alps/plugins/base/smtp.go

package koushinbase

import (
	"bufio"
	"fmt"
	"io"
	"mime/multipart"
	"strings"
	"time"

	"github.com/emersion/go-message/mail"
	"github.com/emersion/go-smtp"
)

func quote(r io.Reader) (string, error) {
	scanner := bufio.NewScanner(r)
	var builder strings.Builder
	for scanner.Scan() {
		builder.WriteString("> ")
		builder.Write(scanner.Bytes())
		builder.WriteString("\n")
	}
	if err := scanner.Err(); err != nil {
		return "", fmt.Errorf("quote: failed to read original message: %s", err)
	}
	return builder.String(), nil
}

type OutgoingMessage struct {
	From        string
	To          []string
	Subject     string
	InReplyTo   string
	Text        string
	Attachments []*multipart.FileHeader
}

func (msg *OutgoingMessage) ToString() string {
	return strings.Join(msg.To, ", ")
}

func writeAttachment(mw *mail.Writer, att *multipart.FileHeader) error {
	var h mail.AttachmentHeader
	h.Set("Content-Type", att.Header.Get("Content-Type"))
	h.SetFilename(att.Filename)

	aw, err := mw.CreateAttachment(h)
	if err != nil {
		return fmt.Errorf("failed to create attachment: %v", err)
	}
	defer aw.Close()

	f, err := att.Open()
	if err != nil {
		return fmt.Errorf("failed to open attachment: %v", err)
	}
	defer f.Close()

	if _, err := io.Copy(aw, f); err != nil {
		return fmt.Errorf("failed to write attachment: %v", err)
	}

	if err := f.Close(); err != nil {
		return fmt.Errorf("failed to close attachment: %v", err)
	}
	if err := aw.Close(); err != nil {
		return fmt.Errorf("failed to close attachment writer: %v", err)
	}

	return nil
}

func (msg *OutgoingMessage) WriteTo(w io.Writer) error {
	from := []*mail.Address{{"", msg.From}}

	to := make([]*mail.Address, len(msg.To))
	for i, addr := range msg.To {
		to[i] = &mail.Address{"", addr}
	}

	var h mail.Header
	h.SetDate(time.Now())
	h.SetAddressList("From", from)
	h.SetAddressList("To", to)
	if msg.Subject != "" {
		h.SetText("Subject", msg.Subject)
	}
	if msg.InReplyTo != "" {
		h.Set("In-Reply-To", msg.InReplyTo)
	}

	mw, err := mail.CreateWriter(w, h)
	if err != nil {
		return fmt.Errorf("failed to create mail writer: %v", err)
	}

	var th mail.InlineHeader
	th.Set("Content-Type", "text/plain; charset=utf-8")

	tw, err := mw.CreateSingleInline(th)
	if err != nil {
		return fmt.Errorf("failed to create text part: %v", err)
	}
	defer tw.Close()

	if _, err := io.WriteString(tw, msg.Text); err != nil {
		return fmt.Errorf("failed to write text part: %v", err)
	}

	if err := tw.Close(); err != nil {
		return fmt.Errorf("failed to close text part: %v", err)
	}

	for _, att := range msg.Attachments {
		if err := writeAttachment(mw, att); err != nil {
			return err
		}
	}

	if err := mw.Close(); err != nil {
		return fmt.Errorf("failed to close mail writer: %v", err)
	}

	return nil
}

func sendMessage(c *smtp.Client, msg *OutgoingMessage) error {
	if err := c.Mail(msg.From, nil); err != nil {
		return fmt.Errorf("MAIL FROM failed: %v", err)
	}

	for _, to := range msg.To {
		if err := c.Rcpt(to); err != nil {
			return fmt.Errorf("RCPT TO failed: %v", err)
		}
	}

	w, err := c.Data()
	if err != nil {
		return fmt.Errorf("DATA failed: %v", err)
	}
	defer w.Close()

	if err := msg.WriteTo(w); err != nil {
		return fmt.Errorf("failed to write outgoing message: %v", err)
	}

	if err := w.Close(); err != nil {
		return fmt.Errorf("failed to close SMTP data writer: %v", err)
	}

	return nil
}