Update Client.java and add unit tests (#2336)

* Update Client.java

Fix Isuue #1721 Content-Length may be added twice

* format code

* Add ClientTest unit tests

* update license header

* Update comment of ClientTest

core/src/main/java/feign/Client.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 The Feign Authors
+ * Copyright 2012-2024 The Feign 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
@@ -188,7 +188,7 @@ HttpURLConnection convertAndSend(Request request, Options options) throws IOExce
             }
           }
           // Avoid add "Accept-encoding" twice or more when "compression" option is enabled
-          if (field.equals(ACCEPT_ENCODING)) {
+          else if (field.equals(ACCEPT_ENCODING)) {
             connection.addRequestProperty(field, String.join(", ", request.headers().get(field)));
             break;
           } else {

core/src/test/java/feign/ClientTest.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2012-2024 The Feign 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
+ *
+ * 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.
+ */
+package feign;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentMatchers;
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.nio.charset.Charset;
+import java.util.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+class ClientTest {
+
+  @Test
+  void testClientExecute() throws IOException {
+    Client client = mock(Client.class);
+    RequestTemplate requestTemplate = mock(RequestTemplate.class);
+    Request request =
+        Request.create(Request.HttpMethod.GET, "http://example.com", Collections.emptyMap(),
+            null, requestTemplate);
+    when(client.execute(ArgumentMatchers.any(Request.class),
+        ArgumentMatchers.any())).thenReturn(Response.builder()
+            .status(200).request(request)
+            .body("Hello, World!", Charset.defaultCharset())
+            .build());
+    Response response = client.execute(request, null);
+    String result = Util.toString(response.body().asReader(Charset.defaultCharset()));
+    assertEquals("Hello, World!", result);
+  }
+
+  @Test
+  void testConvertAndSendWithAcceptEncoding() throws IOException {
+    Map<String, Collection<String>> headers = new HashMap<>();
+    List<String> acceptEncoding = new ArrayList<>();
+    acceptEncoding.add("gzip");
+    acceptEncoding.add("deflate");
+    headers.put(Util.ACCEPT_ENCODING, acceptEncoding);
+
+    RequestTemplate requestTemplate = mock(RequestTemplate.class);
+    Request.Body body = mock(Request.Body.class);
+    Request.Options options = mock(Request.Options.class);
+    Client client = mock(Client.class);
+
+    Request request = Request.create(Request.HttpMethod.GET, "http://example.com", headers, body,
+        requestTemplate);
+    Client.Default defaultClient = new Client.Default(null, null);
+    HttpURLConnection urlConnection = defaultClient.convertAndSend(request, options);
+    Map<String, List<String>> requestProperties = urlConnection.getRequestProperties();
+    // Test Avoid add "Accept-encoding" twice or more when "compression" option is enabled
+    assertEquals(1, requestProperties.get(Util.ACCEPT_ENCODING).size());
+  }
+
+  @Test
+  void testConvertAndSendWithContentLength() throws IOException {
+    Map<String, Collection<String>> headers = new HashMap<>();
+    List<String> acceptEncoding = new ArrayList<>();
+    headers.put(Util.CONTENT_LENGTH, Collections.singletonList("100"));
+
+    RequestTemplate requestTemplate = mock(RequestTemplate.class);
+    Request.Body body = mock(Request.Body.class);
+    Request.Options options = mock(Request.Options.class);
+    Client client = mock(Client.class);
+
+    Request request = Request.create(Request.HttpMethod.GET, "http://example.com", headers, body,
+        requestTemplate);
+    Client.Default defaultClient = new Client.Default(null, null);
+    HttpURLConnection urlConnection = defaultClient.convertAndSend(request, options);
+    Map<String, List<String>> requestProperties = urlConnection.getRequestProperties();
+    String requestProperty = urlConnection.getRequestProperty(Util.CONTENT_LENGTH);
+    /*
+     * By default, "Content-Length" will not be added because this key is in the
+     * restrictedHeaderSet of HttpURLConnection.
+     * Unless set system property "sun.net.http.allowRestrictedHeaders" to "true"
+     */
+    assertNull(requestProperties.get(Util.CONTENT_LENGTH));
+  }
+
+}