[3.0.0 prep] Windows runtime dynamic loading

[cicku]

This PR removes the SDK dependency on Windows, which unlocks cross build and fixes several other issues (#408 will be rebased onto this PR once merged).

Tested with winpcap 4.1.3, npcap 1.00~1.89.

UN*X behavior remains unchanged, tested with libpcap 1.10.7 and 1.11.0.

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Fixes #246, #396.

[cicku]

@Wojtek242 let me know your thoughts on this one.

[Wojtek242]

Apologies for the delay.

Looks good, but I am confused by the requires_library method. I understand why you would want to build pcap without build-time linking, but isn't a library required at runtime anyway making a requires_library call sprinkled throughout the call a bit redundant?

What I'm worried about is that as you seem to have implemented it adding a requires_library call requires a good understanding of where to place it making it vulnerable to future mistakes. Is it possible to either not have it or centralise it in one place so that it's called once and that's it.

[cicku]

I am trying to allow a binary built against the crate now starts on a machine with no Npcap installed, and Error::LibraryNotFound is how it finds out then. In another word, this is not a redundant work. #396 links several external issues, so does cross compiling.

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Is it possible to either not have it or centralise it in one place so that it's called once and that's it.

The easiest is to shrink the surface by routing Capture::dead and dead_with_precision through a shared private open_dead, the three Linktype lookups through a shared private lookup, and write the rule down once above require_library instead of leaving it implied.

Or, I can split the FFI declarations into two groups and give the handle-free group a leading &Library parameter. Personally I do not see a single call being feasible.

Feel free to decide and I can adjust then.

[Wojtek242]

Or, I can split the FFI declarations into two groups and give the handle-free group a leading &Library parameter. Personally I do not see a single call being feasible.

I like this option. It makes the assumptions clear to the next programmer.

But if it starts getting too clunky/ugly feel free to push back and try the other option you suggested as well.

[cicku]

I made some changes, let me know if this is fine or not.

[Wojtek242]

Thanks for the update. LGTM