mudb/src/stream/codec.ts

Real-time database for multiplayer games

// Taken from https://github.com/feross/buffer
function utf8ToBytes(str:string) : number[] {
    let codePoint;
    const strLength = str.length;
    let leadSurrogate;
    const bytes:number[] = [];

    for (let i = 0; i < strLength; ++i) {
        codePoint = str.charCodeAt(i);

        // is surrogate component
        if (codePoint > 0xD7FF && codePoint < 0xE000) {
            // last char was a lead
            if (!leadSurrogate) {
                // no lead yet
                if (codePoint > 0xDBFF) {
                    // unexpected trail
                    bytes.push(0xEF, 0xBF, 0xBD);
                    continue;
                } else if (i + 1 === strLength) {
                    // unpaired lead
                    bytes.push(0xEF, 0xBF, 0xBD);
                    continue;
                }

                // valid lead
                leadSurrogate = codePoint;

                continue;
            }

            // 2 leads in a row
            if (codePoint < 0xDC00) {
                bytes.push(0xEF, 0xBF, 0xBD);
                leadSurrogate = codePoint;
                continue;
            }

            // valid surrogate pair
            codePoint = (leadSurrogate - 0xD800 << 10 | codePoint - 0xDC00) + 0x10000;
        } else if (leadSurrogate) {
            // valid bmp char, but last char was a lead
            bytes.push(0xEF, 0xBF, 0xBD);
        }

        leadSurrogate = undefined;

        // encode utf8
        if (codePoint < 0x80) {
            bytes.push(codePoint);
        } else if (codePoint < 0x800) {
            bytes.push(
                codePoint >> 0x6 | 0xC0,
                codePoint & 0x3F | 0x80,
            );
        } else if (codePoint < 0x10000) {
            bytes.push(
                codePoint >> 0xC | 0xE0,
                codePoint >> 0x6 & 0x3F | 0x80,
                codePoint & 0x3F | 0x80,
            );
        } else if (codePoint < 0x110000) {
            bytes.push(
                codePoint >> 0x12 | 0xF0,
                codePoint >> 0xC & 0x3F | 0x80,
                codePoint >> 0x6 & 0x3F | 0x80,
                codePoint & 0x3F | 0x80,
            );
        } else {
            throw new Error('mudb/stream: invalid code point');
        }
    }

    return bytes;
}

export function encode (str:string) {
    return new Uint8Array(utf8ToBytes(str));
}

// Taken from https://github.com/feross/buffer
function decodeCodePointsArray (codePoints:number[]) : string {
    // Based on http://stackoverflow.com/a/22747272/680742, the browser with
    // the lowest limit is Chrome, with 0x10000 args.
    // We go 1 magnitude less, for safety
    const MAX_ARGUMENTS_LENGTH = 0x1000;

    const len = codePoints.length;
    if (len <= MAX_ARGUMENTS_LENGTH) {
        return String.fromCharCode.apply(String, codePoints); // avoid extra slice()
    }

    // Decode in chunks to avoid "call stack size exceeded".
    let res = '';
    let i = 0;
    while (i < len) {
        res += String.fromCharCode.apply(
            String,
            codePoints.slice(i, i += MAX_ARGUMENTS_LENGTH),
        );
    }
    return res;
}

// Taken from https://github.com/feross/buffer
export function decode (bytes:Uint8Array) : string {
    const { byteLength } = bytes;
    const res:number[] = [];

    let i = 0;
    while (i < byteLength) {
        const firstByte = bytes[i];
        let codePoint;
        let bytesPerSequence = (firstByte > 0xEF) ? 4
            : (firstByte > 0xDF) ? 3
                : (firstByte > 0xBF) ? 2
                    : 1;

        if (i + bytesPerSequence <= byteLength) {
            let secondByte;
            let thirdByte;
            let fourthByte;
            let tempCodePoint;

            switch (bytesPerSequence) {
                case 1:
                    if (firstByte < 0x80) {
                        codePoint = firstByte;
                    }
                    break;
                case 2:
                    secondByte = bytes[i + 1];
                    if ((secondByte & 0xC0) === 0x80) {
                        tempCodePoint = (firstByte & 0x1F) << 0x6 | (secondByte & 0x3F);
                        if (tempCodePoint > 0x7F) {
                            codePoint = tempCodePoint;
                        }
                    }
                    break;
                case 3:
                    secondByte = bytes[i + 1];
                    thirdByte = bytes[i + 2];
                    if ((secondByte & 0xC0) === 0x80 && (thirdByte & 0xC0) === 0x80) {
                        tempCodePoint = (firstByte & 0xF) << 0xC | (secondByte & 0x3F) << 0x6 | (thirdByte & 0x3F);
                        if (tempCodePoint > 0x7FF && (tempCodePoint < 0xD800 || tempCodePoint > 0xDFFF)) {
                            codePoint = tempCodePoint;
                        }
                    }
                    break;
                case 4:
                    secondByte = bytes[i + 1];
                    thirdByte = bytes[i + 2];
                    fourthByte = bytes[i + 3];
                    if ((secondByte & 0xC0) === 0x80 && (thirdByte & 0xC0) === 0x80 && (fourthByte & 0xC0) === 0x80) {
                        tempCodePoint = (firstByte & 0xF) << 0x12 | (secondByte & 0x3F) << 0xC | (thirdByte & 0x3F) << 0x6 | (fourthByte & 0x3F);
                        if (tempCodePoint > 0xFFFF && tempCodePoint < 0x110000) {
                            codePoint = tempCodePoint;
                        }
                    }
            }
        }

        if (codePoint == undefined) {
            // we did not generate a valid codePoint so insert a
            // replacement char (U+FFFD) and advance only 1 byte
            codePoint = 0xFFFD;
            bytesPerSequence = 1;
        } else if (codePoint > 0xFFFF) {
            // encode to utf16 (surrogate pair dance)
            codePoint -= 0x10000;
            res.push(codePoint >>> 10 & 0x3FF | 0xD800);
            codePoint = 0xDC00 | codePoint & 0x3FF;
        }

        res.push(codePoint);
        i += bytesPerSequence;
    }

    return decodeCodePointsArray(res);
}