When using new ApacheDockerHttpClient.Builder().build(), the ApacheDockerHttpClientImpl ctor is in turn called which builds an HttpClient using

httpClient = HttpClients.custom() .setRequestExecutor(new HijackingHttpRequestExecutor(null)) .setConnectionManager(connectionManager) .setDefaultRequestConfig(defaultRequest.build()) .disableConnectionState() .build();
(https://github.com/docker-java/docker-java/blob/main/docker-java-transport-httpclient5/src/main/java/com/github/dockerjava/httpclient5/ApacheDockerHttpClientImpl.java#L122)

Looking at the javadoc for HttpClients, https://hc.apache.org/httpcomponents-client-5.2.x/current/httpclient5/apidocs/ it says that it will use the native system properties for specifying proxy hosts only if useSystemProperties() is called before calling build().

If I'm following this correctly, the code above is calling build() without calling useSystemProperties() and therefore we are not able to specify a https proxy host using the system properties with ApacheDockerHttpClient.

Should that call be inserted just before .build() or was it intentionally left out? If it was left out on purpose, how would one specify an http proxy host when using ApacheDockerHttpClient?

To give context, I followed a rabbit hole from https://github.com/bmuschko/gradle-docker-plugin/blob/master/src/main/java/com/bmuschko/gradle/docker/internal/services/DockerClientService.java#L107 that lead me here.