From the name verify you could be excused from thinking that all it does is a form of validation.

Indeed the majority of the message does do this, checking sequence numbers and so-on.

But the last line is to call fromCallback

This radically expands the verify method to actually being the point of entry to the Application for FIX traffic.

I can see two options

1. Rename verify to verifyAndProcessMessage
2. Move the fromCallback call outside verify and restructuring callers.