Add Base64 encoding and decoding

[davidgaspardev]

Description

Implement Base64 encoding and decoding to convert binary data into a text-safe representation using 64 printable ASCII characters.

// binary → base64 string
byte_t to_base64(cbytes_t src, unsigned int src_len, bytes_t dst, unsigned long sizeof_dst);

// base64 string → binary
byte_t from_base64(cbytes_t b64, bytes_t dst, unsigned long sizeof_dst);

How it works

Every 3 bytes of input are split into 4 groups of 6 bits, each mapped to a character in the Base64 alphabet (A-Z, a-z, 0-9, +, /). Output is padded with = to align to 4-byte groups.

Use cases

• Embedding binary data in JSON / XML
• HTTP Basic Auth headers
• Email attachments (MIME)
• Data URIs

References

• Algorithm: Base64
• Standard: RFC 4648 — The Base16, Base32, and Base64 Data Encodings (2006)
• Authors: Simon Josefsson (RFC editor)
• RFC: https://datatracker.ietf.org/doc/html/rfc4648
• Wikipedia: https://en.wikipedia.org/wiki/Base64