_read(size) {
        if (this.pushedBytesLength >= this.byteLength) {
            this.push(null);
        }
        if (!size) {
            size = this.readableHighWaterMark;
        }
        const outBuffers = [];
        let i = 0;
        while (i < size && this.pushedBytesLength < this.byteLength) {
            // The last buffer may be longer than the data it contains.
            const remainingDataInAllBuffers = this.byteLength - this.pushedBytesLength;
            const remainingCapacityInThisBuffer = this.buffers[this.bufferIndex].byteLength - this.byteOffsetInCurrentBuffer;
            const remaining = Math.min(remainingCapacityInThisBuffer, remainingDataInAllBuffers);
            if (remaining > size - i) {
                // chunkSize = size - i
                const end = this.byteOffsetInCurrentBuffer + size - i;
                outBuffers.push(this.buffers[this.bufferIndex].slice(this.byteOffsetInCurrentBuffer, end));
                this.pushedBytesLength += size - i;
                this.byteOffsetInCurrentBuffer = end;
                i = size;
                break;
            }
            else {
                // chunkSize = remaining
                const end = this.byteOffsetInCurrentBuffer + remaining;
                outBuffers.push(this.buffers[this.bufferIndex].slice(this.byteOffsetInCurrentBuffer, end));
                if (remaining === remainingCapacityInThisBuffer) {
                    // this.buffers[this.bufferIndex] used up, shift to next one
                    this.byteOffsetInCurrentBuffer = 0;
                    this.bufferIndex++;
                }
                else {
                    this.byteOffsetInCurrentBuffer = end;
                }
                this.pushedBytesLength += remaining;
                i += remaining;
            }
        }
        if (outBuffers.length > 1) {
            this.push(Buffer.concat(outBuffers));
        }
        else if (outBuffers.length === 1) {
            this.push(outBuffers[0]);
        }
    }
Internal _read() that will be called when the stream wants to pull more data in.

@param size - Optional. The size of data to be read