Handle EOF from multipart form file readers (#438)

util.go

@@ -202,7 +202,7 @@ func writeMultipartFormFile(w *multipart.Writer, fieldName, fileName string, r i
 	// Auto detect actual multipart content type
 	cbuf := make([]byte, 512)
 	size, err := r.Read(cbuf)
-	if err != nil {
+	if err != nil && err != io.EOF {
 		return err
 	}
 

util_test.go

@@ -5,6 +5,8 @@
 package resty
 
 import (
+	"bytes"
+	"mime/multipart"
 	"testing"
 )
 
@@ -79,3 +81,17 @@ func TestIsXMLType(t *testing.T) {
 		}
 	}
 }
+
+func TestWriteMultipartFormFileReaderEmpty(t *testing.T) {
+	w := multipart.NewWriter(bytes.NewBuffer(nil))
+	defer func() { _ = w.Close() }()
+	if err := writeMultipartFormFile(w, "foo", "bar", bytes.NewReader(nil)); err != nil {
+		t.Errorf("Got unexpected error: %v", err)
+	}
+}
+
+func TestWriteMultipartFormFileReaderError(t *testing.T) {
+	err := writeMultipartFormFile(nil, "", "", &brokenReadCloser{})
+	assertNotNil(t, err)
+	assertEqual(t, "read error", err.Error())
+}