protected String getFileDir(String filename) throws IOException {
		switch (storageLevel) {
			case 0:
				return "";
			case 1:
				return filename + "/";
			case 2:
				if (filename.length() <= 2) {
					throw new IOException(
						"Symbol filename too short to store in two-level index: " + filename);
				}
				return filename.substring(0, 2).toLowerCase() + "/" + filename + "/";
			default:
				throw new IllegalArgumentException(
					"Unsupported Symbol Server storage level: " + storageLevel);
		}
	}
Common functionality of File and Http symbol servers.
Ghidra/Features/PDB/src/main/java/pdb/symbolserver/AbstractSymbolServer.java