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[tech] tls user_canceled issue with Java server + Go client

Alan gemini at bunburya.eu

Sun Apr 18 15:41:13 BST 2021

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Hi Gary,

That solved it, thanks! A simple fix but you're right, I couldn't find anything about it. Good to know there is a solution.

Thanks,

Alan

On 18/04/2021 01:04, Gary Johnson wrote:

Alan<gemini at bunburya.eu> writes:

When using the Amfora browser, I was unable to view "20" responses,

getting instead the following error: "/Issuing creating page: remote

error: tls: user//canceled/". Unusually, every other response is

displayed fine.

Hi Alan,

I'm the author of Space-Age, a Gemini server written in Clojure.

=

https://gitlab.com/lambdatronic/space-age/

The tls_user_canceled issue you are running into is coming from the Java

side. It also mystified me last year when I was writing my server since

I was constantly getting that error in elpher (the Emacs Gemini client)

whenever I tried to browse pages from my capsule.

You have to force your SSLSocket to send the tls_close_notify alert to

the client before closing the socket. This is exceptionally poorly

documented in the JSSE Reference Guide, but I eventually figured out the

solution through trial and error.

All you need to do is to make sure you call socket.shutdownOutput()

immediately before calling socket.close().

Here's my function for writing a Gemini response back to the client for reference:

```

(defn- write-socket! [^SSLSocket socket {:keys [status meta body]}]

(doto (io/writer socket)

(.write (str status " " meta "\r\n"))

(.flush))

(when body

(with-open [in-stream (io/input-stream (if (string? body)

(.getBytes ^String body)

body))]

(let [out-stream (io/output-stream socket)]

(.transferTo in-stream out-stream)

(.flush out-stream))))

(.shutdownOutput socket))

```

This is called from another function that then calls socket.close() to

terminate the connection.

Here is my full Gemini server implementation for further reference:

=

https://gitlab.com/lambdatronic/space-age/-/blob/master/src/space_age/server.clj

Happy hacking!

Gary