Custom data for multipart request

client.go

@@ -300,19 +300,20 @@ func (c *Client) SetAuthToken(token string) *Client {
 // R method creates a request instance, its used for Get, Post, Put, Delete, Patch, Head and Options.
 func (c *Client) R() *Request {
 	r := &Request{
-		URL:            "",
-		Method:         "",
-		QueryParam:     url.Values{},
-		FormData:       url.Values{},
-		Header:         http.Header{},
-		Body:           nil,
-		Result:         nil,
-		Error:          nil,
-		RawRequest:     nil,
-		client:         c,
-		bodyBuf:        nil,
-		multipartFiles: []*File{},
-		pathParams:     make(map[string]string),
+		URL:                 "",
+		Method:              "",
+		QueryParam:          url.Values{},
+		FormData:            url.Values{},
+		Header:              http.Header{},
+		Body:                nil,
+		Result:              nil,
+		Error:               nil,
+		RawRequest:          nil,
+		client:              c,
+		bodyBuf:             nil,
+		multipartFiles:      []*File{},
+		multipartCustomData: []*MultipartCustomData{},
+		pathParams:          make(map[string]string),
 	}
 
 	return r
@@ -865,3 +866,10 @@ type File struct {
 func (f *File) String() string {
 	return fmt.Sprintf("ParamName: %v; FileName: %v", f.ParamName, f.Name)
 }
+
+// MultipartCustomData represent custom data part for multipart request
+type MultipartCustomData struct {
+	Params      map[string]string
+	ContentType string
+	io.Reader
+}

middleware.go

@@ -300,6 +300,16 @@ func handleMultipart(c *Client, r *Request) (err error) {
 		}
 	}
 
+	// adding custom data support
+	if len(r.multipartCustomData) > 0 {
+		for _, cd := range r.multipartCustomData {
+			err = addCustomDataReader(w, cd)
+			if err != nil {
+				return
+			}
+		}
+	}
+
 	r.Header.Set(hdrContentTypeKey, w.FormDataContentType())
 	err = w.Close()
 

request.go

@@ -279,6 +279,19 @@ func (r *Request) SetFileReader(param, fileName string, reader io.Reader) *Reque
 	return r
 }
 
+// SetMultipartData method is to set custom data using io.Reader for multipart upload.
+func (r *Request) SetMultipartData(params map[string]string, contentType string, reader io.Reader) *Request {
+	r.isMultiPart = true
+
+	r.multipartCustomData = append(r.multipartCustomData, &MultipartCustomData{
+		Params:      params,
+		ContentType: contentType,
+		Reader:      reader,
+	})
+
+	return r
+}
+
 // SetContentLength method sets the HTTP header `Content-Length` value for current request.
 // By default go-resty won't set `Content-Length`. Also you have an option to enable for every
 // request. See `resty.SetContentLength`

request16.go

@@ -43,6 +43,7 @@ type Request struct {
 	isSaveResponse      bool
 	outputFile          string
 	multipartFiles      []*File
+	multipartCustomData []*MultipartCustomData
 	notParseResponse    bool
 	fallbackContentType string
 	pathParams          map[string]string

request17.go

@@ -44,6 +44,7 @@ type Request struct {
 	isSaveResponse      bool
 	outputFile          string
 	multipartFiles      []*File
+	multipartCustomData []*MultipartCustomData
 	notParseResponse    bool
 	ctx                 context.Context
 	fallbackContentType string

util.go

@@ -107,6 +107,24 @@ func escapeQuotes(s string) string {
 	return quoteEscaper.Replace(s)
 }
 
+func writeMultipartFormCustomData(w *multipart.Writer, params map[string]string, contentType string, r io.Reader) error {
+	h := make(textproto.MIMEHeader)
+	var bufContDisp bytes.Buffer
+	bufContDisp.WriteString("form-data;")
+	for k, v := range params {
+		bufContDisp.WriteString(fmt.Sprintf(` %s="%s";`, k, escapeQuotes(v)))
+	}
+	h.Set("Content-Disposition", bufContDisp.String())
+	h.Set("Content-Type", contentType)
+	partWriter, err := w.CreatePart(h)
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(partWriter, r)
+	return err
+}
+
 func writeMultipartFormFile(w *multipart.Writer, fieldName, fileName string, r io.Reader) error {
 	// Auto detect actual multipart content type
 	cbuf := make([]byte, 512)
@@ -148,6 +166,10 @@ func addFileReader(w *multipart.Writer, f *File) error {
 	return writeMultipartFormFile(w, f.ParamName, f.Name, f.Reader)
 }
 
+func addCustomDataReader(w *multipart.Writer, cd *MultipartCustomData) error {
+	return writeMultipartFormCustomData(w, cd.Params, cd.ContentType, cd.Reader)
+}
+
 func getPointer(v interface{}) interface{} {
 	vv := valueOf(v)
 	if vv.Kind() == reflect.Ptr {