http assign logic should be the same as grpc assign

similar logic as bebbc9fe44

weed/server/master_server_handlers.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/operation"
 	"github.com/seaweedfs/seaweedfs/weed/security"
@@ -119,6 +120,13 @@ func (ms *MasterServer) dirAssignHandler(w http.ResponseWriter, r *http.Request)
 
 	vl := ms.Topo.GetVolumeLayout(option.Collection, option.ReplicaPlacement, option.Ttl, option.DiskType)
 
+	var (
+		lastErr    error
+		maxTimeout = time.Second * 10
+		startTime  = time.Now()
+	)
+
+	for time.Now().Sub(startTime) < maxTimeout {
 		fid, count, dnList, shouldGrow, err := ms.Topo.PickForWrite(requestedCount, option, vl)
 		if shouldGrow && !vl.HasGrowRequest() {
 			// if picked volume is almost full, trigger a volume-grow request
@@ -140,13 +148,24 @@ func (ms *MasterServer) dirAssignHandler(w http.ResponseWriter, r *http.Request)
 				return
 			}
 		}
-	if err == nil {
+		if err != nil {
+			// glog.Warningf("PickForWrite %+v: %v", req, err)
+			lastErr = err
+			time.Sleep(200 * time.Millisecond)
+			continue
+		} else {
 			ms.maybeAddJwtAuthorization(w, fid, true)
 			dn := dnList.Head()
 
 			writeJsonQuiet(w, r, http.StatusOK, operation.AssignResult{Fid: fid, Url: dn.Url(), PublicUrl: dn.PublicUrl, Count: count})
+			return
+		}
+	}
+
+	if lastErr != nil {
+		writeJsonQuiet(w, r, http.StatusNotAcceptable, operation.AssignResult{Error: lastErr.Error()})
 	} else {
-		writeJsonQuiet(w, r, http.StatusNotAcceptable, operation.AssignResult{Error: err.Error()})
+		writeJsonQuiet(w, r, http.StatusRequestTimeout, operation.AssignResult{Error: "request timeout"})
 	}
 }