Base64 Encoding/Decoding Library

Overview

This library provides a simple and efficient implementation of Base64 encoding and decoding in C. It supports both standard and URL-safe Base64 alphabets.

Features

• Encode binary data to Base64 strings
• Decode Base64 strings to binary data
• Support for both standard and URL-safe Base64 alphabets
• Efficient length calculations for encoded and decoded data
• Character validation for Base64 alphabet

API

The library exposes the following functions:

bool is_base64_char(char c, bool url_safe);
int base64_encoded_length(size_t input_length);
int base64_decoded_length(const char* input, size_t input_length, bool url_safe);
int base64_encode(char* output, const char* input, size_t input_length, bool url_safe);
int base64_decode(char* output, const char* input, size_t input_length, bool url_safe);

For detailed function descriptions, please refer to the base64.h header file.

Usage

Here's a simple example of how to use the library:

#include "base64.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
    const char* input = "Hello, World!";
    size_t input_length = strlen(input);
    
    // Calculate the required buffer size for encoding
    int encoded_length = base64_encoded_length(input_length);
    char* encoded = malloc(encoded_length + 1);  // +1 for null terminator
    
    // Encode the input
    if (base64_encode(encoded, input, input_length, false) == 0) {
        printf("Encoded: %s\n", encoded);
        
        // Calculate the required buffer size for decoding
        int decoded_length = base64_decoded_length(encoded, encoded_length, false);
        char* decoded = malloc(decoded_length + 1);  // +1 for null terminator
        
        // Decode the Base64 string
        if (base64_decode(decoded, encoded, encoded_length, false) > 0) {
            printf("Decoded: %s\n", decoded);
        }
        
        free(decoded);
    }
    
    free(encoded);
    return 0;
}

Output:

Encoded: SGVsbG8sIFdvcmxkIQ==
Decoded: Hello, World!

Building

To use this library in your project, include the base64.h header file and compile the base64.c source file along with your code.

Testing

To compile and run the tests, run cc -DDEBUG -o test base64_test.c base64.c; ./test in the terminal.

Author, Licence

Copyright ©️ 2025 Alan Tseng

MIT Licence