Function assertValidHeaders

packages/common/http/src/headers.ts:283–294

* Verifies that the headers object has the right shape: the values * must be either strings, numbers or arrays. Throws an error if an invalid * header value is present.

(
  headers: Record<string, unknown> | Headers,
)

 * header value is present.
 */
function assertValidHeaders(
  headers: Record<string, unknown> | Headers,
): asserts headers is Record<string, string | string[] | number | number[]> {
  for (const [key, value] of Object.entries(headers)) {
    if (!(typeof value === 'string' || typeof value === 'number') && !Array.isArray(value)) {
      throw new Error(
        `Unexpected value of the \`${key}\` header provided. ` +
          `Expecting either a string, a number or an array, but got: \`${value}\`.`,
      );
    }
  }
}