content: /*
   * Copyright (C) 2014 The Android Open Source Project
   * Copyright (c) 1995, 2016, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package java.net;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.util.Hashtable;
  import java.util.Date;
  import java.util.StringTokenizer;
  import java.util.Collections;
  import java.util.Map;
  import java.util.List;
  import java.security.Permission;
  import java.security.AccessController;
  import sun.security.util.SecurityConstants;
  import sun.net.www.MessageHeader;
  
  /**
   * The abstract class {@code URLConnection} is the superclass
   * of all classes that represent a communications link between the
   * application and a URL. Instances of this class can be used both to
   * read from and to write to the resource referenced by the URL. In
   * general, creating a connection to a URL is a multistep process:
   *
   * <center><table border=2 summary="Describes the process of creating a connection to a URL: openConnection() and connect() over time.">
   * <tr><th>{@code openConnection()}</th>
   *     <th>{@code connect()}</th></tr>
   * <tr><td>Manipulate parameters that affect the connection to the remote
   *         resource.</td>
   *     <td>Interact with the resource; query header fields and
   *         contents.</td></tr>
   * </table>
   * ----------------------------&gt;
   * <br>time</center>
   *
   * <ol>
   * <li>The connection object is created by invoking the
   *     {@code openConnection} method on a URL.
   * <li>The setup parameters and general request properties are manipulated.
   * <li>The actual connection to the remote object is made, using the
   *    {@code connect} method.
   * <li>The remote object becomes available. The header fields and the contents
   *     of the remote object can be accessed.
   * </ol>
   * <p>
   * The setup parameters are modified using the following methods:
   * <ul>
   *   <li>{@code setAllowUserInteraction}
   *   <li>{@code setDoInput}
   *   <li>{@code setDoOutput}
   *   <li>{@code setIfModifiedSince}
   *   <li>{@code setUseCaches}
   * </ul>
   * <p>
   * and the general request properties are modified using the method:
   * <ul>
   *   <li>{@code setRequestProperty}
   * </ul>
   * <p>
   * Default values for the {@code AllowUserInteraction} and
   * {@code UseCaches} parameters can be set using the methods
   * {@code setDefaultAllowUserInteraction} and
   * {@code setDefaultUseCaches}.
   * <p>
   * Each of the above {@code set} methods has a corresponding
   * {@code get} method to retrieve the value of the parameter or
   * general request property. The specific parameters and general
   * request properties that are applicable are protocol specific.
   * <p>
   * The following methods are used to access the header fields and
   * the contents after the connection is made to the remote object:
   * <ul>
   *   <li>{@code getContent}
   *   <li>{@code getHeaderField}
   *   <li>{@code getInputStream}
   *   <li>{@code getOutputStream}
   * </ul>
   * <p>
   * Certain header fields are accessed frequently. The methods:
   * <ul>
   *   <li>{@code getContentEncoding}
   *   <li>{@code getContentLength}
   *   <li>{@code getContentType}
   *   <li>{@code getDate}
   *   <li>{@code getExpiration}
   *   <li>{@code getLastModifed}
   * </ul>
   * <p>
   * provide convenient access to these fields. The
   * {@code getContentType} method is used by the
   * {@code getContent} method to determine the type of the remote
   * object; subclasses may find it convenient to override the
   * {@code getContentType} method.
   * <p>
   * In the common case, all of the pre-connection parameters and
   * general request properties can be ignored: the pre-connection
   * parameters and request properties default to sensible values. For
   * most clients of this interface, there are only two interesting
   * methods: {@code getInputStream} and {@code getContent},
   * which are mirrored in the {@code URL} class by convenience methods.
   * <p>
   * More information on the request properties and header fields of
   * an {@code http} connection can be found at:
   * <blockquote><pre>
   * <a href="http://www.ietf.org/rfc/rfc2616.txt">http://www.ietf.org/rfc/rfc2616.txt</a>
   * </pre></blockquote>
   *
   * Invoking the {@code close()} methods on the {@code InputStream} or {@code OutputStream} of an
   * {@code URLConnection} after a request may free network resources associated with this
   * instance, unless particular protocol specifications specify different behaviours
   * for it.
   *
   * @author  James Gosling
   * @see     URL#openConnection()
   * @see     URLConnection#connect()
   * @see     URLConnection#getContent()
   * @see     URLConnection#getContentEncoding()
   * @see     URLConnection#getContentLength()
   * @see     URLConnection#getContentType()
   * @see     URLConnection#getDate()
   * @see     URLConnection#getExpiration()
   * @see     URLConnection#getHeaderField(int)
   * @see     URLConnection#getHeaderField(String)
   * @see     URLConnection#getInputStream()
   * @see     URLConnection#getLastModified()
   * @see     URLConnection#getOutputStream()
   * @see     URLConnection#setAllowUserInteraction(boolean)
   * @see     URLConnection#setDefaultUseCaches(boolean)
   * @see     URLConnection#setDoInput(boolean)
   * @see     URLConnection#setDoOutput(boolean)
   * @see     URLConnection#setIfModifiedSince(long)
   * @see     URLConnection#setRequestProperty(String, String)
   * @see     URLConnection#setUseCaches(boolean)
   * @since   JDK1.0
   */
  public abstract class URLConnection {
  
     /**
       * The URL represents the remote object on the World Wide Web to
       * which this connection is opened.
       * <p>
       * The value of this field can be accessed by the
       * {@code getURL} method.
       * <p>
       * The default value of this variable is the value of the URL
       * argument in the {@code URLConnection} constructor.
       *
       * @see     URLConnection#getURL()
       * @see     URLConnection#url
       */
      protected URL url;
  
     /**
       * This variable is set by the {@code setDoInput} method. Its
       * value is returned by the {@code getDoInput} method.
       * <p>
       * A URL connection can be used for input and/or output. Setting the
       * {@code doInput} flag to {@code true} indicates that
       * the application intends to read data from the URL connection.
       * <p>
       * The default value of this field is {@code true}.
       *
       * @see     URLConnection#getDoInput()
       * @see     URLConnection#setDoInput(boolean)
       */
      protected boolean doInput = true;
  
     /**
       * This variable is set by the {@code setDoOutput} method. Its
       * value is returned by the {@code getDoOutput} method.
       * <p>
       * A URL connection can be used for input and/or output. Setting the
       * {@code doOutput} flag to {@code true} indicates
       * that the application intends to write data to the URL connection.
       * <p>
       * The default value of this field is {@code false}.
       *
       * @see     URLConnection#getDoOutput()
       * @see     URLConnection#setDoOutput(boolean)
       */
      protected boolean doOutput = false;
  
      private static boolean defaultAllowUserInteraction = false;
  
     /**
       * If {@code true}, this {@code URL} is being examined in
       * a context in which it makes sense to allow user interactions such
       * as popping up an authentication dialog. If {@code false},
       * then no user interaction is allowed.
       * <p>
       * The value of this field can be set by the
       * {@code setAllowUserInteraction} method.
       * Its value is returned by the
       * {@code getAllowUserInteraction} method.
       * Its default value is the value of the argument in the last invocation
       * of the {@code setDefaultAllowUserInteraction} method.
       *
       * @see     URLConnection#getAllowUserInteraction()
       * @see     URLConnection#setAllowUserInteraction(boolean)
       * @see     URLConnection#setDefaultAllowUserInteraction(boolean)
       */
      protected boolean allowUserInteraction = defaultAllowUserInteraction;
  
      private static boolean defaultUseCaches = true;
  
