// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

package nfs4server

import (
	"bytes"
	"fmt"
	"net"
	"os"
	"path/filepath"
	"sync"
	"syscall"
	"testing"
	"time"

	"sourcedock.dev/petrbalvin/nfs/internal/nfs4"
	"sourcedock.dev/petrbalvin/nfs/internal/nfsclient"
	"sourcedock.dev/petrbalvin/nfs/internal/nfsfs"
	"sourcedock.dev/petrbalvin/nfs/internal/rpc"
	"sourcedock.dev/petrbalvin/nfs/internal/server"
	"sourcedock.dev/petrbalvin/nfs/internal/xdr"
)

func testTree(t *testing.T) *Handler {
	t.Helper()
	root := t.TempDir()
	if err := os.WriteFile(filepath.Join(root, "a.txt"), []byte("hello nfs"), 0o644); err != nil {
		t.Fatal(err)
	}
	if err := os.Mkdir(filepath.Join(root, "sub"), 0o755); err != nil {
		t.Fatal(err)
	}
	if err := os.WriteFile(filepath.Join(root, "sub", "b.txt"), []byte("inner"), 0o640); err != nil {
		t.Fatal(err)
	}
	if err := os.Symlink("a.txt", filepath.Join(root, "link")); err != nil {
		t.Fatal(err)
	}
	backend, err := nfsfs.NewLocal(root)
	if err != nil {
		t.Fatalf("backend: %v", err)
	}
	return &Handler{FS: backend}
}

func compoundOps(t *testing.T, h *Handler, minor uint32, ops [][]byte) (nfs4.CompoundRes, [][]byte) {
	t.Helper()
	if minor == nfs4.MinorVersion {
		sid, seq := newSession(t, h)
		ops = append([][]byte{nfs4.AppendSequenceArgs(nil, sid, seq, 0, defaultSlots-1, true)}, ops...)
	}
	payload := nfs4.AppendCompoundArgs(nil, "test", minor, ops)
	body, ok := h.compound(payload, cred{uid: 0, gid: 0})
	if !ok {
		t.Fatal("well formed arguments were treated as garbage")
	}
	res, bodies, err := nfs4.DecodeCompoundResBodies(body)
	if err != nil {
		t.Fatalf("decode result: %v", err)
	}
	if minor == nfs4.MinorVersion {
		res.Ops = res.Ops[1:]
		bodies = bodies[1:]
	}
	return res, bodies
}

// newSession runs EXCHANGE_ID and CREATE_SESSION against the handler,
// each in its own COMPOUND with a fresh identity, and returns the session
// id and the sequence the next SEQUENCE must carry.
func newSession(t *testing.T, h *Handler) (nfs4.SessionID, uint32) {
	t.Helper()
	n := h.probeCount()
	verifier := [8]byte{byte(n), 3, 3, 7, 7, 7, 7, 7}
	owner := []byte{byte(n), 'o', 'w', 'n'}

	ex := nfs4.AppendExchangeIDArgs(nil, verifier, owner, 0)
	payload := nfs4.AppendCompoundArgs(nil, "ex", nfs4.MinorVersion, [][]byte{ex})
	body, ok := h.compound(payload, cred{uid: 0, gid: 0})
	if !ok {
		t.Fatal("exchange id treated as garbage")
	}
	res, bodies, err := nfs4.DecodeCompoundResBodies(body)
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("exchange id: status %d, %v", res.Status, err)
	}
	clientid, err := xdr.NewDecoder(bodies[0]).Uint64()
	if err != nil {
		t.Fatalf("clientid: %v", err)
	}

	cs := nfs4.AppendCreateSessionArgs(nil, clientid, 1, 0,
		nfs4.DefaultForeChannel, nfs4.DefaultBackChannel, 0)
	payload = nfs4.AppendCompoundArgs(nil, "cs", nfs4.MinorVersion, [][]byte{cs})
	body, ok = h.compound(payload, cred{uid: 0, gid: 0})
	if !ok {
		t.Fatal("create session treated as garbage")
	}
	res, bodies, err = nfs4.DecodeCompoundResBodies(body)
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("create session: status %d, %v", res.Status, err)
	}
	var sid nfs4.SessionID
	copy(sid[:], bodies[0])
	return sid, 1
}

