@yume-chan/adb/src/utils/base64.ts

TypeScript implementation of Android Debug Bridge (ADB) protocol.

const [charToIndex, indexToChar, paddingChar] = /* #__PURE__ */ (() => {
    // Array is faster than object literal or `Map`
    const charToIndex: number[] = [];
    const indexToChar: number[] = [];
    const paddingChar = "=".charCodeAt(0);

    function addRange(start: string, end: string) {
        const charCodeStart = start.charCodeAt(0);
        const charCodeEnd = end.charCodeAt(0);

        for (
            let charCode = charCodeStart;
            charCode <= charCodeEnd;
            charCode += 1
        ) {
            charToIndex[charCode] = indexToChar.length;
            indexToChar.push(charCode);
        }
    }

    addRange("A", "Z");
    addRange("a", "z");
    addRange("0", "9");
    addRange("+", "+");
    addRange("/", "/");

    return [charToIndex, indexToChar, paddingChar];
})();

/**
 * Calculate the required length of the output buffer for the given input length.
 *
 * @param inputLength Length of the input in bytes
 * @returns Length of the output in bytes
 */
export function calculateBase64EncodedLength(
    inputLength: number,
): [outputLength: number, paddingLength: number] {
    const remainder = inputLength % 3;
    const paddingLength = remainder !== 0 ? 3 - remainder : 0;
    return [((inputLength + paddingLength) / 3) * 4, paddingLength];
}

/**
 * Encode the given input buffer into base64.
 *
 * @param input The input buffer
 * @returns The encoded output buffer
 */
export function encodeBase64(input: Uint8Array): Uint8Array;
/**
 * Encode the given input into base64 and write it to the output buffer.
 *
 * The output buffer must be at least as long as the value returned by `calculateBase64EncodedLength`.
 * It can points to the same buffer as the input, as long as `output.offset <= input.offset - input.length / 3`,
 * or `output.offset >= input.offset - 1`
 *
 * @param input The input buffer
 * @param output The output buffer
 * @returns The number of bytes written to the output buffer
 */
export function encodeBase64(input: Uint8Array, output: Uint8Array): number;
export function encodeBase64(
    input: Uint8Array,
    output?: Uint8Array,
): Uint8Array | number {
    const [outputLength, paddingLength] = calculateBase64EncodedLength(
        input.length,
    );

    if (!output) {
        output = new Uint8Array(outputLength);
        encodeForward(input, output, paddingLength);
        return output;
    } else {
        if (output.length < outputLength) {
            throw new TypeError("output buffer is too small");
        }

        output = output.subarray(0, outputLength);

        // When input and output are on same ArrayBuffer,
        // we check if it's possible to encode in-place.
        if (input.buffer !== output.buffer) {
            encodeForward(input, output, paddingLength);
        } else if (
            output.byteOffset + output.length - (paddingLength + 1) <=
            input.byteOffset + input.length
        ) {
            // Output ends before input ends.
            // Can encode forwards, because writing output won't catch up with reading input.

            // The output end is subtracted by `(paddingLength + 1)` because
            // depending on padding length, it's possible to write 1-3 extra bytes after input ends.
            //
            // The following diagrams show how the last read from input and the last write to output
            // are not conflicting.
            //
            // spell: disable
            //
            // `paddingLength === 2` can write 3 extra bytes:
            //
            //   input:  | aaaaaabb |          |          |          |
            //   output: |  aaaaaa  |  bb0000  |    =     |    =     |
            //
            // `paddingLength === 1` can write 2 extra bytes:
            //
            //   input:  | aaaaaabb | bbbbcccc |          |          |
            //   output: |  aaaaaa  |  bbbbbb  |  cccc00  |    =     |
            //
            // `paddingLength === 0` can write 1 extra byte:
            //
            //   input:  | aaaaaabb | bbbbcccc | ccdddddd |          |
            //   output: |  aaaaaa  |  bbbbbb  |  cccccc  |  dddddd  |
            //
            // spell: enable

            encodeForward(input, output, paddingLength);
        } else if (output.byteOffset >= input.byteOffset - 1) {
            // Output starts after input starts
            // So in backwards, writing output won't catch up with reading input.

            // The input start is subtracted by `1`, Because as the first 3 bytes becomes 4 bytes,
            // it's possible to write 1 extra byte before input starts.
            // spell: disable-next-line
            //   input:  |          | aaaaaabb | bbbbcccc | ccdddddd |
            //   output: |  aaaaaa  |  bbbbbb  |  cccccc  |  dddddd  |

            // Must encode backwards.
            encodeBackward(input, output, paddingLength);
        } else {
            // Input is in the middle of output,
            // It's not possible to read either the first or the last three bytes
            // before they are overwritten by the output.
            throw new TypeError("input and output cannot overlap");
        }

        return outputLength;
    }
}

function encodeForward(
    input: Uint8Array,
    output: Uint8Array,
    paddingLength: number,
) {
    let inputIndex = 0;
    let outputIndex = 0;

    while (inputIndex < input.length - 2) {
        /* cspell: disable-next-line */
        // aaaaaabb
        const x = input[inputIndex]!;
        inputIndex += 1;

        /* cspell: disable-next-line */
        // bbbbcccc
        const y = input[inputIndex]!;
        inputIndex += 1;