     /**
       * If {@code true}, the protocol is allowed to use caching
       * whenever it can. If {@code false}, the protocol must always
       * try to get a fresh copy of the object.
       * <p>
       * This field is set by the {@code setUseCaches} method. Its
       * value is returned by the {@code getUseCaches} method.
       * <p>
       * Its default value is the value given in the last invocation of the
       * {@code setDefaultUseCaches} method.
       *
       * @see     URLConnection#setUseCaches(boolean)
       * @see     URLConnection#getUseCaches()
       * @see     URLConnection#setDefaultUseCaches(boolean)
       */
      protected boolean useCaches = defaultUseCaches;
  
     /**
       * Some protocols support skipping the fetching of the object unless
       * the object has been modified more recently than a certain time.
       * <p>
       * A nonzero value gives a time as the number of milliseconds since
       * January 1, 1970, GMT. The object is fetched only if it has been
       * modified more recently than that time.
       * <p>
       * This variable is set by the {@code setIfModifiedSince}
       * method. Its value is returned by the
       * {@code getIfModifiedSince} method.
       * <p>
       * The default value of this field is {@code 0}, indicating
       * that the fetching must always occur.
       *
       * @see     URLConnection#getIfModifiedSince()
       * @see     URLConnection#setIfModifiedSince(long)
       */
      protected long ifModifiedSince = 0;
  
     /**
       * If {@code false}, this connection object has not created a
       * communications link to the specified URL. If {@code true},
       * the communications link has been established.
       */
      protected boolean connected = false;
  
      /**
       * @since 1.5
       */
      private int connectTimeout;
      private int readTimeout;
  
      /**
       * @since 1.6
       */
      private MessageHeader requests;
  
     /**
      * @since   JDK1.1
      */
      private static FileNameMap fileNameMap;
  
      // BEGIN Android-changed: Android has its own mime table.
      /*
      /**
       * @since 1.2.2
       *
      private static boolean fileNameMapLoaded = false;
  
      /**
       * Loads filename map (a mimetable) from a data file. It will
       * first try to load the user-specific table, defined
       * by &quot;content.types.user.table&quot; property. If that fails,
       * it tries to load the default built-in table.
       *
       * @return the FileNameMap
       * @since 1.2
       * @see #setFileNameMap(java.net.FileNameMap)
       *
      public static synchronized FileNameMap getFileNameMap() {
          if ((fileNameMap == null) && !fileNameMapLoaded) {
              fileNameMap = sun.net.www.MimeTable.loadTable();
              fileNameMapLoaded = true;
          }
  
          return new FileNameMap() {
              private FileNameMap map = fileNameMap;
              public String getContentTypeFor(String fileName) {
                  return map.getContentTypeFor(fileName);
              }
          };
      }
      */
      /**
       * Returns a {@link FileNameMap} implementation suitable for guessing a
       * content type based on a URL's "file" component.
       *
       * @see #guessContentTypeFromName(String)
       * @see #setFileNameMap(FileNameMap)
       *
       */
      public static synchronized FileNameMap getFileNameMap() {
          if (fileNameMap == null) {
              fileNameMap = new DefaultFileNameMap();
          }
          return fileNameMap;
      }
      // END Android-changed: Android has its own mime table.
  
      /**
       * Sets the FileNameMap.
       * <p>
       * If there is a security manager, this method first calls
       * the security manager's {@code checkSetFactory} method
       * to ensure the operation is allowed.
       * This could result in a SecurityException.
       *
       * @param map the FileNameMap to be set
       * @exception  SecurityException  if a security manager exists and its
       *             {@code checkSetFactory} method doesn't allow the operation.
       * @see        SecurityManager#checkSetFactory
       * @see #getFileNameMap()
       * @since 1.2
       */
      public static void setFileNameMap(FileNameMap map) {
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) sm.checkSetFactory();
          fileNameMap = map;
      }
  
      /**
       * Opens a communications link to the resource referenced by this
       * URL, if such a connection has not already been established.
       * <p>
       * If the {@code connect} method is called when the connection
       * has already been opened (indicated by the {@code connected}
       * field having the value {@code true}), the call is ignored.
       * <p>
       * URLConnection objects go through two phases: first they are
       * created, then they are connected.  After being created, and
       * before being connected, various options can be specified
       * (e.g., doInput and UseCaches).  After connecting, it is an
       * error to try to set them.  Operations that depend on being
       * connected, like getContentLength, will implicitly perform the
       * connection, if necessary.
       *
       * @throws SocketTimeoutException if the timeout expires before
       *               the connection can be established
       * @exception  IOException  if an I/O error occurs while opening the
       *               connection.
       * @see URLConnection#connected
       * @see #getConnectTimeout()
       * @see #setConnectTimeout(int)
       */
      abstract public void connect() throws IOException;
  
      // Android-changed: Add javadoc to specify Android's timeout behavior.
      /**
       * Sets a specified timeout value, in milliseconds, to be used
       * when opening a communications link to the resource referenced
       * by this URLConnection.  If the timeout expires before the
       * connection can be established, a
       * java.net.SocketTimeoutException is raised. A timeout of zero is
       * interpreted as an infinite timeout.
  
       * <p> Some non-standard implementation of this method may ignore
       * the specified timeout. To see the connect timeout set, please
       * call getConnectTimeout().
       *
       * <p><strong>Warning</strong>: If the hostname resolves to multiple IP
       * addresses, Android's default implementation of {@link HttpURLConnection}
       * will try each in
       * <a href="http://www.ietf.org/rfc/rfc3484.txt">RFC 3484</a> order. If
       * connecting to each of these addresses fails, multiple timeouts will
       * elapse before the connect attempt throws an exception. Host names
       * that support both IPv6 and IPv4 always have at least 2 IP addresses.
       *
       * @param timeout an {@code int} that specifies the connect
       *               timeout value in milliseconds
       * @throws IllegalArgumentException if the timeout parameter is negative
       *
       * @see #getConnectTimeout()
       * @see #connect()
       * @since 1.5
       */
      public void setConnectTimeout(int timeout) {
          if (timeout < 0) {
              throw new IllegalArgumentException("timeout can not be negative");
          }
          connectTimeout = timeout;
      }
  
      /**
       * Returns setting for connect timeout.
       * <p>
       * 0 return implies that the option is disabled
       * (i.e., timeout of infinity).
       *
       * @return an {@code int} that indicates the connect timeout
       *         value in milliseconds
       * @see #setConnectTimeout(int)
       * @see #connect()
       * @since 1.5
       */
      public int getConnectTimeout() {
          return connectTimeout;
      }
  