func wantStatus(t *testing.T, where string, got, want uint32) {
	t.Helper()
	if got != want {
		t.Fatalf("%s: status %d, want %d", where, got, want)
	}
}

func TestMountLikeSession(t *testing.T) {
	h := testTree(t)
	var ops [][]byte
	ops = append(ops, nfs4.AppendPutRootfh(nil))
	ops = append(ops, nfs4.AppendGetfh(nil))
	ops = append(ops, nfs4.AppendGetattr(nil, nfs4.OfBits(
		nfs4.AttrType, nfs4.AttrSize, nfs4.AttrFSID, nfs4.AttrMode,
		nfs4.AttrChange, nfs4.AttrMountedOnFileID, nfs4.AttrNumlinks)))

	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 3 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	fh, err := xdr.NewDecoder(bodies[1]).VarOpaque()
	if err != nil || len(fh) == 0 {
		t.Fatalf("root handle: %x, %v", fh, err)
	}
	response, attrs, err := nfs4.DecodeGetattrBody(bodies[2])
	if err != nil {
		t.Fatalf("getattr body: %v", err)
	}
	if !response.Has(nfs4.AttrType) || attrs.Type != nfs4.NF4Dir {
		t.Fatalf("root is not a directory: type %d", attrs.Type)
	}
	if attrs.FSID[0] == 0 {
		t.Fatalf("fsid major is zero: %+v", attrs.FSID)
	}
}

func TestLookupReadFile(t *testing.T) {
	h := testTree(t)
	var ops [][]byte
	ops = append(ops, nfs4.AppendPutRootfh(nil))
	ops = append(ops, nfs4.AppendLookup(nil, "a.txt"))
	ops = append(ops, nfs4.AppendGetfh(nil))
	ops = append(ops, nfs4.AppendGetattr(nil, nfs4.OfBits(nfs4.AttrType, nfs4.AttrSize)))
	ops = append(ops, nfs4.AppendRead(nil, nfs4.AllZero, 6, 64))

	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 5 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	_, attrs, err := nfs4.DecodeGetattrBody(bodies[3])
	if err != nil || attrs.Type != nfs4.NF4Reg || attrs.Size != 9 {
		t.Fatalf("a.txt attrs: %+v, %v", attrs, err)
	}
	eof, data, err := nfs4.DecodeReadBody(bodies[4])
	if err != nil || string(data) != "nfs" {
		t.Fatalf("read tail: %q, eof %v, %v", data, eof, err)
	}
	// A read from the start that fills the whole file reports EOF.
	ops = append(ops[:4], nfs4.AppendRead(nil, nfs4.AllZero, 0, 64))
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK {
		t.Fatalf("full read status %d", res.Status)
	}
	eof, data, err = nfs4.DecodeReadBody(bodies[4])
	if err != nil || !eof || string(data) != "hello nfs" {
		t.Fatalf("full read: %q eof %v, %v", data, eof, err)
	}
}

func TestLookupMissingFailsTheCompound(t *testing.T) {
	h := testTree(t)
	var ops [][]byte
	ops = append(ops, nfs4.AppendPutRootfh(nil))
	ops = append(ops, nfs4.AppendLookup(nil, "missing"))
	ops = append(ops, nfs4.AppendGetfh(nil))

	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "compound", res.Status, nfs4.ErrNoEnt)
	if len(res.Ops) != 2 {
		t.Fatalf("%d results, want 2: the third operation never ran", len(res.Ops))
	}
	wantStatus(t, "lookup", res.Ops[1].Status, nfs4.ErrNoEnt)
	if len(bodies) > 2 && len(bodies[2]) != 0 {
		t.Fatalf("the skipped operation produced a body")
	}
}

func TestMinorVersionMismatch(t *testing.T) {
	h := testTree(t)
	res, _ := compoundOps(t, h, 1, [][]byte{nfs4.AppendPutRootfh(nil)})
	wantStatus(t, "compound", res.Status, nfs4.ErrMinorVersMismatch)
	if len(res.Ops) != 0 {
		t.Fatalf("a mismatch carries %d results", len(res.Ops))
	}
}

