add support for sending emails

Change-Id: I9749cda3b997d70271cb4ca709a7cca82a9a0948

mail.go

@@ -0,0 +1,69 @@
+package vain
+
+import (
+	"bytes"
+	"fmt"
+	"net/mail"
+	"net/smtp"
+)
+
+// A Mailer is a type that knows how to send smtp mail.
+type Mailer interface {
+	Send(to mail.Address, subject, msg string) error
+}
+
+// NewEmail returns *Email struct to be able to send smtp
+// or an error if it can't correctly parse the email address.
+func NewEmail(from, host string, port int) (*Email, error) {
+	if _, err := mail.ParseAddress(from); err != nil {
+		return nil, fmt.Errorf("can't parse an email address for 'from': %v", err)
+	}
+	r := &Email{
+		host: host,
+		port: port,
+		from: from,
+	}
+	return r, nil
+}
+
+// Email stores information required to use smtp.
+type Email struct {
+	host string
+	port int
+	from string
+}
+
+// Send sends a smtp email using the host and port in the Email struct and
+//returns an error if there was a problem sending the email.
+func (e Email) Send(to mail.Address, subject, msg string) error {
+	c, err := smtp.Dial(fmt.Sprintf("%s:%d", e.host, e.port))
+	if err != nil {
+		return fmt.Errorf("couldn't dial mail server: %v", err)
+	}
+	defer c.Close()
+	if err := c.Mail(e.from); err != nil {
+		return err
+	}
+	if err := c.Rcpt(to.String()); err != nil {
+		return err
+	}
+	wc, err := c.Data()
+	if err != nil {
+		return fmt.Errorf("problem sending mail: %v", err)
+	}
+	buf := bytes.NewBufferString("Subject: " + subject + "\n\n" + msg)
+	buf.WriteTo(wc)
+	if err := c.Quit(); err != nil {
+		return nil
+	}
+	return err
+}
+
+type mockMail struct {
+	msg string
+}
+
+func (m *mockMail) Send(to mail.Address, subject, msg string) error {
+	m.msg = msg
+	return nil
+}