      /**
       * Sets the read timeout to a specified timeout, in
       * milliseconds. A non-zero value specifies the timeout when
       * reading from Input stream when a connection is established to a
       * resource. If the timeout expires before there is data available
       * for read, a java.net.SocketTimeoutException is raised. A
       * timeout of zero is interpreted as an infinite timeout.
       *
       *<p> Some non-standard implementation of this method ignores the
       * specified timeout. To see the read timeout set, please call
       * getReadTimeout().
       *
       * @param timeout an {@code int} that specifies the timeout
       * value to be used in milliseconds
       * @throws IllegalArgumentException if the timeout parameter is negative
       *
       * @see #getReadTimeout()
       * @see InputStream#read()
       * @since 1.5
       */
      public void setReadTimeout(int timeout) {
          if (timeout < 0) {
              throw new IllegalArgumentException("timeout can not be negative");
          }
          readTimeout = timeout;
      }
  
      /**
       * Returns setting for read timeout. 0 return implies that the
       * option is disabled (i.e., timeout of infinity).
       *
       * @return an {@code int} that indicates the read timeout
       *         value in milliseconds
       *
       * @see #setReadTimeout(int)
       * @see InputStream#read()
       * @since 1.5
       */
      public int getReadTimeout() {
          return readTimeout;
      }
  
      /**
       * Constructs a URL connection to the specified URL. A connection to
       * the object referenced by the URL is not created.
       *
       * @param   url   the specified URL.
       */
      protected URLConnection(URL url) {
          this.url = url;
      }
  
      /**
       * Returns the value of this {@code URLConnection}'s {@code URL}
       * field.
       *
       * @return  the value of this {@code URLConnection}'s {@code URL}
       *          field.
       * @see     URLConnection#url
       */
      public URL getURL() {
          return url;
      }
  
      /**
       * Returns the value of the {@code content-length} header field.
       * <P>
       * <B>Note</B>: {@link #getContentLengthLong() getContentLengthLong()}
       * should be preferred over this method, since it returns a {@code long}
       * instead and is therefore more portable.</P>
       *
       * @return  the content length of the resource that this connection's URL
       *          references, {@code -1} if the content length is not known,
       *          or if the content length is greater than Integer.MAX_VALUE.
       */
      public int getContentLength() {
          long l = getContentLengthLong();
          if (l > Integer.MAX_VALUE)
              return -1;
          return (int) l;
      }
  
      /**
       * Returns the value of the {@code content-length} header field as a
       * long.
       *
       * @return  the content length of the resource that this connection's URL
       *          references, or {@code -1} if the content length is
       *          not known.
       * @since 7.0
       */
      public long getContentLengthLong() {
          return getHeaderFieldLong("content-length", -1);
      }
  
      /**
       * Returns the value of the {@code content-type} header field.
       *
       * @return  the content type of the resource that the URL references,
       *          or {@code null} if not known.
       * @see     URLConnection#getHeaderField(String)
       */
      public String getContentType() {
          return getHeaderField("content-type");
      }
  
      /**
       * Returns the value of the {@code content-encoding} header field.
       *
       * @return  the content encoding of the resource that the URL references,
       *          or {@code null} if not known.
       * @see     URLConnection#getHeaderField(String)
       */
      public String getContentEncoding() {
          return getHeaderField("content-encoding");
      }
  
      /**
       * Returns the value of the {@code expires} header field.
       *
       * @return  the expiration date of the resource that this URL references,
       *          or 0 if not known. The value is the number of milliseconds since
       *          January 1, 1970 GMT.
       * @see     URLConnection#getHeaderField(String)
       */
      public long getExpiration() {
          return getHeaderFieldDate("expires", 0);
      }
  
      /**
       * Returns the value of the {@code date} header field.
       *
       * @return  the sending date of the resource that the URL references,
       *          or {@code 0} if not known. The value returned is the
       *          number of milliseconds since January 1, 1970 GMT.
       * @see     URLConnection#getHeaderField(String)
       */
      public long getDate() {
          return getHeaderFieldDate("date", 0);
      }
  
      /**
       * Returns the value of the {@code last-modified} header field.
       * The result is the number of milliseconds since January 1, 1970 GMT.
       *
       * @return  the date the resource referenced by this
       *          {@code URLConnection} was last modified, or 0 if not known.
       * @see     URLConnection#getHeaderField(String)
       */
      public long getLastModified() {
          return getHeaderFieldDate("last-modified", 0);
      }
  
      /**
       * Returns the value of the named header field.
       * <p>
       * If called on a connection that sets the same header multiple times
       * with possibly different values, only the last value is returned.
       *
       *
       * @param   name   the name of a header field.
       * @return  the value of the named header field, or {@code null}
       *          if there is no such field in the header.
       */
      public String getHeaderField(String name) {
          return null;
      }
  
      /**
       * Returns an unmodifiable Map of the header fields.
       * The Map keys are Strings that represent the
       * response-header field names. Each Map value is an
       * unmodifiable List of Strings that represents
       * the corresponding field values.
       *
       * @return a Map of header fields
       * @since 1.4
       */
      public Map<String,List<String>> getHeaderFields() {
          return Collections.emptyMap();
      }
  
      /**
       * Returns the value of the named field parsed as a number.
       * <p>
       * This form of {@code getHeaderField} exists because some
       * connection types (e.g., {@code http-ng}) have pre-parsed
       * headers. Classes for that connection type can override this method
       * and short-circuit the parsing.
       *
       * @param   name      the name of the header field.
       * @param   Default   the default value.
       * @return  the value of the named field, parsed as an integer. The
       *          {@code Default} value is returned if the field is
       *          missing or malformed.
       */
      public int getHeaderFieldInt(String name, int Default) {
          String value = getHeaderField(name);
          try {
              return Integer.parseInt(value);
          } catch (Exception e) { }
          return Default;
      }
  
      /**
       * Returns the value of the named field parsed as a number.
       * <p>
       * This form of {@code getHeaderField} exists because some
       * connection types (e.g., {@code http-ng}) have pre-parsed
       * headers. Classes for that connection type can override this method
       * and short-circuit the parsing.
       *
       * @param   name      the name of the header field.
       * @param   Default   the default value.
       * @return  the value of the named field, parsed as a long. The
       *          {@code Default} value is returned if the field is
       *          missing or malformed.
       * @since 7.0
       */
      public long getHeaderFieldLong(String name, long Default) {
          String value = getHeaderField(name);
          try {
              return Long.parseLong(value);
          } catch (Exception e) { }
          return Default;
      }
  
      /**
       * Returns the value of the named field parsed as date.
       * The result is the number of milliseconds since January 1, 1970 GMT
       * represented by the named field.
       * <p>
       * This form of {@code getHeaderField} exists because some
       * connection types (e.g., {@code http-ng}) have pre-parsed
       * headers. Classes for that connection type can override this method
       * and short-circuit the parsing.
       *
       * @param   name     the name of the header field.
       * @param   Default   a default value.
       * @return  the value of the field, parsed as a date. The value of the
       *          {@code Default} argument is returned if the field is
       *          missing or malformed.
       */
      @SuppressWarnings("deprecation")
      public long getHeaderFieldDate(String name, long Default) {
          String value = getHeaderField(name);
          try {
              return Date.parse(value);
          } catch (Exception e) { }
          return Default;
      }
  
      /**
       * Returns the key for the {@code n}<sup>th</sup> header field.
       * It returns {@code null} if there are fewer than {@code n+1} fields.
       *
       * @param   n   an index, where {@code n>=0}
       * @return  the key for the {@code n}<sup>th</sup> header field,
       *          or {@code null} if there are fewer than {@code n+1}
       *          fields.
       */
      public String getHeaderFieldKey(int n) {
          return null;
      }
  