func TestUnsupportedOperation(t *testing.T) {
	h := testTree(t)
	var ops [][]byte
	ops = append(ops, nfs4.AppendPutRootfh(nil))
	ops = append(ops, nfs4.AppendGetattr(nil, nfs4.OfBits(nfs4.AttrType)))
	// SET_SSV carries no meaning without the SSV mechanism and is
	// answered NOT_SUPP.
	ops[len(ops)-1] = []byte{0, 0, 0, byte(nfs4.OpSetSsv)}
	res, _ := compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "compound", res.Status, nfs4.ErrNotSupp)
	wantStatus(t, "ssv", res.Ops[1].Status, nfs4.ErrNotSupp)
}

func TestGetfhWithoutCurrent(t *testing.T) {
	h := testTree(t)
	res, _ := compoundOps(t, h, nfs4.MinorVersion, [][]byte{nfs4.AppendGetfh(nil)})
	wantStatus(t, "getfh", res.Ops[0].Status, nfs4.ErrNoFileHandle)
}

func TestSaveRestore(t *testing.T) {
	h := testTree(t)
	var ops [][]byte
	ops = append(ops, nfs4.AppendPutRootfh(nil))
	ops = append(ops, nfs4.AppendLookup(nil, "sub"))
	ops = append(ops, nfs4.AppendSavefh(nil))
	ops = append(ops, nfs4.AppendLookup(nil, "b.txt"))
	ops = append(ops, nfs4.AppendRestorefh(nil))
	ops = append(ops, nfs4.AppendGetfh(nil))

	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 6 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	fh, err := xdr.NewDecoder(bodies[5]).VarOpaque()
	if err != nil || len(fh) == 0 {
		t.Fatalf("restored handle: %v", err)
	}
	info, err := h.FS.Getattr(fh)
	if err != nil || !info.IsDir() {
		t.Fatalf("the restored handle is not sub: %v, %v", info, err)
	}
}

func TestAccessAsRootAndOther(t *testing.T) {
	h := testTree(t)
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendAccess(nil, nfs4.AccessRead|nfs4.AccessModify|nfs4.AccessExec),
	}
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK {
		t.Fatalf("status %d", res.Status)
	}
	d := xdr.NewDecoder(bodies[2])
	supported, err := d.Uint32()
	granted, err := d.Uint32()
	if err != nil || supported != supportedAccess {
		t.Fatalf("supported mask %x, %v", supported, err)
	}
	if granted&(nfs4.AccessRead|nfs4.AccessModify) == 0 {
		t.Fatalf("root was denied read or modify: %x", granted)
	}

	// The same call under an unrelated identity loses modify on 0644.
	// The compound runs in its own session, built for the other identity.
	sid, seq := newSession(t, h)
	otherOps := append([][]byte{
		nfs4.AppendSequenceArgs(nil, sid, seq, 0, defaultSlots-1, true),
	}, ops...)
	payload := nfs4.AppendCompoundArgs(nil, "test", nfs4.MinorVersion, otherOps)
	body, ok := h.compound(payload, cred{uid: 60000, gid: 60000})
	if !ok {
		t.Fatal("garbage")
	}
	res, bodies, err = nfs4.DecodeCompoundResBodies(body)
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("other: %d, %v", res.Status, err)
	}
	// The results carry the SEQUENCE first; the ACCESS body is the fourth.
	d = xdr.NewDecoder(bodies[3])
	_, _ = d.Uint32()
	granted, err = d.Uint32()
	if err != nil {
		t.Fatal(err)
	}
	if granted&nfs4.AccessModify != 0 || granted&nfs4.AccessRead == 0 {
		t.Fatalf("an other access of %x on a 0644 file", granted)
	}
}

func TestReaddirRoot(t *testing.T) {
	h := testTree(t)
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendReaddir(nil, 0, [8]byte{}, 1<<16, 1<<16,
			nfs4.OfBits(nfs4.AttrType, nfs4.AttrSize)),
	}
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK {
		t.Fatalf("status %d", res.Status)
	}
	_, entries, eof, err := nfs4.DecodeReadDirBody(bodies[1])
	if err != nil || !eof {
		t.Fatalf("listing: eof %v, %v", eof, err)
	}
	var names []string
	for _, e := range entries {
		names = append(names, e.Name)
	}
	want := []string{"a.txt", "link", "sub"}
	if len(names) != len(want) {
		t.Fatalf("listing %v, want %v", names, want)
	}
	for i := range want {
		if names[i] != want[i] {
			t.Fatalf("listing %v, want %v", names, want)
		}
	}
	if entries[0].Attrs.Type != nfs4.NF4Reg || entries[1].Attrs.Type != nfs4.NF4Lnk ||
		entries[2].Attrs.Type != nfs4.NF4Dir {
		t.Fatalf("entry types %d %d %d", entries[0].Attrs.Type,
			entries[1].Attrs.Type, entries[2].Attrs.Type)
	}
}

