xref: /libcore/ojluni/src/main/java/java/net/HttpURLConnection.java

/*
 * Copyright (c) 1996, 2011, 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.InputStream;
import java.io.IOException;
import java.security.Permission;
import java.util.Date;

/**
 * A URLConnection with support for HTTP-specific features. See
 * <A HREF="http://www.w3.org/pub/WWW/Protocols/"> the spec </A> for
 * details.
 * <p>
 *
 * <p>Uses of this class follow a pattern:
 * <ol>
 *   <li>Obtain a new {@code HttpURLConnection} by calling {@link
 *       URL#openConnection() URL.openConnection()} and casting the result to
 *       {@code HttpURLConnection}.
 *   <li>Prepare the request. The primary property of a request is its URI.
 *       Request headers may also include metadata such as credentials, preferred
 *       content types, and session cookies.
 *   <li>Optionally upload a request body. Instances must be configured with
 *       {@link #setDoOutput(boolean) setDoOutput(true)} if they include a
 *       request body. Transmit data by writing to the stream returned by {@link
 *       #getOutputStream()}.
 *   <li>Read the response. Response headers typically include metadata such as
 *       the response body's content type and length, modified dates and session
 *       cookies. The response body may be read from the stream returned by {@link
 *       #getInputStream()}. If the response has no body, that method returns an
 *       empty stream.
 *   <li>Disconnect. Once the response body has been read, the {@code
 *       HttpURLConnection} should be closed by calling {@link #disconnect()}.
 *       Disconnecting releases the resources held by a connection so they may
 *       be closed or reused.
 * </ol>
 *
 * <p>For example, to retrieve the webpage at {@code http://www.android.com/}:
 * <pre>   {@code
 *   URL url = new URL("http://www.android.com/");
 *   HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
 *   try {
 *     InputStream in = new BufferedInputStream(urlConnection.getInputStream());
 *     readStream(in);
 *   } finally {
 *     urlConnection.disconnect();
 *   }
 * }</pre>
 *
 * <h3>Secure Communication with HTTPS</h3>
 * Calling {@link URL#openConnection()} on a URL with the "https"
 * scheme will return an {@code HttpsURLConnection}, which allows for
 * overriding the default {@link javax.net.ssl.HostnameVerifier
 * HostnameVerifier} and {@link javax.net.ssl.SSLSocketFactory
 * SSLSocketFactory}. An application-supplied {@code SSLSocketFactory}
 * created from an {@link javax.net.ssl.SSLContext SSLContext} can
 * provide a custom {@link javax.net.ssl.X509TrustManager
 * X509TrustManager} for verifying certificate chains and a custom
 * {@link javax.net.ssl.X509KeyManager X509KeyManager} for supplying
 * client certificates. See {@link javax.net.ssl.HttpsURLConnection
 * HttpsURLConnection} for more details.
 *
 * <h3>Response Handling</h3>
 * {@code HttpURLConnection} will follow up to five HTTP redirects. It will
 * follow redirects from one origin server to another. This implementation
 * doesn't follow redirects from HTTPS to HTTP or vice versa.
 *
 * <p>If the HTTP response indicates that an error occurred, {@link
 * #getInputStream()} will throw an {@link IOException}. Use {@link
 * #getErrorStream()} to read the error response. The headers can be read in
 * the normal way using {@link #getHeaderFields()},
 *
 * <h3>Posting Content</h3>
 * To upload data to a web server, configure the connection for output using
 * {@link #setDoOutput(boolean) setDoOutput(true)}.
 *
 * <p>For best performance, you should call either {@link
 * #setFixedLengthStreamingMode(int)} when the body length is known in advance,
 * or {@link #setChunkedStreamingMode(int)} when it is not. Otherwise {@code
 * HttpURLConnection} will be forced to buffer the complete request body in
 * memory before it is transmitted, wasting (and possibly exhausting) heap and
 * increasing latency.
 *
 * <p>For example, to perform an upload: <pre>   {@code
 *   HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
 *   try {
