如何解压缩我用zlib压缩的NSS​​tring

Question

我从网络服务器获得的NSString（例如eNoLycgsVgChvILSEoWS1IoSPQBFZgb4）只是使用zlib压缩的普通字符串。如何在Objective-C中解压缩？我找到了一些库，但它们只接受完整的文件，而不是简单的字符串。

Answer 1

基于上面的确定，你似乎并不真正知道格式是什么 - 但似乎它是ZLib deflate，Base64编码。无耻地从其他StackOverflow答案中剔除，这里有一大块代码可以解压缩您的数据：

#import <Foundation/Foundation.h>
#import <zlib.h>

int main( int argc, const char * argv[] )
{
    @autoreleasepool
    {
        NSLog( @"Starting..." );

        NSString      * base64String     = @"eJwLycgsVgChvILSEoWS1IoSPQBFZgb4";
        NSData        * compressedData   = [ [ NSData alloc ] initWithBase64EncodedString: base64String options: 0 ];
        NSUInteger      full_length      = [ compressedData length ];
        NSUInteger      half_length      = [ compressedData length ] / 2;
        NSMutableData * decompressedData = [ NSMutableData dataWithLength: full_length + half_length ];
        BOOL            done             = NO;
        int             status;
        z_stream        strm;

        strm.next_in   = ( Bytef * )[ compressedData bytes  ];
        strm.avail_in  = ( unsigned int ) full_length;
        strm.total_out = 0;
        strm.zalloc    = Z_NULL;
        strm.zfree     = Z_NULL;

        if ( inflateInit2( &strm, ( 15 + 32 ) ) != Z_OK )
        {
            NSLog( @"Could not initialise ZLib" );
            return EXIT_FAILURE;
        }

        while ( done == NO )
        {
            // Make sure we have enough room and reset the lengths.

            if ( strm.total_out >= [ decompressedData length ] )
            {
                [ decompressedData increaseLengthBy: half_length ];
            }

            strm.next_out  = [ decompressedData mutableBytes ] + strm.total_out;
            strm.avail_out = ( unsigned int )( [ decompressedData 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 )
            {
                NSLog( @"Decompression failed with status %i", status );
                break;
            }
        }

        if ( inflateEnd( &strm ) != Z_OK )
        {
            NSLog( @"Could not complete decompression" );
            return EXIT_FAILURE;
        }

        // Set real length.

        if ( done )
        {
            [ decompressedData setLength: strm.total_out ];

            NSString * string = [ [ NSString alloc ] initWithData: decompressedData
                                                         encoding: NSUTF8StringEncoding ];

            NSLog( @"String: %@", string );
        }
        else
        {
            return EXIT_FAILURE;
        }
    }

    NSLog( @"...Success" );

    return EXIT_SUCCESS;
}

运行时，会显示如下内容：

2016-06-16 12:40:14.454 Objective Z[82569:7532295] Starting...
2016-06-16 12:40:14.455 Objective Z[82569:7532295] String: This is input text.
2016-06-16 12:40:14.455 Objective Z[82569:7532295] ...Success
Program ended with exit code: 0

您需要确保链接ZLib。从XCode项目的Build Phases部分，在“Link Binary With Libraries”下，“+”按钮提供一个可搜索的弹出窗口;寻找“libz”。这可能不会出现在iOS上;它出现在OS X SDK中;这超出了这个答案的范围，如果你遇到麻烦，谷歌无疑会迅速提出答案。