iphone 实现解压缩 gzip

最近做的一个东西中，需要从网络获取xml文件，但是该文件用了gzip压缩的。搜索一 下有人说gzip压缩的用urlrequest可以自己解压，但是这必须从服务器返回的header中有accept－Encoding说明是gzip 的。也就是用这句就可以实现自解压：
[urlRequest addValue:@"gzip" forHTTPHeaderField:@"Accept-Encoding"];
这个在我的项目中没有作用，因为服务器返回的header中没有Accept－Encoding的说明。这就需要手动解压了！解压需要导入libz.1.2.3.dylib库，导入#import "zlib.h"
下面是解压的代码：

-(NSData *)uncompressZippedData:(NSData *)compressedData 
{ 

    if ([compressedData length] == 0) return compressedData; 

    unsigned full_length = [compressedData length]; 

    unsigned half_length = [compressedData length] / 2; 
    NSMutableData *decompressed = [NSMutableData dataWithLength: full_length + half_length]; 
    BOOL done = NO; 
    int status; 
    z_stream strm; 
    strm.next_in = (Bytef *)[compressedData bytes]; 
    strm.avail_in = [compressedData 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; 
    } 
}