 *     urlConnection.setDoOutput(true);
 *     urlConnection.setChunkedStreamingMode(0);
 *
 *     OutputStream out = new BufferedOutputStream(urlConnection.getOutputStream());
 *     writeStream(out);
 *
 *     InputStream in = new BufferedInputStream(urlConnection.getInputStream());
 *     readStream(in);
 *   } finally {
 *     urlConnection.disconnect();
 *   }
 * }</pre>
 *
 * <h3>Performance</h3>
 * The input and output streams returned by this class are <strong>not
 * buffered</strong>. Most callers should wrap the returned streams with {@link
 * java.io.BufferedInputStream BufferedInputStream} or {@link
 * java.io.BufferedOutputStream BufferedOutputStream}. Callers that do only bulk
 * reads or writes may omit buffering.
 *
 * <p>When transferring large amounts of data to or from a server, use streams
 * to limit how much data is in memory at once. Unless you need the entire
 * body to be in memory at once, process it as a stream (rather than storing
 * the complete body as a single byte array or string).
 *
 * <p>To reduce latency, this class may reuse the same underlying {@code Socket}
 * for multiple request/response pairs. As a result, HTTP connections may be
 * held open longer than necessary. Calls to {@link #disconnect()} may return
 * the socket to a pool of connected sockets. This behavior can be disabled by
 * setting the {@code http.keepAlive} system property to {@code false} before
 * issuing any HTTP requests. The {@code http.maxConnections} property may be
 * used to control how many idle connections to each server will be held.
 *
 * <p>By default, this implementation of {@code HttpURLConnection} requests that
 * servers use gzip compression and it automatically decompresses the data for
 * callers of {@link #getInputStream()}. The Content-Encoding and Content-Length
 * response headers are cleared in this case. Gzip compression can be disabled by
 * setting the acceptable encodings in the request header: <pre>   {@code
 *   urlConnection.setRequestProperty("Accept-Encoding", "identity");
 * }</pre>
 *
 * <p>Setting the Accept-Encoding request header explicitly disables automatic
 * decompression and leaves the response headers intact; callers must handle
 * decompression as needed, according to the Content-Encoding header of the
 * response.
 *
 * <p>{@link #getContentLength()} returns the number of bytes transmitted and
 * cannot be used to predict how many bytes can be read from
 * {@link #getInputStream()} for compressed streams. Instead, read that stream
 * until it is exhausted, i.e. when {@link InputStream#read} returns -1.
 *
 * <h3>Handling Network Sign-On</h3>
 * Some Wi-Fi networks block Internet access until the user clicks through a
 * sign-on page. Such sign-on pages are typically presented by using HTTP
 * redirects. You can use {@link #getURL()} to test if your connection has been
 * unexpectedly redirected. This check is not valid until <strong>after</strong>
 * the response headers have been received, which you can trigger by calling
 * {@link #getHeaderFields()} or {@link #getInputStream()}. For example, to
 * check that a response was not redirected to an unexpected host:
 * <pre>   {@code
 *   HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
 *   try {
 *     InputStream in = new BufferedInputStream(urlConnection.getInputStream());
 *     if (!url.getHost().equals(urlConnection.getURL().getHost())) {
 *       // we were redirected! Kick the user out to the browser to sign on?
 *     }
 *     ...
 *   } finally {
 *     urlConnection.disconnect();
 *   }
 * }</pre>
 *
 * <h3>HTTP Authentication</h3>
 * {@code HttpURLConnection} supports <a
 * href="http://www.ietf.org/rfc/rfc2617">HTTP basic authentication</a>. Use
 * {@link Authenticator} to set the VM-wide authentication handler:
 * <pre>   {@code
 *   Authenticator.setDefault(new Authenticator() {
 *     protected PasswordAuthentication getPasswordAuthentication() {
 *       return new PasswordAuthentication(username, password.toCharArray());
 *     }
 *   });
 * }</pre>
 * Unless paired with HTTPS, this is <strong>not</strong> a secure mechanism for
