今天遇到一个Base64解码的问题，因此在这里记录一下。

一. 问题

问题是这样，服务器下发的Base64加密请求回复内容，客户端接到回复内容，调用系统解码，安卓可以解出来，iOS解不出来。回复内容如下:

NSString *tmpStr = @"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";

二.解决方法

• 先调用ASCII解码，然后再调用Base64解码。

   NSString *tmpStr = @"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";
  
    NSData *base64Data = [tmpStr dataUsingEncoding:NSASCIIStringEncoding];
  
    NSData *data = [[NSData alloc] initWithBase64EncodedData:base64Data options:0];
    NSString *outputString = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
    NSLog(@"outputString = %@", outputString);
  

• 解出内容

   outputString = [{"bannerList":[{"imgUrl":"http://shopxx.wei20.cn/UserDocument/hmjs888/Picture/2017814_151208.jpg","type":"javascript:;","id":""},{"imgUrl":"http://shopxx.wei20.cn/UserDocument/hmjs888/Picture/2017814_151146.jpg","type":"javascript:;","id":""},{"imgUrl":"http://shopxx.wei20.cn/UserDocument/hmjs888/Picture/2017814_151225.jpg","type":"javascript:;","id":""}]},{"datas":[{"shopImageUrl":"http://shop.wei20.cn/UserDocument/hmjs888/Picture/2017816_144232.jpg","shopLink":"http://wx4.wei20.com/gouwu/wish3d/home.shtml?id\u003d356"},{"shopImageUrl":"http://shop.wei20.cn/UserDocument/hmjs888/Picture/2017816_115937.jpg","shopLink":"http://wx4.wei20.com/gouwu/wish3d/list/list?id\u003d356\u0026nid\u003dÉ̳ǷÖÀà´úÂë"},{"shopImageUrl":"http://shop.wei20.cn/UserDocument/hmjs888/Picture/2017816_115947.jpg","shopLink":""},{"shopImageUrl":"http://shop.wei20.cn/UserDocument/hmjs888/Picture/2017816_115955.jpg","shopLink":""}]},{"datas":[{"shopImageUrl":"http://139.224.57.105:8080/picture/../picture/template/2_1/20170718/695e459c-7c01-459c-b153-0c66638b36e6.jpg","shopLink":"smore/smore?tid\u003d\u0026sid\u003d17864\u0026id\u003d618\u0026nid\u003d4100"}]},{"datas":[{"shopImageUrl":"http://139.224.57.105:8080/picture/../picture/template/2_1/20170718/b74f1bf9-00e5-40bd-9417-1d868f231973.jpg","shopLink":""}]},{"datas":[{"shopImageUrl":"http://139.224.57.105:8080/picture/../picture/template/2_1/20170718/4ee9287b-f568-4de5-875d-ee126b7023ec.jpg","shopLink":""}]},{"datas":[{"shopImageUrl":"http://139.224.57.105:8080/picture/../picture/template/2_1/20170718/c6d687e5-7c23-40db-b9ed-bc6697d47ba4.png","shopLink":""}]}]
  

三. 原因

可能原因就是服务器先进行ASCII转码，然后在进行BASE64编码。因此客户端也要进行相应的ASCII解码，再进行BASE64解码。