iOS gzip 压缩和解压
压缩：
#import
@interface LFCGzipUtility : NSObject {
}
+(NSData*) gzipData: (NSData*)pUncompressedData;
@end
#import "zlib.h"
#import "LFCGzipUtility.h"
@implementation LFCGzipUtility
+(NSData*) gzipData: (NSData*)pUncompressedData
{
if (!pUncompressedData || [pUncompressedData length] == 0)
{
NSLog(@"%s: Error: Can't compress an empty or null NSData object.", __func__);
return nil;
}
int deflateStatus;
float buffer = 1.1;
do {
z_stream zlibStreamStruct;
zlibStreamStruct.zalloc = Z_NULL; // Set zalloc, zfree, and opaque to Z_NULL so
zlibStreamStruct.zfree = Z_NULL; // that when we call deflateInit2 they will be
zlibStreamStruct.opaque = Z_NULL; // updated to use default allocation functions.
zlibStreamStruct.total_out = 0; // Total number of output bytes produced so far
zlibStreamStruct.next_in = (Bytef*)[pUncompressedData bytes]; // Pointer to input bytes
zlibStreamStruct.avail_in = (uInt)[pUncompressedData length]; // Number of input bytes left to process
int initError = deflateInit2(&zlibStreamStruct, Z_DEFAULT_COMPRESSION, Z_DEFLATED, (15+16), 8, Z_DEFAULT_STRATEGY);
if (initError != Z_OK)
{
NSString *errorMsg = nil;
switch (initError)
{
case Z_STREAM_ERROR:
errorMsg = @"Invalid parameter passed in to function.";
break;
case Z_MEM_ERROR:
errorMsg = @"Insufficient memory.";
break;
case Z_VERSION_ERROR:
errorMsg = @"The version of zlib.h and the version of the library linked do not match.";
break;
default:
errorMsg = @"Unknown error code.";
break;
}
NSLog(@"%s: deflateInit2() Error: \"%@\" Message: \"%s\"", __func__, errorMsg, zlibStreamStruct.msg);
return nil;
}
// Create output memory buffer for compressed data. The zlib documentation states that
// destination buffer size must be at least 0.1% larger than avail_in plus 12 bytes.
NSMutableData *compressedData = [NSMutableData dataWithLength:[pUncompressedData length] * buffer + 12];
do {
// Store location where next byte should be put in next_out
zlibStreamStruct.next_out = [compressedData mutableBytes] + zlibStreamStruct.total_out;
// Calculate the amount of remaining free space in the output buffer
// by subtracting the number of bytes that have been written so far
// from the buffer's total capacity
zlibStreamStruct.avail_out = (uInt)([compressedData length] - zlibStreamStruct.total_out);
deflateStatus = deflate(&zlibStreamStruct, Z_FINISH);
} while ( deflateStatus == Z_OK );
if (deflateStatus == Z_BUF_ERROR && buffer < 32) {
continue;
}
// Check for zlib error and convert code to usable error message if appropriate
if (deflateStatus != Z_STREAM_END) {
NSString *errorMsg = nil;
switch (deflateStatus)
{
case Z_ERRNO:
errorMsg = @"Error occured while reading file.";
break;
case Z_STREAM_ERROR:
errorMsg = @"The stream state was inconsistent (e.g., next_in or next_out was NULL).";
break;
case Z_DATA_ERROR:
errorMsg = @"The deflate data was invalid or incomplete.";
break;
case Z_MEM_ERROR:
errorMsg = @"Memory could not be allocated for processing.";
break;
case Z_BUF_ERROR:
errorMsg = @"Ran out of output buffer for writing compressed bytes.";
break;
case Z_VERSION_ERROR:
errorMsg = @"The version of zlib.h and the version of the library linked do not match.";
break;
default:
errorMsg = @"Unknown error code.";
break;
}
NSLog(@"%s: zlib error while attempting compression: \"%@\" Message: \"%s\"", __func__, errorMsg, zlibStreamStruct.msg);
// Free data structures that were dynamically created for the stream.
deflateEnd(&zlibStreamStruct);
return nil;
}
// Free data structures that were dynamically created for the stream.
deflateEnd(&zlibStreamStruct);
[compressedData setLength: zlibStreamStruct.total_out];
return compressedData;
} while ( false );
return nil;
}
@end
解压：
服务端使用gzip压缩，可以大幅度减小传输包的体积，加快客户端网络请求速度，为用户节省流量。当服务器返回的httpHeader的"Content-Encoding" 属性的值是gzip时，数据会自动被解压缩，但有时候在客户端还没拿到数据的时候，就已经被某些网关解压了，这样gzip就没有起到作用。因此可以约定其他策略，防止网关解压，例如在别的头属性中标记gzip。
如此，就需要我们自己来解压gzip数据。
方法如下：
添加framework库中的libbz2.1.0.dylib；
给NSData添加方法：
引入头文件 #import "zlib.h"
- (NSData *)gzipUnpack
{
if ([self length] == 0) return self;
unsigned full_length = [self length];
unsigned half_length = [self length] / 2;
NSMutableData *decompressed = [NSMutableData dataWithLength: full_length + half_length];
BOOL done = NO;
int status;
z_stream strm;
strm.next_in = (Bytef *)[self bytes];
strm.avail_in = [self length];
strm.total_out = 0;
strm.zalloc = Z_NULL;
strm.zfree = Z_NULL;
if (inflateInit2(&strm, (15+32)) != Z_OK) return nil;
while (!done){
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];
}
return nil;
}