fix read failure from system tables tiflash_segments and `tiflash_t…

…ables` when some tiflash node is down (#19714)

Co-authored-by: crazycs <crazycs520@gmail.com>
Co-authored-by: ti-srebot <66930949+ti-srebot@users.noreply.github.com>

executor/infoschema_reader.go

@@ -1892,8 +1892,16 @@ func (e *TiFlashSystemTableRetriever) initialize(sctx sessionctx.Context, tiflas
 					if len(tiflashInstances) > 0 && !tiflashInstances.Exist(id) {
 						continue
 					}
-					// TODO: Support https in tiflash
-					url := fmt.Sprintf("http://%s", ev.Value)
+					url := fmt.Sprintf("%s://%s", util.InternalHTTPSchema(), ev.Value)
+					req, err := http.NewRequest(http.MethodGet, url, nil)
+					if err != nil {
+						return errors.Trace(err)
+					}
+					_, err = util.InternalHTTPClient().Do(req)
+					if err != nil {
+						sctx.GetSessionVars().StmtCtx.AppendWarning(err)
+						continue
+					}
 					e.instanceInfos = append(e.instanceInfos, tiflashInstanceInfo{
 						id:  id,
 						url: url,
@@ -1933,7 +1941,6 @@ func (e *TiFlashSystemTableRetriever) dataForTiFlashSystemTables(ctx sessionctx.
 	}
 	sql = fmt.Sprintf("%s LIMIT %d, %d", sql, e.rowIdx, maxCount)
 	notNumber := "nan"
-	httpClient := http.DefaultClient
 	instanceInfo := e.instanceInfos[e.instanceIdx]
 	url := instanceInfo.url
 	req, err := http.NewRequest(http.MethodGet, url, nil)
@@ -1943,7 +1950,7 @@ func (e *TiFlashSystemTableRetriever) dataForTiFlashSystemTables(ctx sessionctx.
 	q := req.URL.Query()
 	q.Add("query", sql)
 	req.URL.RawQuery = q.Encode()
-	resp, err := httpClient.Do(req)
+	resp, err := util.InternalHTTPClient().Do(req)
 	if err != nil {
 		return nil, errors.Trace(err)
 	}