export default function mapRange()

in function/nodejs_14_x/src/response/range_mapper.ts [20:65]
34 lines of code
9 McCabe index (conditional complexity)

export default function mapRange (rangeHeaderValue: string, transformedObject: Buffer): RangeResponse {
  const matchArray = rangeHeaderValue.match(/^([a-z]+)=(\d+)?-(\d+)?$/);

  if (matchArray === null) { // check if the range matches what we support
    return getRangeInvalidResponse(rangeHeaderValue);
  }

  const [, rangeUnitStr, rangeStartStr, rangeEndStr] = matchArray;
  let rangeStart: number;
  let rangeEnd: number;

  if (rangeUnitStr.toLowerCase() !== SUPPORTED_UNIT) {
    return getRangeInvalidResponse(rangeHeaderValue,
            `Cannot process units other than ${SUPPORTED_UNIT}`);
  }

  const isRangeStartPresent = rangeStartStr !== undefined;
  const isRangeEndPresent = rangeEndStr !== undefined;

  if (!isRangeStartPresent && !isRangeEndPresent) { // At least one should be present
    return getRangeInvalidResponse(rangeHeaderValue);
  } else if (!isRangeStartPresent) {
    /* Range request was of the form <unit>=-<suffix-length> so we return the last `suffix-length` bytes. */

    const suffixLength = Number(rangeEndStr);
    rangeEnd = transformedObject.byteLength;
    rangeStart = rangeEnd - suffixLength;
  } else if (!isRangeEndPresent) {
    /* Range request was of the form <unit>=<range-start>- so we return from range-start to the end
        of the object. */
    rangeStart = Number(rangeStartStr);
    rangeEnd = transformedObject.byteLength;
  } else {
    /* Range request was of the form <unit>=<range-start>-<range-end> so we process both. */
    rangeStart = Number(rangeStartStr);
    const expectedLength = Number(rangeEndStr) + 1; // Add 1 as rangeEnd is inclusive
    rangeEnd = Math.min(transformedObject.byteLength, expectedLength); // Should not exceed object length
  }

  const isRangeValid = rangeStart >= 0 && rangeStart <= rangeEnd;
  if (!isRangeValid) {
    return getRangeInvalidResponse(rangeHeaderValue);
  }

  return { object: transformedObject.slice(rangeStart, rangeEnd), hasError: false };
}