[GitHub] [httpcomponents-core] ok2c commented on a diff in pull request #390: Add a "Forwarded" HttpRequestInterceptor to add the "Forwarded" HTTP header.

["ok2c (via GitHub)" <gi...@apache.org>]

ok2c commented on code in PR #390:
URL: https://github.com/apache/httpcomponents-core/pull/390#discussion_r1104408830


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httpcore5/src/main/java/org/apache/hc/core5/http/protocol/ForwardedRequest.java:
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@@ -0,0 +1,159 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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
+ *
+ *   http://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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+
+package org.apache.hc.core5.http.protocol;
+
+import java.io.IOException;
+
+import org.apache.hc.core5.annotation.Contract;
+import org.apache.hc.core5.annotation.ThreadingBehavior;
+import org.apache.hc.core5.http.EndpointDetails;
+import org.apache.hc.core5.http.EntityDetails;
+import org.apache.hc.core5.http.Header;
+import org.apache.hc.core5.http.HttpException;
+import org.apache.hc.core5.http.HttpRequest;
+import org.apache.hc.core5.http.HttpRequestInterceptor;
+import org.apache.hc.core5.http.HttpVersion;
+import org.apache.hc.core5.http.ProtocolException;
+import org.apache.hc.core5.http.ProtocolVersion;
+import org.apache.hc.core5.http.message.BasicHeader;
+import org.apache.hc.core5.net.URIAuthority;
+import org.apache.hc.core5.util.Args;
+
+/**
+ * The ForwardedHeaderInterceptor class is a `HttpRequestInterceptor` that can be used to add the
+ * Forwarded header to an HTTP request. The Forwarded header is used to capture information about
+ * the intermediate nodes that a request has passed through. This information can be useful for
+ * security purposes or for debugging purposes.
+ * <p>
+ * The Forwarded header consists of a list of key-value pairs separated by semicolons. The keys that
+ * can be used in the Forwarded header include "host", "port", "proto", "for", and "by". The host
+ * key is used to specify the host name or IP address of the request authority. The port key is used
+ * to specify the port number of the request authority. The proto key is used to specify the
+ * protocol version of the request. The for key is used to specify the IP address of the client
+ * making the request. The by key is used to specify the IP address of the node adding the Forwarded
+ * header.
+ * <p>
+ * When multiple proxy servers are involved in forwarding a request, each proxy can add its own
+ * Forwarded header to the request. This allows for the capture of information about each
+ * intermediate node that the request passes through.
+ * <p>
+ * In this implementation, the Forwarded header is added to the request by the `process` method. The
+ * method first retrieves the ProtocolVersion and URIAuthority from the HttpContext. The
+ * ProtocolVersion is used to determine the proto key value and the URIAuthority is used to
+ * determine the host and port key values. The method also retrieves the EndpointDetails and
+ * "X-Forwarded-For" header from the HttpContext, if they exist. The EndpointDetails is used to
+ * determine the for key value and the "X-Forwarded-For" header is used to determine the by key
+ * value. If the "X-Forwarded-For" header does not exist, the by key value is set to "unknown".
+ * <p>
+ * The Forwarded header is added to the request by calling the `HttpRequest.addHeader` method. If a
+ * Forwarded header already exists in the request, the new key-value pairs are appended to the
+ * existing header.
+ *
+ * @since 5.3
+ */
+@Contract(threading = ThreadingBehavior.IMMUTABLE)
+public class ForwardedRequest implements HttpRequestInterceptor {
+
+    /**
+     * The name of the header to set in the HTTP request.
+     */
+    private static final String X_FORWARDED_HEADER_NAME = "X-Forwarded-For";
+
+    /**
+     * The name of the header to set in the HTTP request.
+     */
+    private static final String FORWARDED_HEADER_NAME = "Forwarded";
+
+
+    /**
+     * Singleton instance.
+     */
+    public static final HttpRequestInterceptor INSTANCE = new ForwardedRequest();
+
+
+    /**
+     * Adds a Forwarded header to the specified HTTP request.
+     *
+     * @param request the HTTP request to add the Forwarded header to
+     * @param entity  the entity details associated with the request, or null if the request does
+     *                not contain an entity
+     * @param context the HTTP context for the request
+     * @throws HttpException if an error occurs while adding the header
+     * @throws IOException   if an I/O error occurs while adding the header
+     */
+    @Override
+    public void process(final HttpRequest request, final EntityDetails entity, final HttpContext context) throws HttpException, IOException {
+
+        Args.notNull(request, "HTTP request");
+        Args.notNull(context, "HTTP context");
+
+        final ProtocolVersion ver = context.getProtocolVersion() != null ? context.getProtocolVersion() : HttpVersion.HTTP_1_1;
+
+        final URIAuthority authority = request.getAuthority();
+        if (authority == null) {
+            throw new ProtocolException("Request authority not specified");
+        }
+
+        final int port = authority.getPort();
+
+        final StringBuilder valueBuilder = new StringBuilder();
+        valueBuilder.append("host=").append(authority.getHostName());
+
+        if (port != -1) {
+            valueBuilder.append(";port=").append(port);
+        }
+
+        final String protoValue = ver.getProtocol();
+        if (protoValue != null) {
+            valueBuilder.append("proto=").append(protoValue);
+        }
+
+
+        final EndpointDetails endpointDetails = (EndpointDetails) context.getAttribute(HttpCoreContext.CONNECTION_ENDPOINT);
+
+        // Add the "for" property
+        if (endpointDetails != null) {
+            valueBuilder.append(";for=").append(endpointDetails.getRemoteAddress().toString());
+        }
+
+        final String byValue = (String) context.getAttribute(X_FORWARDED_HEADER_NAME);
+        if (byValue != null) {
+            valueBuilder.append(";by=").append(byValue);
+        } else {
+            valueBuilder.append(";by=unknown");
+        }
+
+        final Header header = request.getFirstHeader(X_FORWARDED_HEADER_NAME);

Review Comment:
   @arturobernalg If all you want is to override a header value if it has already been set, use `Header#setHeader`. It is massively more efficient then `Header#getFirstHeader`, `Header#removeHeader`, `Header#addHeader` sequence.



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