SMTP connection read welcome message

Question

I try to connect on smtp server and read welcome message. This is my code:

package main

import (
    "fmt"
    "net"
    "time"
    "net/smtp"
    "bufio"
)

func main() {
    // attempt a connection
    conn, _ := net.DialTimeout("tcp", "88.198.24.108:25", 15 * time.Second)

    buf := bufio.NewReader(conn)
    bytes, _ := buf.ReadBytes('\n')
    fmt.Printf("%s", bytes)


    client, err := smtp.NewClient(conn, "88.198.24.108")
    if err != nil {
        fmt.Println("1>>", err)
        return
    }

    client.Quit()
    conn.Close()
}

Problem is after read welcome message stop running and wait to go in timeout, I want to read/print welcome message and continue.

220 example.me ESMTP Haraka/2.8.18 ready
1>> 421 timeout

Answer 1

An inspection of the standard library source indicates that smtp.NewClient() reads the SMTP banner from the remote host and throws it away.

func NewClient(conn net.Conn, host string) (*Client, error) {
    text := textproto.NewConn(conn)
    _, _, err := text.ReadResponse(220)
    if err != nil {
        text.Close()
        return nil, err
    }
    c := &Client{Text: text, conn: conn, serverName: host, localName: "localhost"}
    _, c.tls = conn.(*tls.Conn)
    return c, nil
}

You want to read this banner and decide whether to send mail based on its contents.

Since you have already read the banner yourself, and presumably will make a decision on that, instead of calling smtp.NewClient() you should then implement the rest of NewClient() in your own code, possibly something like this:

    client := &smtp.Client{Text: text, conn: conn, serverName: host, localName: "localhost"}
    _, client.tls = conn.(*tls.Conn)