Add HttpStatusClass

Related: #3157

Motivation:

It should be convenient to have an easy way to classify an
HttpResponseStatus based on the first digit of the HTTP status code, as
defined in the RFC 2616:

- Information 1xx
- Success 2xx
- Redirection 3xx
- Client Error 4xx
- Server Error 5xx

Modification:

- Add HttpStatusClass
- Add HttpResponseStatus.codeClass() that returns the class of the HTTP
  status code

Result:

It's easier to determine the class of an HTTP status

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

@@ -435,25 +435,7 @@ public class HttpResponseStatus implements Comparable<HttpResponseStatus> {
             return NETWORK_AUTHENTICATION_REQUIRED;
         }
 
-        final String reasonPhrase;
+        return new HttpResponseStatus(code);
-
-        if (code < 100) {
-            reasonPhrase = "Unknown Status";
-        } else if (code < 200) {
-            reasonPhrase = "Informational";
-        } else if (code < 300) {
-            reasonPhrase = "Successful";
-        } else if (code < 400) {
-            reasonPhrase = "Redirection";
-        } else if (code < 500) {
-            reasonPhrase = "Client Error";
-        } else if (code < 600) {
-            reasonPhrase = "Server Error";
-        } else {
-            reasonPhrase = "Unknown Status";
-        }
-
-        return new HttpResponseStatus(code, reasonPhrase + " (" + code + ')');
     }
 
     /**
@@ -488,13 +470,20 @@ public class HttpResponseStatus implements Comparable<HttpResponseStatus> {
 
     private final int code;
     private final AsciiString codeAsText;
+    private HttpStatusClass codeClass;
 
     private final String reasonPhrase;
     private final byte[] bytes;
 
     /**
-     * Creates a new instance with the specified {@code code} and its
+     * Creates a new instance with the specified {@code code} and the auto-generated default reason phrase.
-     * {@code reasonPhrase}.
+     */
+    private HttpResponseStatus(int code) {
+        this(code, HttpStatusClass.valueOf(code).defaultReasonPhrase() + " (" + code + ')', false);
+    }
+
+    /**
+     * Creates a new instance with the specified {@code code} and its {@code reasonPhrase}.
      */
     public HttpResponseStatus(int code, String reasonPhrase) {
         this(code, reasonPhrase, false);
@@ -552,6 +541,17 @@ public class HttpResponseStatus implements Comparable<HttpResponseStatus> {
         return reasonPhrase;
     }
 
+    /**
+     * Returns the class of this {@link HttpResponseStatus}
+     */
+    public HttpStatusClass codeClass() {
+        HttpStatusClass type = this.codeClass;
+        if (type == null) {
+            this.codeClass = type = HttpStatusClass.valueOf(code);
+        }
+        return type;
+    }
+
     @Override
     public int hashCode() {
         return code();

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

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2014 The Netty Project
+ *
+ * The Netty Project licenses this file to you 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 io.netty.handler.codec.http;
+
+import io.netty.handler.codec.AsciiString;
+
+/**
+ * The class of HTTP status.
+ */
+public enum HttpStatusClass {
+    /**
+     * The informational class (1xx)
+     */
+    INFORMATIONAL(100, 200, "Informational"),
+    /**
+     * The success class (2xx)
+     */
+    SUCCESS(200, 300, "Success"),
+    /**
+     * The redirection class (3xx)
+     */
+    REDIRECTION(300, 400, "Redirection"),
+    /**
+     * The client error class (4xx)
+     */
+    CLIENT_ERROR(400, 500, "Client Error"),
+    /**
+     * The server error class (5xx)
+     */
+    SERVER_ERROR(500, 600, "Server Error"),
+    /**
+     * The unknown class
+     */
+    UNKNOWN(0, 0, "Unknown Status") {
+        @Override
+        public boolean contains(int code) {
+            return code < 100 || code >= 600;
+        }
+    };
+
+    /**
+     * Returns the class of the specified HTTP status code.
+     */
+    public static HttpStatusClass valueOf(int code) {
+        if (INFORMATIONAL.contains(code)) {
+            return INFORMATIONAL;
+        }
+        if (SUCCESS.contains(code)) {
+            return SUCCESS;
+        }
+        if (REDIRECTION.contains(code)) {
+            return REDIRECTION;
+        }
+        if (CLIENT_ERROR.contains(code)) {
+            return CLIENT_ERROR;
+        }
+        if (SERVER_ERROR.contains(code)) {
+            return SERVER_ERROR;
+        }
+        return UNKNOWN;
+    }
+
+    private final int min;
+    private final int max;
+    private final AsciiString defaultReasonPhrase;
+
+    HttpStatusClass(int min, int max, String defaultReasonPhrase) {
+        this.min = min;
+        this.max = max;
+        this.defaultReasonPhrase = new AsciiString(defaultReasonPhrase);
+    }
+
+    /**
+     * Returns {@code true} if and only if the specified HTTP status code falls into this class.
+     */
+    public boolean contains(int code) {
+        return code >= min && code < max;
+    }
+
+    /**
+     * Returns the default reason phrase of this HTTP status class.
+     */
+    AsciiString defaultReasonPhrase() {
+        return defaultReasonPhrase;
+    }
+}