calling pcap_loop from Swift 3

Question

I was trying this code from https://github.com/dfrencham/swiftPCap

pcap_loop(pcapSession, numberOfPackets,

        {
            (args: UnsafeMutablePointer<u_char>,
             pkthdr:UnsafePointer<pcap_pkthdr>,
             packet: UnsafePointer<u_char>) ->Void in
                    // lets handle the result using a call to a singleton
                    // we can keep state this way, and not have to
                    // tool around by passing pointers to UnsafePointers
                    // and dereferencing later
                    let pa = PacketAnalyser.sharedInstance
                    pa.Process()
        },
        nil)

Now it is Swift 3, I cannot compile with the following errors cannot convert value of type '(UnsafeMutablePointer, UnsafePointer, UnsafePointer) -> Void' to expected argument type 'pcap_handler!'

Not really sure how to proceed, pretty much a newbie at referencing C code from Swift. I have read the documentation, but not having much luck.

Thanks

Swift

412

Posted by

JohnMcM

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Answer 1

In situations like this it’s best to leave off the closure types and then let Xcode help you figure things out. For example, this code compiles:

let p = … create this with pcap_create …
let status = pcap_loop(p, 0, { (user, packetHeader, packetData) in
    print(user as Any)
    print(packetHeader as Any)
    print(packetData as Any)
}, nil)

You can then option click on

user

,

packetHeader

, and

packetData

to work out the types that were inferred.

ps If you want to do anything useful inside your callback, you’ll probably want to use the

user

pointer (passing everything off to a singleton is less than ideal). For an example of how to put a Swift object reference into this

user

pointer and how to get it back out again, you can look at this post.

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eskimo

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calling pcap_loop from Swift 3

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