Asset.h revision 16c4d154dca43c662571129af31b27433b919a32
1/*
2 * Copyright (C) 2006 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//
18// Class providing access to a read-only asset.  Asset objects are NOT
19// thread-safe, and should not be shared across threads.
20//
21#ifndef __LIBS_ASSET_H
22#define __LIBS_ASSET_H
23
24#include <stdio.h>
25#include <sys/types.h>
26
27#include <utils/Compat.h>
28#include <utils/Errors.h>
29#include <utils/FileMap.h>
30#include <utils/String8.h>
31
32namespace android {
33
34/*
35 * Instances of this class provide read-only operations on a byte stream.
36 *
37 * Access may be optimized for streaming, random, or whole buffer modes.  All
38 * operations are supported regardless of how the file was opened, but some
39 * things will be less efficient.  [pass that in??]
40 *
41 * "Asset" is the base class for all types of assets.  The classes below
42 * provide most of the implementation.  The AssetManager uses one of the
43 * static "create" functions defined here to create a new instance.
44 */
45class Asset {
46public:
47    virtual ~Asset(void);
48
49    static int32_t getGlobalCount();
50    static String8 getAssetAllocations();
51
52    /* used when opening an asset */
53    typedef enum AccessMode {
54        ACCESS_UNKNOWN = 0,
55
56        /* read chunks, and seek forward and backward */
57        ACCESS_RANDOM,
58
59        /* read sequentially, with an occasional forward seek */
60        ACCESS_STREAMING,
61
62        /* caller plans to ask for a read-only buffer with all data */
63        ACCESS_BUFFER,
64    } AccessMode;
65
66    /*
67     * Read data from the current offset.  Returns the actual number of
68     * bytes read, 0 on EOF, or -1 on error.
69     */
70    virtual ssize_t read(void* buf, size_t count) = 0;
71
72    /*
73     * Seek to the specified offset.  "whence" uses the same values as
74     * lseek/fseek.  Returns the new position on success, or (off64_t) -1
75     * on failure.
76     */
77    virtual off64_t seek(off64_t offset, int whence) = 0;
78
79    /*
80     * Close the asset, freeing all associated resources.
81     */
82    virtual void close(void) = 0;
83
84    /*
85     * Get a pointer to a buffer with the entire contents of the file.
86     */
87    virtual const void* getBuffer(bool wordAligned) = 0;
88
89    /*
90     * Get the total amount of data that can be read.
91     */
92    virtual off64_t getLength(void) const = 0;
93
94    /*
95     * Get the total amount of data that can be read from the current position.
96     */
97    virtual off64_t getRemainingLength(void) const = 0;
98
99    /*
100     * Open a new file descriptor that can be used to read this asset.
101     * Returns -1 if you can not use the file descriptor (for example if the
102     * asset is compressed).
103     */
104    virtual int openFileDescriptor(off64_t* outStart, off64_t* outLength) const = 0;
105
106    /*
107     * Return whether this asset's buffer is allocated in RAM (not mmapped).
108     * Note: not virtual so it is safe to call even when being destroyed.
109     */
110    virtual bool isAllocated(void) const { return false; }
111
112    /*
113     * Get a string identifying the asset's source.  This might be a full
114     * path, it might be a colon-separated list of identifiers.
115     *
116     * This is NOT intended to be used for anything except debug output.
117     * DO NOT try to parse this or use it to open a file.
118     */
119    const char* getAssetSource(void) const { return mAssetSource.string(); }
120
121protected:
122    Asset(void);        // constructor; only invoked indirectly
123
124    /* handle common seek() housekeeping */
125    off64_t handleSeek(off64_t offset, int whence, off64_t curPosn, off64_t maxPosn);
126
127    /* set the asset source string */
128    void setAssetSource(const String8& path) { mAssetSource = path; }
129
130    AccessMode getAccessMode(void) const { return mAccessMode; }
131
132private:
133    /* these operations are not implemented */
134    Asset(const Asset& src);
135    Asset& operator=(const Asset& src);
136
137    /* AssetManager needs access to our "create" functions */
138    friend class AssetManager;
139
140    /*
141     * Create the asset from a named file on disk.
142     */
143    static Asset* createFromFile(const char* fileName, AccessMode mode);
144
145    /*
146     * Create the asset from a named, compressed file on disk (e.g. ".gz").
147     */
148    static Asset* createFromCompressedFile(const char* fileName,
149        AccessMode mode);
150
151#if 0
152    /*
153     * Create the asset from a segment of an open file.  This will fail
154     * if "offset" and "length" don't fit within the bounds of the file.
155     *
156     * The asset takes ownership of the file descriptor.
157     */
158    static Asset* createFromFileSegment(int fd, off64_t offset, size_t length,
159        AccessMode mode);
160
161    /*
162     * Create from compressed data.  "fd" should be seeked to the start of
163     * the compressed data.  This could be inside a gzip file or part of a
164     * Zip archive.
165     *
166     * The asset takes ownership of the file descriptor.
167     *
168     * This may not verify the validity of the compressed data until first
169     * use.
