crypto/tls: Dial returns io.EOF

[joneskoo]

If the server closes the connection before handshake completes, net/tls returns a non-descriptive error "EOF".

https://play.golang.org/p/zI-MazOG7v

Also locally go version go1.8 darwin/amd64

This may be same as #13523 (comment) @rsc @bradfitz .

What did you expect to see?

A more descriptive error similar to other errors from net/tls.

• dial tcp 127.0.0.1:8081: getsockopt: connection refused
• x509: cannot validate certificate for 216.58.209.132 because it doesn't contain any IP SANs

What did you see instead?

_, err := tls.Dial("tcp", "127.0.0.1:8080", nil)
if err != nil {
	fmt.Println(err)
	fmt.Printf("%#v == io.EOF: %v", err, err == io.EOF)
}

Output:

EOF
&errors.errorString{s:"EOF"} == io.EOF: true

Of course there is nothing that can be done, the closing of underlying connection is fatal, but is it possible to improve the error?

[bradfitz]

Yes,Dial could probably return map io.EOF to something else if Handshake returns io.EOF. I wouldn't change Handshake's behavior, though.

[gopherbot]

CL https://golang.org/cl/40190 mentions this issue.

[gopherbot]

Change https://golang.org/cl/86715 mentions this issue: crypto/tls: make DialWithDialer return more descriptive error

[namusyaka]

I'd like to hear @mikioh's opinion, so I've just this issue marked NeedDecision.
/cc @bradfitz