X: Teach NEO/go to handle multiple master nodes

See kirr/neo!2 for discussion,
context and details.

/reviewed-by @kirr

* t-with-multiple-master-nodes:
  fixup! client_test: Add nmaster={1,2} to test matrix
  fixup! client_test: Support test cluster /w >1 master
  fixup! TalkMaster: Switch master if dialed M is secondary
  fixup! Node: Add support for NEO cluster with > 1 master
  fixup! Dial: Catch NotPrimaryMaster & return custom error
  fixup! proto: Implement Error for NotPrimaryMaster
  fixup! proto.NotPrimaryMaster: Fix .Primary data type (2)
  fixup! proto.NotPrimaryMaster: Fix .Primary data type (1)
  client_test: Add nmaster={1,2} to test matrix
  client_test: Support test cluster /w >1 master
  proto.NotPrimaryMaster: Fix .Primary data type
  TalkMaster: Switch master if dialed M is secondary
  Dial: Catch NotPrimaryMaster & return custom error
  proto: Implement Error for NotPrimaryMaster
  openClientByURL: Fix for >1 master (split URL host)
  Client.URL: Fix incomplete URL if > 1 master nodes
  Node: Add support for NEO cluster with > 1 master

go/neo/client.go

-// Copyright (C) 2017-2021  Nexedi SA and Contributors.
+// Copyright (C) 2017-2023  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -78,11 +78,11 @@ var _ zodb.IStorageDriver = (*Client)(nil)
 
 // NewClient creates new client node.
 //
-// It will connect to master @masterAddr and identify with specified cluster name.
+// It will connect to a master with address from masterAddrSlice and identify with specified cluster name.
 // Use Run to actually start running the node.
-func NewClient(clusterName, masterAddr string, net xnet.Networker) *Client {
+func NewClient(clusterName string, masterAddrSlice []string, net xnet.Networker) *Client {
 	c := &Client{
-		node:     newMasteredNode(proto.CLIENT, clusterName, net, masterAddr),
+		node:     newMasteredNode(proto.CLIENT, clusterName, net, masterAddrSlice),
 		at0Ready: make(chan struct{}),
 		closed:   make(chan struct{}),
 	}
@@ -483,7 +483,7 @@ func openClientByURL(ctx context.Context, u *url.URL, opt *zodb.DriverOptions) (
 		return nil, zodb.InvalidTid, err
 	}
 
-	c := NewClient(name, u.Host, net)
+	c := NewClient(name, strings.Split(u.Host, ","), net)
 	c.ownNet = true
 	c.watchq = opt.Watchq
 	defer func() {
@@ -542,7 +542,8 @@ func (c *Client) URL() string {
 	if strings.Contains(c.node.Net.Network(), "+tls") {
 		zurl += "s"
 	}
-	zurl += fmt.Sprintf("://%s/%s", c.node.MasterAddr, c.node.ClusterName)
+	zurl += fmt.Sprintf("://%s/%s", strings.Join(c.node.MasterAddrSlice, ","), c.node.ClusterName,
+	)
 	return zurl
 }
 

go/neo/client_test.go

@@ -63,7 +63,7 @@ type NEOSrv interface {
 type NEOSrvOptions struct {
 	workdir string // location for database and log files
 	name    string // name of the cluster
-	// nmaster
+	nmaster int    // how many masters our cluster has
 	// npartition
 	// nreplica
 
@@ -82,7 +82,7 @@ type NEOPySrv struct {
 	done    chan struct{} // ready after Wait completes
 	errExit error         // error from Wait
 
-	masterAddr string // address of master in spawned cluster
+	masterAddrSlice []string // addresses of master in spawned cluster
 }
 
 func (_ *NEOPySrv) Bugs() []string {
@@ -96,11 +96,11 @@ func (_ *NEOPySrv) BugEncFixed() (bool, proto.Encoding) {
 
 // StartNEOPySrv starts NEO/py server specified by options.
 func StartNEOPySrv(opt NEOSrvOptions) (_ *NEOPySrv, err error) {
-	workdir := opt.workdir
-	defer xerr.Contextf(&err, "start neo/py %s/%s", workdir, opt.name)
+	defer xerr.Contextf(&err, "start neo/py %s", opt)
 
 	ctx, cancel := context.WithCancel(context.Background())
 
