/*
 * Copyright (c) 1995, 2017, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.net;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.PrivilegedAction;
import java.util.Hashtable;
import java.util.concurrent.ConcurrentHashMap;
import java.util.Date;
import java.util.Iterator;
import java.util.Locale;
import java.util.Objects;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
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;
import sun.security.action.GetPropertyAction;

/**
 * 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.
 *
 * <p>
 * In general, creating a connection to a URL is a multistep process:
 * <ol>
 * <li>The connection object is created by invoking the
 * {@link URL#openConnection() 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
 * {@link #connect() 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 getLastModified}
 * </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 java.net.URL#openConnection()
 * @see java.net.URLConnection#connect()
 * @see java.net.URLConnection#getContent()
 * @see java.net.URLConnection#getContentEncoding()
 * @see java.net.URLConnection#getContentLength()
 * @see java.net.URLConnection#getContentType()
 * @see java.net.URLConnection#getDate()
 * @see java.net.URLConnection#getExpiration()
 * @see java.net.URLConnection#getHeaderField(int)
 * @see java.net.URLConnection#getHeaderField(java.lang.String)
 * @see java.net.URLConnection#getInputStream()
 * @see java.net.URLConnection#getLastModified()
 * @see java.net.URLConnection#getOutputStream()
 * @see java.net.URLConnection#setAllowUserInteraction(boolean)
 * @see java.net.URLConnection#setDefaultUseCaches(boolean)
 * @see java.net.URLConnection#setDoInput(boolean)
 * @see java.net.URLConnection#setDoOutput(boolean)
 * @see java.net.URLConnection#setIfModifiedSince(long)
 * @see java.net.URLConnection#setRequestProperty(java.lang.String, java.lang.String)
 * @see java.net.URLConnection#setUseCaches(boolean)
 * @since 1.0
 */
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 java.net.URLConnection#getURL()
 * @see java.net.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 java.net.URLConnection#getDoInput()
 * @see java.net.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 java.net.URLConnection#getDoOutput()
 * @see java.net.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 java.net.URLConnection#getAllowUserInteraction()
 * @see java.net.URLConnection#setAllowUserInteraction(boolean)
 * @see java.net.URLConnection#setDefaultAllowUserInteraction(boolean)
 */
 protected boolean allowUserInteraction = defaultAllowUserInteraction;

 private static volatile 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.
 * <p>
 * The default setting may be overridden per protocol with
 * {@link #setDefaultUseCaches(String,boolean)}.
 *
 * @see java.net.URLConnection#setUseCaches(boolean)
 * @see java.net.URLConnection#getUseCaches()
 * @see java.net.URLConnection#setDefaultUseCaches(boolean)
 */
 protected boolean useCaches;

 private static final ConcurrentHashMap<String,Boolean> defaultCaching =
 new ConcurrentHashMap<>();

 /**
 * 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 java.net.URLConnection#getIfModifiedSince()
 * @see java.net.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 1.1
 */
 private static volatile FileNameMap fileNameMap;

 /**
 * 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 FileNameMap getFileNameMap() {
 FileNameMap map = fileNameMap;

 if (map == null) {
 fileNameMap = map = new FileNameMap() {
 private FileNameMap internalMap =
 sun.net.www.MimeTable.loadTable();

 public String getContentTypeFor(String fileName) {
 return internalMap.getContentTypeFor(fileName);
 }
 };
 }

 return map;
 }

 /**
 * 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 java.net.URLConnection#connected
 * @see #getConnectTimeout()
 * @see #setConnectTimeout(int)
 */
 public abstract void connect() throws IOException;

 /**
 * 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().
 *
 * @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;
 if (url == null) {
 this.useCaches = defaultUseCaches;
 } else {
 this.useCaches = getDefaultUseCaches(url.getProtocol());
 }
 }

