Smarter API version handling

[rhuss]

Description

As described in fabric8io/fabric8-maven-plugin#1200 the minimal version 1.18 used by d-m-p gets rejected for newer Docker daemons (e.g. those having 1.35).

Actually we are compliant with the newer versions (its a minimal version after all), so I see two solutions:

• If possible, we don't send an API version. However when we use features which require a minimal version of 1.21 this still will still break.

• We send a test request to the Daemon, and check whether it succeeds. In the return response there's a header Api-Version: which holds the actual Docker daemon version. So if this test request because of a too low version, we can just pick up that version and use it as minimal version for us.

[rohanKanojia]

@rhuss : Could you please give some code pointer related to this?

[rhuss]

During initialization we check which features are used and then calculate the minimal version required:

docker-maven-plugin/src/main/java/io/fabric8/maven/docker/AbstractDockerMojo.java

Line 215 in ccb3adb

this.minimalApiVersion = initImageConfiguration(getBuildTimestamp());

If nothing special is used its, the default of 1.18 for now.The docker client will be created with this version

docker-maven-plugin/src/main/java/io/fabric8/maven/docker/service/DockerAccessFactory.java

Lines 38 to 39 in 9e59f35

	String version = dockerAccessContext.getMinimalApiVersion() != null ? dockerAccessContext.getMinimalApiVersion() : API_VERSION;
	DockerAccess access = new DockerAccessWithHcClient("v" + version, connectionParam.getUrl(),

Then, for each request this version is send to the daemon

docker-maven-plugin/src/main/java/io/fabric8/maven/docker/access/UrlBuilder.java

Line 209 in ee113cd

return String.format("%s/%s/%s", baseUrl, apiVersion, path);

Actually when we get back an error that indicates that's a version mismatch like in the first post, we should adapt the minimal version to that provided in the response header.

Alternatively, and actually i like that better, we could send a single request to some version endpoint and pick up the api version. If this version is larger then our minimal version we just use that for our minimal version. otherwise we throw an error that we can't talk to the daemon (as our minimal version is higher of what the daemon provides).