      /**
       * Returns the value for the {@code n}<sup>th</sup> header field.
       * It returns {@code null} if there are fewer than
       * {@code n+1}fields.
       * <p>
       * This method can be used in conjunction with the
       * {@link #getHeaderFieldKey(int) getHeaderFieldKey} method to iterate through all
       * the headers in the message.
       *
       * @param   n   an index, where {@code n>=0}
       * @return  the value of the {@code n}<sup>th</sup> header field
       *          or {@code null} if there are fewer than {@code n+1} fields
       * @see     URLConnection#getHeaderFieldKey(int)
       */
      public String getHeaderField(int n) {
          return null;
      }
  
      /**
       * Retrieves the contents of this URL connection.
       * <p>
       * This method first determines the content type of the object by
       * calling the {@code getContentType} method. If this is
       * the first time that the application has seen that specific content
       * type, a content handler for that content type is created:
       * <ol>
       * <li>If the application has set up a content handler factory instance
       *     using the {@code setContentHandlerFactory} method, the
       *     {@code createContentHandler} method of that instance is called
       *     with the content type as an argument; the result is a content
       *     handler for that content type.
       * <li>If no content handler factory has yet been set up, or if the
       *     factory's {@code createContentHandler} method returns
       *     {@code null}, then the application loads the class named:
       *     <blockquote><pre>
       *         sun.net.www.content.&lt;<i>contentType</i>&gt;
       *     </pre></blockquote>
       *     where &lt;<i>contentType</i>&gt; is formed by taking the
       *     content-type string, replacing all slash characters with a
       *     {@code period} ('.'), and all other non-alphanumeric characters
       *     with the underscore character '{@code _}'. The alphanumeric
       *     characters are specifically the 26 uppercase ASCII letters
       *     '{@code A}' through '{@code Z}', the 26 lowercase ASCII
       *     letters '{@code a}' through '{@code z}', and the 10 ASCII
       *     digits '{@code 0}' through '{@code 9}'. If the specified
       *     class does not exist, or is not a subclass of
       *     {@code ContentHandler}, then an
       *     {@code UnknownServiceException} is thrown.
       * </ol>
       *
       * @return     the object fetched. The {@code instanceof} operator
       *               should be used to determine the specific kind of object
       *               returned.
       * @exception  IOException              if an I/O error occurs while
       *               getting the content.
       * @exception  UnknownServiceException  if the protocol does not support
       *               the content type.
       * @see        ContentHandlerFactory#createContentHandler(String)
       * @see        URLConnection#getContentType()
       * @see        URLConnection#setContentHandlerFactory(ContentHandlerFactory)
       */
      public Object getContent() throws IOException {
          // Must call getInputStream before GetHeaderField gets called
          // so that FileNotFoundException has a chance to be thrown up
          // from here without being caught.
          getInputStream();
          return getContentHandler().getContent(this);
      }
  
      /**
       * Retrieves the contents of this URL connection.
       *
       * @param classes the {@code Class} array
       * indicating the requested types
       * @return     the object fetched that is the first match of the type
       *               specified in the classes array. null if none of
       *               the requested types are supported.
       *               The {@code instanceof} operator should be used to
       *               determine the specific kind of object returned.
       * @exception  IOException              if an I/O error occurs while
       *               getting the content.
       * @exception  UnknownServiceException  if the protocol does not support
       *               the content type.
       * @see        URLConnection#getContent()
       * @see        ContentHandlerFactory#createContentHandler(String)
       * @see        URLConnection#getContent(Class[])
       * @see        URLConnection#setContentHandlerFactory(ContentHandlerFactory)
       * @since 1.3
       */
      public Object getContent(Class[] classes) throws IOException {
          // Must call getInputStream before GetHeaderField gets called
          // so that FileNotFoundException has a chance to be thrown up
          // from here without being caught.
          getInputStream();
          return getContentHandler().getContent(this, classes);
      }
  
      /**
       * Returns a permission object representing the permission
       * necessary to make the connection represented by this
       * object. This method returns null if no permission is
       * required to make the connection. By default, this method
       * returns {@code java.security.AllPermission}. Subclasses
       * should override this method and return the permission
       * that best represents the permission required to make a
       * a connection to the URL. For example, a {@code URLConnection}
       * representing a {@code file:} URL would return a
       * {@code java.io.FilePermission} object.
       *
       * <p>The permission returned may dependent upon the state of the
       * connection. For example, the permission before connecting may be
       * different from that after connecting. For example, an HTTP
       * sever, say foo.com, may redirect the connection to a different
       * host, say bar.com. Before connecting the permission returned by
       * the connection will represent the permission needed to connect
       * to foo.com, while the permission returned after connecting will
       * be to bar.com.
       *
       * <p>Permissions are generally used for two purposes: to protect
       * caches of objects obtained through URLConnections, and to check
       * the right of a recipient to learn about a particular URL. In
       * the first case, the permission should be obtained
       * <em>after</em> the object has been obtained. For example, in an
       * HTTP connection, this will represent the permission to connect
       * to the host from which the data was ultimately fetched. In the
       * second case, the permission should be obtained and tested
       * <em>before</em> connecting.
       *
       * @return the permission object representing the permission
       * necessary to make the connection represented by this
       * URLConnection.
       *
       * @exception IOException if the computation of the permission
       * requires network or file I/O and an exception occurs while
       * computing it.
       */
      public Permission getPermission() throws IOException {
          return SecurityConstants.ALL_PERMISSION;
      }
  
      /**
       * Returns an input stream that reads from this open connection.
       *
       * A SocketTimeoutException can be thrown when reading from the
       * returned input stream if the read timeout expires before data
       * is available for read.
       *
       * @return     an input stream that reads from this open connection.
       * @exception  IOException              if an I/O error occurs while
       *               creating the input stream.
       * @exception  UnknownServiceException  if the protocol does not support
       *               input.
       * @see #setReadTimeout(int)
       * @see #getReadTimeout()
       */
      public InputStream getInputStream() throws IOException {
          throw new UnknownServiceException("protocol doesn't support input");
      }
  
      /**
       * Returns an output stream that writes to this connection.
       *
       * @return     an output stream that writes to this connection.
       * @exception  IOException              if an I/O error occurs while
       *               creating the output stream.
       * @exception  UnknownServiceException  if the protocol does not support
       *               output.
       */
      public OutputStream getOutputStream() throws IOException {
          throw new UnknownServiceException("protocol doesn't support output");
      }
  
      /**
       * Returns a {@code String} representation of this URL connection.
       *
       * @return  a string representation of this {@code URLConnection}.
       */
      public String toString() {
          return this.getClass().getName() + ":" + url;
      }
  
      /**
       * Sets the value of the {@code doInput} field for this
       * {@code URLConnection} to the specified value.
       * <p>
       * A URL connection can be used for input and/or output.  Set the DoInput
       * flag to true if you intend to use the URL connection for input,
       * false if not.  The default is true.
       *
       * @param   doinput   the new value.
       * @throws IllegalStateException if already connected
       * @see     URLConnection#doInput
       * @see #getDoInput()
       */
      public void setDoInput(boolean doinput) {
          if (connected)
              throw new IllegalStateException("Already connected");
          doInput = doinput;
      }
  