+	workdir := opt.workdir
 	readyf := workdir + "/ready"
 	err = os.Remove(readyf)
 	if os.IsNotExist(err) {
@@ -113,11 +113,11 @@ func StartNEOPySrv(opt NEOSrvOptions) (_ *NEOPySrv, err error) {
 	n := &NEOPySrv{opt: opt, cancel: cancel, done: make(chan struct{})}
 
 	// TODO set $PYTHONPATH to top, so that `import neo` works without `pip install -e .`
-	n.pysrv = xexec.Command("./py/runneo.py", workdir, opt.name)
+	n.pysrv = xexec.Command("./py/runneo.py", workdir, opt.name, "master_count="+fmt.Sprintf("%d", opt.nmaster))
 	if opt.SSL {
-		n.pysrv.Args = append(n.pysrv.Args, "ca="  +opt.CA())
-		n.pysrv.Args = append(n.pysrv.Args, "cert="+opt.Cert())
-		n.pysrv.Args = append(n.pysrv.Args, "key=" +opt.Key())
+		n.pysrv.Args = append(n.pysrv.Args, fmt.Sprintf("ca=%q",   opt.CA()))
+		n.pysrv.Args = append(n.pysrv.Args, fmt.Sprintf("cert=%q", opt.Cert()))
+		n.pysrv.Args = append(n.pysrv.Args, fmt.Sprintf("key=%q",  opt.Key()))
 	}
 	// $TEMP -> workdir  (else NEO/py creates another one for e.g. coverage)
 	n.pysrv.Env = append(os.Environ(), "TEMP="+workdir)
@@ -160,12 +160,12 @@ func StartNEOPySrv(opt NEOSrvOptions) (_ *NEOPySrv, err error) {
 		time.Sleep(10*time.Millisecond)
 	}
 
-	// retrieve master address
-	masterAddr, err := ioutil.ReadFile(readyf)
+	// retrieve masters addresses
+	maddrv, err := ioutil.ReadFile(readyf)
 	if err != nil {
 		return nil, err
 	}
-	n.masterAddr = string(masterAddr)
+	n.masterAddrSlice = strings.Split(string(maddrv), " ")
 
 	return n, nil
 }
@@ -175,7 +175,7 @@ func (n *NEOPySrv) clusterName() string {
 }
 
 func (n *NEOPySrv) URL() string {
-	return fmt.Sprintf("%s%s/%s", n.opt.URLPrefix(), n.masterAddr, n.clusterName())
+	return fmt.Sprintf("%s%s/%s", n.opt.URLPrefix(), strings.Join(n.masterAddrSlice, ","), n.clusterName())
 }
 
 func (n *NEOPySrv) LogTail() (string, error) {
@@ -253,7 +253,10 @@ func (_ *NEOGoSrv) BugEncFixed() (bool, proto.Encoding) {
 
 // StartNEOGoSrv starts NEO/go server specified by options.
 func StartNEOGoSrv(opt NEOSrvOptions) (_ *NEOGoSrv, err error) {
-	defer xerr.Contextf(&err, "start neo/go %s/%s", opt.workdir, opt.name)
+	defer xerr.Contextf(&err, "start neo/go %s", opt)
+	if opt.nmaster > 1 {
+		return nil, fmt.Errorf("TODO: nmaster > 1 not implemented")
+	}
 
 	ctx, cancel := context.WithCancel(context.Background())
 	serveWG := xsync.NewWorkGroup(ctx)
@@ -290,7 +293,7 @@ func StartNEOGoSrv(opt NEOSrvOptions) (_ *NEOGoSrv, err error) {
 	if err != nil {
 		return nil, err
 	}
-	n.S = NewStorage(opt.name, n.masterAddr(), net, n.Sback)
+	n.S = NewStorage(opt.name, n.masterAddrSlice(), net, n.Sback)
 	serveWG.Go(func(ctx context.Context) error {
 		return n.S.Run(ctx, n.Sl)
 	})
@@ -353,12 +356,12 @@ func (n *NEOGoSrv) Close() (err error) {
 	return err
 }
 
