*
 * @throws IllegalArgumentException if this is not a well-formed media type.
 */
internal fun String.commonToMediaType(): MediaType {
  val typeSubtype: MatchResult =
    TYPE_SUBTYPE.matchAtPolyfill(this, 0)
      ?: throw IllegalArgumentException("No subtype found for: \"$this\"")
  val type = typeSubtype.groupValues[1].lowercase()
  val subtype = typeSubtype.groupValues[2].lowercase()

import okio.FileSystem
import okio.IOException
import okio.Options
import okio.Path
import okio.use

// TODO: migrate callers to [Regex.matchAt] when that API is not experimental.
internal fun Regex.matchAtPolyfill(
  input: CharSequence,
  index: Int,
): MatchResult? {
  val candidate = find(input, index) ?: return null
  if (candidate.range.first != index) return null // Didn't match where it should have.
  return candidate