 * user authentication. In particular, the username, password, request and
 * response are all transmitted over the network without encryption.
 *
 * <h3>Sessions with Cookies</h3>
 * To establish and maintain a potentially long-lived session between client
 * and server, {@code HttpURLConnection} includes an extensible cookie manager.
 * Enable VM-wide cookie management using {@link CookieHandler} and {@link
 * CookieManager}: <pre>   {@code
 *   CookieManager cookieManager = new CookieManager();
 *   CookieHandler.setDefault(cookieManager);
 * }</pre>
 * By default, {@code CookieManager} accepts cookies from the <a
 * href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec1.html">origin
 * server</a> only. Two other policies are included: {@link
 * CookiePolicy#ACCEPT_ALL} and {@link CookiePolicy#ACCEPT_NONE}. Implement
 * {@link CookiePolicy} to define a custom policy.
 *
 * <p>The default {@code CookieManager} keeps all accepted cookies in memory. It
 * will forget these cookies when the VM exits. Implement {@link CookieStore} to
 * define a custom cookie store.
 *
 * <p>In addition to the cookies set by HTTP responses, you may set cookies
 * programmatically. To be included in HTTP request headers, cookies must have
 * the domain and path properties set.
 *
 * <p>By default, new instances of {@code HttpCookie} work only with servers
 * that support <a href="http://www.ietf.org/rfc/rfc2965.txt">RFC 2965</a>
 * cookies. Many web servers support only the older specification, <a
 * href="http://www.ietf.org/rfc/rfc2109.txt">RFC 2109</a>. For compatibility
 * with the most web servers, set the cookie version to 0.
 *
 * <p>For example, to receive {@code www.twitter.com} in French: <pre>   {@code
 *   HttpCookie cookie = new HttpCookie("lang", "fr");
 *   cookie.setDomain("twitter.com");
 *   cookie.setPath("/");
 *   cookie.setVersion(0);
 *   cookieManager.getCookieStore().add(new URI("http://twitter.com/"), cookie);
 * }</pre>
 *
 * <h3>HTTP Methods</h3>
 * <p>{@code HttpURLConnection} uses the {@code GET} method by default. It will
 * use {@code POST} if {@link #setDoOutput setDoOutput(true)} has been called.
 * Other HTTP methods ({@code OPTIONS}, {@code HEAD}, {@code PUT}, {@code
 * DELETE} and {@code TRACE}) can be used with {@link #setRequestMethod}.
 *
 * <h3>Proxies</h3>
 * By default, this class will connect directly to the <a
 * href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec1.html">origin
 * server</a>. It can also connect via an {@link Proxy.Type#HTTP HTTP} or {@link
 * Proxy.Type#SOCKS SOCKS} proxy. To use a proxy, use {@link
 * URL#openConnection(Proxy) URL.openConnection(Proxy)} when creating the
 * connection.
 *
 * <h3>IPv6 Support</h3>
 * <p>This class includes transparent support for IPv6. For hosts with both IPv4
 * and IPv6 addresses, it will attempt to connect to each of a host's addresses
 * until a connection is established.
 *
 * <h3>Response Caching</h3>
 * Android 4.0 (Ice Cream Sandwich, API level 15) includes a response cache. See
 * {@code android.net.http.HttpResponseCache} for instructions on enabling HTTP
 * caching in your application.
 *
 * <h3>Avoiding Bugs In Earlier Releases</h3>
 * Prior to Android 2.2 (Froyo), this class had some frustrating bugs. In
 * particular, calling {@code close()} on a readable {@code InputStream} could
 * <a href="http://code.google.com/p/android/issues/detail?id=2939">poison the
 * connection pool</a>. Work around this by disabling connection pooling:
 * <pre>   {@code
 * private void disableConnectionReuseIfNecessary() {
 *   // Work around pre-Froyo bugs in HTTP connection reuse.
 *   if (Integer.parseInt(Build.VERSION.SDK) < Build.VERSION_CODES.FROYO) {
 *     System.setProperty("http.keepAlive", "false");
 *   }
 * }}</pre>
 *
 * <p>Each instance of {@code HttpURLConnection} may be used for one
 * request/response pair. Instances of this class are not thread safe.
 *
 * @since JDK1.1
 */
abstract public class HttpURLConnection extends URLConnection {
    /* instance variables */