-func (n *NEOGoSrv) masterAddr() string {
-	return n.Ml.Addr().String()
+func (n *NEOGoSrv) masterAddrSlice() []string {
+	return []string {n.Ml.Addr().String()}
 }
 
 func (n *NEOGoSrv) URL() string {
-	return fmt.Sprintf("%s%s/%s", n.opt.URLPrefix(), n.masterAddr(), n.opt.name)
+	return fmt.Sprintf("%s%s/%s", n.opt.URLPrefix(), strings.Join(n.masterAddrSlice(), ","), n.opt.name)
 }
 
 
@@ -366,6 +369,13 @@ func (n *NEOGoSrv) URL() string {
 
 const npytests = "../../neo/tests/"
 
+// String returns human-readble representation of server options.
+func (opt NEOSrvOptions) String() string {
+	s := fmt.Sprintf("%s/%s M%d ", opt.workdir, opt.name, opt.nmaster)
+	if opt.SSL { s += "ssl" } else { s += "!ssl" }
+	return s
+}
+
 // CA/Cert/Key files to use if opt.SSL=y; empty if SSL=n.
 func (opt NEOSrvOptions) CA() string {
 	if !opt.SSL { return "" }
@@ -435,15 +445,17 @@ func withNEOSrv(t *testing.T, f func(t *testing.T, nsrv NEOSrv), optv ...tOption
 		f(work)
 	}
 
-	// TODO + all variants with nreplica=X, npartition=Y, nmaster=Z, ... ?
+	// TODO + all variants with nreplica=X, npartition=Y, ... ?
 
+	for _, nmaster := range []int{1, 2} {
 		for _, ssl := range []bool{false, true} {
-		kind := ""
-		if ssl { kind = "ssl" } else { kind = "!ssl" }
+			kind := fmt.Sprintf("M%d/", nmaster)
+			if ssl { kind += "ssl" } else { kind += "!ssl" }
 
 			neoOpt := NEOSrvOptions{
 				name:    "1",
 				SSL:     ssl,
+				nmaster: nmaster,
 			}
 
 			// startNEOpy starts NEO/py server with database in workdir/
@@ -468,7 +480,9 @@ func withNEOSrv(t *testing.T, f func(t *testing.T, nsrv NEOSrv), optv ...tOption
 					}
 					cmd.Args = append(cmd.Args,
 						opt.Preload,
-					npy.masterAddr,
+						// py internal representation of master_nodes is a
+						// string where each addr is separated by 1 space
+						strings.Join(npy.masterAddrSlice, " "),
 					)
 					cmd.Stdin  = nil
 					cmd.Stdout = os.Stdout
@@ -497,6 +511,9 @@ func withNEOSrv(t *testing.T, f func(t *testing.T, nsrv NEOSrv), optv ...tOption
 			// NEO/go
 			t.Run("go/"+kind, func(t *testing.T) {
 				t.Helper()
+				if neoOpt.nmaster > 1 {
+					t.Skip("nmaster > 1 is TODO for NEO/go server")
+				}
 				inWorkDir(t, func(workdir string) {
 					X := xtesting.FatalIf(t)
 
@@ -531,6 +548,7 @@ func withNEOSrv(t *testing.T, f func(t *testing.T, nsrv NEOSrv), optv ...tOption
 				})
 			})
 		}
+	}
 }
 
 // withNEO tests f on all kinds of NEO servers connected to by NEO client with

go/neo/master.go

@@ -160,7 +160,7 @@ func (_ *_ΔStateCode) δClusterState() {}
 // Use Run to actually start running the node.
 func NewMaster(clusterName string, net xnet.Networker) *Master {
 	return &Master{
-		node: xneo.NewNode(proto.MASTER, clusterName, net, ""),
+		node: xneo.NewNode(proto.MASTER, clusterName, net, []string{}),
 
 		ctlStart:   make(chan chan error),
 		ctlStop:    make(chan chan struct{}),
@@ -219,7 +219,8 @@ func (m *Master) Run(ctx context.Context, l xnet.Listener) (err error) {
 	if err != nil {
 		return err
 	}
-	m.node.MasterAddr = addr.String()
+	// XXX How can this master node know the address of the other master nodes?
+	m.node.MasterAddrSlice = []string{addr.String()}
 	m.node.MyInfo = proto.NodeInfo{
 		Type:	proto.MASTER,
 		Addr:	naddr,

go/neo/mastered.go

-// Copyright (C) 2017-2021  Nexedi SA and Contributors.
+// Copyright (C) 2017-2023  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -84,10 +84,12 @@ const (
 	δPartTabPassThrough _MasteredNodeFlags = 1 << iota
 )
 
