Help: asyncore/asynchat and terminator string

[David Hirschfield]

I'm implementing a relatively simple inter-application communication 
system that uses asyncore/asynchat to send messages back and forth.

The messages are prefixed by a length value and terminator string, to 
signal that a message is incoming, and an integer value specifying the 
size of the message, followed by the message data.

My question is: how can I produce a short terminator string that won't 
show up (or has an extremely small chance of showing up) in the binary 
data that I send as messages?

Frankly, I'm not so sure this is even an important question, but is 
nagging me. If my communication is a kind of state machine:

sender: sends message length value, followed by terminator string, 
followed by message data
receiver: waiting for terminator string via set_terminator(<terminator 
string>)
    continually save what comes in via collect_incoming_data()
receiver: when sender's message arrives, found_terminator() is called
    pull message length from previously received data
    set terminator to be the length of the message via 
set_terminator(<message length>)
receiver: collect_incoming_data() collects the message data
receiver: found_terminator() called when full message length is read, 
receiver goes back to waiting for message terminator string

I hope I explained that clearly enough.

The only time I can conceive that the system will get confused by 
finding a terminator string in the binary data of the message is if 
something goes haywire and I end up looking for a terminator string when 
the other side is sending the message data. What gotchas do I need to 
look out for here? I'm not a networking person, so I'm relying on the 
underlying libraries to be stable and just let me handle the high-level 
stuff here. This isn't going to be used in a malicious environment, the 
only thing I have to contend with is network hiccups...nobody is 
actively going to try and break this system.

Any advice/help would be appreciated,
-Dave

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