/*
 * Copyright 2005-2006 Sun Microsystems, Inc.  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.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package com.sun.net.httpserver;

import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.net.*;
import javax.net.ssl.*;
import java.util.*;
import sun.net.www.MessageHeader;

/**
 * This class encapsulates a HTTP request received and a
 * response to be generated in one exchange. It provides methods
 * for examining the request from the client, and for building and
 * sending the response.
 * <p>
 * The typical life-cycle of a HttpExchange is shown in the sequence
 * below.
 * <ol><li>{@link #getRequestMethod()} to determine the command
 * <li>{@link #getRequestHeaders()} to examine the request headers (if needed)
 * <li>{@link #getRequestBody()} returns a {@link java.io.InputStream} for reading the request body.
 *     After reading the request body, the stream is close.
 * <li>{@link #getResponseHeaders()} to set any response headers, except content-length
 * <li>{@link #sendResponseHeaders(int,long)} to send the response headers. Must be called before
 * next step.
 * <li>{@link #getResponseBody()} to get a {@link java.io.OutputStream} to send the response body.
 *      When the response body has been written, the stream must be closed to terminate the exchange.
 * </ol>
 * <b>Terminating exchanges</b>
 * <br>
 * Exchanges are terminated when both the request InputStream and response OutputStream are closed.
 * Closing the OutputStream, implicitly closes the InputStream (if it is not already closed).
 * However, it is recommended
 * to consume all the data from the InputStream before closing it.
 * The convenience method {@link #close()} does all of these tasks.
 * Closing an exchange without consuming all of the request body is not an error
 * but may make the underlying TCP connection unusable for following exchanges.
 * The effect of failing to terminate an exchange is undefined, but will typically
 * result in resources failing to be freed/reused.
 * @since 1.6
 */

public abstract class HttpExchange {

    protected HttpExchange () {
    }

    /**
     * Returns an immutable Map containing the HTTP headers that were
     * included with this request. The keys in this Map will be the header
     * names, while the values will be a List of Strings containing each value
     * that was included (either for a header that was listed several times,
     * or one that accepts a comma-delimited list of values on a single line).
     * In either of these cases, the values for the header name will be
     * presented in the order that they were included in the request.
     * <p>
     * The keys in Map are case-insensitive.
     * @return a read-only Map which can be used to access request headers
     */
    public abstract Headers getRequestHeaders () ;

    /**
     * Returns a mutable Map into which the HTTP response headers can be stored
     * and which will be transmitted as part of this response. The keys in the
     * Map will be the header names, while the values must be a List of Strings
     * containing each value that should be included multiple times
     * (in the order that they should be included).
     * <p>
     * The keys in Map are case-insensitive.
     * @return a writable Map which can be used to set response headers.
     */
    public abstract Headers getResponseHeaders () ;

    /**
     * Get the request URI
     *
     * @return the request URI
     */
    public abstract URI getRequestURI () ;

    /**
     * Get the request method
     * @return the request method
     */
    public abstract String getRequestMethod ();

    /**
     * Get the HttpContext for this exchange
     * @return the HttpContext
     */
    public abstract HttpContext getHttpContext ();

    /**
     * Ends this exchange by doing the following in sequence:<p><ol>
     * <li>close the request InputStream, if not already closed<p></li>
     * <li>close the response OutputStream, if not already closed. </li>
     * </ol>
     */
    public abstract void close () ;

    /**
     * returns a stream from which the request body can be read.
     * Multiple calls to this method will return the same stream.
     * It is recommended that applications should consume (read) all of the
     * data from this stream before closing it. If a stream is closed
     * before all data has been read, then the close() call will
     * read and discard remaining data (up to an implementation specific
     * number of bytes).
     * @return the stream from which the request body can be read.
     */
    public abstract InputStream getRequestBody () ;

    /**
     * returns a stream to which the response body must be
     * written. {@link #sendResponseHeaders(int,long)}) must be called prior to calling
     * this method. Multiple calls to this method (for the same exchange)
     * will return the same stream. In order to correctly terminate
     * each exchange, the output stream must be closed, even if no
     * response body is being sent.
     * <p>
     * Closing this stream implicitly
     * closes the InputStream returned from {@link #getRequestBody()}
     * (if it is not already closed).
     * <P>
     * If the call to sendResponseHeaders() specified a fixed response
     * body length, then the exact number of bytes specified in that
     * call must be written to this stream. If too many bytes are written,
     * then write() will throw an IOException. If too few bytes are written
     * then the stream close() will throw an IOException. In both cases,
     * the exchange is aborted and the underlying TCP connection closed.
     * @return the stream to which the response body is written
     */
    public abstract OutputStream getResponseBody () ;


