net/smtp: NewClient should initialize tls based on the incoming connection type #22166
Description
What version of Go are you using (go version)?
1.9.1
Does this issue reproduce with the latest release?
Yes.
What operating system and processor architecture are you using (go env)?
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/aron/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/ts/s940qvdj5vj1czr9qh07fvtw0000gn/T/go-build463641693=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
What did you do?
Attempted to perform SMTP PLAIN authentication over an SSL connection (without STARTTLS).
Code resembles:
conn, err := tls.Dial("tcp", "hostname:port", tlsConfig)
client, err := smtp.NewClient(conn, "hostname")
auth := smtp.PlainAuth(identity, "username", "password", "hostname")
err := client.Auth(&auth)What did you expect to see?
Successful authentication and mail-sending.
What did you see instead?
Authentication failed with an "unencrypted connection" error.
This approach worked before #22134/#22133
smtp.NewClient could look at its incoming net.Conn and if it is an *tls.Conn, initialize Client.tls as true.