Properly testing Android certificate verification logic requires calling
into framework code. That cannot be done through Robolectric (framework
APIs are faked). Hence, actual instrumentation tests are needed.

Having said that, after some exploration on the state of Bazel/Android
instrumentation tests, I've realized that the current state of things is
non-optimal. As a stopgap solution (until the infrastructure improves),
we've decided to test the JNI layer through unittests which fake
X509Util. This should be a reasonable middle ground, as X509Util is mostly a
compatibility layer on top of Android's API.

This CL introduces FakeX509Util and adds allows tests to swap that in by
adding a test-only API to AndroidNetworkLibrary.

FakeX509Util is not particularly clever: from its perspective a
certificate is just a string and for a verification to succeeds, all
certificates in a chain must be root certificates (weird, but we don't
really care about its logic).

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Add utility functions to translate between:
- C++ strings and Java strings
- C++ vector of bytes and Java array of bytes

These utility functions will be used in the next commit to implement the
JNI layer for certificate verifications (and its unit tests).

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Add native hooks for AndroidNetworkLibrary Java APIs.

Write unittests that mimic calls from native to Java for these new
hooks, by making use of a fake X509Util and additional test-only Java
-> C++ JNI calls.

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Signed-off-by: Stefano Duo <stefanoduo@google.com>

* Extend FakeX509Util with host and authType checks
* Add tests for host and authType
* Refactor UTF conversion in its own library
* Add unit tests for them

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Drop string conversion utilities since they're no longer needed. The
conversion is now handled on the Java side.
Document the expectation that strings passed to
jvm_verify_x509_cert_chain and call_jvm_verify_x509_cert_chain must be
UTF-8 encoded.

Also add a missing DeleteLocalRef.

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Signed-off-by: Stefano Duo <stefanoduo@google.com>

Signed-off-by: Stefano Duo <stefanoduo@google.com>