I have a string in base64 that contains = symbols. What is the best way to remove them from the

What is the best method for removing "=" characters when concatenating base64 strings?

I transmitted a byte stream[] of data from the servlet as an http response, and on the client side I am attempting to open the pdf viewer. However, I am unable to view it due to these additional characters.

I have experimented with concatenating using +=, join, and concat, but am still left with the = character at the end of each substring.

Is there a way to concatenate the strings without including the last character?

javascriptstringbase64concatenation

Answer №1

The common base-64 encoding transforms three bytes (3 * 8 bits) into 4 characters (4 * 6 bits). In cases where the original data has a number of bytes that is not divisible by 3, additional padding characters = are included - two if the remainder was 1, and one if the remainder was 2.

Regrettably, merging two base-64 encoded strings is not possible if the first string concludes with padding characters =. The recommended approach is to first decode both strings, combine them into a binary string, and then re-encode it. Failure to follow this process may result in the latter part being out of sync, causing incorrect decoding of all bytes from the second string.

[*] While it isn't absolutely necessary to re-encode the first part entirely, optimizing for this step may not offer significant benefits.

Answer №2

It seems like there might be some confusion regarding your question, but it appears that you are trying to combine multiple Base64-encoded strings and then decode them. Unfortunately, this approach will not work, even if you take into account the "=" characters.

To illustrate, consider the following examples of Base64 encodings:

X20    -> IA==
X20 20 -> ICA=

However, combining "IAIA" and decoding it will yield "X 20 02 00".

The issue arises because each character in Base64 encoding can represent parts of more than one unencoded byte, and conversely, each unencoded byte might be represented by more than one Base64 character.

Therefore, as Antti Haapala pointed out correctly, the correct approach is to decode the individual strings first and then concatenate the decoded output rather than attempting to do so before decoding.

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