IllegalRefCountException in FullHttp[Request|Response].hashCode()

Motivation:
FullHttp[Request|Response].hashCode() uses a releasable object and in vulnerable to a IllegalRefCountException if that object has been released.

Modifications:
- Ensure the released object is not used.

Result:
No more IllegalRefCountException.

codec-http/src/main/java/io/netty/handler/codec/http/DefaultFullHttpRequest.java

@@ -17,15 +17,19 @@ package io.netty.handler.codec.http;
 
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
+import io.netty.util.IllegalReferenceCountException;
 
 /**
  * Default implementation of {@link FullHttpRequest}.
  */
 public class DefaultFullHttpRequest extends DefaultHttpRequest implements FullHttpRequest {
-    private static final int HASH_CODE_PRIME = 31;
     private final ByteBuf content;
     private final HttpHeaders trailingHeader;
     private final boolean validateHeaders;
+    /**
+     * Used to cache the value of the hash code and avoid {@link IllegalRefCountException}.
+     */
+    private int hash;
 
     public DefaultFullHttpRequest(HttpVersion httpVersion, HttpMethod method, String uri) {
         this(httpVersion, method, uri, Unpooled.buffer(0));
@@ -163,11 +167,23 @@ public class DefaultFullHttpRequest extends DefaultHttpRequest implements FullHt
 
     @Override
     public int hashCode() {
-        int result = 1;
-        result = HASH_CODE_PRIME * result + content().hashCode();
-        result = HASH_CODE_PRIME * result + trailingHeaders().hashCode();
-        result = HASH_CODE_PRIME * result + super.hashCode();
-        return result;
+        int hash = this.hash;
+        if (hash == 0) {
+            if (content().refCnt() != 0) {
+                try {
+                    hash = 31 + content().hashCode();
+                } catch (IllegalReferenceCountException ignored) {
+                    // Handle race condition between checking refCnt() == 0 and using the object.
+                    hash = 31;
+                }
+            } else {
+                hash = 31;
+            }
+            hash = 31 * hash + trailingHeaders().hashCode();
+            hash = 31 * hash + super.hashCode();
+            this.hash = hash;
+        }
+        return hash;
     }
 
     @Override

codec-http/src/main/java/io/netty/handler/codec/http/DefaultFullHttpResponse.java

@@ -15,9 +15,11 @@
  */
 package io.netty.handler.codec.http;
 
-import static io.netty.util.internal.ObjectUtil.checkNotNull;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
+import io.netty.util.IllegalReferenceCountException;
+
+import static io.netty.util.internal.ObjectUtil.checkNotNull;
 
 /**
  * Default implementation of a {@link FullHttpResponse}.
@@ -27,6 +29,10 @@ public class DefaultFullHttpResponse extends DefaultHttpResponse implements Full
     private final ByteBuf content;
     private final HttpHeaders trailingHeaders;
     private final boolean validateHeaders;
+    /**
+     * Used to cache the value of the hash code and avoid {@link IllegalRefCountException}.
+     */
+    private int hash;
 
     public DefaultFullHttpResponse(HttpVersion version, HttpResponseStatus status) {
         this(version, status, Unpooled.buffer(0));
@@ -164,6 +170,40 @@ public class DefaultFullHttpResponse extends DefaultHttpResponse implements Full
         return duplicate;
     }
 
+    @Override
+    public int hashCode() {
+        int hash = this.hash;
+        if (hash == 0) {
+            if (content().refCnt() != 0) {
+                try {
+                    hash = 31 + content().hashCode();
+                } catch (IllegalReferenceCountException ignored) {
+                    // Handle race condition between checking refCnt() == 0 and using the object.
+                    hash = 31;
+                }
+            } else {
+                hash = 31;
+            }
+            hash = 31 * hash + trailingHeaders().hashCode();
+            hash = 31 * hash + super.hashCode();
+            this.hash = hash;
+        }
+        return hash;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (!(o instanceof DefaultFullHttpResponse)) {
+            return false;
+        }
+
+        DefaultFullHttpResponse other = (DefaultFullHttpResponse) o;
+
+        return super.equals(other) &&
+               content().equals(other.content()) &&
+               trailingHeaders().equals(other.trailingHeaders());
+    }
+
     @Override
     public String toString() {
         return HttpMessageUtil.appendFullResponse(new StringBuilder(256), this).toString();