Bundling a message stream

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I am looking to 'bundle' a stream of ROS messages (on different topics) into a single message that contains bundles (i.e. tuples) of the individual message. Is there a package out there that does something similar?

To give a concrete example, I might have two topics A and B that publish messages at possibly different rates (horizontal space is time):

A: a_1,     a_2,      a_3, ... 
B: b_1, b_2, b_3, b_4, b_5, b_6, ...

and I want a single stream of tupled message bundles:

Bundles: (a_1, b_1), (a_2, b_3), (a_3, b_5), ....

For example, these could be stereo image pairs or pairs of sensor data measurements.

Before I write a solution, does someone know if such a bundler package exist?