[RESTEASY-1274] (#920)

Clean out Content-Encoding header in ClientInvocation when setting a new
entity.

resteasy-client/src/main/java/org/jboss/resteasy/client/jaxrs/internal/ClientInvocation.java

@@ -322,6 +322,7 @@ public void setEntity(Entity<?> entity)
          Variant v = entity.getVariant();
          headers.setMediaType(v.getMediaType());
          headers.setLanguage(v.getLanguage());
+         headers.header("Content-Encoding", null);
          headers.header("Content-Encoding", v.getEncoding());
       }
 

testsuite/unit-tests/src/test/java/org/jboss/resteasy/test/client/ContentEncodingInvocationTest.java

@@ -0,0 +1,54 @@
+package org.jboss.resteasy.test.client;
+import java.net.URISyntaxException;
+
+import javax.ws.rs.client.Client;
+import javax.ws.rs.client.ClientBuilder;
+import javax.ws.rs.client.Entity;
+import javax.ws.rs.client.Invocation.Builder;
+import javax.ws.rs.client.WebTarget;
+import javax.ws.rs.core.MediaType;
+import javax.ws.rs.core.Variant;
+
+import org.jboss.resteasy.client.jaxrs.internal.ClientInvocation;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * @tpSubChapter Requests
+ * @tpChapter Unit tests
+ * @tpTestCaseDetails Regression test for RESTEASY-1274
+ * @tpSince RESTEasy 3.0.20
+ */
+public class ContentEncodingInvocationTest
+{
+   @Test
+   public void test() throws URISyntaxException
+   {
+      Client client = ClientBuilder.newClient();
+      WebTarget target = client.target("http://localhost:8081");
+      Builder builder = target.request();
+      Variant variant = new Variant(MediaType.TEXT_PLAIN_TYPE, "lang", "encoding");
+      ClientInvocation invocation = null;
+      for (int i = 0; i < 5; i++)
+      {
+         invocation = (ClientInvocation) builder.buildPost(Entity.entity("entity", variant));
+      }
+      String contentEncoding = invocation.getHeaders().getHeader("Content-Encoding");
+      System.out.println("encoding: " + contentEncoding);
+      System.out.println("count: " + countEncoding(contentEncoding));
+      Assert.assertEquals(1, countEncoding(contentEncoding));
+
+   }
+
+   private int countEncoding(String s)
+   {
+      int i = 0;
+      int count = 0;
+      while (s.substring(i).indexOf("encoding") > -1)
+      {
+         count++;
+         i += "encoding".length();
+      }
+      return count;
+   }
+}