a45a8008c6
Compressed assets larger than one megabyte are now decompressed on demand rather than being decompressed in their entirety and held in memory. Reading the data in order is relatively efficient, as is seeking forward in the stream. Seeking backwards is supported, but requires reprocessing the compressed data from the beginning, so is very inefficient. In addition, the size limit on compressed assets has been eliminated. Change-Id: I6e68247957e6c53e7e8ba70d12764695f1723bad
321 lines
9.9 KiB
C++
321 lines
9.9 KiB
C++
/*
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* Copyright (C) 2006 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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//
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// Class providing access to a read-only asset. Asset objects are NOT
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// thread-safe, and should not be shared across threads.
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//
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#ifndef __LIBS_ASSET_H
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#define __LIBS_ASSET_H
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#include <stdio.h>
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#include <sys/types.h>
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#include "FileMap.h"
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#include "String8.h"
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#include "Errors.h"
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namespace android {
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/*
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* Instances of this class provide read-only operations on a byte stream.
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*
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* Access may be optimized for streaming, random, or whole buffer modes. All
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* operations are supported regardless of how the file was opened, but some
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* things will be less efficient. [pass that in??]
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*
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* "Asset" is the base class for all types of assets. The classes below
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* provide most of the implementation. The AssetManager uses one of the
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* static "create" functions defined here to create a new instance.
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*/
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class Asset {
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public:
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virtual ~Asset(void);
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static int32_t getGlobalCount();
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static String8 getAssetAllocations();
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/* used when opening an asset */
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typedef enum AccessMode {
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ACCESS_UNKNOWN = 0,
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/* read chunks, and seek forward and backward */
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ACCESS_RANDOM,
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/* read sequentially, with an occasional forward seek */
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ACCESS_STREAMING,
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/* caller plans to ask for a read-only buffer with all data */
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ACCESS_BUFFER,
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} AccessMode;
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/*
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* Read data from the current offset. Returns the actual number of
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* bytes read, 0 on EOF, or -1 on error.
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*/
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virtual ssize_t read(void* buf, size_t count) = 0;
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/*
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* Seek to the specified offset. "whence" uses the same values as
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* lseek/fseek. Returns the new position on success, or (off_t) -1
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* on failure.
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*/
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virtual off_t seek(off_t offset, int whence) = 0;
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/*
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* Close the asset, freeing all associated resources.
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*/
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virtual void close(void) = 0;
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/*
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* Get a pointer to a buffer with the entire contents of the file.
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*/
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virtual const void* getBuffer(bool wordAligned) = 0;
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/*
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* Get the total amount of data that can be read.
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*/
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virtual off_t getLength(void) const = 0;
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/*
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* Get the total amount of data that can be read from the current position.
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*/
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virtual off_t getRemainingLength(void) const = 0;
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/*
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* Open a new file descriptor that can be used to read this asset.
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* Returns -1 if you can not use the file descriptor (for example if the
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* asset is compressed).
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*/
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virtual int openFileDescriptor(off_t* outStart, off_t* outLength) const = 0;
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/*
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* Return whether this asset's buffer is allocated in RAM (not mmapped).
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* Note: not virtual so it is safe to call even when being destroyed.
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*/
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virtual bool isAllocated(void) const { return false; }
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/*
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* Get a string identifying the asset's source. This might be a full
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* path, it might be a colon-separated list of identifiers.
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*
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* This is NOT intended to be used for anything except debug output.
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* DO NOT try to parse this or use it to open a file.
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*/
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const char* getAssetSource(void) const { return mAssetSource.string(); }
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protected:
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Asset(void); // constructor; only invoked indirectly
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/* handle common seek() housekeeping */
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off_t handleSeek(off_t offset, int whence, off_t curPosn, off_t maxPosn);
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/* set the asset source string */
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void setAssetSource(const String8& path) { mAssetSource = path; }
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AccessMode getAccessMode(void) const { return mAccessMode; }
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private:
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/* these operations are not implemented */
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Asset(const Asset& src);
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Asset& operator=(const Asset& src);
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/* AssetManager needs access to our "create" functions */
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friend class AssetManager;
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/*
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* Create the asset from a named file on disk.
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*/
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static Asset* createFromFile(const char* fileName, AccessMode mode);
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/*
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* Create the asset from a named, compressed file on disk (e.g. ".gz").
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*/
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static Asset* createFromCompressedFile(const char* fileName,
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AccessMode mode);
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#if 0
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/*
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* Create the asset from a segment of an open file. This will fail
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* if "offset" and "length" don't fit within the bounds of the file.
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*
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* The asset takes ownership of the file descriptor.
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*/
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static Asset* createFromFileSegment(int fd, off_t offset, size_t length,
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AccessMode mode);
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/*
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* Create from compressed data. "fd" should be seeked to the start of
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* the compressed data. This could be inside a gzip file or part of a
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* Zip archive.
