@fedify/fedify/esm/runtime/multibase/rfc4648.js

An ActivityPub server framework

const decode = (string, alphabet, bitsPerChar) => {
    // Build the character lookup table:
    const codes = {};
    for (let i = 0; i < alphabet.length; ++i) {
        codes[alphabet[i]] = i;
    }
    // Count the padding bytes:
    let end = string.length;
    while (string[end - 1] === "=") {
        --end;
    }
    // Allocate the output:
    const out = new Uint8Array((end * bitsPerChar / 8) | 0);
    // Parse the data:
    let bits = 0; // Number of bits currently in the buffer
    let buffer = 0; // Bits waiting to be written out, MSB first
    let written = 0; // Next byte to write
    for (let i = 0; i < end; ++i) {
        // Read one character from the string:
        const value = codes[string[i]];
        if (value === undefined) {
            throw new SyntaxError("Invalid character " + string[i]);
        }
        // Append the bits to the buffer:
        buffer = (buffer << bitsPerChar) | value;
        bits += bitsPerChar;
        // Write out some bits if the buffer has a byte's worth:
        if (bits >= 8) {
            bits -= 8;
            out[written++] = 0xff & (buffer >> bits);
        }
    }
    // Verify that we have received just enough bits:
    if (bits >= bitsPerChar || 0xff & (buffer << (8 - bits))) {
        throw new SyntaxError("Unexpected end of data");
    }
    return out;
};
const encode = (data, alphabet, bitsPerChar) => {
    const pad = alphabet[alphabet.length - 1] === "=";
    const mask = (1 << bitsPerChar) - 1;
    let out = "";
    let bits = 0; // Number of bits currently in the buffer
    let buffer = 0; // Bits waiting to be written out, MSB first
    for (let i = 0; i < data.length; ++i) {
        // Slurp data into the buffer:
        buffer = (buffer << 8) | data[i];
        bits += 8;
        // Write out as much as we can:
        while (bits > bitsPerChar) {
            bits -= bitsPerChar;
            out += alphabet[mask & (buffer >> bits)];
        }
    }
    // Partial character:
    if (bits) {
        out += alphabet[mask & (buffer << (bitsPerChar - bits))];
    }
    // Add padding characters until we hit a byte boundary:
    if (pad) {
        while ((out.length * bitsPerChar) & 7) {
            out += "=";
        }
    }
    return out;
};
/**
 * RFC4648 Factory
 */
export const rfc4648 = (bitsPerChar) => (alphabet) => {
    return {
        encode(input) {
            return encode(input, alphabet, bitsPerChar);
        },
        decode(input) {
            return decode(input, alphabet, bitsPerChar);
        },
    };
};