 /**
 * Returns the value of this {@code URLConnection}'s {@code URL}
 * field.
 *
 * @return the value of this {@code URLConnection}'s {@code URL}
 * field.
 * @see java.net.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 1.7
 */
 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 java.net.URLConnection#getHeaderField(java.lang.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 java.net.URLConnection#getHeaderField(java.lang.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 java.net.URLConnection#getHeaderField(java.lang.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 java.net.URLConnection#getHeaderField(java.lang.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 java.net.URLConnection#getHeaderField(java.lang.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 1.7
 */
 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 java.net.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.
 * <p> This is done as follows:
 * <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 {@code ContentHandlerFactory} has yet been set up,
 * or if the factory's {@code createContentHandler} method
 * returns {@code null}, then the {@linkplain java.util.ServiceLoader
 * ServiceLoader} mechanism is used to locate {@linkplain
 * java.net.ContentHandlerFactory ContentHandlerFactory}
 * implementations using the system class
 * loader. The order that factories are located is implementation
 * specific, and an implementation is free to cache the located
 * factories. A {@linkplain java.util.ServiceConfigurationError
 * ServiceConfigurationError}, {@code Error} or {@code RuntimeException}
 * thrown from the {@code createContentHandler}, if encountered, will
 * be propagated to the calling thread. The {@code
 * createContentHandler} method of each factory, if instantiated, is
 * invoked, with the content type, until a factory returns non-null,
 * or all factories have been exhausted.
 * <li>Failing that, this method tries to load a content handler
 * class as defined by {@link java.net.ContentHandler ContentHandler}.
 * If the 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 java.net.ContentHandlerFactory#createContentHandler(java.lang.String)
 * @see java.net.URLConnection#getContentType()
 * @see java.net.URLConnection#setContentHandlerFactory(java.net.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 java.net.URLConnection#getContent()
 * @see java.net.ContentHandlerFactory#createContentHandler(java.lang.String)
 * @see java.net.URLConnection#getContent(java.lang.Class[])
 * @see java.net.URLConnection#setContentHandlerFactory(java.net.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 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 java.net.URLConnection#doInput
 * @see #getDoInput()
 */
 public void setDoInput(boolean doinput) {
 checkConnected();
 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) {
 checkConnected();
 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) {
 checkConnected();
 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>
 * This 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. A default value can also be set per-protocol using
 * {@link #setDefaultUseCaches(String,boolean)}.
 *
 * @param usecaches a {@code boolean} indicating whether
 * or not to allow caching
 * @throws IllegalStateException if already connected
 * @see #getUseCaches()
 */
 public void setUseCaches(boolean usecaches) {
 checkConnected();
 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) {
 checkConnected();
 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>
 * This 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. This default value can be over-ridden
 * per protocol using {@link #setDefaultUseCaches(String,boolean)}
 *
 * @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. This default value can be over-ridden
 * per protocol using {@link #setDefaultUseCaches(String,boolean)}
 *
 * @param defaultusecaches the new value.
 * @see #getDefaultUseCaches()
 */
 public void setDefaultUseCaches(boolean defaultusecaches) {
 defaultUseCaches = defaultusecaches;
 }

 /**
 * Sets the default value of the {@code useCaches} field for the named
 * protocol to the given value. This value overrides any default setting
 * set by {@link #setDefaultUseCaches(boolean)} for the given protocol.
 * Successive calls to this method change the setting and affect the
 * default value for all future connections of that protocol. The protocol
 * name is case insensitive.
 *
 * @param protocol the protocol to set the default for
 * @param defaultVal whether caching is enabled by default for the given protocol
 * @since 9
 */
 public static void setDefaultUseCaches(String protocol, boolean defaultVal) {
 protocol = protocol.toLowerCase(Locale.US);
 defaultCaching.put(protocol, defaultVal);
 }

 /**
 * Returns the default value of the {@code useCaches} flag for the given protocol. If
 * {@link #setDefaultUseCaches(String,boolean)} was called for the given protocol,
 * then that value is returned. Otherwise, if {@link #setDefaultUseCaches(boolean)}
 * was called, then that value is returned. If neither method was called,
 * the return value is {@code true}. The protocol name is case insensitive.
 *
 * @param protocol the protocol whose defaultUseCaches setting is required
 * @return the default value of the {@code useCaches} flag for the given protocol.
 * @since 9
 */
 public static boolean getDefaultUseCaches(String protocol) {
 Boolean protoDefault = defaultCaching.get(protocol.toLowerCase(Locale.US));
 if (protoDefault != null) {
 return protoDefault.booleanValue();
 } else {
 return 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}
 * @see #getRequestProperty(java.lang.String)
 */
 public void setRequestProperty(String key, String value) {
 checkConnected();
 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) {
 checkConnected();
 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(java.lang.String, java.lang.String)
 */
 public String getRequestProperty(String key) {
 checkConnected();

