lib/smtp: provide an example of how to create MailTx from email package

If one read the current documentation on how to use the Client.SendTx,
there is a missing link on how to create and populate MailTx.

This changes provide the example using the email package to generate
the MailTx Data.

1 files changed, 95 insertions, 0 deletions

diff --git a/lib/smtp/mail_tx_example_test.go b/lib/smtp/mail_tx_example_test.go
new file mode 100644
index 00000000..28e3653f
--- /dev/null
+++ b/lib/smtp/mail_tx_example_test.go
@@ -0,0 +1,95 @@
+// Copyright 2022, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package smtp
+
+import (
+	"bytes"
+	"fmt"
+	"log"
+	"math/rand"
+
+	"github.com/shuLhan/share/lib/email"
+)
+
+func ExampleNewMailTx() {
+	// Example on how to create MailTx Data using email package [1].
+	//
+	// [1] github.com/shuLhan/share/lib/email
+
+	var (
+		txFrom      = "Postmaster <postmaster@mail.example.com>"
+		fromAddress = []byte("Noreply <noreply@example.com>")
+		subject     = []byte(`Example subject`)
+		bodyText    = []byte(`Email body as plain text`)
+		bodyHtml    = []byte(`Email body as <b>HTML</b>`)
+		toAddresses = []byte("John <john@example.com>, Jane <jane@example.com>")
+
+		recipients []string
+		mboxes     []*email.Mailbox
+		msg        *email.Message
+		mailtx     *MailTx
+		data       []byte
+		err        error
+	)
+
+	rand.Seed(42)
+
+	mboxes, err = email.ParseMailboxes(toAddresses)
+	if err != nil {
+		log.Fatal(err)
+	}
+	for _, mbox := range mboxes {
+		recipients = append(recipients, mbox.Address)
+	}
+
+	msg, err = email.NewMultipart(
+		fromAddress,
+		toAddresses,
+		subject,
+		bodyText,
+		bodyHtml,
+	)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// The From parameter is not necessary equal to the fromAddress.
+	// The From in MailTx define the account that authorize or allowed
+	// sending the email on behalf of fromAddress domain, while the
+	// fromAddress define the address that viewed by recipients.
+	mailtx = NewMailTx(txFrom, recipients, msg.Pack())
+
+	fmt.Printf("Tx From: %s\n", mailtx.From)
+	fmt.Printf("Tx Recipients: %s\n", mailtx.Recipients)
+
+	// In order to make the example Output works, we need to replace all
+	// CRLF with LF.
+	data = bytes.ReplaceAll(mailtx.Data, []byte("\r\n"), []byte("\n"))
+
+	fmt.Printf("Tx Data:\n%s", data)
+	//Output:
+	//Tx From: Postmaster <postmaster@mail.example.com>
+	//Tx Recipients: [john@example.com jane@example.com]
+	//Tx Data:
+	//from: Noreply <noreply@example.com>
+	//to: John <john@example.com>, Jane <jane@example.com>
+	//subject: Example subject
+	//mime-version: 1.0
+	//content-type: multipart/alternative; boundary=1b4df158039f7cce49f0a64b0ea7b7dd
+	//
+	//--1b4df158039f7cce49f0a64b0ea7b7dd
+	//content-type: text/plain; charset="utf-8"
+	//mime-version: 1.0
+	//content-transfer-encoding: quoted-printable
+	//
+	//Email body as plain text
+	//--1b4df158039f7cce49f0a64b0ea7b7dd
+	//content-type: text/html; charset="utf-8"
+	//mime-version: 1.0
+	//content-transfer-encoding: quoted-printable
+	//
+	//Email body as <b>HTML</b>
+	//--1b4df158039f7cce49f0a64b0ea7b7dd--
+}