Add interceptors before MAIN_TRANSPORT so they won't be ignored (#272)

httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/H2AsyncClientBuilder.java

@@ -752,7 +752,9 @@ public class H2AsyncClientBuilder {
                         execChainDefinition.addFirst(entry.interceptor, entry.name);
                         break;
                     case LAST:
-                        execChainDefinition.addLast(entry.interceptor, entry.name);
+                        // Don't add last, after H2AsyncMainClientExec, as that does not delegate to the chain
+                        // Instead, add the interceptor just before it, making it effectively the last interceptor
+                        execChainDefinition.addBefore(ChainElement.MAIN_TRANSPORT.name(), entry.interceptor, entry.name);
                         break;
                 }
             }

httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/HttpAsyncClientBuilder.java

@@ -959,7 +959,9 @@ public class HttpAsyncClientBuilder {
                         execChainDefinition.addFirst(entry.interceptor, entry.name);
                         break;
                     case LAST:
-                        execChainDefinition.addLast(entry.interceptor, entry.name);
+                        // Don't add last, after HttpAsyncMainClientExec, as that does not delegate to the chain
+                        // Instead, add the interceptor just before it, making it effectively the last interceptor
+                        execChainDefinition.addBefore(ChainElement.MAIN_TRANSPORT.name(), entry.interceptor, entry.name);
                         break;
                 }
             }

httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpClientBuilder.java

@@ -930,7 +930,9 @@ public class HttpClientBuilder {
                         execChainDefinition.addFirst(entry.interceptor, entry.name);
                         break;
                     case LAST:
-                        execChainDefinition.addLast(entry.interceptor, entry.name);
+                        // Don't add last, after MainClientExec, as that does not delegate to the chain
+                        // Instead, add the interceptor just before it, making it effectively the last interceptor
+                        execChainDefinition.addBefore(ChainElement.MAIN_TRANSPORT.name(), entry.interceptor, entry.name);
                         break;
                 }
             }

httpclient5/src/test/java/org/apache/hc/client5/http/impl/classic/TestHttpClientBuilderInterceptors.java

@@ -0,0 +1,112 @@
+/*
+ * ====================================================================
+ * 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.client5.http.impl.classic;
+
+import java.io.IOException;
+
+import org.apache.hc.client5.http.classic.ExecChain;
+import org.apache.hc.client5.http.classic.ExecChainHandler;
+import org.apache.hc.client5.http.classic.ExecChain.Scope;
+import org.apache.hc.client5.http.classic.methods.HttpPost;
+import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuilder;
+import org.apache.hc.client5.http.io.HttpClientConnectionManager;
+import org.apache.hc.core5.http.ClassicHttpRequest;
+import org.apache.hc.core5.http.ClassicHttpResponse;
+import org.apache.hc.core5.http.Header;
+import org.apache.hc.core5.http.HttpException;
+import org.apache.hc.core5.http.impl.bootstrap.HttpServer;
+import org.apache.hc.core5.http.impl.bootstrap.ServerBootstrap;
+import org.apache.hc.core5.http.io.HttpRequestHandler;
+import org.apache.hc.core5.http.protocol.HttpContext;
+import org.apache.hc.core5.io.CloseMode;
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+@SuppressWarnings("boxing") // test code
+public class TestHttpClientBuilderInterceptors {
+
+    private HttpServer localServer;
+    private String uri;
+    private CloseableHttpClient httpClient;
+
+    @Before
+    public void before() throws Exception {
+        this.localServer = ServerBootstrap.bootstrap()
+                .register("/test", new HttpRequestHandler() {
+
+            @Override
+            public void handle(
+                    final ClassicHttpRequest request,
+                    final ClassicHttpResponse response,
+                    final HttpContext context) throws HttpException, IOException {
+                final Header testInterceptorHeader = request.getHeader("X-Test-Interceptor");
+                if (testInterceptorHeader != null) {
+                    response.setHeader(testInterceptorHeader);
+                }
+                response.setCode(200);
+            }
+        }).create();
+
+        this.localServer.start();
+        uri = "http://localhost:" + this.localServer.getLocalPort() + "/test";
+        final HttpClientConnectionManager cm = PoolingHttpClientConnectionManagerBuilder.create()
+                .setMaxConnPerRoute(5)
+                .build();
+        httpClient = HttpClientBuilder.create()
+                .setConnectionManager(cm)
+                .addExecInterceptorLast("test-interceptor", new ExecChainHandler() {
+
+                    @Override
+                    public ClassicHttpResponse execute(
+                            final ClassicHttpRequest request,
+                            final Scope scope,
+                            final ExecChain chain) throws IOException, HttpException {
+                        request.setHeader("X-Test-Interceptor", "active");
+                        return chain.proceed(request, scope);
+                    }
+                })
+                .build();
+    }
+
+    @After
+    public void after() throws Exception {
+        this.httpClient.close(CloseMode.IMMEDIATE);
+        this.localServer.stop();
+    }
+
+    @Test
+    public void testAddExecInterceptorLastShouldBeExecuted() throws IOException, HttpException {
+        final ClassicHttpRequest request = new HttpPost(uri);
+        final ClassicHttpResponse response = httpClient.execute(request);
+        Assert.assertEquals(200, response.getCode());
+        final Header testFilterHeader = response.getHeader("X-Test-Interceptor");
+        Assert.assertNotNull(testFilterHeader);
+    }
+
+}