Sender IP address in UDP

Question

Created Mar ’21

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When receiving a UDP packet using NWConnection.receiveMessage(), how can I find the sender's IP address?
For example, in C, the recvfrom() function writes the sender IP and port to a struct sockaddr that I can later examine. Is there something equivalent in Swift?

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Answer 1

DTS Engineer OP

Apple

Mar ’21

A UDP NWConnection always represents a flow of datagrams, that is, it always has the same source IP/destination IP/source port/destination port tuple. You can access the destination IP and port using the connection’s endpoint property.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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Answer 2

JudahL OP

Mar ’21

@eskimo That's what I tried, (from here https://developer.apple.com/documentation/network/nwendpoint), but when I type

Code Block incomingConnection.endpoint.IPv4Address

it says "Value of type NWEndpoint has no member IPv4Address". In other words, I don't see how to get the IP address or port out of endpoint.

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Answer 3

DTS Engineer OP

Apple

Mar ’21

NWEndpoint is an enum that supports multiple different cases. In this specific instance, however, it’ll always be the .hostPort(host:port:) case. You can extract the associated host and port values with code like this:

Code Block  guard case .hostPort(host: let host, port: let port) = endpoint else { fatalError() }

You’ll have to decide what to do if you get one of the other cases. In my code I typically just fatalError because I can’t imagine a situation where this would fail.

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

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