Handle HTTP 407 with clear error message

Refine error handling logic so that HTTP 407 (Proxy Authentication
Required) responses from the Docker daemon are treated as plain
text rather than JSON.

See gh-47180

Signed-off-by: Siva Sai Udayagiri <[email protected]>

Author: siva-sai-udaygiri

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

@@ -22,6 +22,7 @@
 import java.io.OutputStream;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.nio.charset.StandardCharsets;
 
 import org.apache.hc.client5.http.classic.HttpClient;
 import org.apache.hc.client5.http.classic.methods.HttpDelete;
@@ -36,6 +37,7 @@
 import org.apache.hc.core5.http.HttpEntity;
 import org.apache.hc.core5.http.HttpHost;
 import org.apache.hc.core5.http.HttpRequest;
+import org.apache.hc.core5.http.HttpStatus;
 import org.apache.hc.core5.http.io.entity.AbstractHttpEntity;
 
 import org.springframework.boot.buildpack.platform.io.Content;
@@ -160,14 +162,27 @@ private Response execute(HttpUriRequest request) {
 			beforeExecute(request);
 			ClassicHttpResponse response = this.client.executeOpen(this.host, request, null);
 			int statusCode = response.getCode();
+
 			if (statusCode >= 400 && statusCode <= 500) {
 				byte[] content = readContent(response);
 				response.close();
+
+				if (statusCode == HttpStatus.SC_PROXY_AUTHENTICATION_REQUIRED) {
+					String detail = (content != null && content.length > 0)
+							? new String(content, StandardCharsets.UTF_8) : null;
+
+					String msg = "Proxy authentication required for host: " + this.host.toHostString() + ", uri: "
+							+ request.getUri() + (StringUtils.hasText(detail) ? " - " + detail : "");
+
+					throw new ProxyAuthenticationException(msg);
+				}
+
 				Errors errors = (statusCode != 500) ? deserializeErrors(content) : null;
 				Message message = deserializeMessage(content);
 				throw new DockerEngineException(this.host.toHostString(), request.getUri(), statusCode,
 						response.getReasonPhrase(), errors, message);
 			}
+
 			return new HttpClientResponse(response);
 		}
 		catch (IOException | URISyntaxException ex) {

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

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2012-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.buildpack.platform.docker.transport;
+
+public class ProxyAuthenticationException extends RuntimeException {
+
+	public ProxyAuthenticationException(String message) {
+		super(message);
+	}
+
+	public ProxyAuthenticationException(String message, Throwable cause) {
+		super(message, cause);
+	}
+
+}