      /**
       * Returns the value of this {@code URLConnection}'s
       * {@code doInput} flag.
       *
       * @return  the value of this {@code URLConnection}'s
       *          {@code doInput} flag.
       * @see     #setDoInput(boolean)
       */
      public boolean getDoInput() {
          return doInput;
      }
  
      /**
       * Sets the value of the {@code doOutput} field for this
       * {@code URLConnection} to the specified value.
       * <p>
       * A URL connection can be used for input and/or output.  Set the DoOutput
       * flag to true if you intend to use the URL connection for output,
       * false if not.  The default is false.
       *
       * @param   dooutput   the new value.
       * @throws IllegalStateException if already connected
       * @see #getDoOutput()
       */
      public void setDoOutput(boolean dooutput) {
          if (connected)
              throw new IllegalStateException("Already connected");
          doOutput = dooutput;
      }
  
      /**
       * Returns the value of this {@code URLConnection}'s
       * {@code doOutput} flag.
       *
       * @return  the value of this {@code URLConnection}'s
       *          {@code doOutput} flag.
       * @see     #setDoOutput(boolean)
       */
      public boolean getDoOutput() {
          return doOutput;
      }
  
      /**
       * Set the value of the {@code allowUserInteraction} field of
       * this {@code URLConnection}.
       *
       * @param   allowuserinteraction   the new value.
       * @throws IllegalStateException if already connected
       * @see     #getAllowUserInteraction()
       */
      public void setAllowUserInteraction(boolean allowuserinteraction) {
          if (connected)
              throw new IllegalStateException("Already connected");
          allowUserInteraction = allowuserinteraction;
      }
  
      /**
       * Returns the value of the {@code allowUserInteraction} field for
       * this object.
       *
       * @return  the value of the {@code allowUserInteraction} field for
       *          this object.
       * @see     #setAllowUserInteraction(boolean)
       */
      public boolean getAllowUserInteraction() {
          return allowUserInteraction;
      }
  
      /**
       * Sets the default value of the
       * {@code allowUserInteraction} field for all future
       * {@code URLConnection} objects to the specified value.
       *
       * @param   defaultallowuserinteraction   the new value.
       * @see     #getDefaultAllowUserInteraction()
       */
      public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction) {
          defaultAllowUserInteraction = defaultallowuserinteraction;
      }
  
      /**
       * Returns the default value of the {@code allowUserInteraction}
       * field.
       * <p>
       * Ths default is "sticky", being a part of the static state of all
       * URLConnections.  This flag applies to the next, and all following
       * URLConnections that are created.
       *
       * @return  the default value of the {@code allowUserInteraction}
       *          field.
       * @see     #setDefaultAllowUserInteraction(boolean)
       */
      public static boolean getDefaultAllowUserInteraction() {
          return defaultAllowUserInteraction;
      }
  
      /**
       * Sets the value of the {@code useCaches} field of this
       * {@code URLConnection} to the specified value.
       * <p>
       * Some protocols do caching of documents.  Occasionally, it is important
       * to be able to "tunnel through" and ignore the caches (e.g., the
       * "reload" button in a browser).  If the UseCaches flag on a connection
       * is true, the connection is allowed to use whatever caches it can.
       *  If false, caches are to be ignored.
       *  The default value comes from DefaultUseCaches, which defaults to
       * true.
       *
       * @param usecaches a {@code boolean} indicating whether
       * or not to allow caching
       * @throws IllegalStateException if already connected
       * @see #getUseCaches()
       */
      public void setUseCaches(boolean usecaches) {
          if (connected)
              throw new IllegalStateException("Already connected");
          useCaches = usecaches;
      }
  
      /**
       * Returns the value of this {@code URLConnection}'s
       * {@code useCaches} field.
       *
       * @return  the value of this {@code URLConnection}'s
       *          {@code useCaches} field.
       * @see #setUseCaches(boolean)
       */
      public boolean getUseCaches() {
          return useCaches;
      }
  
      /**
       * Sets the value of the {@code ifModifiedSince} field of
       * this {@code URLConnection} to the specified value.
       *
       * @param   ifmodifiedsince   the new value.
       * @throws IllegalStateException if already connected
       * @see     #getIfModifiedSince()
       */
      public void setIfModifiedSince(long ifmodifiedsince) {
          if (connected)
              throw new IllegalStateException("Already connected");
          ifModifiedSince = ifmodifiedsince;
      }
  
      /**
       * Returns the value of this object's {@code ifModifiedSince} field.
       *
       * @return  the value of this object's {@code ifModifiedSince} field.
       * @see #setIfModifiedSince(long)
       */
      public long getIfModifiedSince() {
          return ifModifiedSince;
      }
  
     /**
       * Returns the default value of a {@code URLConnection}'s
       * {@code useCaches} flag.
       * <p>
       * Ths default is "sticky", being a part of the static state of all
       * URLConnections.  This flag applies to the next, and all following
       * URLConnections that are created.
       *
       * @return  the default value of a {@code URLConnection}'s
       *          {@code useCaches} flag.
       * @see     #setDefaultUseCaches(boolean)
       */
      public boolean getDefaultUseCaches() {
          return defaultUseCaches;
      }
  
     /**
       * Sets the default value of the {@code useCaches} field to the
       * specified value.
       *
       * @param   defaultusecaches   the new value.
       * @see     #getDefaultUseCaches()
       */
      public void setDefaultUseCaches(boolean defaultusecaches) {
          defaultUseCaches = defaultusecaches;
      }
  
      /**
       * Sets the general request property. If a property with the key already
       * exists, overwrite its value with the new value.
       *
       * <p> NOTE: HTTP requires all request properties which can
       * legally have multiple instances with the same key
       * to use a comma-separated list syntax which enables multiple
       * properties to be appended into a single property.
       *
       * @param   key     the keyword by which the request is known
       *                  (e.g., "{@code Accept}").
       * @param   value   the value associated with it.
       * @throws IllegalStateException if already connected
       * @throws NullPointerException if key is <CODE>null</CODE>
       * @see #getRequestProperty(String)
       */
      public void setRequestProperty(String key, String value) {
          if (connected)
              throw new IllegalStateException("Already connected");
          if (key == null)
              throw new NullPointerException ("key is null");
  
          if (requests == null)
              requests = new MessageHeader();
  
          requests.set(key, value);
      }
  
      /**
       * Adds a general request property specified by a
       * key-value pair.  This method will not overwrite
       * existing values associated with the same key.
       *
       * @param   key     the keyword by which the request is known
       *                  (e.g., "{@code Accept}").
       * @param   value  the value associated with it.
       * @throws IllegalStateException if already connected
       * @throws NullPointerException if key is null
       * @see #getRequestProperties()
       * @since 1.4
       */
      public void addRequestProperty(String key, String value) {
          if (connected)
              throw new IllegalStateException("Already connected");
          if (key == null)
              throw new NullPointerException ("key is null");
  
          if (requests == null)
              requests = new MessageHeader();
  
