, then ran the full test suite of a Swift FFI consumer (PactSwiftMockServer) against the resulting static libraries:

• Before: the two TLS mock server tests never complete — 2 CryptoProvider panics and 2 aborts per run.
• After: 54 passed / 0 failed on both macOS and iOS, 0 panics, 0 aborts. The previously fatal pactffi_get_tls_ca_certificate and HTTPS-transport mock server cases now pass.
• Confirmed nm reports no aws_lc symbols and ring_core symbols present in all three archives.

I have not run the pact-reference Rust test suite itself — worth a CI run, particularly anything covering pact_verifier's HTTPS client, since that is the code path whose provider selection now comes from the process-level default rather than from reqwest's feature.

Test logs after applying changes and re-building libpact_ffi binaries to use with PactSwiftMockServer:
pact-swift-mock-server_tests.log

[rholshausen]

Leave this one with me, it looks like it breaks things. I've had lots of issues with aws-lc-sys (just as they sorted out all the issues with ring someone decided we needed new issues). Didn't know about rustls-no-provider

[rholshausen]

I have released FFI 0.5.6 which hopefully fixes this issue. I'll close this PR.

[mefellows]

Awesome, thanks Ron