我没有看到有关这个主题的任何文档,但这并不意味着它不存在。
我没有看到有关这个主题的任何文档,但这并不意味着它不存在。
在@Zaph和@Brad Larson的帖子之后,以下是两种方法gzipInflate
和gzipDeflate
,它们可以很好地压缩/解压缩NSData
。(代码格式化自cocoadev.com/wiki/NSDataCategory)
#import "zlib.h"
// don't forget to add libz.1.2.x.dylib into your project
- (NSData *)gzipInflate:(NSData*)data
{
if ([data length] == 0) return data;
unsigned full_length = [data length];
unsigned half_length = [data length] / 2;
NSMutableData *decompressed = [NSMutableData dataWithLength: full_length + half_length];
BOOL done = NO;
int status;
z_stream strm;
strm.next_in = (Bytef *)[data bytes];
strm.avail_in = [data length];
strm.total_out = 0;
strm.zalloc = Z_NULL;
strm.zfree = Z_NULL;
if (inflateInit2(&strm, (15+32)) != Z_OK) return nil;
while (!done)
{
// Make sure we have enough room and reset the lengths.
if (strm.total_out >= [decompressed length])
[decompressed increaseLengthBy: half_length];
strm.next_out = [decompressed mutableBytes] + strm.total_out;
strm.avail_out = [decompressed length] - strm.total_out;
// Inflate another chunk.
status = inflate (&strm, Z_SYNC_FLUSH);
if (status == Z_STREAM_END) done = YES;
else if (status != Z_OK) break;
}
if (inflateEnd (&strm) != Z_OK) return nil;
// Set real length.
if (done)
{
[decompressed setLength: strm.total_out];
return [NSData dataWithData: decompressed];
}
else return nil;
}
- (NSData *)gzipDeflate:(NSData*)data
{
if ([data length] == 0) return data;
z_stream strm;
strm.zalloc = Z_NULL;
strm.zfree = Z_NULL;
strm.opaque = Z_NULL;
strm.total_out = 0;
strm.next_in=(Bytef *)[data bytes];
strm.avail_in = [data length];
// Compresssion Levels:
// Z_NO_COMPRESSION
// Z_BEST_SPEED
// Z_BEST_COMPRESSION
// Z_DEFAULT_COMPRESSION
if (deflateInit2(&strm, Z_DEFAULT_COMPRESSION, Z_DEFLATED, (15+16), 8, Z_DEFAULT_STRATEGY) != Z_OK) return nil;
NSMutableData *compressed = [NSMutableData dataWithLength:16384]; // 16K chunks for expansion
do {
if (strm.total_out >= [compressed length])
[compressed increaseLengthBy: 16384];
strm.next_out = [compressed mutableBytes] + strm.total_out;
strm.avail_out = [compressed length] - strm.total_out;
deflate(&strm, Z_FINISH);
} while (strm.avail_out == 0);
deflateEnd(&strm);
[compressed setLength: strm.total_out];
return [NSData dataWithData:compressed];
}
从日志中:
[data length] (orig):989631
[data length] (gz): 102757
[data length] (ungz):989631
#import "bzlib.h"
,确保库libbz2.1.x.dylib
已经添加在“Build Phases -> Link Binary with Libraries”中,它应该可以正常编译。 - lucasartBuild Settings
-> Other Linker Flags
。就可以了。 - lucasartMPMediaItem
并将其保存到服务器上。但是长度仅从15313956减少到14805754。它需要更多的压缩。我使用此链接上的代码将MPMediaItem更改为NSData- http://stackoverflow.com/questions/18824983/nsdata-from-mpmediaitem#comment27770517_18826374 - Badi8beachgzlib.c
中的lseek
以及像read
和write
这样的其他函数是无效的。但是从我阅读的博客来看,这不应该是一个问题。非常感谢任何对此的帮助。 - Badi8beachiOS 9.0开始内置支持几种更多的压缩算法。该库名为libcompression,支持LZ4、LZMA、ZLIB和LZFSE。
下面是一个使用libcompression解压LZMA算法的Swift示例。虽然冗长,但避免了外部依赖,并且可以隐藏在NSData
的扩展中。
import Compression
let streamPtr = UnsafeMutablePointer<compression_stream>.alloc(1)
var stream = streamPtr.memory
var status: compression_status
status = compression_stream_init(&stream, COMPRESSION_STREAM_DECODE, COMPRESSION_LZMA)
stream.src_ptr = UnsafePointer<UInt8>(compressedData.bytes)
stream.src_size = compressedData.length
let dstBufferSize: size_t = 4096
let dstBufferPtr = UnsafeMutablePointer<UInt8>.alloc(dstBufferSize)
stream.dst_ptr = dstBufferPtr
stream.dst_size = dstBufferSize
let decompressedData = NSMutableData()
repeat {
status = compression_stream_process(&stream, 0)
switch status {
case COMPRESSION_STATUS_OK:
if stream.dst_size == 0 {
decompressedData.appendBytes(dstBufferPtr, length: dstBufferSize)
stream.dst_ptr = dstBufferPtr
stream.dst_size = dstBufferSize
}
case COMPRESSION_STATUS_END:
if stream.dst_ptr > dstBufferPtr {
decompressedData.appendBytes(dstBufferPtr, length: stream.dst_ptr - dstBufferPtr)
}
default:
break
}
}
while status == COMPRESSION_STATUS_OK
compression_stream_destroy(&stream)
if status == COMPRESSION_STATUS_END {
// Decompression succeeded, do something with decompressedData
}
else {
// Decompression failed
}
这是一个Swift 3的libcompression封装,支持(ZLIB, LZFSE, LZMA, LZ4, deflate, RFC-1950, RFC-1951)等数据类型。可以作为Data类型的扩展使用。 https://github.com/mw99/DataCompression
通过Swift libcompression封装实现了对数据的压缩和解压缩(支持ZLIB、LZFSE、LZMA、LZ4、deflate、RFC-1950、RFC-1951)
在playground中可进行有趣的操作: playground compression rates
NSData
的新 compressed
方法:let compressedData = try? NSData(data: data).compressed(using: .zlib)
不幸的是,这种方法还没有移植到Swift本地的Data
类中,但是可以通过在上面的代码行后添加as Data
来将NSData
简单地转换为Data
。