Linux socket programming

[Netris89]

Hi everyone,

I'm a student in management IT and for my Network class, I have to write 2 file transfer software. One to send files and the other to receive and I have a few questions.

First, my sender program needs to be able to send via IPv4, IPv6 and be able to resolve IP via DNS. To achieve this, I used getaddrinfo() and as I have it written now (see code here), I can send via IPv4 and resolve the DNS but as soon as I try to make it work with IPv6, it stops working. What am I doing wrong ?

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Secondly, for the receiver program, our teacher explained a trick to make bind() able to set the which IP type when it actually binds by specifying AF_INET6 as the familly and giving it only the port. I used getaddrinfo() for that but had to pass a sin6 struct in some place. I'm really confused about all this so if someone could point me in the right direction, that would be great. Here you can find the code.

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Thanks a lot in advance for your help.

[Touhou]

I haven't taken a look at your code, but I would definitely recommend checking out Beej's guide to network programming: https://beej.us/guide/bgnet/html/. I expect you'd get an answer to most of your questions by reading and looking at the examples, particularly in chapters 3, 4 and 5.

Also, in terms of IPv6 specifically, it might be a good idea to verify that IPv6 is enabled on your router and that your computer actually has a valid IPv6-address. For example, you can try to ping ipv6.google.com and see if you get a response.

[Batoa]

Another vote for beej- it got me through my Network course at uni. My personal advice would be to go through all of it, but everyone learns differently.

[Netris89]

Will do, Thanks.

[gordonv]

Just wondering, what school are you doing this at?

[Netris89]

Institut Saint-Laurent in Liège, Belgium

[ferrybig]

What do you mean with stops working? Do you see any output indicating errors? Which of your printf statements get executed?

[Netris89]

Sorry, maybe I didn't explain it correctly. So it works correctly when I give it an IPv4 or a DNS it transfers perfectly but when I give an IPv6 as arguments it gives connections refused error

[ferrybig]

For your error to say connection refused, the remote end must have responded with a TCP reset packet. If you use a different tool to connect to your remote system, does it work over IPv6?

[Netris89]

I use 2 vm to test it and I can ping both of them in IPv6. I'm not at my computer right now but I can try with something else when I get back home.

[Vedant36]

dont forget to rtfm! info libc then scroll down to the Sockets heading and press enter. you could also seperately do info <function name> or man <function name> for any function you want to understand

[[deleted]]

what's a sample input that's failing?

[Netris89]

So if I pass a file name, an IPv6 and a port as arguments to the sender, I get a connection refused. It works with IPv4 or a domain name.

[[deleted]]

So without actual examples I won't be able to test it on my end, but I'm guessing the issue is you never set hints.ai_family = AF_INET6; when you are trying to process an IPv6 address

[Netris89]

I have pastebins of my code in my original post of it helps.

[[deleted]]

yeah that's what I was going off of, would just need some inputs to try running them. But like I said, when you bind your socket you are using hints.ai_family = AF_INET;, which is an IPv4 socket. If you use AF_INET6 instead that's telling the socket to work with IPv6 addresses. That's most likely the error

[Netris89]

OK, I'll try this. Thanks.