Show current parallelism for hostgroup when printing stats

[djcater]

When you press Enter during a scan and get the stats output, it would be useful to see what parallelism value Nmap is using for the current hostgroup. As the value is dynamic, it's not obvious what value it is using at any particular time. Something like:

Current sending rates: 170.40 packets / s, 1903.31 bytes / s. Current parallelism: x probes.

This could help in debugging and optimising something like #1907.

[dmiller-nmap]

The "current parallelism" within the ultrascan engine is called the "congestion window" and is stored in the cwnd member of struct ultra_timing_vals. It is already printed as part of the **TIMING STATS** output at debug level 3 or greater. The calculation of this value is described in Nmap Network Scanning in chapter 5 in the section "Scan Code and Algorithms".

[djcater]

Thanks @dmiller-nmap. I've now tried with -ddd and can see the cwnd value, but I notice that it only gets printed during the port scan phase.

For me it would be useful to see this during the service scan phase when showing the timing stats there.

Shall I open a new issue specifically mentioning the service scan phase?

[dmiller-nmap]

Not sure if it's worthwhile for service scan phase. The "ideal parallelism" is calculated once at the start of the scan and does not change during the scan. See #55.

[djcater]

@dmiller-nmap: My use case is that I typically start a scan with either no debug level, or debug level 1, and therefore don't see the low-level stats including cwnd. If the port scan phase doesn't take that long, but then the service scan parts is taking a very long time, I will interactively increase the debugging level (with the d key), to try and work out what's happening. It would be useful to see the cwnd value at this point, but it's not possible, as it's not printed during the service scan phase, and I can't go back in time and increase the debugging level.

If this small feature was added, then it would be possible, without having to run every scan with debug level 3.