Add more robust file support for webhooks

restapi.go

@@ -2174,7 +2174,60 @@ func (s *Session) WebhookExecute(webhookID, token string, wait bool, data *Webho
 		uri += "?wait=true"
 	}
 
-	response, err := s.RequestWithBucketID("POST", uri, data, EndpointWebhookToken("", ""))
+	var response []byte
+	if len(data.Files) > 0 {
+		body := &bytes.Buffer{}
+		bodywriter := multipart.NewWriter(body)
+
+		var payload []byte
+		payload, err = json.Marshal(data)
+		if err != nil {
+			return
+		}
+
+		var p io.Writer
+
+		h := make(textproto.MIMEHeader)
+		h.Set("Content-Disposition", `form-data; name="payload_json"`)
+		h.Set("Content-Type", "application/json")
+
+		p, err = bodywriter.CreatePart(h)
+		if err != nil {
+			return
+		}
+
+		if _, err = p.Write(payload); err != nil {
+			return
+		}
+
+		for i, file := range data.Files {
+			h := make(textproto.MIMEHeader)
+			h.Set("Content-Disposition", fmt.Sprintf(`form-data; name="file%d"; filename="%s"`, i, quoteEscaper.Replace(file.Name)))
+			contentType := file.ContentType
+			if contentType == "" {
+				contentType = "application/octet-stream"
+			}
+			h.Set("Content-Type", contentType)
+
+			p, err = bodywriter.CreatePart(h)
+			if err != nil {
+				return
+			}
+
+			if _, err = io.Copy(p, file.Reader); err != nil {
+				return
+			}
+		}
+
+		err = bodywriter.Close()
+		if err != nil {
+			return
+		}
+
+		response, err = s.request("POST", uri, bodywriter.FormDataContentType(), body.Bytes(), uri, 0)
+	} else {
+		response, err = s.RequestWithBucketID("POST", uri, data, uri)
+	}
 	if !wait || err != nil {
 		return
 	}

webhook.go

@@ -31,7 +31,7 @@ type WebhookParams struct {
 	Username        string                  `json:"username,omitempty"`
 	AvatarURL       string                  `json:"avatar_url,omitempty"`
 	TTS             bool                    `json:"tts,omitempty"`
-	File            string                  `json:"file,omitempty"`
+	Files           []*File                 `json:"-"`
 	Embeds          []*MessageEmbed         `json:"embeds,omitempty"`
 	AllowedMentions *MessageAllowedMentions `json:"allowed_mentions,omitempty"`
 }