Method readVersion

app/src/main/java/androidx/room/DBUtil.java:158–176

Reads the user version number out of the database header from the given file. @param databaseFile the database file. @return the database version @throws IOException if something goes wrong reading the file, such as bad database header or missing permissions. @see <a href="https://www.sqlite.org/f

(@NonNull File databaseFile)

     * Number</a>.
     */
    public static int readVersion(@NonNull File databaseFile) throws IOException {
        FileChannel input = null;
        try {
            ByteBuffer buffer = ByteBuffer.allocate(4);
            input = new FileInputStream(databaseFile).getChannel();
            input.tryLock(60, 4, true);
            input.position(60);
            int read = input.read(buffer);
            if (read != 4) {
                throw new IOException("Bad database header, unable to read 4 bytes at offset 60");
            }
            buffer.rewind();
            return buffer.getInt(); // ByteBuffer is big-endian by default
        } finally {
            if (input != null) {
                input.close();
            }
        }
    }

    /**
     * CancellationSignal is only available from API 16 on. This function will create a new