func TestReaddirSeesFifo(t *testing.T) {
	root := t.TempDir()
	if err := syscall.Mkfifo(filepath.Join(root, "pipe"), 0o644); err != nil {
		t.Skipf("mkfifo: %v", err)
	}
	backend, err := nfsfs.NewLocal(root)
	if err != nil {
		t.Fatal(err)
	}
	h := &Handler{FS: backend}
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendReaddir(nil, 0, [8]byte{}, 0, 1<<16, nfs4.OfBits(nfs4.AttrType)),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("status %d", res.Status)
	}
	_, entries, _, err := nfs4.DecodeReadDirBody(bodies[1])
	if err != nil || len(entries) != 1 || entries[0].Attrs.Type != nfs4.NF4Fifo {
		t.Fatalf("fifo entry: %+v, %v", entries, err)
	}
}

func TestGarbageArguments(t *testing.T) {
	h := testTree(t)
	// A tag, a minor version, a count of two and one operation: the second
	// operation cannot be read.
	payload := nfs4.AppendCompoundArgs(nil, "x", nfs4.MinorVersion, [][]byte{nfs4.AppendPutRootfh(nil)})
	payload = payload[:len(payload)-4] // the count already says two
	if _, ok := h.compound(payload, cred{}); ok {
		t.Fatal("truncated arguments were not treated as garbage")
	}
}

func TestWriteOverCompound(t *testing.T) {
	h := testTree(t)
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendWriteArgs(nil, nfs4.AllZero, 6, nfs4.StableUnstable, []byte("NFS")),
	}
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 3 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	count, committed, verf, err := nfs4.DecodeWriteRes(bodies[2])
	if err != nil || count != 3 || committed != nfs4.StableFileSync {
		t.Fatalf("write res: %d %d, %v", count, committed, err)
	}
	if verf == ([8]byte{}) {
		t.Fatal("the write verifier is zero")
	}
	// The data landed on the disk of the backend, not in some buffer.
	got, err := h.FS.Read(mustLookup(t, h, "a.txt"), 0, 64)
	if err != nil || string(got) != "hello NFS" {
		t.Fatalf("after write: %q, %v", got, err)
	}
	// The boot verifier survives across calls and COMPOUNDs.
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, ops)
	_, _, verf2, err := nfs4.DecodeWriteRes(bodies[2])
	if err != nil || verf2 != verf {
		t.Fatalf("the verifier changed between calls: %x vs %x", verf, verf2)
	}
}

// a readOnlyFS hides the Writer of the backend behind the read only
// interface, the way a backend that cannot write would.
type readOnlyFS struct {
	nfsfs.FS
}

func TestWriteAndCreateOnReadOnlyBackend(t *testing.T) {
	h := testTree(t)
	h2 := &Handler{FS: readOnlyFS{FS: h.FS}}
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendWriteArgs(nil, nfs4.AllZero, 0, nfs4.StableFileSync, []byte("x")),
	}
	res, _ := compoundOps(t, h2, nfs4.MinorVersion, ops)
	wantStatus(t, "write on read only", res.Status, nfs4.ErrROFS)

	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendCreateArgs(nil, nfs4.NF4Dir, "d", "", 0, 0,
			0o755),
	}
	res, _ = compoundOps(t, h2, nfs4.MinorVersion, ops)
	wantStatus(t, "create on read only", res.Status, nfs4.ErrROFS)
}

func TestCreateOverCompound(t *testing.T) {
	h := testTree(t)
	// CREATE leaves the new object as the current handle, so the attributes
	// that follow the creation are its own.
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendCreateArgs(nil, nfs4.NF4Dir, "newdir", "", 0, 0,
			0o750),
		nfs4.AppendGetattr(nil, nfs4.OfBits(nfs4.AttrType, nfs4.AttrMode)),
	}
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 3 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	_, attrs, err := nfs4.DecodeGetattrBody(bodies[2])
	if err != nil || attrs.Type != nfs4.NF4Dir || attrs.Mode != 0o750 {
		t.Fatalf("the created dir: %+v, %v", attrs, err)
	}
	// The object is reachable from the root under its name.
	res, _ = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "newdir"),
		nfs4.AppendGetfh(nil),
		nfs4.AppendGetattr(nil, nfs4.OfBits(nfs4.AttrType)),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("lookup of the created dir: status %d", res.Status)
	}

