aws s3 calculate upload parts for multipart

getUploadParts.ts

const MIN_CHUNK_SIZE = 5242880; // 5MB in bytes
const DEFAULT_CHUNK_SIZE = 26214400; // 25MB in bytes

export function getUploadParts(contentLength: number, chunkSize: number = DEFAULT_CHUNK_SIZE): string[] {
  if (contentLength <= 0) {
    throw new Error('ContentLength should be greater than 0 bytes');
  }

  if (chunkSize < MIN_CHUNK_SIZE) {
    throw new Error('ChunkSize should be greater or equal to 5 mb');
  }

  const chunks = Math.floor(contentLength / chunkSize);

  if (chunks <= 1) {
    return [`0-${contentLength - 1}`];
  }

  const parts = [];
  const tail = contentLength % chunkSize;

  for (let offset = 0; offset < chunks; offset++) {
    const start = offset * chunkSize;
    const end = (offset + 1) * chunkSize - 1;
    const last = offset + 1 === chunks;
    parts.push(`${start}-${last ? end + tail : end}`);
  }

  return parts;
}