Don't use null charset in RequestLogger (#22197)

If the response comes back with a content type with a `null`
charset we were blindly using it, causing `NullPointerException`s.

Closes #22190

client/rest/src/main/java/org/elasticsearch/client/RequestLogger.java

@@ -152,7 +152,7 @@ final class RequestLogger {
             httpResponse.setEntity(entity);
             ContentType contentType = ContentType.get(entity);
             Charset charset = StandardCharsets.UTF_8;
-            if (contentType != null) {
+            if (contentType != null && contentType.getCharset() != null) {
                 charset = contentType.getCharset();
             }
             try (BufferedReader reader = new BufferedReader(new InputStreamReader(entity.getContent(), charset))) {

client/rest/src/test/java/org/elasticsearch/client/RequestLoggerTests.java

@@ -44,6 +44,7 @@ import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 
 import static org.hamcrest.CoreMatchers.equalTo;
@@ -51,7 +52,6 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertThat;
 
 public class RequestLoggerTests extends RestClientTestCase {
-
     public void testTraceRequest() throws IOException, URISyntaxException {
         HttpHost host = new HttpHost("localhost", 9200, randomBoolean() ? "http" : "https");
         String expectedEndpoint = "/index/type/_api";
@@ -69,7 +69,7 @@ public class RequestLoggerTests extends RestClientTestCase {
             expected += " -d '" + requestBody + "'";
             HttpEntityEnclosingRequest enclosingRequest = (HttpEntityEnclosingRequest) request;
             HttpEntity entity;
-            switch(randomIntBetween(0, 3)) {
+            switch(randomIntBetween(0, 4)) {
                 case 0:
                     entity = new StringEntity(requestBody, StandardCharsets.UTF_8);
                     break;
@@ -82,6 +82,10 @@ public class RequestLoggerTests extends RestClientTestCase {
                 case 3:
                     entity = new NByteArrayEntity(requestBody.getBytes(StandardCharsets.UTF_8));
                     break;
+                case 4:
+                    // Evil entity without a charset
+                    entity = new StringEntity(requestBody, (Charset) null);
+                    break;
                 default:
                     throw new UnsupportedOperationException();
             }
@@ -116,11 +120,20 @@ public class RequestLoggerTests extends RestClientTestCase {
             expected += "\n#   \"field\": \"value\"";
             expected += "\n# }";
             HttpEntity entity;
-            if (getRandom().nextBoolean()) {
+            switch(randomIntBetween(0, 2)) {
+            case 0:
                 entity = new StringEntity(responseBody, StandardCharsets.UTF_8);
-            } else {
+                break;
+            case 1:
                 //test a non repeatable entity
                 entity = new InputStreamEntity(new ByteArrayInputStream(responseBody.getBytes(StandardCharsets.UTF_8)));
+                break;
+            case 2:
+                // Evil entity without a charset
+                entity = new StringEntity(responseBody, (Charset) null);
+                break;
+            default:
+                throw new UnsupportedOperationException();
             }
             httpResponse.setEntity(entity);
         }