Introduce logic to resolve volume replica placement within EC rebalancing. (#6254)

* Rename `command_ec_encode_test.go` to `command_ec_common_test.go`.

All tests defined in this file are now for `command_ec_common.go`.

* Minor code cleanups.

- Fix broken `ec.balance` test.
- Rework integer ceiling division to not use floats, which can introduce precision errors.

* Introduce logic to resolve volume replica placement within EC rebalancing.

This will be used to make rebalancing logic topology-aware.

* Give shell.EcNode.dc a dedicated DataCenterId type.

weed/shell/command_ec_common_test.go

@@ -0,0 +1,87 @@
+package shell
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
+	"github.com/seaweedfs/seaweedfs/weed/storage/erasure_coding"
+	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
+	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
+)
+
+func TestEcDistribution(t *testing.T) {
+
+	topologyInfo := parseOutput(topoData)
+
+	// find out all volume servers with one slot left.
+	ecNodes, totalFreeEcSlots := collectEcVolumeServersByDc(topologyInfo, "")
+
+	sortEcNodesByFreeslotsDescending(ecNodes)
+
+	if totalFreeEcSlots < erasure_coding.TotalShardsCount {
+		t.Errorf("not enough free ec shard slots: %d", totalFreeEcSlots)
+	}
+	allocatedDataNodes := ecNodes
+	if len(allocatedDataNodes) > erasure_coding.TotalShardsCount {
+		allocatedDataNodes = allocatedDataNodes[:erasure_coding.TotalShardsCount]
+	}
+
+	for _, dn := range allocatedDataNodes {
+		// fmt.Printf("info %+v %+v\n", dn.info, dn)
+		fmt.Printf("=> %+v %+v\n", dn.info.Id, dn.freeEcSlot)
+	}
+}
+
+func TestVolumeIdToReplicaPlacement(t *testing.T) {
+	topo1 := parseOutput(topoData)
+	topo2 := parseOutput(topoData2)
+
+	testCases := []struct {
+		topology *master_pb.TopologyInfo
+		vid      string
+		want     string
+		wantErr  string
+	}{
+		{topo1, "", "", "failed to resolve replica placement for volume ID 0"},
+		{topo1, "0", "", "failed to resolve replica placement for volume ID 0"},
+		{topo1, "1", "100", ""},
+		{topo1, "296", "100", ""},
+		{topo2, "", "", "failed to resolve replica placement for volume ID 0"},
+		{topo2, "19012", "", "failed to resolve replica placement for volume ID 19012"},
+		{topo2, "6271", "002", ""},
+		{topo2, "17932", "002", ""},
+	}
+
+	for _, tc := range testCases {
+		vid, _ := needle.NewVolumeId(tc.vid)
+		ecNodes, _ := collectEcVolumeServersByDc(tc.topology, "")
+		got, gotErr := volumeIdToReplicaPlacement(vid, ecNodes)
+
+		if tc.wantErr == "" && gotErr != nil {
+			t.Errorf("expected no error for volume '%s', got '%s'", tc.vid, gotErr.Error())
+			continue
+		}
+		if tc.wantErr != "" {
+			if gotErr == nil {
+				t.Errorf("got no error for volume '%s', expected '%s'", tc.vid, tc.wantErr)
+				continue
+			}
+			if gotErr.Error() != tc.wantErr {
+				t.Errorf("expected error '%s' for volume '%s', got '%s'", tc.wantErr, tc.vid, gotErr.Error())
+				continue
+			}
+		}
+
+		if got == nil {
+			if tc.want != "" {
+				t.Errorf("expected replica placement '%s' for volume '%s', got nil", tc.want, tc.vid)
+			}
+			continue
+		}
+		want, _ := super_block.NewReplicaPlacementFromString(tc.want)
+		if !got.Equals(want) {
+			t.Errorf("got replica placement '%s' for volune '%s', want '%s'", got.String(), tc.vid, want.String())
+		}
+	}
+}