Скачать или смотреть How to Correctly Decode Base64 Strings in C# Using Convert.FromBase64String

This guide provides a solution to the common error when decoding Base64 strings in C# . Learn how to correctly pad your Base64 strings for successful decoding.
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This video is based on the question https://stackoverflow.com/q/62874112/ asked by the user 'Vikas Pandey' ( https://stackoverflow.com/u/11582004/ ) and on the answer https://stackoverflow.com/a/62874375/ provided by the user 'Karl-Johan Sjögren' ( https://stackoverflow.com/u/547640/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem

Base64 encoding is a method used to convert binary data into ASCII string format, which can be easily transmitted over media that only supports text. However, when working with C# , you might encounter errors while decoding these strings.

Common Issue: Many developers face the challenge of receiving an error indicating that the input string is not valid when using the Convert.FromBase64String method. The error might read:

"The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters."

This can be frustrating, especially when you have successfully decoded the string using other tools, such as Notepad+ + .

The Solution: Properly Padding Base64 Strings

The root of the problem is often related to the padding of the Base64 string. Base64 strings need to adhere to certain formatting rules to be correctly decoded:

They must be a multiple of four characters in length.

They can be padded with zero to two equal signs (=) at the end to make the length compliant.

Steps to Properly Pad Your Base64 String

Here’s how you can ensure your Base64 encoded string is properly formatted before attempting to decode it in C# :

Check the Length: Before you call Convert.FromBase64String, first check if the length of your string is divisible by 4.

Add Padding if Necessary: If your string's length mod 4 is not zero, append the necessary number of equal signs to the end of the string.

Example Code

Here’s a sample code snippet to illustrate how you can correctly pad your string before decoding it:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

Line 1: The Base64 encoded string is defined.

Lines 3-4: A check is made to determine if the string’s length is a multiple of 4. If not, appropriate padding is added.

Line 6: The string is decoded into a byte array using the Convert.FromBase64String method.

Conclusion

When you encounter troubles with Base64 decoding in C# , remember that proper padding is crucial for successful decoding. By ensuring your string length is divisible by four and adding padding as needed, you can avoid common errors and effectively handle Base64 encoded data.

Using this approach, you can seamlessly decode Base64 strings in your C# applications without running into issues. Happy coding!