 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() {
 checkConnected();

 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 java.net.URLConnection#setRequestProperty(java.lang.String,java.lang.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(java.lang.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 java.net.URLConnection#getRequestProperty(java.lang.String)
 *
 * @deprecated The instance specific getRequestProperty method
 * should be used after an appropriate instance of URLConnection
 * is obtained.
 *
 * @see #setDefaultRequestProperty(java.lang.String, java.lang.String)
 */
 @Deprecated
 public static String getDefaultRequestProperty(String key) {
 return null;
 }

 /**
 * The ContentHandler factory.
 */
 private static volatile 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 java.net.ContentHandlerFactory
 * @see java.net.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 final Hashtable<String, ContentHandler> handlers = new Hashtable<>();

 /**
 * Gets the Content Handler appropriate for this connection.
 */
 private ContentHandler getContentHandler() throws UnknownServiceException {
 String contentType = stripOffParameters(getContentType());
 if (contentType == null) {
 throw new UnknownServiceException("no content-type");
 }

 ContentHandler handler = handlers.get(contentType);
 if (handler != null)
 return handler;

 if (factory != null) {
 handler = factory.createContentHandler(contentType);
 if (handler != null)
 return handler;
 }

 handler = lookupContentHandlerViaProvider(contentType);

 if (handler != null) {
 ContentHandler h = handlers.putIfAbsent(contentType, handler);
 return Objects.requireNonNullElse(h, handler);
 }

 try {
 handler = lookupContentHandlerClassFor(contentType);
 } catch (Exception e) {
 e.printStackTrace();
 handler = UnknownContentHandler.INSTANCE;
 }

 assert handler != null;

 ContentHandler h = handlers.putIfAbsent(contentType, handler);
 return Objects.requireNonNullElse(h, 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-definable set of places.
 * By default it looks in {@value #contentClassPrefix}, but users can define
 * a vertical-bar delimited set of class prefixes to search through in
 * addition by defining the {@value #contentPathProp} 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) {
 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) {
 @SuppressWarnings("deprecation")
 Object tmp = cls.newInstance();
 return (ContentHandler) tmp;
 }
 } catch(Exception ignored) { }
 }

 return UnknownContentHandler.INSTANCE;
 }

 private ContentHandler lookupContentHandlerViaProvider(String contentType) {
 return AccessController.doPrivileged(
 new PrivilegedAction<>() {
 @Override
 public ContentHandler run() {
 ClassLoader cl = ClassLoader.getSystemClassLoader();
 ServiceLoader<ContentHandlerFactory> sl =
 ServiceLoader.load(ContentHandlerFactory.class, cl);

 Iterator<ContentHandlerFactory> iterator = sl.iterator();

 ContentHandler handler = null;
 while (iterator.hasNext()) {
 ContentHandlerFactory f;
 try {
 f = iterator.next();
 } catch (ServiceConfigurationError e) {
 if (e.getCause() instanceof SecurityException) {
 continue;
 }
 throw e;
 }
 handler = f.createContentHandler(contentType);
 if (handler != null) {
 break;
 }
 }
 return handler;
 }
 });
 }

 /**
 * 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 {@value #contentClassPrefix}
 * is always the last one on the returned package list.
 */
 private String getContentHandlerPkgPrefixes() {
 String packagePrefixList =
 GetPropertyAction.privilegedGetProperty(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 java.net.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 java.io.InputStream#mark(int)
 * @see java.io.InputStream#markSupported()
 * @see java.net.URLConnection#getContentType()
 */
 public static 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 == 0x49 && c2 == 0x49 && c3 == 0x2a && c4 == 0x00)
 || (c1 == 0x4d && c2 == 0x4d && c3 == 0x00 && c4 == 0x2a)) {
 return "image/tiff";
 }

 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.
 */
 private static 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
 */
 private static 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
 */
 private static 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;
 }

 private void checkConnected() {
 if (connected)
 throw new IllegalStateException("Already connected");
 }
}

class UnknownContentHandler extends ContentHandler {
 static final ContentHandler INSTANCE = new UnknownContentHandler();

 public Object getContent(URLConnection uc) throws IOException {
 return uc.getInputStream();
 }
}