Golang imap.DialTLS Config example - ssl

Question

I used to be able to connect to port 143 of a mail server like this:
c, err := imap.Dial(mailServer)
The code above connects to port 143 of the mailServer. Now I have a new mail server only accepts port 993. Looking at the Golang imap source code, the function DialTLS will connect to port 993. The signature of DialTLS looks like this:
func DialTLS(addr string, config *tls.Config) (c *Client, err error)
Now I don't know how to construct the *tls.Config. I Googled around, but didn't not find anything really useful. Can someone show me some example how to construct the *tls.Config?
I tried to pass in nil as the second parameter, it compiles, and I didn't get any runtime error. But it seems no new mails were fetched, even I believe there should be.
My fetch mail code looks like this:
// testimap
package main
import (
"bytes"
"code.google.com/p/go-imap/go1/imap"
"fmt"
"net/mail"
"time"
)
type Mail struct {
Subject string
Body string
From string
Uid uint32
}
func FetchMail(lastUid uint32) []*Mail {
defer func() {
if err := recover(); err != nil {
fmt.Println(err)
}
}()
//
// Note: most of error handling code is omitted for brevity
//
var (
c *imap.Client
cmd *imap.Command
rsp *imap.Response
)
// Connect to the server
c, err := imap.DialTLS(mailServer, nil)
if err != nil {
fmt.Println(err)
}
// Remember to log out and close the connection when finished
defer c.Logout(30 * time.Second)
// Print server greeting (first response in the unilateral server data queue)
//fmt.Println("Server says hello:", c.Data[0].Info)
c.Data = nil
// Enable encryption, if supported by the server
if c.Caps["STARTTLS"] {
c.StartTLS(nil)
}
// Authenticate
if c.State() == imap.Login {
c.Login(mailSupportUser, mailSupportPw)
}
//// List all top-level mailboxes, wait for the command to finish
cmd, err = imap.Wait(c.List("", "%"))
if err != nil {
fmt.Println(err)
}
// Print mailbox information
//fmt.Println("\nTop-level mailboxes:")
//for _, rsp = range cmd.Data {
// fmt.Println("|--", rsp.MailboxInfo())
//}
// Check for new unilateral server data responses
//for _, rsp = range c.Data {
// fmt.Println("Server data:", rsp)
//}
c.Data = nil
// Open a mailbox (synchronous command - no need for imap.Wait)
c.Select("INBOX", true)
//fmt.Print("\nMailbox status:\n", c.Mailbox)
// Fetch the headers of the 10 most recent messages
set, err := imap.NewSeqSet(fmt.Sprint(lastUid, ":*"))
if err != nil {
fmt.Println(err)
}
//if c.Mailbox.Messages >= 10 {
// set.AddRange(c.Mailbox.Messages-9, c.Mailbox.Messages)
//} else {
// set.Add("1:*")
//}
cmd, err = c.UIDFetch(set, "RFC822.HEADER", "RFC822.TEXT")
if err != nil {
fmt.Println(err)
}
// Process responses while the command is running
//fmt.Println("\nMost recent messages:")
mails := make([]*Mail, 0, 10)
for cmd.InProgress() {
// Wait for the next response (no timeout)
c.Recv(-1)
// Process command data
for _, rsp = range cmd.Data {
if err != nil {
fmt.Println(err)
}
header := imap.AsBytes(rsp.MessageInfo().Attrs["RFC822.HEADER"])
uid := imap.AsNumber((rsp.MessageInfo().Attrs["UID"]))
body := imap.AsBytes(rsp.MessageInfo().Attrs["RFC822.TEXT"])
if msg, err := mail.ReadMessage(bytes.NewReader(header)); msg != nil {
if err != nil {
fmt.Println(err)
}
mail := &Mail{
Subject: msg.Header.Get("Subject"),
From: msg.Header.Get("FROM"),
Body: string(body),
Uid: uid,
}
if mail.Uid < lastUid {
continue
}
mails = append(mails, mail)
}
}
cmd.Data = nil
c.Data = nil
}
// Check command completion status
if rsp, err := cmd.Result(imap.OK); err != nil {
if err == imap.ErrAborted {
fmt.Println("Fetch command aborted")
} else {
fmt.Println("Fetch error:", rsp.Info)
}
}
fmt.Println(mails)
return mails
}

Answer 1

First off, you should be using the project's GitHub repo as the Google Code project stated development was moving to GitHub due to Google Code shutting down. It's a few commits ahead of the Google Code repo too, so you won't be getting any updates if you don't migrate to the GitHub repo.
Secondly, looking at the package's demo, passing nil to DialTLS as the TLS client seems to be the proper way to connect with a default TLS client.
From the information you've given, it seems like it may be an issue with your server accepting connections over that port. I would look into if the port is open to the client you're trying to connect from or if your IMAP server is even accepting TLS connections.
If you're absolutely sure it's not a server issue after further debugging, I would file an issue on the project's GitHub issue tracker to get help from people who are more familiar with the package, seeing that it's a third party package.