    /**
     * The HTTP method (GET,POST,PUT,etc.).
     */
    protected String method = "GET";

    /**
     * The chunk-length when using chunked encoding streaming mode for output.
     * A value of <code>-1</code> means chunked encoding is disabled for output.
     * @since 1.5
     */
    protected int chunkLength = -1;

    /**
     * The fixed content-length when using fixed-length streaming mode.
     * A value of <code>-1</code> means fixed-length streaming mode is disabled
     * for output.
     *
     * <P> <B>NOTE:</B> {@link #fixedContentLengthLong} is recommended instead
     * of this field, as it allows larger content lengths to be set.
     *
     * @since 1.5
     */
    protected int fixedContentLength = -1;

    /**
     * The fixed content-length when using fixed-length streaming mode.
     * A value of {@code -1} means fixed-length streaming mode is disabled
     * for output.
     *
     * @since 1.7
     */
    protected long fixedContentLengthLong = -1;

    /**
     * Returns the key for the <code>n</code><sup>th</sup> header field.
     * Some implementations may treat the <code>0</code><sup>th</sup>
     * header field as special, i.e. as the status line returned by the HTTP
     * server. In this case, {@link #getHeaderField(int) getHeaderField(0)} returns the status
     * line, but <code>getHeaderFieldKey(0)</code> returns null.
     *
     * @param   n   an index, where n >=0.
     * @return  the key for the <code>n</code><sup>th</sup> header field,
     *          or <code>null</code> if the key does not exist.
     */
    public String getHeaderFieldKey (int n) {
        return null;
    }

    /**
     * This method is used to enable streaming of a HTTP request body
     * without internal buffering, when the content length is known in
     * advance.
     * <p>
     * An exception will be thrown if the application
     * attempts to write more data than the indicated
     * content-length, or if the application closes the OutputStream
     * before writing the indicated amount.
     * <p>
     * When output streaming is enabled, authentication
     * and redirection cannot be handled automatically.
     * A HttpRetryException will be thrown when reading
     * the response if authentication or redirection are required.
     * This exception can be queried for the details of the error.
     * <p>
     * This method must be called before the URLConnection is connected.
     * <p>
     * <B>NOTE:</B> {@link #setFixedLengthStreamingMode(long)} is recommended
     * instead of this method as it allows larger content lengths to be set.
     *
     * @param   contentLength The number of bytes which will be written
     *          to the OutputStream.
     *
     * @throws  IllegalStateException if URLConnection is already connected
     *          or if a different streaming mode is already enabled.
     *
     * @throws  IllegalArgumentException if a content length less than
     *          zero is specified.
     *
     * @see     #setChunkedStreamingMode(int)
     * @since 1.5
     */
    public void setFixedLengthStreamingMode (int contentLength) {
        if (connected) {
            throw new IllegalStateException ("Already connected");
        }
        if (chunkLength != -1) {
            throw new IllegalStateException ("Chunked encoding streaming mode set");
        }
        if (contentLength < 0) {
            throw new IllegalArgumentException ("invalid content length");
        }
        fixedContentLength = contentLength;
    }

    /**
     * This method is used to enable streaming of a HTTP request body
     * without internal buffering, when the content length is known in
     * advance.
     *
     * <P> An exception will be thrown if the application attempts to write
     * more data than the indicated content-length, or if the application
     * closes the OutputStream before writing the indicated amount.
     *
     * <P> When output streaming is enabled, authentication and redirection
     * cannot be handled automatically. A {@linkplain HttpRetryException} will
     * be thrown when reading the response if authentication or redirection
     * are required. This exception can be queried for the details of the
     * error.
     *
     * <P> This method must be called before the URLConnection is connected.
     *
     * <P> The content length set by invoking this method takes precedence
     * over any value set by {@link #setFixedLengthStreamingMode(int)}.
     *
     * @param  contentLength
     *         The number of bytes which will be written to the OutputStream.
     *
     * @throws  IllegalStateException
     *          if URLConnection is already connected or if a different
     *          streaming mode is already enabled.
     *
     * @throws  IllegalArgumentException
     *          if a content length less than zero is specified.
     *
     * @since 1.7
     */
    public void setFixedLengthStreamingMode(long contentLength) {
        if (connected) {
            throw new IllegalStateException("Already connected");
        }
        if (chunkLength != -1) {
            throw new IllegalStateException(
                "Chunked encoding streaming mode set");
        }
        if (contentLength < 0) {
            throw new IllegalArgumentException("invalid content length");
        }
        fixedContentLengthLong = contentLength;
    }

    /* Default chunk size (including chunk header) if not specified;
     * we want to keep this in sync with the one defined in
     * sun.net.www.http.ChunkedOutputStream
     */
    private static final int DEFAULT_CHUNK_SIZE = 4096;

