Why am I not fully releasing this SSL listener?

[Sage Gerard]

I'm trying to understand how I am failing to shut down an ssl-listener on v7.7.0.5.

https://gist.github.com/zyrolasting/bc5477bfa60d7185d0f53a5142545f88 shows my use of ssl-* procedures to transmit data using test.pem. The problem is that I cannot run the test submodule twice in a row because the listening port is still occupied on subsequent runs. I added ssl-close on top of a custodian shutdown and that problem reproduces.

For comparison, https://gist.github.com/zyrolasting/3feb0ff4ecdf0b49bcf3e0ed8b630a06 avoids the ssl-* procedures and just uses vanilla TCP. I can run the tests fine then.

But in looking at mzssl.rkt in the source, it looks like shutdown requires calling a foreign function via SSL_shutdown. https://github.com/racket/racket/blob/master/racket/collects/openssl/mzssl.rkt#L1417

Do I have to call ports->ssl-ports out of band just so closing them sends a shut down as a side-effect? Or is keeping the port occupied between test runs a bug?

~slg

[Ryan Culpepper]

If you create the ssl-listener with reuse?=true instead, like this

  (define listener (ssl-listen port 5 #f #t ctx))

does the problem go away? If so, the error might happen because the OS reserves the port number for a while after the listener is closed; see the paragraph about TIME_WAIT in the tcp-listener docs. If that's the issue, I'm a little confused why the TCP version would succeed, though.

I believe SSL_shutdown is completely unrelated to the state of the TCP ports. Think of it like a "Connection: close" HTTP header; it announces your intention to close the TCP connection soon, but it has no actual effect on the transport layer.

Ryan

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[Sage Gerard]

Switching the reuse? flag does resolve the issue, thanks! I'm also confused about the part you mention since reuse? is passed right along to tcp-listen in mzssl.rkt. Only difference I can point to is my explicitly calling ssl-close and therefore tcp-close before a custodian shutdown. But it sounds like you are saying the OS may temporarily reserve the port in spite of me doing that.



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