Ensure StreamReader handles one message at a time

Question

I am using the aioisotp library and sometimes messages are received close together. This means that aioisotp can, on occasion, provide 2 messages combined together. For example,

03 7F 36 78 00 00 00 00
02 76 02 00 00 00 00 00

I receive these 2 messages <2ms apart. aioisotp returns it as one combined message: 7f36787602

What I believe is happening:

• StreamReader.feed_data() is receiving the first message (7F3678) and adds to the buffer.
• It then flags for the read() to consume the data using _wakeup_waiter() which sets the result on the future()
• Before the read() can be scheduled to consume the data, the second message (7602) is received; and StreamReader.feed_data() is called and the buffer is extended with the new data. So, the buffer now contains 7F36787602.
• The read() now occurs and both pieces of data are received together.

There is nothing in the received data to tell me this is >1 message so I need to ensure the order of one feed_data() followed by read().

As a test, in StreamReader.feed_data() I changed self._buffer.extend(data) to self._buffer=bytearray(data)

Whilst this worked, it doesn't feel like the correct way of handling this. What would be the correct way to ensure read() only gets one message at a time?