only determine default gateway within docker container if docker host differ from default (#648)

Author: qoomon

core/src/main/java/org/testcontainers/dockerclient/DockerClientConfigUtils.java

@@ -17,11 +17,13 @@ public class DockerClientConfigUtils {
     // See https://github.com/docker/docker/blob/a9fa38b1edf30b23cae3eade0be48b3d4b1de14b/daemon/initlayer/setup_unix.go#L25
     public static final boolean IN_A_CONTAINER = new File("/.dockerenv").exists();
 
+    @Deprecated
     @Getter(lazy = true)
-    private static final Optional<String> detectedDockerHostIp = Optional
-            .of(IN_A_CONTAINER)
-            .filter(it -> it)
-            .map(file -> DockerClientFactory.instance().runInsideDocker(
+    private static final Optional<String> detectedDockerHostIp = IN_A_CONTAINER ? getDefaultGateway() : Optional.empty();
+
+    @Getter(lazy = true)
+    private static final Optional<String> defaultGateway = Optional
+            .ofNullable(DockerClientFactory.instance().runInsideDocker(
                     cmd -> cmd.withCmd("sh", "-c", "ip route|awk '/default/ { print $3 }'"),
                     (client, id) -> {
                         try {
@@ -41,18 +43,21 @@ public class DockerClientConfigUtils {
             .map(StringUtils::trimToEmpty)
             .filter(StringUtils::isNotBlank);
 
+
+
     public static String getDockerHostIpAddress(DockerClientConfig config) {
-        return getDetectedDockerHostIp().orElseGet(() -> {
-            switch (config.getDockerHost().getScheme()) {
-                case "http":
-                case "https":
-                case "tcp":
-                    return config.getDockerHost().getHost();
-                case "unix":
-                    return "localhost";
-                default:
-                    return null;
-            }
-        });
+        switch (config.getDockerHost().getScheme()) {
+            case "http":
+            case "https":
+            case "tcp":
+                return config.getDockerHost().getHost();
+            case "unix":
+                if (IN_A_CONTAINER) {
+                    return getDefaultGateway().orElse("localhost");
+                }
+                return "localhost";
+            default:
+                return null;
+        }
     }
 }