Add support for file attachments in the transactional (tx) API. (#1243)

The original PR accepts files to the `/tx` endpoints as Base64 encoded
strings in the JSON payload. This isn't ideal as the payload size
increase caused by Base64 for larger files can be significant,
in addition to the added clientside API complexity.

This PR adds supports for multipart form posts to `/tx` where the
JSON data (name: `data`) and multiple files can be posted simultaenously
(one or more `file` fields).

--- PR: #1166
* Attachment model for TxMessage
* Don't reassign values, just pass the manager.Messgage
* Read attachment info from API; create attachment Header
* Refactor tx attachments to use multipart form files. Closes #1166.
---

Co-authored-by: MatiSSL <matiss.lidaka@nic.lv>

cmd/tx.go

@@ -1,12 +1,15 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
+	"io/ioutil"
 	"net/http"
 	"net/textproto"
 	"strings"
 
 	"github.com/knadh/listmonk/internal/manager"
+	"github.com/knadh/listmonk/internal/messenger"
 	"github.com/knadh/listmonk/models"
 	"github.com/labstack/echo/v4"
 )
@@ -18,7 +21,48 @@ func handleSendTxMessage(c echo.Context) error {
 		m   models.TxMessage
 	)
 
-	if err := c.Bind(&m); err != nil {
+	// If it's a multipart form, there may be file attachments.
+	if strings.HasPrefix(c.Request().Header.Get("Content-Type"), "multipart/form-data") {
+		form, err := c.MultipartForm()
+		if err != nil {
+			return echo.NewHTTPError(http.StatusBadRequest,
+				app.i18n.Ts("globals.messages.invalidFields", "name", err.Error()))
+		}
+
+		data, ok := form.Value["data"]
+		if !ok || len(data) != 1 {
+			return echo.NewHTTPError(http.StatusBadRequest,
+				app.i18n.Ts("globals.messages.invalidFields", "name", "data"))
+		}
+
+		// Parse the JSON data.
+		if err := json.Unmarshal([]byte(data[0]), &m); err != nil {
+			return echo.NewHTTPError(http.StatusBadRequest,
+				app.i18n.Ts("globals.messages.invalidFields", "name", fmt.Sprintf("data: %s", err.Error())))
+		}
+
+		// Attach files.
+		for _, f := range form.File["file"] {
+			file, err := f.Open()
+			if err != nil {
+				return echo.NewHTTPError(http.StatusInternalServerError,
+					app.i18n.Ts("globals.messages.invalidFields", "name", fmt.Sprintf("file: %s", err.Error())))
+			}
+			defer file.Close()
+
+			b, err := ioutil.ReadAll(file)
+			if err != nil {
+				return echo.NewHTTPError(http.StatusInternalServerError,
+					app.i18n.Ts("globals.messages.invalidFields", "name", fmt.Sprintf("file: %s", err.Error())))
+			}
+
+			m.Attachments = append(m.Attachments, models.TxAttachment{
+				Name:    f.Filename,
+				Header:  messenger.MakeAttachmentHeader(f.Filename, "base64"),
+				Content: b,
+			})
+		}
+	} else if err := c.Bind(&m); err != nil {
 		return err
 	}
 
@@ -85,6 +129,13 @@ func handleSendTxMessage(c echo.Context) error {
 		msg.ContentType = m.ContentType
 		msg.Messenger = m.Messenger
 		msg.Body = m.Body
+		for _, a := range m.Attachments {
+			msg.Attachments = append(msg.Attachments, messenger.Attachment{
+				Name:    a.Name,
+				Header:  a.Header,
+				Content: a.Content,
+			})
+		}
 
 		// Optional headers.
 		if len(m.Headers) != 0 {

internal/manager/manager.go

@@ -411,16 +411,7 @@ func (m *Manager) worker() {
 				return
 			}
 
-			err := m.messengers[msg.Messenger].Push(messenger.Message{
+			err := m.messengers[msg.Messenger].Push(msg.Message)
-				From:        msg.From,
-				To:          msg.To,
-				Subject:     msg.Subject,
-				ContentType: msg.ContentType,
-				Body:        msg.Body,
-				AltBody:     msg.AltBody,
-				Subscriber:  msg.Subscriber,
-				Campaign:    msg.Campaign,
-			})
 			if err != nil {
 				m.logger.Printf("error sending message '%s': %v", msg.Subject, err)
 			}

models/models.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"html/template"
+	"net/textproto"
 	"regexp"
 	"strings"
 	txttpl "text/template"
@@ -361,12 +362,22 @@ type TxMessage struct {
 	ContentType string                 `json:"content_type"`
 	Messenger   string                 `json:"messenger"`
 
+	// File attachments added from multi-part form data.
+	Attachments []TxAttachment `json:"-"`
+
 	Subject    string             `json:"-"`
 	Body       []byte             `json:"-"`
 	Tpl        *template.Template `json:"-"`
 	SubjectTpl *txttpl.Template   `json:"-"`
 }
 
+// TxAttachment is used by TxMessage, consists of FileName and file Content in bytes
+type TxAttachment struct {
+	Name    string
+	Header  textproto.MIMEHeader
+	Content []byte
+}
+
 // markdown is a global instance of Markdown parser and renderer.
 var markdown = goldmark.New(
 	goldmark.WithParserOptions(