          requests.add(key, value);
      }
  
  
      /**
       * Returns the value of the named general request property for this
       * connection.
       *
       * @param key the keyword by which the request is known (e.g., "Accept").
       * @return  the value of the named general request property for this
       *           connection. If key is null, then null is returned.
       * @throws IllegalStateException if already connected
       * @see #setRequestProperty(String, String)
       */
      public String getRequestProperty(String key) {
          if (connected)
              throw new IllegalStateException("Already connected");
  
          if (requests == null)
              return null;
  
          return requests.findValue(key);
      }
  
      /**
       * Returns an unmodifiable Map of general request
       * properties for this connection. The Map keys
       * are Strings that represent the request-header
       * field names. Each Map value is a unmodifiable List
       * of Strings that represents the corresponding
       * field values.
       *
       * @return  a Map of the general request properties for this connection.
       * @throws IllegalStateException if already connected
       * @since 1.4
       */
      public Map<String,List<String>> getRequestProperties() {
          if (connected)
              throw new IllegalStateException("Already connected");
  
          if (requests == null)
              return Collections.emptyMap();
  
          return requests.getHeaders(null);
      }
  
      /**
       * Sets the default value of a general request property. When a
       * {@code URLConnection} is created, it is initialized with
       * these properties.
       *
       * @param   key     the keyword by which the request is known
       *                  (e.g., "{@code Accept}").
       * @param   value   the value associated with the key.
       *
       * @see URLConnection#setRequestProperty(String, String)
       *
       * @deprecated The instance specific setRequestProperty method
       * should be used after an appropriate instance of URLConnection
       * is obtained. Invoking this method will have no effect.
       *
       * @see #getDefaultRequestProperty(String)
       */
      @Deprecated
      public static void setDefaultRequestProperty(String key, String value) {
      }
  
      /**
       * Returns the value of the default request property. Default request
       * properties are set for every connection.
       *
       * @param key the keyword by which the request is known (e.g., "Accept").
       * @return  the value of the default request property
       * for the specified key.
       *
       * @see URLConnection#getRequestProperty(String)
       *
       * @deprecated The instance specific getRequestProperty method
       * should be used after an appropriate instance of URLConnection
       * is obtained.
       *
       * @see #setDefaultRequestProperty(String, String)
       */
      @Deprecated
      public static String getDefaultRequestProperty(String key) {
          return null;
      }
  
      /**
       * The ContentHandler factory.
       */
      static ContentHandlerFactory factory;
  
      /**
       * Sets the {@code ContentHandlerFactory} of an
       * application. It can be called at most once by an application.
       * <p>
       * The {@code ContentHandlerFactory} instance is used to
       * construct a content handler from a content type
       * <p>
       * If there is a security manager, this method first calls
       * the security manager's {@code checkSetFactory} method
       * to ensure the operation is allowed.
       * This could result in a SecurityException.
       *
       * @param      fac   the desired factory.
       * @exception  Error  if the factory has already been defined.
       * @exception  SecurityException  if a security manager exists and its
       *             {@code checkSetFactory} method doesn't allow the operation.
       * @see        ContentHandlerFactory
       * @see        URLConnection#getContent()
       * @see        SecurityManager#checkSetFactory
       */
      public static synchronized void setContentHandlerFactory(ContentHandlerFactory fac) {
          if (factory != null) {
              throw new Error("factory already defined");
          }
          SecurityManager security = System.getSecurityManager();
          if (security != null) {
              security.checkSetFactory();
          }
          factory = fac;
      }
  
      private static Hashtable<String, ContentHandler> handlers = new Hashtable<>();
  
      /**
       * Gets the Content Handler appropriate for this connection.
       */
      synchronized ContentHandler getContentHandler()
          throws IOException
      {
          String contentType = stripOffParameters(getContentType());
          ContentHandler handler = null;
          // BEGIN Android-changed: App Compat. Android guesses content type from name and stream.
          if (contentType == null) {
              if ((contentType = guessContentTypeFromName(url.getFile())) == null) {
                  contentType = guessContentTypeFromStream(getInputStream());
              }
          }
  
          if (contentType == null) {
              return UnknownContentHandler.INSTANCE;
          }
          // END Android-changed: App Compat. Android guesses content type from name and stream.
          try {
              handler = handlers.get(contentType);
              if (handler != null)
                  return handler;
          } catch(Exception e) {
          }
  
          if (factory != null)
              handler = factory.createContentHandler(contentType);
          if (handler == null) {
              try {
                  handler = lookupContentHandlerClassFor(contentType);
              } catch(Exception e) {
                  e.printStackTrace();
                  handler = UnknownContentHandler.INSTANCE;
              }
              handlers.put(contentType, handler);
          }
          return handler;
      }
  
      /*
       * Media types are in the format: type/subtype*(; parameter).
       * For looking up the content handler, we should ignore those
       * parameters.
       */
      private String stripOffParameters(String contentType)
      {
          if (contentType == null)
              return null;
          int index = contentType.indexOf(';');
  
          if (index > 0)
              return contentType.substring(0, index);
          else
              return contentType;
      }
  
      private static final String contentClassPrefix = "sun.net.www.content";
      private static final String contentPathProp = "java.content.handler.pkgs";
  
      /**
       * Looks for a content handler in a user-defineable set of places.
       * By default it looks in sun.net.www.content, but users can define a
       * vertical-bar delimited set of class prefixes to search through in
       * addition by defining the java.content.handler.pkgs property.
       * The class name must be of the form:
       * <pre>
       *     {package-prefix}.{major}.{minor}
       * e.g.
       *     YoyoDyne.experimental.text.plain
       * </pre>
       */
      private ContentHandler lookupContentHandlerClassFor(String contentType)
          throws InstantiationException, IllegalAccessException, ClassNotFoundException {
          String contentHandlerClassName = typeToPackageName(contentType);
  
          String contentHandlerPkgPrefixes =getContentHandlerPkgPrefixes();
  
          StringTokenizer packagePrefixIter =
              new StringTokenizer(contentHandlerPkgPrefixes, "|");
  
          while (packagePrefixIter.hasMoreTokens()) {
              String packagePrefix = packagePrefixIter.nextToken().trim();
  
              try {
                  String clsName = packagePrefix + "." + contentHandlerClassName;
                  Class<?> cls = null;
                  try {
                      cls = Class.forName(clsName);
                  } catch (ClassNotFoundException e) {
                      ClassLoader cl = ClassLoader.getSystemClassLoader();
                      if (cl != null) {
                          cls = cl.loadClass(clsName);
                      }
                  }
                  if (cls != null) {
                      ContentHandler handler =
                          (ContentHandler)cls.newInstance();
                      return handler;
                  }
              } catch(Exception e) {
              }
          }
  
          return UnknownContentHandler.INSTANCE;
      }
  
      /**
       * Utility function to map a MIME content type into an equivalent
       * pair of class name components.  For example: "text/html" would
       * be returned as "text.html"
       */
      private String typeToPackageName(String contentType) {
          // make sure we canonicalize the class name: all lower case
          contentType = contentType.toLowerCase();
          int len = contentType.length();
          char nm[] = new char[len];
          contentType.getChars(0, len, nm, 0);
          for (int i = 0; i < len; i++) {
              char c = nm[i];
              if (c == '/') {
                  nm[i] = '.';
              } else if (!('A' <= c && c <= 'Z' ||
                         'a' <= c && c <= 'z' ||
                         '0' <= c && c <= '9')) {
                  nm[i] = '_';
              }
          }
          return new String(nm);
      }
  