-// newMasteredNode creates new _MasteredNode that connects to masterAddr/cluster via net.
-func newMasteredNode(typ proto.NodeType, clusterName string, net xnet.Networker, masterAddr string) *_MasteredNode {
+// newMasteredNode creates new _MasteredNode that connects to masters/cluster via net.
+//
+// Addresses of known masters are specified by masterAddrSlice.
+func newMasteredNode(typ proto.NodeType, clusterName string, net xnet.Networker, masterAddrSlice []string) *_MasteredNode {
 	node := &_MasteredNode{
-		Node: xneo.NewNode(typ, clusterName, net, masterAddr),
+		Node: xneo.NewNode(typ, clusterName, net, masterAddrSlice),
 		opReady: make(chan struct{}),
 	}
 
@@ -108,19 +110,41 @@ func newMasteredNode(typ proto.NodeType, clusterName string, net xnet.Networker,
 func (node *_MasteredNode) TalkMaster(ctx context.Context, f func(context.Context, *_MasterLink) error) (err error) {
 	// start logging with initial NID (that might be temporary, and which master can tell us to change)
 	ctx0 := ctx
-	defer task.Runningf(&ctx, "%s: talk master(%s)", node.MyInfo.NID, node.MasterAddr)(&err)
+
+	// When a node is created with "NewNode", we don't know yet, which of the
+	// the provided master nodes is the primary master. We'll figure this out here
+	// and simply start with the first node.
+	maddr := node.MasterAddrSlice[0]
+
+	defer task.Runningf(&ctx, "%s: talk master(%s)", node.MyInfo.NID, maddr)(&err)
 
 	for {
 		node.updateOperational(func() {
 			node.mlink = nil
 		})
-		err := node.talkMaster1(ctx, ctx0, f)
+		// TODO log "trying maddr as PM"
+		err := node.talkMaster1(ctx, ctx0, maddr, f)
 		log.Warning(ctx, err)	// XXX Warning -> Error?
 		if errors.Is(err, cmdShutdown) {
 			return err // M commands to shutdown
 		}
+
+		// NotPrimaryMaster -> jump to trying what it says is primary
+		var notPrimaryMaster *proto.NotPrimaryMaster
+		if errors.As(err, &notPrimaryMaster) {
+			p := int(notPrimaryMaster.Primary)
+			if !(0 <= p && p < len(notPrimaryMaster.KnownMasterList)) {
+				log.Warning(ctx, "malformed NotPrimaryMaster reply - ignoring")
+			} else {
+				// TODO update masterRegistry from received KnownMasterList
+				primary := notPrimaryMaster.KnownMasterList[p]
+				maddr = primary.Address.String()
+				log.Info(ctx, "switching to try %s as primary master", maddr)
+			}
+		}
+
 		// TODO if err == "reject identification / protocol error" -> shutdown client?
-		// TODO if err == "not a primary" -> try redirected address
+		// TODO if err == "cannot connect" -> start trying other master nodes from MasterAddrSlice
 
 		// exit on cancel / throttle reconnecting
 		select {
@@ -134,7 +158,7 @@ func (node *_MasteredNode) TalkMaster(ctx context.Context, f func(context.Contex
 	}
 }
 
