How to assign a stream to a circuit?

Question

I have a Python script that is configured to connect to 4 different onion services (call them a, b, c, d), and return a value on a page. I'd like to ensure that I create separate circuits to connect to each so that circuit-1 only connects to a and is never used for b,c, or d.

I'm using Stem and this is an example they provide for issuing a NEWNYM command to the control protocol and create new circuits.

    with Controller.from_port(port = 9150) as controller:
        controller.authenticate()
        controller.signal(Signal.NEWNYM)

I understand this to flush all circuits and re-build new ones.

Is there a better way to specifically control which circuit a Python HTTP request takes? I'd like concurrently make these requests from 4 different circuits at the same time. Basically:

• create new circuit
• assign circuit to a.onion
• issue request
• destroy circuit
• repeat for b, c, and d.onion

Answer 1

Nice timing, we just expanded our tutorials around this! For this you should use new_circuit() and attach_stream() rather than NEWNYM. For an example of doing this see...

https://stem.torproject.org/tutorials/to_russia_with_love.html#custom-path-selection