如何使用zlib gzip NSData？

在iOS开发中，你可以使用zlib库来进行gzip压缩和解压缩操作。以下是一个示例，展示了如何使用zlib库对NSData进行gzip压缩和解压缩：

首先，确保你的项目中已经导入了zlib库。你可以在Build Phases的"Link Binary With Libraries"中添加libz.tbd库。

#import <zlib.h>

// 压缩NSData为gzip格式
- (NSData *)gzipCompressData:(NSData *)data {
    if ([data length] == 0) {
        return nil;
    }
    
    z_stream zlibStreamStruct;
    zlibStreamStruct.zalloc = Z_NULL;
    zlibStreamStruct.zfree = Z_NULL;
    zlibStreamStruct.opaque = Z_NULL;
    zlibStreamStruct.total_out = 0;
    zlibStreamStruct.next_in = (Bytef *)[data bytes];
    zlibStreamStruct.avail_in = (uInt)[data length];
    
    if (deflateInit2(&zlibStreamStruct, Z_DEFAULT_COMPRESSION, Z_DEFLATED, (15+16), 8, Z_DEFAULT_STRATEGY) != Z_OK) {
        return nil;
    }
    
    NSMutableData *compressedData = [NSMutableData dataWithLength:16384];
    do {
        if (zlibStreamStruct.total_out >= [compressedData length]) {
            [compressedData increaseLengthBy:16384];
        }
        
        zlibStreamStruct.next_out = [compressedData mutableBytes] + zlibStreamStruct.total_out;
        zlibStreamStruct.avail_out = (uInt)([compressedData length] - zlibStreamStruct.total_out);
        
        deflate(&zlibStreamStruct, Z_FINISH);
        
    } while (zlibStreamStruct.avail_out == 0);
    
    deflateEnd(&zlibStreamStruct);
    [compressedData setLength:zlibStreamStruct.total_out];
    
    return compressedData;
}

// 解压缩gzip格式的NSData
- (NSData *)gzipDecompressData:(NSData *)compressedData {
    if ([compressedData length] == 0) {
        return nil;
    }
    
    z_stream zlibStreamStruct;
    zlibStreamStruct.zalloc = Z_NULL;
    zlibStreamStruct.zfree = Z_NULL;
    zlibStreamStruct.opaque = Z_NULL;
    zlibStreamStruct.total_out = 0;
    zlibStreamStruct.next_in = (Bytef *)[compressedData bytes];
    zlibStreamStruct.avail_in = (uInt)[compressedData length];
    
    if (inflateInit2(&zlibStreamStruct, (15+32)) != Z_OK) {
        return nil;
    }
    
    NSMutableData *decompressedData = [NSMutableData dataWithLength:(NSUInteger)([compressedData length] * 1.5)];
    do {
        if (zlibStreamStruct.total_out >= [decompressedData length]) {
            [decompressedData increaseLengthBy:(NSUInteger)([compressedData length] * 0.5)];
        }
        
        zlibStreamStruct.next_out = [decompressedData mutableBytes] + zlibStreamStruct.total_out;
        zlibStreamStruct.avail_out = (uInt)([decompressedData length] - zlibStreamStruct.total_out);
        
        inflate(&zlibStreamStruct, Z_SYNC_FLUSH);
        
    } while (zlibStreamStruct.avail_out == 0);
    
    inflateEnd(&zlibStreamStruct);
    [decompressedData setLength:zlibStreamStruct.total_out];
    
    return decompressedData;
}

在上述示例中，gzipCompressData:方法用于将NSData压缩为gzip格式，而gzipDecompressData:方法用于解压缩gzip格式的NSData。

请注意，这只是一个简单的示例，你可能需要根据你的具体需求进行适当的调整和错误处理。