170     */
171    static Asset* createFromCompressedData(int fd, off64_t offset,
172        int compressionMethod, size_t compressedLength,
173        size_t uncompressedLength, AccessMode mode);
174#endif
175
176    /*
177     * Create the asset from a memory-mapped file segment.
178     *
179     * The asset takes ownership of the FileMap.
180     */
181    static Asset* createFromUncompressedMap(FileMap* dataMap, AccessMode mode);
182
183    /*
184     * Create the asset from a memory-mapped file segment with compressed
185     * data.  "method" is a Zip archive compression method constant.
186     *
187     * The asset takes ownership of the FileMap.
188     */
189    static Asset* createFromCompressedMap(FileMap* dataMap, int method,
190        size_t uncompressedLen, AccessMode mode);
191
192
193    /*
194     * Create from a reference-counted chunk of shared memory.
195     */
196    // TODO
197
198    AccessMode  mAccessMode;        // how the asset was opened
199    String8    mAssetSource;       // debug string
200
201    Asset*		mNext;				// linked list.
202    Asset*		mPrev;
203};
204
205
206/*
207 * ===========================================================================
208 *
209 * Innards follow.  Do not use these classes directly.
210 */
211
212/*
213 * An asset based on an uncompressed file on disk.  It may encompass the
214 * entire file or just a piece of it.  Access is through fread/fseek.
215 */
216class _FileAsset : public Asset {
217public:
218    _FileAsset(void);
219    virtual ~_FileAsset(void);
220
221    /*
222     * Use a piece of an already-open file.
223     *
224     * On success, the object takes ownership of "fd".
225     */
226    status_t openChunk(const char* fileName, int fd, off64_t offset, size_t length);
227
228    /*
229     * Use a memory-mapped region.
230     *
231     * On success, the object takes ownership of "dataMap".
232     */
233    status_t openChunk(FileMap* dataMap);
234
235    /*
236     * Standard Asset interfaces.
237     */
238    virtual ssize_t read(void* buf, size_t count);
239    virtual off64_t seek(off64_t offset, int whence);
240    virtual void close(void);
241    virtual const void* getBuffer(bool wordAligned);
242    virtual off64_t getLength(void) const { return mLength; }
243    virtual off64_t getRemainingLength(void) const { return mLength-mOffset; }
244    virtual int openFileDescriptor(off64_t* outStart, off64_t* outLength) const;
245    virtual bool isAllocated(void) const { return mBuf != NULL; }
246
247private:
248    off64_t     mStart;         // absolute file offset of start of chunk
249    off64_t     mLength;        // length of the chunk
250    off64_t     mOffset;        // current local offset, 0 == mStart
251    FILE*       mFp;            // for read/seek
252    char*       mFileName;      // for opening
253
254    /*
255     * To support getBuffer() we either need to read the entire thing into
256     * a buffer or memory-map it.  For small files it's probably best to
257     * just read them in.
258     */
259    enum { kReadVsMapThreshold = 4096 };
260
261    FileMap*    mMap;           // for memory map
262    unsigned char* mBuf;        // for read
263
264    const void* ensureAlignment(FileMap* map);
265};
266
267
268/*
269 * An asset based on compressed data in a file.
270 */
271class _CompressedAsset : public Asset {
272public:
273    _CompressedAsset(void);
274    virtual ~_CompressedAsset(void);
275
276    /*
277     * Use a piece of an already-open file.
278     *
279     * On success, the object takes ownership of "fd".
280     */
281    status_t openChunk(int fd, off64_t offset, int compressionMethod,
282        size_t uncompressedLen, size_t compressedLen);
283
284    /*
285     * Use a memory-mapped region.
286     *
287     * On success, the object takes ownership of "fd".
288     */
289    status_t openChunk(FileMap* dataMap, int compressionMethod,
290        size_t uncompressedLen);
291
292    /*
293     * Standard Asset interfaces.
294     */
295    virtual ssize_t read(void* buf, size_t count);
296    virtual off64_t seek(off64_t offset, int whence);
297    virtual void close(void);
298    virtual const void* getBuffer(bool wordAligned);
299    virtual off64_t getLength(void) const { return mUncompressedLen; }
300    virtual off64_t getRemainingLength(void) const { return mUncompressedLen-mOffset; }
301    virtual int openFileDescriptor(off64_t* outStart, off64_t* outLength) const { return -1; }
302    virtual bool isAllocated(void) const { return mBuf != NULL; }
303
304private:
305    off64_t     mStart;         // offset to start of compressed data
306    off64_t     mCompressedLen; // length of the compressed data
307    off64_t     mUncompressedLen; // length of the uncompressed data
308    off64_t     mOffset;        // current offset, 0 == start of uncomp data
309
310    FileMap*    mMap;           // for memory-mapped input
311    int         mFd;            // for file input
312
313    class StreamingZipInflater* mZipInflater;  // for streaming large compressed assets
314
315    unsigned char*  mBuf;       // for getBuffer()
316};
317
318// need: shared mmap version?
319
320}; // namespace android
321
322#endif // __LIBS_ASSET_H
323