Make Client.Scan work with ES 5.x

goes.go

@@ -286,10 +286,21 @@ func (c *Client) Query(query interface{}, indexList []string, typeList []string,
 	return c.Do(&r)
 }
 
-// Scan starts scroll over an index
+// Scan starts scroll over an index.
+// For ES versions < 5.x, it uses search_type=scan; for 5.x it uses sort=_doc. This means that data
+// will  be returned in the initial response for 5.x versions, but not for older versions. Code
+// wishing to be compatible with both should be written to handle either case.
 func (c *Client) Scan(query interface{}, indexList []string, typeList []string, timeout string, size int) (*Response, error) {
 	v := url.Values{}
+	version, err := c.Version()
+	if err != nil {
+		return nil, err
+	}
+	if version > "5" {
+		v.Add("sort", "_doc")
+	} else {
 		v.Add("search_type", "scan")
+	}
 	v.Add("scroll", timeout)
 	v.Add("size", strconv.Itoa(size))
 
@@ -307,14 +318,24 @@ func (c *Client) Scan(query interface{}, indexList []string, typeList []string,
 
 // Scroll fetches data by scroll id
 func (c *Client) Scroll(scrollID string, timeout string) (*Response, error) {
-	v := url.Values{}
-	v.Add("scroll", timeout)
-
 	r := Request{
 		Method: "POST",
 		API:    "_search/scroll",
-		ExtraArgs: v,
+	}
-		Body:      []byte(scrollID),
+
+	if version, err := c.Version(); err != nil {
+		return nil, err
+	} else if version > "2" {
+		r.Body, err = json.Marshal(map[string]string{"scroll": timeout, "scroll_id": scrollID})
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		v := url.Values{}
+		v.Add("scroll", timeout)
+		v.Add("scroll_id", scrollID)
+
+		r.ExtraArgs = v
 	}
 
 	return c.Do(&r)

goes_test.go

@@ -930,7 +930,8 @@ func (s *GoesTestSuite) TestScroll(c *C) {
 	c.Assert(err, IsNil)
 
 	var query map[string]interface{}
-	if version, _ := conn.Version(); version > "5" {
+	version, _ := conn.Version()
+	if version > "5" {
 		query = map[string]interface{}{
 			"query": map[string]interface{}{
 				"bool": map[string]interface{}{
@@ -956,12 +957,15 @@ func (s *GoesTestSuite) TestScroll(c *C) {
 		}
 	}
 
-	scan, err := conn.Scan(query, []string{indexName}, []string{docType}, "1m", 1)
+	searchResults, err := conn.Scan(query, []string{indexName}, []string{docType}, "1m", 1)
 	c.Assert(err, IsNil)
-	c.Assert(len(scan.ScrollID) > 0, Equals, true)
+	c.Assert(len(searchResults.ScrollID) > 0, Equals, true)
 
-	searchResults, err := conn.Scroll(scan.ScrollID, "1m")
+	// Versions < 5.x don't include results in the initial response
+	if version < "5" {
+		searchResults, err = conn.Scroll(searchResults.ScrollID, "1m")
 		c.Assert(err, IsNil)
+	}
 
 	// some data in first chunk
 	c.Assert(searchResults.Hits.Total, Equals, uint64(2))