Running trust evaluation system api call on worker thread effectively unblocks main isolate when it attempts to establish https connection.
Execution of the worker thread is implemented via dart native port infrastructure which allows to run C++ code as a dart message handler.
TrustEvaluateHandlerFunc (if provided by platform-dependent SSLCertContext) is that handler, only mac(ios) implementation provides it.
Asynchrony of CertificateVerificationCallback (for mac/ios) is implemented via [ssl_verify_retry] return code which allows to suspend ssl handshake until certificate trust is confirmed.
When dart's _RawSecureSocket.secureHandshake() method that initiated ssl's handshake received this return code it knows it has to wait for a future that is completed by another callback([rpEvaluteResponse]) that waits for trust evaluation handler response.
rpEvaluateResponse purpose is to listen for response from TrustEvaluateHandler and also invoke user-provided [badCertficateCallback] that can override trust decision for a given connection request, for a given certificate.
Once that future is completed and CertificateVerificationCallback knows whether to trust a certificate or not, _secureHandshake retries ssl handshake.
Bug: https://github.com/dart-lang/sdk/issues/41519
Change-Id: Ifee18639c78099ec77cad50000444bc6c7b9369b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/165520
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>
Ryan Macnak