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*
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* The asset takes ownership of the file descriptor.
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*
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* This may not verify the validity of the compressed data until first
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* use.
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*/
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static Asset* createFromCompressedData(int fd, off_t offset,
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int compressionMethod, size_t compressedLength,
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size_t uncompressedLength, AccessMode mode);
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#endif
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/*
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* Create the asset from a memory-mapped file segment.
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*
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* The asset takes ownership of the FileMap.
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*/
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static Asset* createFromUncompressedMap(FileMap* dataMap, AccessMode mode);
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/*
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* Create the asset from a memory-mapped file segment with compressed
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* data. "method" is a Zip archive compression method constant.
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*
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* The asset takes ownership of the FileMap.
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*/
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static Asset* createFromCompressedMap(FileMap* dataMap, int method,
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size_t uncompressedLen, AccessMode mode);
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/*
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* Create from a reference-counted chunk of shared memory.
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*/
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// TODO
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AccessMode mAccessMode; // how the asset was opened
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String8 mAssetSource; // debug string
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Asset* mNext; // linked list.
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Asset* mPrev;
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};
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/*
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* ===========================================================================
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*
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* Innards follow. Do not use these classes directly.
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*/
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/*
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* An asset based on an uncompressed file on disk. It may encompass the
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* entire file or just a piece of it. Access is through fread/fseek.
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*/
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class _FileAsset : public Asset {
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public:
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_FileAsset(void);
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virtual ~_FileAsset(void);
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/*
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* Use a piece of an already-open file.
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*
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* On success, the object takes ownership of "fd".
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*/
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status_t openChunk(const char* fileName, int fd, off_t offset, size_t length);
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/*
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* Use a memory-mapped region.
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*
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* On success, the object takes ownership of "dataMap".
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*/
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status_t openChunk(FileMap* dataMap);
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/*
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* Standard Asset interfaces.
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*/
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virtual ssize_t read(void* buf, size_t count);
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virtual off_t seek(off_t offset, int whence);
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virtual void close(void);
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virtual const void* getBuffer(bool wordAligned);
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virtual off_t getLength(void) const { return mLength; }
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virtual off_t getRemainingLength(void) const { return mLength-mOffset; }
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virtual int openFileDescriptor(off_t* outStart, off_t* outLength) const;
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virtual bool isAllocated(void) const { return mBuf != NULL; }
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private:
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off_t mStart; // absolute file offset of start of chunk
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off_t mLength; // length of the chunk
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off_t mOffset; // current local offset, 0 == mStart
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FILE* mFp; // for read/seek
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char* mFileName; // for opening
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/*
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* To support getBuffer() we either need to read the entire thing into
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* a buffer or memory-map it. For small files it's probably best to
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* just read them in.
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*/
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enum { kReadVsMapThreshold = 4096 };
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FileMap* mMap; // for memory map
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unsigned char* mBuf; // for read
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const void* ensureAlignment(FileMap* map);
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};
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/*
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* An asset based on compressed data in a file.
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*/
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class _CompressedAsset : public Asset {
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public:
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_CompressedAsset(void);
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virtual ~_CompressedAsset(void);
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/*
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* Use a piece of an already-open file.
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*
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* On success, the object takes ownership of "fd".
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*/
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status_t openChunk(int fd, off_t offset, int compressionMethod,
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size_t uncompressedLen, size_t compressedLen);
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/*
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* Use a memory-mapped region.
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*
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* On success, the object takes ownership of "fd".
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*/
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status_t openChunk(FileMap* dataMap, int compressionMethod,
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size_t uncompressedLen);
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/*
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* Standard Asset interfaces.
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*/
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virtual ssize_t read(void* buf, size_t count);
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virtual off_t seek(off_t offset, int whence);
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virtual void close(void);
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virtual const void* getBuffer(bool wordAligned);
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virtual off_t getLength(void) const { return mUncompressedLen; }
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virtual off_t getRemainingLength(void) const { return mUncompressedLen-mOffset; }
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virtual int openFileDescriptor(off_t* outStart, off_t* outLength) const { return -1; }
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virtual bool isAllocated(void) const { return mBuf != NULL; }
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private:
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off_t mStart; // offset to start of compressed data
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off_t mCompressedLen; // length of the compressed data
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off_t mUncompressedLen; // length of the uncompressed data
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off_t mOffset; // current offset, 0 == start of uncomp data
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FileMap* mMap; // for memory-mapped input
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int mFd; // for file input
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class StreamingZipInflater* mZipInflater; // for streaming large compressed assets
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unsigned char* mBuf; // for getBuffer()
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};
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// need: shared mmap version?
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}; // namespace android
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#endif // __LIBS_ASSET_H
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