simple_base64 - RFC 4648 Base64 Encoding for Eiffel

Overview

simple_base64 is a lightweight, RFC 4648 compliant Base64 encoding and decoding library for Eiffel. It provides both standard Base64 and URL-safe Base64URL encoding variants, with full Design by Contract support.

Part of the simple_* ecosystem of focused, single-purpose Eiffel libraries.

Quick Start

Installation

Add to your ECF file:

<library name="simple_base64" location="$SIMPLE_BASE64/simple_base64.ecf"/>

Set environment variable:

set SIMPLE_BASE64=D:\path\to\simple_base64

Basic Usage

local
    encoder: SIMPLE_BASE64
    encoded, decoded: STRING
do
    create encoder.make

    -- Encode a string
    encoded := encoder.encode ("Hello, World!")
    -- Result: "SGVsbG8sIFdvcmxkIQ=="

    -- Decode back
    decoded := encoder.decode (encoded)
    -- Result: "Hello, World!"
end

URL-Safe Encoding

-- URL-safe variant (no padding, uses - and _ instead of + and /)
url_safe := encoder.encode_url ("data with special chars")

-- Decode URL-safe
decoded := encoder.decode_url (url_safe)

MIME Encoding (RFC 2045)

-- MIME encoding with line wrapping at 76 characters
mime_encoded := encoder.encode_mime (long_content)

-- Lenient decode handles whitespace and line breaks
decoded := encoder.decode_lenient (mime_encoded)

Data URIs (RFC 2397)

-- Create a data URI
uri := encoder.to_data_uri ("Hello!", "text/plain")
-- Result: "data:text/plain;base64,SGVsbG8h"

-- Extract data from a data URI
data := encoder.from_data_uri (uri)
-- Result: "Hello!"

-- Extract the mediatype
mediatype := encoder.data_uri_mediatype (uri)
-- Result: "text/plain"

Features

Standard Base64

RFC 4648 compliant encoding with proper padding using the standard alphabet (A-Z, a-z, 0-9, +, /).

URL-Safe Base64URL

URL and filename safe variant using - and _ characters. Perfect for JWTs, URLs, and filenames.

Validation

Built-in validation functions to check if strings are valid Base64 or Base64URL encoded.

Design by Contract

Full preconditions, postconditions, and loop variants for correctness verification.

Byte-Level Access

Direct byte array encoding/decoding for binary data handling.

Format Conversion

Convert between standard and URL-safe formats with to_url_safe and to_standard.

MIME Encoding

RFC 2045 compliant encoding with line wrapping at 76 characters. Lenient decoder handles whitespace.

Data URI Support

RFC 2397 data URIs for embedding data inline. Create, parse, and extract mediatypes.

API Summary

Feature	Description
`encode (a_input)`	Encode string to standard Base64
`encode_url (a_input)`	Encode to URL-safe Base64URL (no padding)
`encode_bytes (a_bytes)`	Encode byte array to Base64
`decode (a_input)`	Decode Base64 string
`decode_bytes (a_input)`	Decode to byte array
`is_valid_base64 (a_string)`	Validate standard Base64
`is_valid_base64_url (a_string)`	Validate URL-safe Base64URL
`to_url_safe (a_base64)`	Convert standard to URL-safe format
`to_standard (a_base64url)`	Convert URL-safe to standard format
`encode_mime (a_input)`	Encode with MIME line wrapping (76 chars)
`decode_lenient (a_input)`	Decode ignoring whitespace/line breaks
`to_data_uri (a_data, a_mediatype)`	Create data URI from content
`from_data_uri (a_uri)`	Extract and decode data from data URI
`data_uri_mediatype (a_uri)`	Extract mediatype from data URI
`is_data_uri (a_input)`	Check if string is a data URI

View complete API reference →

Testing

The library includes a comprehensive test suite with 44 tests covering:

Standard RFC 4648 test vectors
Empty string handling
Single, two, and three character inputs (padding edge cases)
URL-safe encoding/decoding
Roundtrip encoding for ASCII and binary data
Validation of valid and invalid inputs
MIME encoding with line wrapping
Lenient decoding with whitespace handling
Data URI creation, parsing, and roundtrip

-- Run tests
ec.exe -batch -config simple_base64.ecf -target simple_base64_tests -tests