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   /*
    * Copyright 2015 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:
    *
    *   https://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;
  
  import java.util.AbstractCollection;
  import java.util.AbstractList;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map.Entry;
  import java.util.Set;
  
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  /**
   * Provides utility methods related to {@link Headers}.
   */
  public final class HeadersUtils {
  
      private HeadersUtils() {
      }
  
      /**
       * {@link Headers#get(Object)} and convert each element of {@link List} to a {@link String}.
       * @param name the name of the header to retrieve
       * @return a {@link List} of header values or an empty {@link List} if no values are found.
       */
      public static <K, V> List<String> getAllAsString(Headers<K, V, ?> headers, K name) {
          final List<V> allNames = headers.getAll(name);
          return new AbstractList<String>() {
              @Override
              public String get(int index) {
                  V value = allNames.get(index);
                  return value != null ? value.toString() : null;
              }
  
              @Override
              public int size() {
                  return allNames.size();
              }
          };
      }
  
      /**
       * {@link Headers#get(Object)} and convert the result to a {@link String}.
       * @param headers the headers to get the {@code name} from
       * @param name the name of the header to retrieve
       * @return the first header value if the header is found. {@code null} if there's no such entry.
       */
      public static <K, V> String getAsString(Headers<K, V, ?> headers, K name) {
          V orig = headers.get(name);
          return orig != null ? orig.toString() : null;
      }
  
      /**
       * {@link Headers#iterator()} which converts each {@link Entry}'s key and value to a {@link String}.
       */
      public static Iterator<Entry<String, String>> iteratorAsString(
              Iterable<Entry<CharSequence, CharSequence>> headers) {
          return new StringEntryIterator(headers.iterator());
      }
  
      /**
       * Helper for implementing toString for {@link DefaultHeaders} and wrappers such as DefaultHttpHeaders.
       * @param headersClass the class of headers
       * @param headersIt the iterator on the actual headers
       * @param size the size of the iterator
       * @return a String representation of the headers
       */
      public static <K, V> String toString(Class<?> headersClass, Iterator<Entry<K, V>> headersIt, int size) {
          String simpleName = headersClass.getSimpleName();
          if (size == 0) {
              return simpleName + "[]";
          } else {
              // original capacity assumes 20 chars per headers
              StringBuilder sb = new StringBuilder(simpleName.length() + 2 + size * 20)
                      .append(simpleName)
                      .append('[');
              while (headersIt.hasNext()) {
                  Entry<?, ?> header = headersIt.next();
                  sb.append(header.getKey()).append(": ").append(header.getValue()).append(", ");
              }
              sb.setLength(sb.length() - 2);
              return sb.append(']').toString();
          }
      }
  
     /**
      * {@link Headers#names()} and convert each element of {@link Set} to a {@link String}.
      * @param headers the headers to get the names from
      * @return a {@link Set} of header values or an empty {@link Set} if no values are found.
      */
     public static Set<String> namesAsString(Headers<CharSequence, CharSequence, ?> headers) {
         return new DelegatingNameSet(headers);
     }
 
     private static final class StringEntryIterator implements Iterator<Entry<String, String>> {
         private final Iterator<Entry<CharSequence, CharSequence>> iter;
 
         StringEntryIterator(Iterator<Entry<CharSequence, CharSequence>> iter) {
             this.iter = iter;
         }
 
         @Override
         public boolean hasNext() {
             return iter.hasNext();
         }
 
         @Override
         public Entry<String, String> next() {
             return new StringEntry(iter.next());
         }
 
         @Override
         public void remove() {
             iter.remove();
         }
     }
 
     private static final class StringEntry implements Entry<String, String> {
         private final Entry<CharSequence, CharSequence> entry;
         private String name;
         private String value;
 
         StringEntry(Entry<CharSequence, CharSequence> entry) {
             this.entry = entry;
         }
 
         @Override
         public String getKey() {
             if (name == null) {
                 name = entry.getKey().toString();
             }
             return name;
         }
 
         @Override
         public String getValue() {
             if (value == null && entry.getValue() != null) {
                 value = entry.getValue().toString();
             }
             return value;
         }
 
         @Override
         public String setValue(String value) {
             String old = getValue();
             entry.setValue(value);
             return old;
         }
 
         @Override
         public String toString() {
             return entry.toString();
         }
     }
 
     private static final class StringIterator<T> implements Iterator<String> {
         private final Iterator<T> iter;
 
         StringIterator(Iterator<T> iter) {
             this.iter = iter;
         }
 
         @Override
         public boolean hasNext() {
             return iter.hasNext();
         }
 
         @Override
         public String next() {
             T next = iter.next();
             return next != null ? next.toString() : null;
         }
 
         @Override
         public void remove() {
             iter.remove();
         }
     }
 
     private static final class DelegatingNameSet extends AbstractCollection<String> implements Set<String> {
         private final Headers<CharSequence, CharSequence, ?> headers;
 
         DelegatingNameSet(Headers<CharSequence, CharSequence, ?> headers) {
             this.headers = checkNotNull(headers, "headers");
         }
 
         @Override
         public int size() {
             return headers.names().size();
         }
 
         @Override
         public boolean isEmpty() {
             return headers.isEmpty();
         }
 
         @Override
         public boolean contains(Object o) {
             return headers.contains(o.toString());
         }
 
         @Override
         public Iterator<String> iterator() {
             return new StringIterator<CharSequence>(headers.names().iterator());
         }
     }
 }