Convert a file from to Base64 using JavaScript and converting it back to file using C#

Question

I am trying to convert pdf and image files to base 64 using javascript and convert it back to file using C# in WEB API.

Javascript

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Answer 1

Because the FileReader.readAsDataURL() produces a string that is prefixed with extra metadata (the "URL" portion), you need to strip it off on the C# side. Here's some sample code:

// Sample string from FileReader.readAsDataURL()
var base64 = "data:image/jpeg;base64,ba9867b6a86ba86b6a6ab6abaa====";

// Some known piece of information that will be in the above string
const string identifier = ";base64,";

// Find where it exists in the input string
var dataIndex = base64.IndexOf(identifier);

// Take the portion after this identifier; that's the real base-64 portion
var cleaned = base64.Substring(dataIndex + identifier.Length);

// Get the bytes
var bytes = Convert.FromBase64String(cleaned);

You could condense this down if it's too verbose, I just wanted to explain it step by step.

var bytes = Convert.FromBase64String(base64.Substring(base64.IndexOf(";base64,") + 8));    

Answer 2

According to MDN: FileReader.readAsDataURL those generated URLs are prefixed with something like data:image/jpeg;base64,. Have a look at your generated string. Look for the occurence of base64, and take the base64 data that starts after this prefix.