  
      /**
       * Returns a vertical bar separated list of package prefixes for potential
       * content handlers.  Tries to get the java.content.handler.pkgs property
       * to use as a set of package prefixes to search.  Whether or not
       * that property has been defined, the sun.net.www.content is always
       * the last one on the returned package list.
       */
      private String getContentHandlerPkgPrefixes() {
          String packagePrefixList = AccessController.doPrivileged(
              new sun.security.action.GetPropertyAction(contentPathProp, ""));
  
          if (packagePrefixList != "") {
              packagePrefixList += "|";
          }
  
          return packagePrefixList + contentClassPrefix;
      }
  
      /**
       * Tries to determine the content type of an object, based
       * on the specified "file" component of a URL.
       * This is a convenience method that can be used by
       * subclasses that override the {@code getContentType} method.
       *
       * @param   fname   a filename.
       * @return  a guess as to what the content type of the object is,
       *          based upon its file name.
       * @see     URLConnection#getContentType()
       */
      public static String guessContentTypeFromName(String fname) {
          return getFileNameMap().getContentTypeFor(fname);
      }
  
      /**
       * Tries to determine the type of an input stream based on the
       * characters at the beginning of the input stream. This method can
       * be used by subclasses that override the
       * {@code getContentType} method.
       * <p>
       * Ideally, this routine would not be needed. But many
       * {@code http} servers return the incorrect content type; in
       * addition, there are many nonstandard extensions. Direct inspection
       * of the bytes to determine the content type is often more accurate
       * than believing the content type claimed by the {@code http} server.
       *
       * @param      is   an input stream that supports marks.
       * @return     a guess at the content type, or {@code null} if none
       *             can be determined.
       * @exception  IOException  if an I/O error occurs while reading the
       *               input stream.
       * @see        InputStream#mark(int)
       * @see        InputStream#markSupported()
       * @see        URLConnection#getContentType()
       */
      static public String guessContentTypeFromStream(InputStream is)
                          throws IOException {
          // If we can't read ahead safely, just give up on guessing
          if (!is.markSupported())
              return null;
  
          is.mark(16);
          int c1 = is.read();
          int c2 = is.read();
          int c3 = is.read();
          int c4 = is.read();
          int c5 = is.read();
          int c6 = is.read();
          int c7 = is.read();
          int c8 = is.read();
          int c9 = is.read();
          int c10 = is.read();
          int c11 = is.read();
          int c12 = is.read();
          int c13 = is.read();
          int c14 = is.read();
          int c15 = is.read();
          int c16 = is.read();
          is.reset();
  
          if (c1 == 0xCA && c2 == 0xFE && c3 == 0xBA && c4 == 0xBE) {
              return "application/java-vm";
          }
  
          if (c1 == 0xAC && c2 == 0xED) {
              // next two bytes are version number, currently 0x00 0x05
              return "application/x-java-serialized-object";
          }
  
          if (c1 == '<') {
              if (c2 == '!'
                  || ((c2 == 'h' && (c3 == 't' && c4 == 'm' && c5 == 'l' ||
                                     c3 == 'e' && c4 == 'a' && c5 == 'd') ||
                  (c2 == 'b' && c3 == 'o' && c4 == 'd' && c5 == 'y'))) ||
                  ((c2 == 'H' && (c3 == 'T' && c4 == 'M' && c5 == 'L' ||
                                  c3 == 'E' && c4 == 'A' && c5 == 'D') ||
                  (c2 == 'B' && c3 == 'O' && c4 == 'D' && c5 == 'Y')))) {
                  return "text/html";
              }
  
              if (c2 == '?' && c3 == 'x' && c4 == 'm' && c5 == 'l' && c6 == ' ') {
                  return "application/xml";
              }
          }
  
          // big and little (identical) endian UTF-8 encodings, with BOM
          if (c1 == 0xef &&  c2 == 0xbb &&  c3 == 0xbf) {
              if (c4 == '<' &&  c5 == '?' &&  c6 == 'x') {
                  return "application/xml";
              }
          }
  
          // big and little endian UTF-16 encodings, with byte order mark
          if (c1 == 0xfe && c2 == 0xff) {
              if (c3 == 0 && c4 == '<' && c5 == 0 && c6 == '?' &&
                  c7 == 0 && c8 == 'x') {
                  return "application/xml";
              }
          }
  
          if (c1 == 0xff && c2 == 0xfe) {
              if (c3 == '<' && c4 == 0 && c5 == '?' && c6 == 0 &&
                  c7 == 'x' && c8 == 0) {
                  return "application/xml";
              }
          }
  
          // big and little endian UTF-32 encodings, with BOM
          if (c1 == 0x00 &&  c2 == 0x00 &&  c3 == 0xfe &&  c4 == 0xff) {
              if (c5  == 0 && c6  == 0 && c7  == 0 && c8  == '<' &&
                  c9  == 0 && c10 == 0 && c11 == 0 && c12 == '?' &&
                  c13 == 0 && c14 == 0 && c15 == 0 && c16 == 'x') {
                  return "application/xml";
              }
          }
  
          if (c1 == 0xff &&  c2 == 0xfe &&  c3 == 0x00 &&  c4 == 0x00) {
              if (c5  == '<' && c6  == 0 && c7  == 0 && c8  == 0 &&
                  c9  == '?' && c10 == 0 && c11 == 0 && c12 == 0 &&
                  c13 == 'x' && c14 == 0 && c15 == 0 && c16 == 0) {
                  return "application/xml";
              }
          }
  
          if (c1 == 'G' && c2 == 'I' && c3 == 'F' && c4 == '8') {
              return "image/gif";
          }
  
          if (c1 == '#' && c2 == 'd' && c3 == 'e' && c4 == 'f') {
              return "image/x-bitmap";
          }
  
          if (c1 == '!' && c2 == ' ' && c3 == 'X' && c4 == 'P' &&
                          c5 == 'M' && c6 == '2') {
              return "image/x-pixmap";
          }
  
          if (c1 == 137 && c2 == 80 && c3 == 78 &&
                  c4 == 71 && c5 == 13 && c6 == 10 &&
                  c7 == 26 && c8 == 10) {
              return "image/png";
          }
  
          if (c1 == 0xFF && c2 == 0xD8 && c3 == 0xFF) {
              if (c4 == 0xE0 || c4 == 0xEE) {
                  return "image/jpeg";
              }
  
              /**
               * File format used by digital cameras to store images.
               * Exif Format can be read by any application supporting
               * JPEG. Exif Spec can be found at:
               * http://www.pima.net/standards/it10/PIMA15740/Exif_2-1.PDF
               */
              if ((c4 == 0xE1) &&
                  (c7 == 'E' && c8 == 'x' && c9 == 'i' && c10 =='f' &&
                   c11 == 0)) {
                  return "image/jpeg";
              }
          }
  
          if (c1 == 0xD0 && c2 == 0xCF && c3 == 0x11 && c4 == 0xE0 &&
              c5 == 0xA1 && c6 == 0xB1 && c7 == 0x1A && c8 == 0xE1) {
  
