Support local socket path in DOCKER_HOST

Prior to this commit, if a DOCKER_HOST environment variable was present
when attempting to communicate with a Docker daemon, it was assumed
that the value of that variable was an address that could be used to
create an HTTP connection to a remote daemon. In some cases, the value
of the variable is the path to a local socket file, which would cause
the HTTP connection to fail.

This commit adds additional validation of the value of the DOCKER_HOST
environment variable to determine whether it is a remote address or
a local socket file and create the appropriate connection type.

Fixes gh-21173

Author: scottfrederick

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

@@ -29,6 +29,7 @@
  * HTTP transport used for docker access.
  *
  * @author Phillip Webb
+ * @author Scott Frederick
  * @since 2.3.0
  */
 public interface HttpTransport {
@@ -94,7 +95,7 @@ static HttpTransport create() {
 	 */
 	static HttpTransport create(Environment environment) {
 		HttpTransport remote = RemoteHttpClientTransport.createIfPossible(environment);
-		return (remote != null) ? remote : LocalHttpClientTransport.create();
+		return (remote != null) ? remote : LocalHttpClientTransport.create(environment);
 	}
 
 	/**

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

@@ -40,6 +40,7 @@
 
 import org.springframework.boot.buildpack.platform.socket.DomainSocket;
 import org.springframework.boot.buildpack.platform.socket.NamedPipeSocket;
+import org.springframework.boot.buildpack.platform.system.Environment;
 
 /**
  * {@link HttpClientTransport} that talks to local Docker.
@@ -49,15 +50,17 @@
  */
 final class LocalHttpClientTransport extends HttpClientTransport {
 
+	private static final String DOCKER_HOST = "DOCKER_HOST";
+
 	private static final HttpHost LOCAL_DOCKER_HOST = HttpHost.create("docker://localhost");
 
 	private LocalHttpClientTransport(CloseableHttpClient client) {
 		super(client, LOCAL_DOCKER_HOST);
 	}
 
-	static LocalHttpClientTransport create() {
+	static LocalHttpClientTransport create(Environment environment) {
 		HttpClientBuilder builder = HttpClients.custom();
-		builder.setConnectionManager(new LocalConnectionManager());
+		builder.setConnectionManager(new LocalConnectionManager(environment.get(DOCKER_HOST)));
 		builder.setSchemePortResolver(new LocalSchemePortResolver());
 		return new LocalHttpClientTransport(builder.build());
 	}
@@ -67,13 +70,13 @@ static LocalHttpClientTransport create() {
 	 */
 	private static class LocalConnectionManager extends BasicHttpClientConnectionManager {
 
-		LocalConnectionManager() {
-			super(getRegistry(), null, null, new LocalDnsResolver());
+		LocalConnectionManager(String host) {
+			super(getRegistry(host), null, null, new LocalDnsResolver());
 		}
 
-		private static Registry<ConnectionSocketFactory> getRegistry() {
+		private static Registry<ConnectionSocketFactory> getRegistry(String host) {
 			RegistryBuilder<ConnectionSocketFactory> builder = RegistryBuilder.create();
-			builder.register("docker", new LocalConnectionSocketFactory());
+			builder.register("docker", new LocalConnectionSocketFactory(host));
 			return builder.build();
 		}
 
@@ -103,12 +106,18 @@ private static class LocalConnectionSocketFactory implements ConnectionSocketFac
 
 		private static final String WINDOWS_NAMED_PIPE_PATH = "//./pipe/docker_engine";
 
+		private final String host;
+
+		LocalConnectionSocketFactory(String host) {
+			this.host = host;
+		}
+
 		@Override
 		public Socket createSocket(HttpContext context) throws IOException {
 			if (Platform.isWindows()) {
-				return NamedPipeSocket.get(WINDOWS_NAMED_PIPE_PATH);
+				return NamedPipeSocket.get((this.host != null) ? this.host : WINDOWS_NAMED_PIPE_PATH);
 			}
-			return DomainSocket.get(DOMAIN_SOCKET_PATH);
+			return DomainSocket.get((this.host != null) ? this.host : DOMAIN_SOCKET_PATH);
 		}
 
