GenericContainer::getHost() returns misleading values across platforms

[ciaranmcnulty]

When running on MacOS with Docker Desktop for Mac getHost() returns an IP address of the Docker host which is running inside a managed VM. This IP address is not routable from MacOS, so tests fail with timeouts.

My understanding of getHost is that it should return the host at which ports are being exposed, which on MacOS should be localhost.

The Ruby implementation roughly does the following:

• Use TC_HOST if it is present
• If DOCKER_HOST or DOCKER_URL are set but not parsable as a URL, use localhost
• If DOCKER_HOST or DOCKER_URL are set and use a network schema (tcp or http*), use the host portion of that URL
• If DOCKER_HOST is not set (so would default to local), or is set to a local schema (unix or npipe):
  • If we are in a container (detected via presence of /.dockerenv), use the default gateway
  • If we are not in a container, use localhost

It'd be worth discussing whether that's the same route we should go with in PHP

[ciaranmcnulty]

The Java version is similar-yet-different:

https://github.com/testcontainers/testcontainers-java/blob/6e2b091390e14e3b97407b4823605441f171fc5f/core/src/main/java/org/testcontainers/dockerclient/DockerClientProviderStrategy.java#L437