crypto/tls: Currently there's no way to find out what protocol was used to negotiate TLS connection on the client

[gopherbot]

by manoj.dayaram@moovweb.com:

As far as I can tell, there's no exposure to what TLS protocol was used after performing
the TLS handshake.  I noticed we store the version that was used here:

http://golang.org/src/pkg/crypto/tls/handshake_client.go#L85

However, this is in a private member of the Connection structure, and there are no
accessors for it.

Now that Go supports more than just TLS1.0 for secure connections from the client side,
it would be nice to expose what protocol was used to perform the handshake.  I figured
adding a Version() method to the connection or perhaps a member in the ConnectionState
struct would work quite nicely.

I scraped/read as much of the crypto/tls package but I'm not super familiar with crypto
stuff.  I couldn't really see a way to be able to determine this information as a user
of the library, so sorry if I'm missing an obvious way to access this.

[bradfitz]

Comment 1:

Owner changed to @agl.

[mikioh]

Comment 2:

Not sure what's your use case but for debugging/developing/dissecting TLS stuff at
plugfest, you can scratch an established tls.Conn by using package reflect like the
following:
func tlsVersion(c *tls.Conn) (int, error) {
        cv := reflect.ValueOf(c)
        switch ce := cv.Elem(); ce.Kind() {
        case reflect.Struct:
                fe := ce.FieldByName("vers")
                return int(fe.Uint()), nil
        }
        return 0, errors.New("something wrong")
}
For managing TLS entities, you can also implement http://tools.ietf.org/html/rfc6353.

[gopherbot]

Comment 3 by manoj.dayaram@moovweb.com:

Eh, this is something I'd like to do on every request, so ideally, I'd like something
very performant.  I'm not sure what the performance hit of using the reflection package
is, but it seems to me that it would be much slower than a straight up dereference check
=/

[agl]

Comment 4:

Agreed. We should have the version in the ConnectionState. Will do for 1.3.

Labels changed: added release-go1.3maybe, repo-main.

[gopherbot]

Comment 5 by manoj.dayaram@moovweb.com:

I've given a crack at adding the patch myself, seemed straight forward enough that I
figured I would give it a try:
https://golang.org/cl/55400044/#ps2

[agl]

Comment 6:

This issue was closed by revision c7612f3.

Status changed to Fixed.