-func (node *_MasteredNode) talkMaster1(ctx, ctxPreTalkM context.Context, f func(context.Context, *_MasterLink) error) error {
+func (node *_MasteredNode) talkMaster1(ctx, ctxPreTalkM context.Context, maddr string, f func(context.Context, *_MasterLink) error) error {
 	reqID := &proto.RequestIdentification{
 		NodeType:	node.MyInfo.Type,
 		NID:		node.MyInfo.NID,
@@ -144,7 +168,7 @@ func (node *_MasteredNode) talkMaster1(ctx, ctxPreTalkM context.Context, f func(
 		DevPath:        nil,                // XXX stub
 		NewNID:         nil,	            // XXX stub
 	}
-	mlink, accept, err := xneo.Dial(ctx, proto.MASTER, node.Net, node.MasterAddr, reqID)
+	mlink, accept, err := xneo.Dial(ctx, proto.MASTER, node.Net, maddr, reqID)
 	if err != nil {
 		return err
 	}

go/neo/proto/proto-misc.go

-// Copyright (C) 2017-2021  Nexedi SA and Contributors.
+// Copyright (C) 2017-2023  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -56,6 +56,19 @@ func (e *Error) Error() string {
 }
 
 
+func (n *NotPrimaryMaster) Error() string {
+	s := "not primary master; primary: "
+	p := int(n.Primary)
+	if 0 <= p && p < len(n.KnownMasterList) {
+		s += n.KnownMasterList[p].String()
+	} else {
+		s += "?"
+	}
+	s += fmt.Sprintf(" ; known masters: %v", n.KnownMasterList)
+	return s
+}
+
+
 // Set sets cluster state value to v.
 //
 // Use Set instead of direct assignment for ClusterState tracing to work.

go/neo/proto/proto-misc_test.go

+// Copyright (C) 2023  Nexedi SA and Contributors.
+//                     Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+package proto
+
+import (
+	"testing"
+)
+
+
+func TestNotPrimaryMasterError(t *testing.T) {
+	var testv = []struct {
+		msg    *NotPrimaryMaster
+		estrok string
+	}{
+		{&NotPrimaryMaster{},
+			"not primary master; primary: ? ; known masters: []",
+		},
+
+		{&NotPrimaryMaster{1, nil},
+			"not primary master; primary: ? ; known masters: []",
+		},
+
+		{&NotPrimaryMaster{1, []struct{Address}{{Address{"α",111}}, {Address{"β",222}}, {Address{"γ",333}}}},
+			"not primary master; primary: β:222 ; known masters: [α:111 β:222 γ:333]",
+		},
+	}
+
+	for _, tt := range testv {
+		estr := tt.msg.Error()
+		if estr != tt.estrok {
+			t.Errorf("%v: invalid error:\nhave: %q\nwant: %q", tt.msg, estr, tt.estrok)
+		}
+	}
+}

go/neo/proto/proto.go

-// Copyright (C) 2006-2021  Nexedi SA and Contributors.
+// Copyright (C) 2006-2023  Nexedi SA and Contributors.
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
 // it under the terms of the GNU General Public License version 3, or (at your
@@ -457,7 +457,7 @@ type AnswerPrimary struct {
 //
 //neo:nodes SM -> *
 type NotPrimaryMaster struct {
-	Primary         NodeID // XXX PSignedNull in py
+	Primary         int32 // index of PM in KnownMasterList
 	KnownMasterList []struct {
 		Address
 	}

go/neo/proto/proto_test.go

-// Copyright (C) 2016-2021  Nexedi SA and Contributors.
+// Copyright (C) 2016-2023  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -356,6 +356,18 @@ func TestMsgMarshal(t *testing.T) {
 			hex("90"),
 		},
 
+		// NotPrimaryMaster (.Primary used to have wrong type)
+		{&NotPrimaryMaster{0x01020304, []struct{Address}{{Address{"m111", 111}}, {Address{"m222", 222}}}},
+			// N
+			u32(0x01020304) + u32(2) + u32(4)+"m111"+u16(111) + u32(4)+"m222"+u16(222),
+			// M
+			hex("92") +
+			hex("d2" + "01020304") +
+			hex("92") +
+				hex("9192") + hex("c4")+u8(4)+"m111" + u8(111) +
+				hex("9192") + hex("c4")+u8(4)+"m222" + hex("ccde"),
+		},
+
 		// TODO we need tests for:
 		// []varsize + trailing
 		// map[]varsize + trailing