 		@Override

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

@@ -16,6 +16,9 @@
 
 package org.springframework.boot.buildpack.platform.docker.transport;
 
+import java.nio.file.Files;
+import java.nio.file.Paths;
+
 import javax.net.ssl.SSLContext;
 
 import org.apache.http.HttpHost;
@@ -53,7 +56,10 @@ static RemoteHttpClientTransport createIfPossible(Environment environment) {
 
 	static RemoteHttpClientTransport createIfPossible(Environment environment, SslContextFactory sslContextFactory) {
 		String host = environment.get(DOCKER_HOST);
-		return (host != null) ? create(environment, sslContextFactory, HttpHost.create(host)) : null;
+		if (host == null || Files.exists(Paths.get(host))) {
+			return null;
+		}
+		return create(environment, sslContextFactory, HttpHost.create(host));
 	}
 
 	private static RemoteHttpClientTransport create(Environment environment, SslContextFactory sslContextFactory,

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

@@ -16,27 +16,40 @@
 
 package org.springframework.boot.buildpack.platform.docker.transport;
 
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.Collections;
 import java.util.Map;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
  * Tests for {@link HttpTransport}.
  *
  * @author Phillip Webb
+ * @author Scott Frederick
  */
 class HttpTransportTests {
 
 	@Test
-	void createWhenHasDockerHostVariableReturnsRemote() {
-		Map<String, String> environment = Collections.singletonMap("DOCKER_HOST", "192.168.1.0");
+	void createWhenDockerHostVariableIsAddressReturnsRemote() {
+		Map<String, String> environment = Collections.singletonMap("DOCKER_HOST", "tcp://192.168.1.0");
 		HttpTransport transport = HttpTransport.create(environment::get);
 		assertThat(transport).isInstanceOf(RemoteHttpClientTransport.class);
 	}
 
+	@Test
+	void createWhenDockerHostVariableIsFileReturnsLocal(@TempDir Path tempDir) throws IOException {
+		String dummySocketFilePath = 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);

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

@@ -16,6 +16,9 @@
 
 package org.springframework.boot.buildpack.platform.docker.transport;
 
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.function.Consumer;
@@ -24,6 +27,7 @@
 
 import org.apache.http.HttpHost;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
 
 import org.springframework.boot.buildpack.platform.docker.ssl.SslContextFactory;
 
@@ -40,7 +44,7 @@
  */
 class RemoteHttpClientTransportTests {
 
-	private Map<String, String> environment = new LinkedHashMap<>();
+	private final Map<String, String> environment = new LinkedHashMap<>();
 
 	@Test
 	void createIfPossibleWhenDockerHostIsNotSetReturnsNull() {
@@ -49,7 +53,16 @@ void createIfPossibleWhenDockerHostIsNotSetReturnsNull() {
 	}
 
 	@Test
-	void createIfPossibleWhenDockerHostIsSetReturnsTransport() {
+	void createIfPossibleWhenDockerHostIsFileReturnsNull(@TempDir Path tempDir) throws IOException {
+		String dummySocketFilePath = Files.createTempFile(tempDir, "remote-transport", null).toAbsolutePath()
+				.toString();
+		this.environment.put("DOCKER_HOST", dummySocketFilePath);
+		RemoteHttpClientTransport transport = RemoteHttpClientTransport.createIfPossible(this.environment::get);
+		assertThat(transport).isNull();
+	}
+
+	@Test
+	void createIfPossibleWhenDockerHostIsAddressReturnsTransport() {
 		this.environment.put("DOCKER_HOST", "tcp://192.168.1.2:2376");
 		RemoteHttpClientTransport transport = RemoteHttpClientTransport.createIfPossible(this.environment::get);
 		assertThat(transport).isNotNull();