DefaultHttpHeader.names().toArray(...) may throw ArrayStoreException

Motivation:

DefaultHttpHeader.names() exposes HTTP header names as a Set<String>. Converting the resulting set to an array using toArray(String[]) throws an exception: java.lang.ArrayStoreException: io.netty.util.AsciiString.

Modifications:

- Remove our custom implementation of toArray(...) (and others) by just extending AbstractCollection.
- Add unit test

Result:

Fixes [#7428].

codec-http/src/test/java/io/netty/handler/codec/http/DefaultHttpHeadersTest.java

@@ -23,16 +23,13 @@ import org.junit.Test;
 import java.util.Arrays;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Set;
 
 import static io.netty.handler.codec.http.HttpHeadersTestUtils.of;
 import static io.netty.util.AsciiString.contentEquals;
 import static java.util.Arrays.asList;
 import static org.hamcrest.CoreMatchers.is;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertThat;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
 public class DefaultHttpHeadersTest {
     private static final CharSequence HEADER_NAME = "testHeader";
@@ -229,6 +226,16 @@ public class DefaultHttpHeadersTest {
                 .toString());
     }
 
+    @Test
+    public void providesHeaderNamesAsArray() throws Exception {
+        Set<String> nettyHeaders = new DefaultHttpHeaders()
+                .add(HttpHeaderNames.CONTENT_LENGTH, 10)
+                .names();
+
+        String[] namesArray = nettyHeaders.toArray(new String[nettyHeaders.size()]);
+        assertArrayEquals(namesArray, new String[] { HttpHeaderNames.CONTENT_LENGTH.toString() });
+    }
+
     private static void assertDefaultValues(final DefaultHttpHeaders headers, final HeaderValue headerValue) {
         assertTrue(contentEquals(headerValue.asList().get(0), headers.get(HEADER_NAME)));
         List<CharSequence> expected = headerValue.asList();

codec/src/main/java/io/netty/handler/codec/HeadersUtils.java

@@ -15,6 +15,7 @@
  */
 package io.netty.handler.codec;
 
+import java.util.AbstractCollection;
 import java.util.AbstractList;
 import java.util.Collection;
 import java.util.Iterator;
@@ -109,7 +110,7 @@ public final class HeadersUtils {
     private static final class StringEntryIterator implements Iterator<Entry<String, String>> {
         private final Iterator<Entry<CharSequence, CharSequence>> iter;
 
-        public StringEntryIterator(Iterator<Entry<CharSequence, CharSequence>> iter) {
+        StringEntryIterator(Iterator<Entry<CharSequence, CharSequence>> iter) {
             this.iter = iter;
         }
 
@@ -170,7 +171,7 @@ public final class HeadersUtils {
     private static final class StringIterator<T> implements Iterator<String> {
         private final Iterator<T> iter;
 
-        public StringIterator(Iterator<T> iter) {
+        StringIterator(Iterator<T> iter) {
             this.iter = iter;
         }
 
@@ -192,7 +193,7 @@ public final class HeadersUtils {
     }
 
     private static final class CharSequenceDelegatingStringSet extends DelegatingStringSet<CharSequence> {
-        public CharSequenceDelegatingStringSet(Set<CharSequence> allNames) {
+        CharSequenceDelegatingStringSet(Set<CharSequence> allNames) {
             super(allNames);
         }
 
@@ -207,10 +208,10 @@ public final class HeadersUtils {
         }
     }
 
-    private abstract static class DelegatingStringSet<T> implements Set<String> {
+    private abstract static class DelegatingStringSet<T> extends AbstractCollection<String> implements Set<String> {
         protected final Set<T> allNames;
 
-        public DelegatingStringSet(Set<T> allNames) {
+        DelegatingStringSet(Set<T> allNames) {
             this.allNames = checkNotNull(allNames, "allNames");
         }
 
@@ -234,71 +235,11 @@ public final class HeadersUtils {
             return new StringIterator<T>(allNames.iterator());
         }
 
-        @Override
-        public Object[] toArray() {
-            Object[] arr = new Object[size()];
-            fillArray(arr);
-            return arr;
-        }
-
-        @SuppressWarnings("unchecked")
-        @Override
-        public <X> X[] toArray(X[] a) {
-            if (a == null || a.length < size()) {
-                X[] arr = (X[]) new Object[size()];
-                fillArray(arr);
-                return arr;
-            }
-            fillArray(a);
-            return a;
-        }
-
-        private void fillArray(Object[] arr) {
-            Iterator<T> itr = allNames.iterator();
-            for (int i = 0; i < size(); ++i) {
-                arr[i] = itr.next();
-            }
-        }
-
         @Override
         public boolean remove(Object o) {
             return allNames.remove(o);
         }
 
-        @Override
-        public boolean containsAll(Collection<?> c) {
-            for (Object o : c) {
-                if (!contains(o)) {
-                    return false;
-                }
-            }
-            return true;
-        }
-
-        @Override
-        public boolean removeAll(Collection<?> c) {
-            boolean modified = false;
-            for (Object o : c) {
-                if (remove(o)) {
-                    modified = true;
-                }
-            }
-            return modified;
-        }
-
-        @Override
-        public boolean retainAll(Collection<?> c) {
-            boolean modified = false;
-            Iterator<String> it = iterator();
-            while (it.hasNext()) {
-                if (!c.contains(it.next())) {
-                    it.remove();
-                    modified = true;
-                }
-            }
-            return modified;
-        }
-
         @Override
         public void clear() {
             allNames.clear();