Base64 Encoding/Decoding

Converting base64-encoded binary content in streaming scenarios may be difficult because .NET standard library provides only low-level operations for encoding/decoding. When the input stream has unpredictable size it's very hard to use such API and reduce memory allocations during decoding in the same time. Moreover, base64-encoded binary content can be represented in two forms:

• As UTF-8 encoded characters in the form of the sequence of bytes
• As UTF-16 encoded characters in the form of the sequence of chars

Base64Decoder type is a specially designed for decoding base64-encoded content for streaming scenarios because it maintains the state in the form of the buffer when input fragment cannot be fully decoded.

The following example demonstrates how to decode base64-encoded content represented by UTF-8 encoded characters from the stream:

using System;
using System.IO;
using DotNext.Buffers;
using DotNext.Buffers.Text;

Base64Decoder decoder = new();
Span<byte> base64 = "AA=="u8;
var bytes = new ArrayBufferWriter<byte>();
decoder.DecodeFromUtf8(base64, bytes);

Base64Encoder type provides encoding for streaming scenarios.

using System.Buffers;
using DotNext.Buffers.Text;

var encoder = new Base64Encoder();
var writer = new ArrayBufferWriter<char>();
encoder.EncodeToUtf16(new byte[] { 10, 20, 30 }, writer);

if (writer.HasBufferedData)
{
    var count = encoder.Flush(writer.GetSpan(Base64Encoder.MaxBufferedDataSize));
    writer.Advance(count);
}