    /**
     * This method is used to enable streaming of a HTTP request body
     * without internal buffering, when the content length is <b>not</b>
     * known in advance. In this mode, chunked transfer encoding
     * is used to send the request body. Note, not all HTTP servers
     * support this mode.
     * <p>
     * When output streaming is enabled, authentication
     * and redirection cannot be handled automatically.
     * A HttpRetryException will be thrown when reading
     * the response if authentication or redirection are required.
     * This exception can be queried for the details of the error.
     * <p>
     * This method must be called before the URLConnection is connected.
     *
     * @param   chunklen The number of bytes to write in each chunk.
     *          If chunklen is less than or equal to zero, a default
     *          value will be used.
     *
     * @throws  IllegalStateException if URLConnection is already connected
     *          or if a different streaming mode is already enabled.
     *
     * @see     #setFixedLengthStreamingMode(int)
     * @since 1.5
     */
    public void setChunkedStreamingMode (int chunklen) {
        if (connected) {
            throw new IllegalStateException ("Can't set streaming mode: already connected");
        }
        if (fixedContentLength != -1 || fixedContentLengthLong != -1) {
            throw new IllegalStateException ("Fixed length streaming mode set");
        }
        chunkLength = chunklen <=0? DEFAULT_CHUNK_SIZE : chunklen;
    }

    /**
     * Returns the value for the <code>n</code><sup>th</sup> header field.
     * Some implementations may treat the <code>0</code><sup>th</sup>
     * header field as special, i.e. as the status line returned by the HTTP
     * server.
     * <p>
     * This method can be used in conjunction with the
     * {@link #getHeaderFieldKey getHeaderFieldKey} method to iterate through all
     * the headers in the message.
     *
     * @param   n   an index, where n>=0.
     * @return  the value of the <code>n</code><sup>th</sup> header field,
     *          or <code>null</code> if the value does not exist.
     * @see     java.net.HttpURLConnection#getHeaderFieldKey(int)
     */
    public String getHeaderField(int n) {
        return null;
    }

    /**
     * An <code>int</code> representing the three digit HTTP Status-Code.
     * <ul>
     * <li> 1xx: Informational
     * <li> 2xx: Success
     * <li> 3xx: Redirection
     * <li> 4xx: Client Error
     * <li> 5xx: Server Error
     * </ul>
     */
    protected int responseCode = -1;

    /**
     * The HTTP response message.
     */
    protected String responseMessage = null;

    /* static variables */

    /* do we automatically follow redirects? The default is true. */
    private static boolean followRedirects = true;

    /**
     * If <code>true</code>, the protocol will automatically follow redirects.
     * If <code>false</code>, the protocol will not automatically follow
     * redirects.
     * <p>
     * This field is set by the <code>setInstanceFollowRedirects</code>
     * method. Its value is returned by the <code>getInstanceFollowRedirects</code>
     * method.
     * <p>
     * Its default value is based on the value of the static followRedirects
     * at HttpURLConnection construction time.
     *
     * @see     java.net.HttpURLConnection#setInstanceFollowRedirects(boolean)
     * @see     java.net.HttpURLConnection#getInstanceFollowRedirects()
     * @see     java.net.HttpURLConnection#setFollowRedirects(boolean)
     */
    protected boolean instanceFollowRedirects = followRedirects;

    /* valid HTTP methods */
    private static final String[] methods = {
        "GET", "POST", "HEAD", "OPTIONS", "PUT", "DELETE", "TRACE"
    };

    /**
     * Constructor for the HttpURLConnection.
     * @param u the URL
     */
    protected HttpURLConnection (URL u) {
        super(u);
    }

    /**
     * Sets whether HTTP redirects  (requests with response code 3xx) should
     * be automatically followed by this class.  True by default.  Applets
     * cannot change this variable.
     * <p>
     * If there is a security manager, this method first calls
     * the security manager's <code>checkSetFactory</code> method
     * to ensure the operation is allowed.
     * This could result in a SecurityException.
     *
     * @param set a <code>boolean</code> indicating whether or not
     * to follow HTTP redirects.
     * @exception  SecurityException  if a security manager exists and its
     *             <code>checkSetFactory</code> method doesn't
     *             allow the operation.
     * @see        SecurityManager#checkSetFactory
     * @see #getFollowRedirects()
     */
    public static void setFollowRedirects(boolean set) {
        SecurityManager sec = System.getSecurityManager();
        if (sec != null) {
            // seems to be the best check here...
            sec.checkSetFactory();
        }
        followRedirects = set;
    }