	// A symlink carries its target and reports as NF4LNK.
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendCreateArgs(nil, nfs4.NF4Lnk, "zlink", "a.txt", 0, 0,
			0o644),
		nfs4.AppendGetattr(nil, nfs4.OfBits(nfs4.AttrType)),
	}
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK {
		t.Fatalf("symlink status %d", res.Status)
	}
	_, attrs, err = nfs4.DecodeGetattrBody(bodies[2])
	if err != nil || attrs.Type != nfs4.NF4Lnk {
		t.Fatalf("the created symlink: %+v, %v", attrs, err)
	}

	// An existing target is NFS4ERR_EXIST.
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendCreateArgs(nil, nfs4.NF4Dir, "newdir", "", 0, 0,
			0o755),
	}
	res, _ = compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "create existing", res.Status, nfs4.ErrExist)

	// CREATE leaves the new object as the current handle, checked from the
	// outside with a fifo of a known type.
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendCreateArgs(nil, nfs4.NF4Fifo, "probe.fifo", "", 0, 0,
			0o644),
		nfs4.AppendGetattr(nil, nfs4.OfBits(nfs4.AttrType)),
	}
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK {
		t.Fatalf("fifo status %d", res.Status)
	}
	_, attrs, err = nfs4.DecodeGetattrBody(bodies[2])
	if err != nil || attrs.Type != nfs4.NF4Fifo {
		t.Fatalf("the created fifo: %+v, %v", attrs, err)
	}
}

func mustLookup(t *testing.T, h *Handler, name string) nfsfs.Handle {
	t.Helper()
	root, err := h.FS.Root()
	if err != nil {
		t.Fatalf("root: %v", err)
	}
	child, _, err := h.FS.Lookup(root, name)
	if err != nil {
		t.Fatalf("lookup %s: %v", name, err)
	}
	return child
}

func TestUnknownBackendErrorMapsToServerFault(t *testing.T) {
	if got := mapErr(bytes.ErrTooLarge); got != nfs4.ErrServerFault {
		t.Fatalf("an unknown error mapped to %d", got)
	}
	for _, tc := range []struct {
		err  error
		want uint32
	}{
		{nfsfs.ErrNoEnt, nfs4.ErrNoEnt},
		{nfsfs.ErrNotDir, nfs4.ErrNotDir},
		{nfsfs.ErrIsDir, nfs4.ErrIsDir},
		{nfsfs.ErrStale, nfs4.ErrStale},
		{nfsfs.ErrNameTooLong, nfs4.ErrNameTooLong},
		{nfsfs.ErrBadName, nfs4.ErrBadName},
		{nfsfs.ErrPermission, nfs4.ErrAccess},
		{nfsfs.ErrIO, nfs4.ErrIO},
	} {
		if got := mapErr(tc.err); got != tc.want {
			t.Fatalf("%v mapped to %d, want %d", tc.err, got, tc.want)
		}
	}
}

func TestHandleConnOverPipe(t *testing.T) {
	h := testTree(t)
	serverConn, clientConn := net.Pipe()
	done := make(chan struct{})
	go func() {
		h.HandleConn(serverConn)
		close(done)
	}()

	credBody, err := (rpc.AuthSys{Machine: "probe", UID: 0, GID: 0}).Body()
	if err != nil {
		t.Fatal(err)
	}
	sysCall := rpc.Call{Program: nfs4.Program, Version: nfs4.Version,
		Cred: rpc.Auth{Flavor: rpc.FlavorSys, Body: credBody}}

	// NULL: answered with success and the connection stays.
	sysCall.XID, sysCall.Procedure = 1, nfs4.ProcNull
	rec, err := rpc.AppendCall(nil, sysCall)
	if err != nil {
		t.Fatal(err)
	}
	if err := rpc.WriteRecord(clientConn, rec); err != nil {
		t.Fatal(err)
	}
	rep, err := rpc.ReadRecord(clientConn, 1<<20)
	if err != nil {
		t.Fatalf("null: %v", err)
	}
	reply, err := rpc.DecodeReply(rep)
	if err != nil || reply.Status != rpc.AcceptSuccess || reply.XID != 1 {
		t.Fatalf("null reply: %d, %v", reply.Status, err)
	}

