Filtering data for pass-through operations
When the source pass-through TCP socket is connected, there are Lua functions that allow filtering of the received and transmitted data.
The use of these functions can allow for stripping of control characters, for masking digits or other operations.
The two function hooks are:
x.chnl[#].pass.rxx.chnl[#].pass.tx(where # is the channel number).
The “rx” function is called whenever data arrives at the source port. Filtering here will alter what the TCP client sees.
The “tx” function is called whenever the TCP client sends data to be transmitted to the source port.
Before the data is sent to the port this filter function is called.
Be aware that these functions do not see “records” or “lines” of data.
Arbitrary sized chunks of data are sent through these filters.
In both cases, Lua will pass two parameters to the filter function:
| Type | Description |
|---|---|
| string | Data to filter |
| table | Protocol table |
For example, in order to strip the top bit of data for incoming pass-through data, apply this script:
function striprx(s,p)
return tools.ascii(s)
end
x.chnl[1].pass.rx = striprx