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      1 /*
      2  * Copyright (C) 2007 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.webkit;
     18 
     19 import android.content.Context;
     20 import android.net.http.EventHandler;
     21 import android.net.http.Headers;
     22 import android.os.Handler;
     23 import android.os.Message;
     24 
     25 import java.io.IOException;
     26 import java.io.InputStream;
     27 
     28 /**
     29  * This abstract class is used for all content loaders that rely on streaming
     30  * content into the rendering engine loading framework.
     31  *
     32  * The class implements a state machine to load the content into the frame in
     33  * a similar manor to the way content arrives from the network. The class uses
     34  * messages to move from one state to the next, which enables async. loading of
     35  * the streamed content.
     36  *
     37  * Classes that inherit from this class must implement two methods, the first
     38  * method is used to setup the InputStream and notify the loading framework if
     39  * it can load it's content. The other method allows the derived class to add
     40  * additional HTTP headers to the response.
     41  *
     42  * By default, content loaded with a StreamLoader is marked with a HTTP header
     43  * that indicates the content should not be cached.
     44  *
     45  */
     46 abstract class StreamLoader implements Handler.Callback {
     47 
     48     private static final int MSG_STATUS = 100;  // Send status to loader
     49     private static final int MSG_HEADERS = 101; // Send headers to loader
     50     private static final int MSG_DATA = 102;  // Send data to loader
     51     private static final int MSG_END = 103;  // Send endData to loader
     52 
     53     protected final Context mContext;
     54     protected final LoadListener mLoadListener; // loader class
     55     protected InputStream mDataStream; // stream to read data from
     56     protected long mContentLength; // content length of data
     57     private byte [] mData; // buffer to pass data to loader with.
     58 
     59     // Handler which will be initialized in the thread where load() is called.
     60     private Handler mHandler;
     61 
     62     /**
     63      * Constructor. Although this class calls the LoadListener, it only calls
     64      * the EventHandler Interface methods. LoadListener concrete class is used
     65      * to avoid the penality of calling an interface.
     66      *
     67      * @param loadlistener The LoadListener to call with the data.
     68      */
     69     StreamLoader(LoadListener loadlistener) {
     70         mLoadListener = loadlistener;
     71         mContext = loadlistener.getContext();
     72     }
     73 
     74     /**
     75      * This method is called when the derived class should setup mDataStream,
     76      * and call mLoadListener.status() to indicate that the load can occur. If it
     77      * fails to setup, it should still call status() with the error code.
     78      *
     79      * @return true if stream was successfully setup
     80      */
     81     protected abstract boolean setupStreamAndSendStatus();
     82 
     83     /**
     84      * This method is called when the headers are about to be sent to the
     85      * load framework. The derived class has the opportunity to add addition
     86      * headers.
     87      *
     88      * @param headers Map of HTTP headers that will be sent to the loader.
     89      */
     90     abstract protected void buildHeaders(Headers headers);
     91 
     92     /**
     93      * Calling this method starts the load of the content for this StreamLoader.
     94      * This method simply creates a Handler in the current thread and posts a
     95      * message to send the status and returns immediately.
     96      */
     97     final void load() {
     98         synchronized (this) {
     99             if (mHandler == null) {
    100                 mHandler = new Handler(this);
    101             }
    102         }
    103 
    104         if (!mLoadListener.isSynchronous()) {
    105             mHandler.sendEmptyMessage(MSG_STATUS);
    106         } else {
    107             // Load the stream synchronously.
    108             if (setupStreamAndSendStatus()) {
    109                 // We were able to open the stream, create the array
    110                 // to pass data to the loader
    111                 mData = new byte[8192];
    112                 sendHeaders();
    113                 while (!sendData() && !mLoadListener.cancelled());
    114                 closeStreamAndSendEndData();
    115                 mLoadListener.loadSynchronousMessages();
    116             }
    117         }
    118     }
    119 
    120     public boolean handleMessage(Message msg) {
    121         if (mLoadListener.isSynchronous()) {
    122             throw new AssertionError();
    123         }
    124         if (mLoadListener.cancelled()) {
    125             closeStreamAndSendEndData();
    126             return true;
    127         }
    128         switch(msg.what) {
    129             case MSG_STATUS:
    130                 if (setupStreamAndSendStatus()) {
    131                     // We were able to open the stream, create the array
    132                     // to pass data to the loader
    133                     mData = new byte[8192];
    134                     mHandler.sendEmptyMessage(MSG_HEADERS);
    135                 }
    136                 break;
    137             case MSG_HEADERS:
    138                 sendHeaders();
    139                 mHandler.sendEmptyMessage(MSG_DATA);
    140                 break;
    141             case MSG_DATA:
    142                 if (sendData()) {
    143                     mHandler.sendEmptyMessage(MSG_END);
    144                 } else {
    145                     mHandler.sendEmptyMessage(MSG_DATA);
    146                 }
    147                 break;
    148             case MSG_END:
    149                 closeStreamAndSendEndData();
    150                 break;
    151             default:
    152                 return false;
    153         }
    154         return true;
    155     }
    156 
    157     /**
    158      * Construct the headers and pass them to the EventHandler.
    159      */
    160     private void sendHeaders() {
    161         Headers headers = new Headers();
    162         if (mContentLength > 0) {
    163             headers.setContentLength(mContentLength);
    164         }
    165         buildHeaders(headers);
    166         mLoadListener.headers(headers);
    167     }
    168 
    169     /**
    170      * Read data from the stream and pass it to the EventHandler.
    171      * If an error occurs reading the stream, then an error is sent to the
    172      * EventHandler, and moves onto the next state - end of data.
    173      * @return True if all the data has been read. False if sendData should be
    174      *         called again.
    175      */
    176     private boolean sendData() {
    177         if (mDataStream != null) {
    178             try {
    179                 int amount = mDataStream.read(mData);
    180                 if (amount > 0) {
    181                     mLoadListener.data(mData, amount);
    182                     return false;
    183                 }
    184             } catch (IOException ex) {
    185                 mLoadListener.error(EventHandler.FILE_ERROR, ex.getMessage());
    186             }
    187         }
    188         return true;
    189     }
    190 
    191     /**
    192      * Close the stream and inform the EventHandler that load is complete.
    193      */
    194     private void closeStreamAndSendEndData() {
    195         if (mDataStream != null) {
    196             try {
    197                 mDataStream.close();
    198             } catch (IOException ex) {
    199                 // ignore.
    200             }
    201         }
    202         mLoadListener.endData();
    203     }
    204 }
    205