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Tcp active open (wip) #9

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Tcp active open (wip) #9

wants to merge 4 commits into from
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little-dude
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This is an attempt at providing a way to initiate a TCP connection (see #7).

I added an example to test the changes but this is not working yet. Here is what I get when running the client side:

[     0.026s] (socket::set): [0]: adding
[     0.026s] (socket::tcp): [0]192.168.69.2:6979:192.168.69.1:6970: state=CLOSED=>SYN-SENT
[     0.027s] (socket::tcp): [0]192.168.69.2:6979:192.168.69.1:6970: sending SYN
-> EthernetII src=02-00-00-00-00-02 dst=02-00-00-00-00-01 type=IPv4
   \ IPv4 src=192.168.69.2 dst=192.168.69.1 proto=TCP
    \ TCP src=6979 dst=6970 syn seq=0 ack=0 win=64 len=0 mss=1446
<- EthernetII src=02-00-00-00-00-01 dst=02-00-00-00-00-02 type=IPv4
   \ IPv4 src=192.168.69.1 dst=192.168.69.2 proto=TCP
    \ TCP src=6970 dst=6979 rst seq=0 ack=1 win=0 len=0
[     0.028s] (socket::tcp): [0]192.168.69.2:6979:192.168.69.1:6970: unacceptable RST|ACK in response to initial SYN

@little-dude
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So the client sends a SYN+ACK instead of SYN, but I don't understand why yet.

@little-dude little-dude changed the title Tcp active open Tcp active open (wip) Mar 5, 2017
@little-dude
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I got this wrong... State should be switched to ESTABLISHED after acknowledging the SYN-ACK...
Will continue tomorrow.

@whitequark
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Don't bother. I am unhappy with the code quality anyway. I'll implement this myself.

@whitequark whitequark closed this Mar 5, 2017
@little-dude
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Well that's pretty harsh. What is particularly bad about my code? Would you mind mentoring me instead? I'd like to learn, that's primarily why I'm playing with redox and smoltcp.

@whitequark
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What is particularly bad about my code?

No tests (an example doesn't count as test), a large amount of missed subtleties of TCP. Ideally I aim for 100% condition/branch coverage though Rust makes it somewhat hard to achieve with all the overflow checks.

Would you mind mentoring me instead?

It took me weeks of full-time work to get a rudimentary understanding of how TCP works and how it should be implemented. I have neither time nor the depth of understanding to transfer that to someone else.

This isn't something about you personally and I intend you no offense. It's rather that my primary goal is to have a TCP stack that actually works decently, and mentoring someone is an extremely inefficient way to get there.

@whitequark
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That being said, I will gladly accept any contributions (or mentor contributors) that don't touch the TCP state machine specifically.

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@little-dude @whitequark