    /**
     * Starts sending the response back to the client using the current set of response headers
     * and the numeric response code as specified in this method. The response body length is also specified
     * as follows. If the response length parameter is greater than zero, this specifies an exact
     * number of bytes to send and the application must send that exact amount of data.
     * If the response length parameter is <code>zero</code>, then chunked transfer encoding is
     * used and an arbitrary amount of data may be sent. The application terminates the
     * response body by closing the OutputStream. If response length has the value <code>-1</code>
     * then no response body is being sent.
     * <p>
     * If the content-length response header has not already been set then
     * this is set to the apropriate value depending on the response length parameter.
     * <p>
     * This method must be called prior to calling {@link #getResponseBody()}.
     * @param rCode the response code to send
     * @param responseLength if > 0, specifies a fixed response body length
     *        and that exact number of bytes must be written
     *        to the stream acquired from getResponseBody(), or else
     *        if equal to 0, then chunked encoding is used,
     *        and an arbitrary number of bytes may be written.
     *        if <= -1, then no response body length is specified and
     *        no response body may be written.
     * @see HttpExchange#getResponseBody()
     */
    public abstract void sendResponseHeaders (int rCode, long responseLength) throws IOException ;

    /**
     * Returns the address of the remote entity invoking this request
     * @return the InetSocketAddress of the caller
     */
    public abstract InetSocketAddress getRemoteAddress ();

    /**
     * Returns the response code, if it has already been set
     * @return the response code, if available. <code>-1</code> if not available yet.
     */
    public abstract int getResponseCode ();

    /**
     * Returns the local address on which the request was received
     * @return the InetSocketAddress of the local interface
     */
    public abstract InetSocketAddress getLocalAddress ();

    /**
     * Returns the protocol string from the request in the form
     * <i>protocol/majorVersion.minorVersion</i>. For example,
     * "HTTP/1.1"
     * @return the protocol string from the request
     */
    public abstract String getProtocol ();

    /**
     * Filter modules may store arbitrary objects with HttpExchange
     * instances as an out-of-band communication mechanism. Other Filters
     * or the exchange handler may then access these objects.
     * <p>
     * Each Filter class will document the attributes which they make
     * available.
     * @param name the name of the attribute to retrieve
     * @return the attribute object, or null if it does not exist
     * @throws NullPointerException if name is <code>null</code>
     */
    public abstract Object getAttribute (String name) ;

    /**
     * Filter modules may store arbitrary objects with HttpExchange
     * instances as an out-of-band communication mechanism. Other Filters
     * or the exchange handler may then access these objects.
     * <p>
     * Each Filter class will document the attributes which they make
     * available.
     * @param name the name to associate with the attribute value
     * @param value the object to store as the attribute value. <code>null</code>
     * value is permitted.
     * @throws NullPointerException if name is <code>null</code>
     */
    public abstract void setAttribute (String name, Object value) ;

    /**
     * Used by Filters to wrap either (or both) of this exchange's InputStream
     * and OutputStream, with the given filtered streams so
     * that subsequent calls to {@link #getRequestBody()} will
     * return the given {@link java.io.InputStream}, and calls to
     * {@link #getResponseBody()} will return the given
     * {@link java.io.OutputStream}. The streams provided to this
     * call must wrap the original streams, and may be (but are not
     * required to be) sub-classes of {@link java.io.FilterInputStream}
     * and {@link java.io.FilterOutputStream}.
     * @param i the filtered input stream to set as this object's inputstream,
     *          or <code>null</code> if no change.
     * @param o the filtered output stream to set as this object's outputstream,
     *          or <code>null</code> if no change.
     */
    public abstract void setStreams (InputStream i, OutputStream o);


    /**
     * If an authenticator is set on the HttpContext that owns this exchange,
     * then this method will return the {@link HttpPrincipal} that represents
     * the authenticated user for this HttpExchange.
     * @return the HttpPrincipal, or <code>null</code> if no authenticator is set.
     */
    public abstract HttpPrincipal getPrincipal ();
}