go/neo/proto/zproto-marshal.go

@@ -787,7 +787,7 @@ func (p *NotPrimaryMaster) neoMsgEncodedLenN() int {
 }
 
 func (p *NotPrimaryMaster) neoMsgEncodeN(data []byte) {
-	binary.BigEndian.PutUint32(data[0:], uint32(int32(p.Primary)))
+	binary.BigEndian.PutUint32(data[0:], uint32(p.Primary))
 	{
 		l := len(p.KnownMasterList)
 		binary.BigEndian.PutUint32(data[4:], uint32(l))
@@ -807,7 +807,7 @@ func (p *NotPrimaryMaster) neoMsgDecodeN(data []byte) (int, error) {
 	if len(data) < 8 {
 		goto overflow
 	}
-	p.Primary = NodeID(int32(binary.BigEndian.Uint32(data[0 : 0+4])))
+	p.Primary = int32(binary.BigEndian.Uint32(data[0 : 0+4]))
 	{
 		l := binary.BigEndian.Uint32(data[4 : 4+4])
 		data = data[8:]
@@ -836,13 +836,13 @@ func (p *NotPrimaryMaster) neoMsgEncodedLenM() int {
 		a := &p.KnownMasterList[i]
 		size += msgpack.BinHeadSize(len((*a).Address.Host)) + len((*a).Address.Host) + msgpack.Uint16Size((*a).Address.Port)
 	}
-	return 1 + msgpack.Int32Size(int32(p.Primary)) + msgpack.ArrayHeadSize(len(p.KnownMasterList)) + len(p.KnownMasterList)*2 + size
+	return 1 + msgpack.Int32Size(p.Primary) + msgpack.ArrayHeadSize(len(p.KnownMasterList)) + len(p.KnownMasterList)*2 + size
 }
 
 func (p *NotPrimaryMaster) neoMsgEncodeM(data []byte) {
 	data[0] = byte(msgpack.FixArray_4 | 2)
 	{
-		n := msgpack.PutInt32(data[1:], int32(p.Primary))
+		n := msgpack.PutInt32(data[1:], p.Primary)
 		data = data[1+n:]
 	}
 	{
@@ -882,7 +882,7 @@ func (p *NotPrimaryMaster) neoMsgDecodeM(data []byte) (int, error) {
 		if err != nil {
 			return 0, mdecodeErr("NotPrimaryMaster.Primary", err)
 		}
-		p.Primary = NodeID(v)
+		p.Primary = v
 		nread += uint64(len(data) - len(tail))
 		data = tail
 	}

go/neo/py/runneo.py

 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
-# Copyright (C) 2020-2021  Nexedi SA and Contributors.
+# Copyright (C) 2020-2023  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -24,14 +24,14 @@ Usage: runneo.py <workdir> <cluster-name>   [k1=v1] [k2=v2] ...
 
 {k->v} dict is optional arguments for NEOCluster.
 
-<workdir>/ready is created with address of master after spawned cluster becomes
+<workdir>/ready is created with addresses of masters after spawned cluster becomes
 operational.
 """
 
 from neo.tests.functional import NEOCluster
 from golang import func, defer
 
-import sys, os
+import sys, os, json
 from time import sleep
 from signal import signal, SIGTERM
 
@@ -45,6 +45,7 @@ def main():
     kw = {'clear_databases': False} # switch default not to clear data on startup
     for arg in sys.argv[3:]:
         k, v = arg.split('=')
+        v = json.loads(v)
         kw[k] = v
 
 
@@ -79,7 +80,7 @@ def main():
 
     # dump information about ready cluster into readyf
     with open("%s.tmp" % readyf, "w") as f:
-        f.write(cluster.master_nodes)    # XXX ' ' separated if multiple masters
+        f.write(cluster.master_nodes)    # NOTE ' ' separated if multiple masters
     os.rename("%s.tmp" % readyf, readyf) # atomic
 
     def _():

go/neo/storage.go

@@ -61,9 +61,9 @@ type Storage struct {
 //
 // The storage uses back as underlying backend for storing data.
 // Use Run to actually start running the node.
-func NewStorage(clusterName, masterAddr string, net xnet.Networker, back storage.Backend) *Storage {
+func NewStorage(clusterName string, masterAddrSlice []string, net xnet.Networker, back storage.Backend) *Storage {
 	return &Storage{
-		node: newMasteredNode(proto.STORAGE, clusterName, net, masterAddr),
+		node: newMasteredNode(proto.STORAGE, clusterName, net, masterAddrSlice),
 		back: back,
 	}
 }