              /* Above is signature of Microsoft Structured Storage.
               * Below this, could have tests for various SS entities.
               * For now, just test for FlashPix.
               */
              if (checkfpx(is)) {
                  return "image/vnd.fpx";
              }
          }
  
          if (c1 == 0x2E && c2 == 0x73 && c3 == 0x6E && c4 == 0x64) {
              return "audio/basic";  // .au format, big endian
          }
  
          if (c1 == 0x64 && c2 == 0x6E && c3 == 0x73 && c4 == 0x2E) {
              return "audio/basic";  // .au format, little endian
          }
  
          if (c1 == 'R' && c2 == 'I' && c3 == 'F' && c4 == 'F') {
              /* I don't know if this is official but evidence
               * suggests that .wav files start with "RIFF" - brown
               */
              return "audio/x-wav";
          }
          return null;
      }
  
      /**
       * Check for FlashPix image data in InputStream is.  Return true if
       * the stream has FlashPix data, false otherwise.  Before calling this
       * method, the stream should have already been checked to be sure it
       * contains Microsoft Structured Storage data.
       */
      static private boolean checkfpx(InputStream is) throws IOException {
  
          /* Test for FlashPix image data in Microsoft Structured Storage format.
           * In general, should do this with calls to an SS implementation.
           * Lacking that, need to dig via offsets to get to the FlashPix
           * ClassID.  Details:
           *
           * Offset to Fpx ClsID from beginning of stream should be:
           *
           * FpxClsidOffset = rootEntryOffset + clsidOffset
           *
           * where: clsidOffset = 0x50.
           *        rootEntryOffset = headerSize + sectorSize*sectDirStart
           *                          + 128*rootEntryDirectory
           *
           *        where:  headerSize = 0x200 (always)
           *                sectorSize = 2 raised to power of uSectorShift,
           *                             which is found in the header at
           *                             offset 0x1E.
           *                sectDirStart = found in the header at offset 0x30.
           *                rootEntryDirectory = in general, should search for
           *                                     directory labelled as root.
           *                                     We will assume value of 0 (i.e.,
           *                                     rootEntry is in first directory)
           */
  
          // Mark the stream so we can reset it. 0x100 is enough for the first
          // few reads, but the mark will have to be reset and set again once
          // the offset to the root directory entry is computed. That offset
          // can be very large and isn't know until the stream has been read from
          is.mark(0x100);
  
          // Get the byte ordering located at 0x1E. 0xFE is Intel,
          // 0xFF is other
          long toSkip = (long)0x1C;
          long posn;
  
          if ((posn = skipForward(is, toSkip)) < toSkip) {
            is.reset();
            return false;
          }
  
          int c[] = new int[16];
          if (readBytes(c, 2, is) < 0) {
              is.reset();
              return false;
          }
  
          int byteOrder = c[0];
  
          posn+=2;
          int uSectorShift;
          if (readBytes(c, 2, is) < 0) {
              is.reset();
              return false;
          }
  
          if(byteOrder == 0xFE) {
              uSectorShift = c[0];
              uSectorShift += c[1] << 8;
          }
          else {
              uSectorShift = c[0] << 8;
              uSectorShift += c[1];
          }
  
          posn += 2;
          toSkip = (long)0x30 - posn;
          long skipped = 0;
          if ((skipped = skipForward(is, toSkip)) < toSkip) {
            is.reset();
            return false;
          }
          posn += skipped;
  
          if (readBytes(c, 4, is) < 0) {
              is.reset();
              return false;
          }
  
          int sectDirStart;
          if(byteOrder == 0xFE) {
              sectDirStart = c[0];
              sectDirStart += c[1] << 8;
              sectDirStart += c[2] << 16;
              sectDirStart += c[3] << 24;
          } else {
              sectDirStart =  c[0] << 24;
              sectDirStart += c[1] << 16;
              sectDirStart += c[2] << 8;
              sectDirStart += c[3];
          }
          posn += 4;
          is.reset(); // Reset back to the beginning
  
          toSkip = 0x200L + (long)(1<<uSectorShift)*sectDirStart + 0x50L;
  
          // Sanity check!
          if (toSkip < 0) {
              return false;
          }
  
          /*
           * How far can we skip? Is there any performance problem here?
           * This skip can be fairly long, at least 0x4c650 in at least
           * one case. Have to assume that the skip will fit in an int.
           * Leave room to read whole root dir
           */
          is.mark((int)toSkip+0x30);
  
          if ((skipForward(is, toSkip)) < toSkip) {
              is.reset();
              return false;
          }
  
          /* should be at beginning of ClassID, which is as follows
           * (in Intel byte order):
           *    00 67 61 56 54 C1 CE 11 85 53 00 AA 00 A1 F9 5B
           *
           * This is stored from Windows as long,short,short,char[8]
           * so for byte order changes, the order only changes for
           * the first 8 bytes in the ClassID.
           *
           * Test against this, ignoring second byte (Intel) since
           * this could change depending on part of Fpx file we have.
           */
  
          if (readBytes(c, 16, is) < 0) {
              is.reset();
              return false;
          }
  
          // intel byte order
          if (byteOrder == 0xFE &&
              c[0] == 0x00 && c[2] == 0x61 && c[3] == 0x56 &&
              c[4] == 0x54 && c[5] == 0xC1 && c[6] == 0xCE &&
              c[7] == 0x11 && c[8] == 0x85 && c[9] == 0x53 &&
              c[10]== 0x00 && c[11]== 0xAA && c[12]== 0x00 &&
              c[13]== 0xA1 && c[14]== 0xF9 && c[15]== 0x5B) {
              is.reset();
              return true;
          }
  
          // non-intel byte order
          else if (c[3] == 0x00 && c[1] == 0x61 && c[0] == 0x56 &&
              c[5] == 0x54 && c[4] == 0xC1 && c[7] == 0xCE &&
              c[6] == 0x11 && c[8] == 0x85 && c[9] == 0x53 &&
              c[10]== 0x00 && c[11]== 0xAA && c[12]== 0x00 &&
              c[13]== 0xA1 && c[14]== 0xF9 && c[15]== 0x5B) {
              is.reset();
              return true;
          }
          is.reset();
          return false;
      }
  
      /**
       * Tries to read the specified number of bytes from the stream
       * Returns -1, If EOF is reached before len bytes are read, returns 0
       * otherwise
       */
      static private int readBytes(int c[], int len, InputStream is)
                  throws IOException {
  
          byte buf[] = new byte[len];
          if (is.read(buf, 0, len) < len) {
              return -1;
          }
  
          // fill the passed in int array
          for (int i = 0; i < len; i++) {
               c[i] = buf[i] & 0xff;
          }
          return 0;
      }
  
  
      /**
       * Skips through the specified number of bytes from the stream
       * until either EOF is reached, or the specified
       * number of bytes have been skipped
       */
      static private long skipForward(InputStream is, long toSkip)
                  throws IOException {
  
          long eachSkip = 0;
          long skipped = 0;
  
          while (skipped != toSkip) {
              eachSkip = is.skip(toSkip - skipped);
  
              // check if EOF is reached
              if (eachSkip <= 0) {
                  if (is.read() == -1) {
                      return skipped ;
                  } else {
                      skipped++;
                  }
              }
              skipped += eachSkip;
          }
          return skipped;
      }
  
  }
  
  
  