Objective-C中的URL Safe Base64

Question

我已经看过很多关于如何在Objective C中解码Base64编码字符串的Stack Overflow帖子,但我仍然遇到问题.

本质上,我正在尝试将Python脚本移植到Objective C. Python代码行是:

zlib.decompress(base64.urlsafe_b64decode(string))

当我通过Python版本的base64.urlsafe_b64decode运行"string"时,它结果正确,然后可以正确地进行Zlib解压缩.当我通过Objective C Base64解码器的任何变体运行"字符串"时,它有点工作,但结果不一样,Zlib解压缩失败.

URL安全Base 64解码与SO上广泛使用的代码之间有区别吗？如果有人之前遇到过这样的困难,那么任何关于该做什么的见解都会受到赞赏.

谢谢,所以!

编辑1:我使用了这里找到的Base 64代码.原始数据(静止Base64编码),可以发现在这里,产生可以发现目标C 这里,和Python的产生可发现此处.理想情况下,我希望Objective C代码解码为与Python脚本相同的文本.

Answer 1

特别感谢Graham指出RFC差异,我能够解决问题.如果将来有人遇到这个,这里是如何解决它:

1. 从这里下载NSData + Base64代码.
2. 在NSData+Base64.m,您需要将查找表更改为以下内容:

//
// Mapping from 6 bit pattern to ASCII character.
//
static unsigned char base64EncodeLookup[65] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";

//
// Definition for "masked-out" areas of the base64DecodeLookup mapping
//
#define xx 65

//
// Mapping from ASCII character to 6 bit pattern.
//
static unsigned char base64DecodeLookup[256] =
{
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 62, xx, xx, 
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, xx, xx, xx, xx, xx, xx, 
    xx,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, xx, xx, xx, xx, 63, 
    xx, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 
};

这将使Objective C的解码等同于Python.

Answer 2

iOS 7.0及更高版本在NSData上具有"base64EncodedStringWithOptions"方法,它将执行上述查找.但是此方法不返回URL安全编码字符串.因此,必须手动执行替换以获取URL安全编码的字符串.见下文..

NSData *originalData = [originalString dataUsingEncoding:NSUTF8StringEncoding];
NSString *base64String = [originalData base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
base64String = [base64String stringByReplacingOccurrencesOfString:@"/" withString:@"_"];
base64String = [base64String stringByReplacingOccurrencesOfString:@"+" withString:@"-"];

结果base64String现在是URL安全的.