        /* cspell: disable-next-line */
        // ccdddddd
        const z = input[inputIndex]!;
        inputIndex += 1;

        output[outputIndex] = indexToChar[x >> 2]!;
        outputIndex += 1;

        output[outputIndex] = indexToChar[((x & 0b11) << 4) | (y >> 4)]!;
        outputIndex += 1;

        output[outputIndex] = indexToChar[((y & 0b1111) << 2) | (z >> 6)]!;
        outputIndex += 1;

        output[outputIndex] = indexToChar[z & 0b111111]!;
        outputIndex += 1;
    }

    if (paddingLength === 2) {
        /* cspell: disable-next-line */
        // aaaaaabb
        const x = input[inputIndex]!;
        inputIndex += 1;

        output[outputIndex] = indexToChar[x >> 2]!;
        outputIndex += 1;

        output[outputIndex] = indexToChar[(x & 0b11) << 4]!;
        outputIndex += 1;

        output[outputIndex] = paddingChar;
        outputIndex += 1;

        output[outputIndex] = paddingChar;
    } else if (paddingLength === 1) {
        /* cspell: disable-next-line */
        // aaaaaabb
        const x = input[inputIndex]!;
        inputIndex += 1;

        /* cspell: disable-next-line */
        // bbbbcccc
        const y = input[inputIndex]!;
        inputIndex += 1;

        output[outputIndex] = indexToChar[x >> 2]!;
        outputIndex += 1;

        output[outputIndex] = indexToChar[((x & 0b11) << 4) | (y >> 4)]!;
        outputIndex += 1;

        output[outputIndex] = indexToChar[(y & 0b1111) << 2]!;
        outputIndex += 1;

        output[outputIndex] = paddingChar;
    }
}

function encodeBackward(
    input: Uint8Array,
    output: Uint8Array,
    paddingLength: number,
) {
    let inputIndex = input.length - 1;
    let outputIndex = output.length - 1;

    if (paddingLength === 2) {
        /* cspell: disable-next-line */
        // aaaaaabb
        const x = input[inputIndex]!;
        inputIndex -= 1;

        output[outputIndex] = paddingChar;
        outputIndex -= 1;

        output[outputIndex] = paddingChar;
        outputIndex -= 1;

        output[outputIndex] = indexToChar[(x & 0b11) << 4]!;
        outputIndex -= 1;

        output[outputIndex] = indexToChar[x >> 2]!;
        outputIndex -= 1;
    } else if (paddingLength === 1) {
        /* cspell: disable-next-line */
        // bbbbcccc
        const y = input[inputIndex]!;
        inputIndex -= 1;

        /* cspell: disable-next-line */
        // aaaaaabb
        const x = input[inputIndex]!;
        inputIndex -= 1;

        output[outputIndex] = paddingChar;
        outputIndex -= 1;

        output[outputIndex] = indexToChar[(y & 0b1111) << 2]!;
        outputIndex -= 1;

        output[outputIndex] = indexToChar[((x & 0b11) << 4) | (y >> 4)]!;
        outputIndex -= 1;

        output[outputIndex] = indexToChar[x >> 2]!;
        outputIndex -= 1;
    }

    while (inputIndex >= 0) {
        /* cspell: disable-next-line */
        // ccdddddd
        const z = input[inputIndex]!;
        inputIndex -= 1;

        /* cspell: disable-next-line */
        // bbbbcccc
        const y = input[inputIndex]!;
        inputIndex -= 1;

        /* cspell: disable-next-line */
        // aaaaaabb
        const x = input[inputIndex]!;
        inputIndex -= 1;

        output[outputIndex] = indexToChar[z & 0b111111]!;
        outputIndex -= 1;

        output[outputIndex] = indexToChar[((y & 0b1111) << 2) | (z >> 6)]!;
        outputIndex -= 1;

        output[outputIndex] = indexToChar[((x & 0b11) << 4) | (y >> 4)]!;
        outputIndex -= 1;

        output[outputIndex] = indexToChar[x >> 2]!;
        outputIndex -= 1;
    }
}

export function decodeBase64(input: string): Uint8Array {
    let padding: number;
    if (input[input.length - 2] === "=") {
        padding = 2;
    } else if (input[input.length - 1] === "=") {
        padding = 1;
    } else {
        padding = 0;
    }

    const result = new Uint8Array((input.length / 4) * 3 - padding);
    let sIndex = 0;
    let dIndex = 0;

    while (sIndex < input.length - (padding !== 0 ? 4 : 0)) {
        const a = charToIndex[input.charCodeAt(sIndex)]!;
        sIndex += 1;

        const b = charToIndex[input.charCodeAt(sIndex)]!;
        sIndex += 1;

        const c = charToIndex[input.charCodeAt(sIndex)]!;
        sIndex += 1;

        const d = charToIndex[input.charCodeAt(sIndex)]!;
        sIndex += 1;

        result[dIndex] = (a << 2) | ((b & 0b11_0000) >> 4);
        dIndex += 1;

        result[dIndex] = ((b & 0b1111) << 4) | ((c & 0b11_1100) >> 2);
        dIndex += 1;

        result[dIndex] = ((c & 0b11) << 6) | d;
        dIndex += 1;
    }

    if (padding === 1) {
        const a = charToIndex[input.charCodeAt(sIndex)]!;
        sIndex += 1;

        const b = charToIndex[input.charCodeAt(sIndex)]!;
        sIndex += 1;

        const c = charToIndex[input.charCodeAt(sIndex)]!;

        result[dIndex] = (a << 2) | ((b & 0b11_0000) >> 4);
        dIndex += 1;

        result[dIndex] = ((b & 0b1111) << 4) | ((c & 0b11_1100) >> 2);
    } else if (padding === 2) {
        const a = charToIndex[input.charCodeAt(sIndex)]!;
        sIndex += 1;

        const b = charToIndex[input.charCodeAt(sIndex)]!;

        result[dIndex] = (a << 2) | ((b & 0b11_0000) >> 4);
    }

    return result;
}