    /**
     * Returns a <code>boolean</code> indicating
     * whether or not HTTP redirects (3xx) should
     * be automatically followed.
     *
     * @return <code>true</code> if HTTP redirects should
     * be automatically followed, <tt>false</tt> if not.
     * @see #setFollowRedirects(boolean)
     */
    public static boolean getFollowRedirects() {
        return followRedirects;
    }

    /**
     * Sets whether HTTP redirects (requests with response code 3xx) should
     * be automatically followed by this <code>HttpURLConnection</code>
     * instance.
     * <p>
     * The default value comes from followRedirects, which defaults to
     * true.
     *
     * @param followRedirects a <code>boolean</code> indicating
     * whether or not to follow HTTP redirects.
     *
     * @see    java.net.HttpURLConnection#instanceFollowRedirects
     * @see #getInstanceFollowRedirects
     * @since 1.3
     */
     public void setInstanceFollowRedirects(boolean followRedirects) {
        instanceFollowRedirects = followRedirects;
     }

     /**
     * Returns the value of this <code>HttpURLConnection</code>'s
     * <code>instanceFollowRedirects</code> field.
     *
     * @return  the value of this <code>HttpURLConnection</code>'s
     *          <code>instanceFollowRedirects</code> field.
     * @see     java.net.HttpURLConnection#instanceFollowRedirects
     * @see #setInstanceFollowRedirects(boolean)
     * @since 1.3
     */
     public boolean getInstanceFollowRedirects() {
         return instanceFollowRedirects;
     }

    /**
     * Set the method for the URL request, one of:
     * <UL>
     *  <LI>GET
     *  <LI>POST
     *  <LI>HEAD
     *  <LI>OPTIONS
     *  <LI>PUT
     *  <LI>DELETE
     *  <LI>TRACE
     * </UL> are legal, subject to protocol restrictions.  The default
     * method is GET.
     *
     * @param method the HTTP method
     * @exception ProtocolException if the method cannot be reset or if
     *              the requested method isn't valid for HTTP.
     * @exception SecurityException if a security manager is set and the
     *              method is "TRACE", but the "allowHttpTrace"
     *              NetPermission is not granted.
     * @see #getRequestMethod()
     */
    public void setRequestMethod(String method) throws ProtocolException {
        if (connected) {
            throw new ProtocolException("Can't reset method: already connected");
        }
        // This restriction will prevent people from using this class to
        // experiment w/ new HTTP methods using java.  But it should
        // be placed for security - the request String could be
        // arbitrarily long.

        for (int i = 0; i < methods.length; i++) {
            if (methods[i].equals(method)) {
                if (method.equals("TRACE")) {
                    SecurityManager s = System.getSecurityManager();
                    if (s != null) {
                        s.checkPermission(new NetPermission("allowHttpTrace"));
                    }
                }
                this.method = method;
                return;
            }
        }
        throw new ProtocolException("Invalid HTTP method: " + method);
    }

    /**
     * Get the request method.
     * @return the HTTP request method
     * @see #setRequestMethod(java.lang.String)
     */
    public String getRequestMethod() {
        return method;
    }

    /**
     * Gets the status code from an HTTP response message.
     * For example, in the case of the following status lines:
     * <PRE>
     * HTTP/1.0 200 OK
     * HTTP/1.0 401 Unauthorized
     * </PRE>
     * It will return 200 and 401 respectively.
     * Returns -1 if no code can be discerned
     * from the response (i.e., the response is not valid HTTP).
     * @throws IOException if an error occurred connecting to the server.
     * @return the HTTP Status-Code, or -1
     */
    public int getResponseCode() throws IOException {
        /*
         * We're got the response code already
         */
        if (responseCode != -1) {
            return responseCode;
        }

        /*
         * Ensure that we have connected to the server. Record
         * exception as we need to re-throw it if there isn't
         * a status line.
         */
        Exception exc = null;
        try {
            getInputStream();
        } catch (Exception e) {
            exc = e;
        }

        /*
         * If we can't a status-line then re-throw any exception
         * that getInputStream threw.
         */
        String statusLine = getHeaderField(0);
        if (statusLine == null) {
            if (exc != null) {
                if (exc instanceof RuntimeException)
                    throw (RuntimeException)exc;
                else
                    throw (IOException)exc;
            }
            return -1;
        }