go/neo/t_cluster_test.go

@@ -319,7 +319,7 @@ func (t *tCluster) Storage(name string) ITestStorage {
 // {New,}Client are similar to {New,}Master but for client nodes.
 func (t *tCluster) NewClient(name, masterAddr string) ITestClient {
 	tnode := t.registerNewNode(name)
-	c := NewClient(t.name, masterAddr, tnode.net)
+	c := NewClient(t.name, []string{masterAddr}, tnode.net)
 	t.gotracer.RegisterNode(c.node.Node, name)
 	t.runWG.Go(func(ctx context.Context) error {
 		return c.Run(ctx)
@@ -346,7 +346,7 @@ type tStorage struct {
 
 func tNewStorage(clusterName, masterAddr, serveAddr string, net xnet.Networker, back storage.Backend) *tStorage {
 	return &tStorage{
-		Storage:   NewStorage(clusterName, masterAddr, net, back),
+		Storage:   NewStorage(clusterName, []string{masterAddr}, net, back),
 		serveAddr: serveAddr,
 	}
 }

go/neo/xneo/connect.go

-// Copyright (C) 2016-2021  Nexedi SA and Contributors.
+// Copyright (C) 2016-2023  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -135,17 +135,43 @@ func Dial(ctx context.Context, typ proto.NodeType, net xnet.Networker, addr stri
 		// start, and if peer sends new connection in that window it will be rejected.
 		//
 		// TODO thinking.
-		err = link.Ask1(reqID, accept)
+
+		conn, err := link.NewConn()
+		if err != nil {
+			return err
+		}
+		defer conn.Close()
+
+		err = conn.Send(reqID)
 		if err != nil {
 			return err
 		}
 
+		// besides AcceptIdentification and Error
+		// also expect NotPrimaryMaster if we are connecting to a master
+		nerr := &proto.Error{}
+		notPrimary := &proto.NotPrimaryMaster{}
+		respv := []proto.Msg{accept, nerr}
+		if typ == proto.MASTER {
+			respv = append(respv, notPrimary)
+		}
+
+		which, err := conn.Expect(respv...)
+
+		switch which {
+		case 0:
 			if accept.NodeType != typ {
 				// TODO send Error to peer?
 				return fmt.Errorf("accepted, but peer is not %s (identifies as %s)", typ, accept.NodeType)
 			}
-
 			return nil
+		case 1:
+			return nerr
+		case 2:
+			return notPrimary
+		}
+		return err
+
 	})
 	if err != nil {
 		return nil, nil, err

go/neo/xneo/xneo.go

@@ -79,7 +79,7 @@ type Node struct {
 	MyInfo          proto.NodeInfo // type, laddr, nid, state, idtime
 	ClusterName     string
 	Net             xnet.Networker // network AP we are sending/receiving on
-	MasterAddr  string         // address of current master  TODO -> masterRegistry
+	MasterAddrSlice []string       // address of all known masters  TODO -> masterRegistry
 
 	// XXX reconsider not using State and have just .NodeTab, .PartTab, .ClusterState
 //	StateMu	sync.RWMutex	// <- XXX unexport ?   XXX not used -> move to MasteredNode ?
@@ -90,7 +90,7 @@ type Node struct {
 }
 
 // NewNode creates new node.
-func NewNode(typ proto.NodeType, clusterName string, net xnet.Networker, masterAddr string) *Node {
+func NewNode(typ proto.NodeType, clusterName string, net xnet.Networker, masterAddrSlice []string) *Node {
 	node := &Node{
 		MyInfo:	proto.NodeInfo{
 			Type:   typ,
@@ -101,7 +101,7 @@ func NewNode(typ proto.NodeType, clusterName string, net xnet.Networker, masterA
 		ClusterName: clusterName,
 
 		Net:             net,
-		MasterAddr: masterAddr,
+		MasterAddrSlice: masterAddrSlice,
 
 		State: ClusterState{
 			NodeTab: &NodeTable{},