[GitHub] [httpcomponents-core] ok2c commented on a diff in pull request #387: Added ViaRequest interceptor

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

ok2c commented on code in PR #387:
URL: https://github.com/apache/httpcomponents-core/pull/387#discussion_r1101928433


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httpcore5/src/main/java/org/apache/hc/core5/http/protocol/ViaRequest.java:
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@@ -0,0 +1,122 @@
+/*
+ * ====================================================================
+ * 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.EntityDetails;
+import org.apache.hc.core5.http.Header;
+import org.apache.hc.core5.http.HttpHeaders;
+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.util.Args;
+
+
+/**
+ * An Apache HttpComponents {@link HttpRequestInterceptor} to add the {@link HttpHeaders#VIA} HTTP
+ * header to requests.
+ * <p>The {@link  HttpHeaders#VIA} header is used to indicate intermediate protocols and recipients
+ * between the user agent and the server (on requests) or between the origin server and the client
+ * (on responses). It can be used for tracking message forwards, avoiding request loops, and
+ * identifying the protocol capabilities of senders along the request/response chain. Each member of
+ * the {@link HttpHeaders#VIA} header field value represents a proxy or gateway that has forwarded
+ * the message.
+ * <p>A proxy <b>MUST</b> send an appropriate {@link  HttpHeaders#VIA} header field, as described
+ * in
+ * the HTTP specification, in each message that it forwards. An HTTP-to-HTTP gateway <b>MUST</b>
+ * send an appropriate {@link HttpHeaders#VIA} header field in each inbound request message and
+ * <b>MAY</b> send a {@link HttpHeaders#VIA} header field in forwarded response messages.
+ * <p>This interceptor ensures that the {@link  HttpHeaders#VIA} header is added to the request
+ * only
+ * if it has not been added previously, as per the HTTP specification. Additionally, it updates the
+ * values in the {@link HttpHeaders#VIA} header correctly in case of multiple intermediate protocols
+ * or recipients, by appending its own information about how the message was received to the end of
+ * the header field value.
+ *
+ * @since 5.3
+ */
+@Contract(threading = ThreadingBehavior.IMMUTABLE)
+public class ViaRequest implements HttpRequestInterceptor {
+
+
+    /**
+     * Singleton instance.
+     */
+    public static final HttpRequestInterceptor INSTANCE = new ViaRequest();
+
+    /**
+     * Constructs a new {@code ViaRequest}.
+     */
+    public ViaRequest() {
+    }
+
+    /**
+     * Adds the HTTP {@link  HttpHeaders#VIA} header to the request if it does not already exist.
+     *
+     * <p>This method ensures that the version of the request is HTTP/1.1 or higher, and adds the
+     * Via header in the format {@code <protocol> <version> <host>}, where {@code <protocol>} is the protocol name,
+     * {@code <version>} is the major and minor version of the request, and {@code <host>} is the value of the Host header.
+     *
+     * <p>In case the {@link  HttpHeaders#VIA} header already exists, this method updates its value by appending
+     * the new protocol information in the same format.
+     *
+     * <p>If the version of the request is lower than HTTP/1.1, this method throws a
+     * {@link ProtocolException}.
+     *
+     * @param request the request object to modify
+     * @param entity the entity for the request, may be {@code null}
+     * @param context the context for the request
+     * @throws ProtocolException if there was a protocol error
+     * @throws IOException if there was an I/O error
+     */
+    @Override
+    public void process(final HttpRequest request, final EntityDetails entity, final HttpContext context) throws ProtocolException, IOException {
+        Args.notNull(request, "HTTP request");
+        Args.notNull(context, "HTTP context");
+        final ProtocolVersion ver = context.getProtocolVersion() != null ? context.getProtocolVersion() : HttpVersion.HTTP_1_1;
+
+        final Header host = request.getHeader(HttpHeaders.HOST);

Review Comment:
   @arturobernalg What happens if this interceptor gets added to an HTTP/2 message pipeline wherein `Host` header is illegal? I think you should be using `HttpRequest#getAuthority` instead.



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