        /*
         * Examine the status-line - should be formatted as per
         * section 6.1 of RFC 2616 :-
         *
         * Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase
         *
         * If status line can't be parsed return -1.
         */
        if (statusLine.startsWith("HTTP/1.")) {
            int codePos = statusLine.indexOf(' ');
            if (codePos > 0) {

                int phrasePos = statusLine.indexOf(' ', codePos+1);
                if (phrasePos > 0 && phrasePos < statusLine.length()) {
                    responseMessage = statusLine.substring(phrasePos+1);
                }

                // deviation from RFC 2616 - don't reject status line
                // if SP Reason-Phrase is not included.
                if (phrasePos < 0)
                    phrasePos = statusLine.length();

                try {
                    responseCode = Integer.parseInt
                            (statusLine.substring(codePos+1, phrasePos));
                    return responseCode;
                } catch (NumberFormatException e) { }
            }
        }
        return -1;
    }

    /**
     * Gets the HTTP response message, if any, returned along with the
     * response code from a server.  From responses like:
     * <PRE>
     * HTTP/1.0 200 OK
     * HTTP/1.0 404 Not Found
     * </PRE>
     * Extracts the Strings "OK" and "Not Found" respectively.
     * Returns null if none could be discerned from the responses
     * (the result was not valid HTTP).
     * @throws IOException if an error occurred connecting to the server.
     * @return the HTTP response message, or <code>null</code>
     */
    public String getResponseMessage() throws IOException {
        getResponseCode();
        return responseMessage;
    }

    public long getHeaderFieldDate(String name, long Default) {
        String dateString = getHeaderField(name);
        try {
            if (dateString.indexOf("GMT") == -1) {
                dateString = dateString+" GMT";
            }
            return Date.parse(dateString);
        } catch (Exception e) {
        }
        return Default;
    }


    /**
     * Indicates that other requests to the server
     * are unlikely in the near future. Calling disconnect()
     * should not imply that this HttpURLConnection
     * instance can be reused for other requests.
     */
    public abstract void disconnect();

    /**
     * Indicates if the connection is going through a proxy.
     * @return a boolean indicating if the connection is
     * using a proxy.
     */
    public abstract boolean usingProxy();

    /**
     * Returns a {@link SocketPermission} object representing the
     * permission necessary to connect to the destination host and port.
     *
     * @exception IOException if an error occurs while computing
     *            the permission.
     *
     * @return a <code>SocketPermission</code> object representing the
     *         permission necessary to connect to the destination
     *         host and port.
     */
    public Permission getPermission() throws IOException {
        int port = url.getPort();
        port = port < 0 ? 80 : port;
        String host = url.getHost() + ":" + port;
        Permission permission = new SocketPermission(host, "connect");
        return permission;
    }

   /**
    * Returns the error stream if the connection failed
    * but the server sent useful data nonetheless. The
    * typical example is when an HTTP server responds
    * with a 404, which will cause a FileNotFoundException
    * to be thrown in connect, but the server sent an HTML
    * help page with suggestions as to what to do.
    *
    * <p>This method will not cause a connection to be initiated.  If
    * the connection was not connected, or if the server did not have
    * an error while connecting or if the server had an error but
    * no error data was sent, this method will return null. This is
    * the default.
    *
    * @return an error stream if any, null if there have been no
    * errors, the connection is not connected or the server sent no
    * useful data.
    */
    public InputStream getErrorStream() {
        return null;
    }

    /**
     * The response codes for HTTP, as of version 1.1.
     */

    // REMIND: do we want all these??
    // Others not here that we do want??

    /* 2XX: generally "OK" */

    /**
     * HTTP Status-Code 200: OK.
     */
    public static final int HTTP_OK = 200;

    /**
     * HTTP Status-Code 201: Created.
     */
    public static final int HTTP_CREATED = 201;

    /**
     * HTTP Status-Code 202: Accepted.
     */
    public static final int HTTP_ACCEPTED = 202;

    /**
     * HTTP Status-Code 203: Non-Authoritative Information.
     */
    public static final int HTTP_NOT_AUTHORITATIVE = 203;

    /**
     * HTTP Status-Code 204: No Content.
     */
    public static final int HTTP_NO_CONTENT = 204;

    /**
     * HTTP Status-Code 205: Reset Content.
     */
    public static final int HTTP_RESET = 205;

