Fix handling of DOCKER_HOST that begins with unix://

Fixes gh-22300

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/main/java/org/springframework/boot/buildpack/platform/docker/transport/LocalHttpClientTransport.java

@@ -50,6 +50,8 @@ import org.springframework.boot.buildpack.platform.system.Environment;
  */
 final class LocalHttpClientTransport extends HttpClientTransport {
 
+	private static final String UNIX_SOCKET_PREFIX = "unix://";
+
 	private static final String DOCKER_HOST = "DOCKER_HOST";
 
 	private static final HttpHost LOCAL_DOCKER_HOST = HttpHost.create("docker://localhost");
@@ -60,11 +62,17 @@ final class LocalHttpClientTransport extends HttpClientTransport {
 
 	static LocalHttpClientTransport create(Environment environment) {
 		HttpClientBuilder builder = HttpClients.custom();
-		builder.setConnectionManager(new LocalConnectionManager(environment.get(DOCKER_HOST)));
+		builder.setConnectionManager(new LocalConnectionManager(socketFilePath(environment)));
 		builder.setSchemePortResolver(new LocalSchemePortResolver());
 		return new LocalHttpClientTransport(builder.build());
 	}
 
+	private static String socketFilePath(Environment environment) {
+		String host = environment.get(DOCKER_HOST);
+		return (host != null && host.startsWith(UNIX_SOCKET_PREFIX)) ? host.substring(UNIX_SOCKET_PREFIX.length())
+				: host;
+	}
+
 	/**
 	 * {@link HttpClientConnectionManager} for local Docker.
 	 */

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/main/java/org/springframework/boot/buildpack/platform/docker/transport/RemoteHttpClientTransport.java

@@ -40,6 +40,8 @@ import org.springframework.util.Assert;
  */
 final class RemoteHttpClientTransport extends HttpClientTransport {
 
+	private static final String UNIX_SOCKET_PREFIX = "unix://";
+
 	private static final String DOCKER_HOST = "DOCKER_HOST";
 
 	private static final String DOCKER_TLS_VERIFY = "DOCKER_TLS_VERIFY";
@@ -63,8 +65,9 @@ final class RemoteHttpClientTransport extends HttpClientTransport {
 	}
 
 	private static boolean isLocalFileReference(String host) {
+		String filePath = host.startsWith(UNIX_SOCKET_PREFIX) ? host.substring(UNIX_SOCKET_PREFIX.length()) : host;
 		try {
-			return Files.exists(Paths.get(host));
+			return Files.exists(Paths.get(filePath));
 		}
 		catch (Exception ex) {
 			return false;

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/test/java/org/springframework/boot/buildpack/platform/docker/transport/HttpTransportTests.java

@@ -50,6 +50,15 @@ class HttpTransportTests {
 		assertThat(transport).isInstanceOf(LocalHttpClientTransport.class);
 	}
 
+	@Test
+	void createWhenDockerHostVariableIsUnixSchemePrefixedFileReturnsLocal(@TempDir Path tempDir) throws IOException {
+		String dummySocketFilePath = "unix://"
+				+ Files.createTempFile(tempDir, "http-transport", null).toAbsolutePath().toString();
+		Map<String, String> environment = Collections.singletonMap("DOCKER_HOST", dummySocketFilePath);
+		HttpTransport transport = HttpTransport.create(environment::get);
+		assertThat(transport).isInstanceOf(LocalHttpClientTransport.class);
+	}
+
 	@Test
 	void createWhenDoesNotHaveDockerHostVariableReturnsLocal() {
 		HttpTransport transport = HttpTransport.create((name) -> null);