js-dicom/src/dicomParser/readSequenceItem.js

this is js-dicom

import readTag from './readTag.js';

/**
 * Internal helper functions for parsing DICOM elements
 */

/**
 * Reads the tag and length of a sequence item and returns them as an object with the following properties
 *  tag : string for the tag of this element in the format xggggeeee
 *  length: the number of bytes in this item or 4294967295 if undefined
 *  dataOffset: the offset into the byteStream of the data for this item
 * @param byteStream the byte
 * @returns {{tag: string, length: integer, dataOffset: integer}}
 */
export default function readSequenceItem (byteStream) {
  if (byteStream === undefined) {
    throw 'dicomParser.readSequenceItem: missing required parameter \'byteStream\'';
  }

  const element = {
    tag: readTag(byteStream),
    length: byteStream.readUint32(),
    dataOffset: byteStream.position
  };

  if (element.tag !== 'xfffee000') {
    throw `dicomParser.readSequenceItem: item tag (FFFE,E000) not found at offset ${byteStream.position}`;
  }

  return element;
}