    /**
     * HTTP Status-Code 206: Partial Content.
     */
    public static final int HTTP_PARTIAL = 206;

    /* 3XX: relocation/redirect */

    /**
     * HTTP Status-Code 300: Multiple Choices.
     */
    public static final int HTTP_MULT_CHOICE = 300;

    /**
     * HTTP Status-Code 301: Moved Permanently.
     */
    public static final int HTTP_MOVED_PERM = 301;

    /**
     * HTTP Status-Code 302: Temporary Redirect.
     */
    public static final int HTTP_MOVED_TEMP = 302;

    /**
     * HTTP Status-Code 303: See Other.
     */
    public static final int HTTP_SEE_OTHER = 303;

    /**
     * HTTP Status-Code 304: Not Modified.
     */
    public static final int HTTP_NOT_MODIFIED = 304;

    /**
     * HTTP Status-Code 305: Use Proxy.
     */
    public static final int HTTP_USE_PROXY = 305;

    /* 4XX: client error */

    /**
     * HTTP Status-Code 400: Bad Request.
     */
    public static final int HTTP_BAD_REQUEST = 400;

    /**
     * HTTP Status-Code 401: Unauthorized.
     */
    public static final int HTTP_UNAUTHORIZED = 401;

    /**
     * HTTP Status-Code 402: Payment Required.
     */
    public static final int HTTP_PAYMENT_REQUIRED = 402;

    /**
     * HTTP Status-Code 403: Forbidden.
     */
    public static final int HTTP_FORBIDDEN = 403;

    /**
     * HTTP Status-Code 404: Not Found.
     */
    public static final int HTTP_NOT_FOUND = 404;

    /**
     * HTTP Status-Code 405: Method Not Allowed.
     */
    public static final int HTTP_BAD_METHOD = 405;

    /**
     * HTTP Status-Code 406: Not Acceptable.
     */
    public static final int HTTP_NOT_ACCEPTABLE = 406;

    /**
     * HTTP Status-Code 407: Proxy Authentication Required.
     */
    public static final int HTTP_PROXY_AUTH = 407;

    /**
     * HTTP Status-Code 408: Request Time-Out.
     */
    public static final int HTTP_CLIENT_TIMEOUT = 408;

    /**
     * HTTP Status-Code 409: Conflict.
     */
    public static final int HTTP_CONFLICT = 409;

    /**
     * HTTP Status-Code 410: Gone.
     */
    public static final int HTTP_GONE = 410;

    /**
     * HTTP Status-Code 411: Length Required.
     */
    public static final int HTTP_LENGTH_REQUIRED = 411;

    /**
     * HTTP Status-Code 412: Precondition Failed.
     */
    public static final int HTTP_PRECON_FAILED = 412;

    /**
     * HTTP Status-Code 413: Request Entity Too Large.
     */
    public static final int HTTP_ENTITY_TOO_LARGE = 413;

    /**
     * HTTP Status-Code 414: Request-URI Too Large.
     */
    public static final int HTTP_REQ_TOO_LONG = 414;

    /**
     * HTTP Status-Code 415: Unsupported Media Type.
     */
    public static final int HTTP_UNSUPPORTED_TYPE = 415;

    /* 5XX: server error */

    /**
     * HTTP Status-Code 500: Internal Server Error.
     * @deprecated   it is misplaced and shouldn't have existed.
     */
    @Deprecated
    public static final int HTTP_SERVER_ERROR = 500;

    /**
     * HTTP Status-Code 500: Internal Server Error.
     */
    public static final int HTTP_INTERNAL_ERROR = 500;

    /**
     * HTTP Status-Code 501: Not Implemented.
     */
    public static final int HTTP_NOT_IMPLEMENTED = 501;

    /**
     * HTTP Status-Code 502: Bad Gateway.
     */
    public static final int HTTP_BAD_GATEWAY = 502;

    /**
     * HTTP Status-Code 503: Service Unavailable.
     */
    public static final int HTTP_UNAVAILABLE = 503;

    /**
     * HTTP Status-Code 504: Gateway Timeout.
     */
    public static final int HTTP_GATEWAY_TIMEOUT = 504;

    /**
     * HTTP Status-Code 505: HTTP Version Not Supported.
     */
    public static final int HTTP_VERSION = 505;

}