validate
fun validateChildFileExistsUnderParent(intendedParentDirectory: String, childFilePath: String): String
Validates that the provided filename's canonical path exists under the intended directory. Throws IllegalStateException if not.
Return
The canonical path for the childFilePath.
Parameters
intended
The intended parent directory for the input file.
child
The full path for the file.
Throws
when intendedParentDirectory is not a parent directory for childFilePath.