add attachments to the email

mail/mail.go

@@ -1,9 +1,14 @@
 package mail
 
 import (
+	"bytes"
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"mime/multipart"
+	"net/http"
 	"os"
+	"path/filepath"
 	"strings"
 
 	"github.com/go-playground/validator/v10"
@@ -11,12 +16,34 @@ import (
 
 var validate *validator.Validate
 
+// getgetAttachmentsContent collects attachment data from a list of attachment paths.
+func getAttachmentsContent(attachments []string) (map[string][]byte, error) {
+	if len(attachments) == 0 {
+		return nil, nil
+	}
+
+	attachmentsData := map[string][]byte{}
+
+	for _, attachmentPath := range attachments {
+		b, err := os.ReadFile(attachmentPath)
+		if err != nil {
+			return nil, err
+		}
+
+		_, filename := filepath.Split(attachmentPath)
+		attachmentsData[filename] = b
+	}
+
+	return attachmentsData, nil
+}
+
 type Email struct {
-	Path      string
-	Sender    string `json:"sender" validate:"required,email"`
-	Receivers string `json:"receivers" validate:"required"`
-	Subject   string `json:"subject" validate:"required"`
-	Content   string `json:"content" validate:"required"`
+	Path        string
+	Sender      string `json:"sender" validate:"required,email"`
+	Receivers   string `json:"receivers" validate:"required"`
+	Subject     string `json:"subject" validate:"required"`
+	Content     string `json:"content" validate:"required"`
+	Attachments string `json:"attachments,omitempty"`
 }
 
 func FromJSON(path string) (Email, error) {
@@ -42,15 +69,56 @@ func (e *Email) GetReceivers() []string {
 	return strings.Split(e.Receivers, ",")
 }
 
-func (e *Email) Generate() []byte {
-	mail := fmt.Sprintf(
-		"To: %s\nFrom: %s\nContent-Type: text/html;charset=utf-8\nSubject: %s\n\n%s",
-		e.Receivers,
-		e.Sender,
-		e.Subject,
-		e.Content,
-	)
-	return []byte(mail)
+func (e *Email) GetAttachments() []string {
+	if e.Attachments == "" {
+		return []string{}
+	}
+
+	return strings.Split(e.Attachments, ",")
+}
+
+func (e *Email) Generate() ([]byte, error) {
+	buf := bytes.NewBuffer(nil)
+	attachments := e.GetAttachments()
+	withAttachments := len(attachments) != 0
+
+	fmt.Fprintf(buf, "To: %s\n", strings.Join(e.GetReceivers(), ","))
+	fmt.Fprintf(buf, "From: %s\n", e.Sender)
+	fmt.Fprintf(buf, "Subject: %s\n", e.Subject)
+	buf.WriteString("MIME-Version: 1.0\n")
+
+	writer := multipart.NewWriter(buf)
+	boundary := writer.Boundary()
+	if withAttachments {
+		fmt.Fprintf(buf, "Content-Type: multipart/mixed; boundary=%s\n\n", boundary)
+		fmt.Fprintf(buf, "--%s\n", boundary)
+	}
+
+	buf.WriteString("Content-Type: text/html; charset=utf-8\n\n")
+	buf.WriteString(e.Content)
+
+	if withAttachments {
+		attachmentsData, err := getAttachmentsContent(attachments)
+		if err != nil {
+			return nil, err
+		}
+
+		for filename, data := range attachmentsData {
+			fmt.Fprintf(buf, "\n\n--%s\n", boundary)
+			fmt.Fprintf(buf, "Content-Type: %s\n", http.DetectContentType(data))
+			buf.WriteString("Content-Transfer-Encoding: base64\n")
+			fmt.Fprintf(buf, "Content-Disposition: attachment; filename=%s\n\n", filename)
+
+			b := make([]byte, base64.StdEncoding.EncodedLen(len(data)))
+			base64.StdEncoding.Encode(b, data)
+			buf.Write(b)
+			fmt.Fprintf(buf, "\n\n--%s", boundary)
+		}
+
+		buf.WriteString("--")
+	}
+
+	return buf.Bytes(), nil
 }
 
 func (e *Email) Validate() error {

services/sender.go

@@ -33,7 +33,12 @@ func NewSender(config cfg.SMTPConfig, outboxPath string) Sender {
 }
 
 func (s Sender) SendMail(email *mail.Email) error {
-	if err := smtp.SendMail(s.smtpURL, s.auth, email.Sender, email.GetReceivers(), email.Generate()); err != nil {
+	content, err := email.Generate()
+	if err != nil {
+		return err
+	}
+
+	if err := smtp.SendMail(s.smtpURL, s.auth, email.Sender, email.GetReceivers(), content); err != nil {
 		return err
 	}