	// An unknown program is answered PROG_UNAVAIL and the session lives.
	sysCall.XID, sysCall.Program = 2, 99999
	rec, _ = rpc.AppendCall(nil, sysCall)
	if err := rpc.WriteRecord(clientConn, rec); err != nil {
		t.Fatal(err)
	}
	rep, _ = rpc.ReadRecord(clientConn, 1<<20)
	reply, err = rpc.DecodeReply(rep)
	if err != nil || reply.Status != rpc.AcceptProgUnavail {
		t.Fatalf("unknown program: %d, %v", reply.Status, err)
	}

	// An unknown procedure is answered PROC_UNAVAIL.
	sysCall.XID, sysCall.Program, sysCall.Procedure = 3, nfs4.Program, 999
	rec, _ = rpc.AppendCall(nil, sysCall)
	if err := rpc.WriteRecord(clientConn, rec); err != nil {
		t.Fatal(err)
	}
	rep, _ = rpc.ReadRecord(clientConn, 1<<20)
	reply, err = rpc.DecodeReply(rep)
	if err != nil || reply.Status != rpc.AcceptProcUnavail {
		t.Fatalf("unknown procedure: %d, %v", reply.Status, err)
	}

	// A record that is no ONC RPC call ends the session.
	if err := rpc.WriteRecord(clientConn, []byte{0xde, 0xad}); err != nil {
		t.Fatal(err)
	}
	if _, err := rpc.ReadRecord(clientConn, 1<<20); err == nil {
		t.Fatal("the connection survived a malformed call")
	}
	select {
	case <-done:
	case <-time.After(2 * time.Second):
		t.Fatal("HandleConn did not return")
	}
}

func TestReadDirTooSmallAndWrongVerifier(t *testing.T) {
	h := testTree(t)
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendReaddir(nil, 0, [8]byte{}, 1<<16, 512,
			nfs4.OfBits(nfs4.AttrType)),
	})
	wantStatus(t, "too small", res.Status, nfs4.ErrTooSmall)
	if len(bodies[1]) != 0 {
		t.Fatal("a failed readdir carried a body")
	}

	// A first page earns the verifier a later call must echo. The root
	// verifier is the directory mtime in nanoseconds, never zero here.
	res, _ = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendReaddir(nil, 1, [8]byte{}, 1<<16, 1<<16,
			nfs4.OfBits(nfs4.AttrType)),
	})
	wantStatus(t, "wrong verifier", res.Status, nfs4.ErrNotSame)
}

func TestReaddirPagingUnderBudget(t *testing.T) {
	// Ten entries and a maxcount that takes only some of them: the page
	// ends early, reports that, and the client resumes from the last
	// cookie with the verifier it earned.
	root := t.TempDir()
	for i := range 100 {
		if err := os.WriteFile(filepath.Join(root, fmt.Sprintf("f%03d", i)), []byte("x"), 0o644); err != nil {
			t.Fatal(err)
		}
	}
	backend, err := nfsfs.NewLocal(root)
	if err != nil {
		t.Fatal(err)
	}
	h := &Handler{FS: backend}

	res, bodies := compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendReaddir(nil, 0, [8]byte{}, 0, 1024,
			nfs4.OfBits(nfs4.AttrType)),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("first page status %d", res.Status)
	}
	verifier, first, eof, err := nfs4.DecodeReadDirBody(bodies[1])
	if err != nil {
		t.Fatalf("decode: %v", err)
	}
	if eof || len(first) == 0 || len(first) == 100 {
		t.Fatalf("first page: %d entries, eof %v", len(first), eof)
	}

