Add mailgun handler (WIP)

cmd/courier/main.go

@@ -45,6 +45,7 @@ import (
 	_ "github.com/nyaruka/courier/handlers/line"
 	_ "github.com/nyaruka/courier/handlers/m3tech"
 	_ "github.com/nyaruka/courier/handlers/macrokiosk"
+	_ "github.com/nyaruka/courier/handlers/mailgun"
 	_ "github.com/nyaruka/courier/handlers/mblox"
 	_ "github.com/nyaruka/courier/handlers/messagebird"
 	_ "github.com/nyaruka/courier/handlers/messangi"

handlers/mailgun/handler.go

@@ -0,0 +1,130 @@
+package mailgun
+
+import (
+	"bytes"
+	"context"
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"mime/multipart"
+	"net/http"
+
+	"github.com/buger/jsonparser"
+	"github.com/nyaruka/courier"
+	"github.com/nyaruka/courier/handlers"
+)
+
+const (
+	configSubject           = "subject"
+	configWebhookSigningKey = "webhook_signing_key"
+)
+
+var (
+	defaultAPIURL = "https://api.mailgun.net/v3"
+)
+
+func init() {
+	courier.RegisterHandler(newHandler())
+}
+
+type handler struct {
+	handlers.BaseHandler
+}
+
+func newHandler() courier.ChannelHandler {
+	return &handler{handlers.NewBaseHandler(courier.ChannelType("MLG"), "Mailgun")}
+}
+
+func (h *handler) Initialize(s courier.Server) error {
+	h.SetServer(s)
+	s.AddHandlerRoute(h, http.MethodPost, "receive", courier.ChannelLogTypeMsgReceive, h.receive)
+	return nil
+}
+
+type receiveRequest struct {
+	Recipient       string `form:"recipient"     validate:"required,email"`
+	Sender          string `form:"sender"        validate:"required,email"`
+	From            string `form:"From"`
+	ReplyTo         string `form:"Reply-To"`
+	MessageID       string `form:"Message-Id"    validate:"required"`
+	Subject         string `form:"subject"       validate:"required"`
+	PlainBody       string `form:"body-plain"`
+	StrippedText    string `form:"stripped-text" validate:"required"`
+	HTMLBody        string `form:"body-html"`
+	Timestamp       string `form:"timestamp"     validate:"required"`
+	Token           string `form:"token"         validate:"required"`
+	Signature       string `form:"signature"     validate:"required"`
+	AttachmentCount int    `form:"attachment-count"`
+}
+
+// see https://documentation.mailgun.com/en/latest/user_manual.html#securing-webhooks
+func (r *receiveRequest) verify(signingKey string) bool {
+	v := r.Timestamp + r.Token
+
+	mac := hmac.New(sha256.New, []byte(signingKey))
+	mac.Write([]byte(v))
+	expectedMAC := hex.EncodeToString(mac.Sum(nil))
+
+	return hmac.Equal([]byte(r.Signature), []byte(expectedMAC))
+}
+
+func (h *handler) receive(ctx context.Context, c courier.Channel, w http.ResponseWriter, r *http.Request, clog *courier.ChannelLog) ([]courier.Event, error) {
+	signingKey := c.StringConfigForKey(configWebhookSigningKey, "")
+	if signingKey == "" {
+		return nil, fmt.Errorf("missing signing key for %s channel", h.ChannelName())
+	}
+
+	request := &receiveRequest{}
+	if err := handlers.DecodeAndValidateForm(request, r); err != nil {
+		return nil, handlers.WriteAndLogRequestError(ctx, h, c, w, r, err)
+	}
+
+	if !request.verify(signingKey) {
+		return nil, handlers.WriteAndLogRequestError(ctx, h, c, w, r, errors.New("invalid signing key")) // TODO should return 406
+	}
+
+	// TODO
+
+	return nil, nil
+}
+
+func (h *handler) Send(ctx context.Context, msg courier.MsgOut, clog *courier.ChannelLog) (courier.StatusUpdate, error) {
+	domain := msg.Channel().Address()
+	sendURL := fmt.Sprintf("%s/%s/messages", defaultAPIURL, domain)
+
+	sendingKey := msg.Channel().StringConfigForKey(courier.ConfigAuthToken, "")
+	if sendingKey == "" {
+		return nil, fmt.Errorf("missing sending key for %s channel", h.ChannelName())
+	}
+
+	subject := msg.Channel().StringConfigForKey(configSubject, "Chat with TextIt")
+
+	b := &bytes.Buffer{}
+	w := multipart.NewWriter(b)
+	w.WriteField("from", fmt.Sprintf("no-reply@%s", domain))
+	w.WriteField("to", msg.URN().Path())
+	w.WriteField("subject", subject)
+	w.WriteField("text", msg.Text())
+
+	// TODO add attachments
+
+	w.Close()
+
+	req, _ := http.NewRequest("POST", sendURL, b)
+	req.Header.Set("Content-Type", w.FormDataContentType())
+	req.SetBasicAuth("api", sendingKey)
+
+	status := h.Backend().NewStatusUpdate(msg.Channel(), msg.ID(), courier.MsgStatusWired, clog)
+
+	resp, respBody, err := h.RequestHTTP(req, clog)
+	if err != nil || resp.StatusCode/100 != 2 {
+		status.SetStatus(courier.MsgStatusErrored)
+	} else {
+		id, _ := jsonparser.GetString(respBody, "id")
+		status.SetExternalID(id)
+	}
+
+	return status, nil
+}