根据 Base64 编码的字符串长度计算实际数据大小 [英] Calculate actual data size from Base64 encoded string length

问题描述

给定编码为 Base64 编码字符串的数据，我是否可以通过查看 Base64 编码字符串的长度以某种方式计算已编码的原始数据的实际长度仅?p>

如果没有必要，我不想遍历字符串(这还包括对编码字符串的尾随字符进行字符串操作以检查填充).

解决方案

确切的长度无法计算，除非您查看填充.在不寻找填充的情况下，您可以做的最好的事情是通过将编码字符串长度乘以 3/4 来计算长度的上限(保证编码长度可以被 4 整除).

因此计算的上限将是 N、N+1 或 N+2，其中 N 是原始数据的长度.

Given data encoded as a Base64-encoded string, can I somehow calculate the actual length of the raw data that has been encoded only by looking at the length of the Base64-encoded string?

I don't want to traverse the string if not necessary (this also includes string operations on the trailling characters of the encoded string to check for padding).

解决方案

The exact length cannot be calculated unless you look at the padding. Without looking for padding, the best you can do is calculate an upper bound for the length by multiplying the encoded-string length with 3/4 (the encoded length is guaranteed to be exactly divisible by 4).

The upper bound calculated thus will be either N, N+1 or N+2, where N is the length of the raw data.

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