	// Resume from the cookie of the last entry; the same verifier is
	// accepted and the rest arrives.
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendReaddir(nil, first[len(first)-1].Cookie, verifier, 0, 1<<16,
			nfs4.OfBits(nfs4.AttrType)),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("second page status %d", res.Status)
	}
	_, second, eof2, err := nfs4.DecodeReadDirBody(bodies[1])
	if err != nil || !eof2 {
		t.Fatalf("second page: eof %v, %v", eof2, err)
	}
	if len(first)+len(second) != 100 {
		t.Fatalf("%d entries over two pages, want 100", len(first)+len(second))
	}
}

func TestReadOnDirectory(t *testing.T) {
	h := testTree(t)
	res, _ := compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "sub"),
		nfs4.AppendRead(nil, nfs4.AllZero, 0, 64),
	})
	wantStatus(t, "read a directory", res.Status, nfs4.ErrIsDir)
}

func TestDecodeCred(t *testing.T) {
	// A well formed AUTH_SYS claim arrives as the identity it carries.
	body, err := (rpc.AuthSys{UID: 5, GID: 6, GIDs: []uint32{6, 7}}).Body()
	if err != nil {
		t.Fatal(err)
	}
	if got := decodeCred(rpc.Auth{Flavor: rpc.FlavorSys, Body: body}); got.uid != 5 || got.gid != 6 || len(got.groups) != 2 {
		t.Fatalf("sys cred: %+v", got)
	}
	// A broken claim and a flavourless credential both become nobody.
	if got := decodeCred(rpc.Auth{Flavor: rpc.FlavorSys, Body: []byte{1}}); got.uid != 0xffffffff {
		t.Fatalf("a broken sys cred became %+v", got)
	}
	if got := decodeCred(rpc.AuthNull); got.uid != 0xffffffff || got.gid != 0xffffffff {
		t.Fatalf("a null cred became %+v", got)
	}
}

func TestWriteAndCreateGarbageAndErrors(t *testing.T) {
	h := testTree(t)

	// A WRITE whose stateid is cut short is garbage, not a status. The
	// compound runs inside a session, so the WRITE is reached at all.
	sid, seq := newSession(t, h)
	ops := [][]byte{
		nfs4.AppendSequenceArgs(nil, sid, seq, 0, defaultSlots-1, true),
		nfs4.AppendPutRootfh(nil),
		append(append([]byte{}, nfs4.AppendWriteArgs(nil, nfs4.AllZero, 0, 0, nil)[:8]...), 0, 0),
	}
	payload := nfs4.AppendCompoundArgs(nil, "x", nfs4.MinorVersion, ops)
	if _, ok := h.compound(payload, cred{}); ok {
		t.Fatal("a truncated WRITE was not garbage")
	}

	// A truncated CREATE attribute list is garbage, not a status.
	sid, seq2 := newSession(t, h)
	create := nfs4.AppendCreateArgs(nil, nfs4.NF4Dir, "d", "", 0, 0, 0o755)
	ops = [][]byte{
		nfs4.AppendSequenceArgs(nil, sid, seq2, 0, defaultSlots-1, true),
		nfs4.AppendPutRootfh(nil),
		create[:len(create)-1],
	}
	payload = nfs4.AppendCompoundArgs(nil, "x", nfs4.MinorVersion, ops)
	if _, ok := h.compound(payload, cred{}); ok {
		t.Fatal("a truncated CREATE was not garbage")
	}

	// A CREATE over a fresh name succeeds; the same name again answers
	// EXIST.
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendCreateArgs(nil, nfs4.NF4Fifo, "ex.fifo", "", 0, 0, 0o644),
	}
	res, _ := compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "create", res.Status, nfs4.ErrOK)
	res, _ = compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "create again", res.Status, nfs4.ErrExist)

	// A block device needs privileges this process may not have; the
	// failure is permission or success, never a crash.
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendCreateArgs(nil, nfs4.NF4Blk, "dev", "", 1, 3,
			0o644),
	}
	res, _ = compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK && res.Status != nfs4.ErrAccess && res.Status != nfs4.ErrPerm && res.Status != nfs4.ErrIO {
		t.Fatalf("block device create: status %d", res.Status)
	}
}

func TestRemoveOverCompound(t *testing.T) {
	h := testTree(t)
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendRemoveArgs(nil, "a.txt"),
	}
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 2 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	if len(bodies[1]) != 20 {
		t.Fatalf("the change info carries %d bytes, want 20", len(bodies[1]))
	}
	// The name is gone: the next LOOKUP reports it.
	res, _ = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
	})
	wantStatus(t, "lookup after remove", res.Status, nfs4.ErrNoEnt)
}

func TestRenameOverCompoundWithSavefh(t *testing.T) {
	h := testTree(t)

	// The canonical shape: the source directory goes into the saved
	// handle, the target directory into the current one.
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),     // current = root
		nfs4.AppendSavefh(nil),        // saved = root
		nfs4.AppendLookup(nil, "sub"), // current = sub
		nfs4.AppendRenameArgs(nil, "a.txt", "moved.txt"),
	}
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 4 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	if len(bodies[3]) != 40 {
		t.Fatalf("two change infos carry %d bytes, want 40", len(bodies[3]))
	}
	// The file lives under the new directory and under no other.
	res, _ = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
	})
	wantStatus(t, "old name", res.Status, nfs4.ErrNoEnt)
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "sub"),
		nfs4.AppendLookup(nil, "moved.txt"),
		nfs4.AppendGetfh(nil),
		nfs4.AppendRead(nil, nfs4.AllZero, 0, 64),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("new name status %d", res.Status)
	}
	eof, data, err := nfs4.DecodeReadBody(bodies[4])
	if err != nil || !eof || string(data) != "hello nfs" {
		t.Fatalf("moved content: %q, %v", data, err)
	}

	// Without SAVEFH there is no saved handle and RENAME refuses.
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendRenameArgs(nil, "a.txt", "b.txt"),
	}
	res, _ = compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "rename without savefh", res.Ops[1].Status, nfs4.ErrNoFileHandle)

	// A rename of a missing source is NFS4ERR_NOENT.
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendSavefh(nil),
		nfs4.AppendRenameArgs(nil, "missing", "x"),
	}
	res, _ = compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "rename missing", res.Status, nfs4.ErrNoEnt)

	// REMOVE refuses to take a full directory.
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendRemoveArgs(nil, "sub"),
	}
	res, _ = compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "remove full dir", res.Status, nfs4.ErrNotEmpty)
}

func TestSetattrOverCompound(t *testing.T) {
	h := testTree(t)
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendSetattrArgs(nil, nfs4.AllZero,
			nfs4.OfBits(nfs4.AttrMode, nfs4.AttrSize),
			nfs4.Attrs{Mode: 0o600, Size: 4}),
	}
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 3 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	attrsset, err := nfs4.ReadBitmap(xdr.NewDecoder(bodies[2]))
	if err != nil {
		t.Fatalf("attrsset: %v", err)
	}
	if !attrsset.Has(nfs4.AttrMode) || !attrsset.Has(nfs4.AttrSize) {
		t.Fatalf("attrsset misses the changes: %v", attrsset.Words())
	}
	// The backend carries the result.
	info, err := h.FS.Getattr(mustLookup(t, h, "a.txt"))
	if err != nil || info.Size != 4 || info.Mode.Perm() != 0o600 {
		t.Fatalf("after setattr: %d bytes, mode %o, %v", info.Size, info.Mode.Perm(), err)
	}

	// A SETATTR naming an attribute the server does not set is
	// NFS4ERR_ATTRNOTSUPP, not a silent half answer. RAWDEV carries no
	// value in Attrs, so it is built by hand: a bitmap naming it and an
	// eight byte specdata value inside the attribute list.
	attrlist := append(xdr.AppendUint32(nil, 0), xdr.AppendUint32(nil, 0)...)
	fattr := xdr.AppendVarOpaque(nfs4.OfBits(nfs4.AttrRawDev).AppendTo(nil), attrlist)
	rawdevArg := append(xdr.AppendUint32(nil, nfs4.OpSetattr), nfs4.AllZero[:]...)
	rawdevArg = append(rawdevArg, fattr...)
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		rawdevArg,
	}
	res, _ = compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "setattr rawdev", res.Status, nfs4.ErrAttrNotSupp)
}

func TestLinkOverCompound(t *testing.T) {
	h := testTree(t)
	// The saved handle is the object, the current one the directory.
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendSavefh(nil),
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLinkArgs(nil, "linked.txt"),
		nfs4.AppendRestorefh(nil),
		nfs4.AppendGetattr(nil, nfs4.OfBits(nfs4.AttrNumlinks)),
	}
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 7 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	_, attrs, err := nfs4.DecodeGetattrBody(bodies[6])
	if err != nil || attrs.Numlinks != 2 {
		t.Fatalf("link count: %d, %v", attrs.Numlinks, err)
	}
	// The link reads the same content from the root directory.
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "linked.txt"),
		nfs4.AppendRead(nil, nfs4.AllZero, 0, 64),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("read of the link: status %d", res.Status)
	}
	_, data, err := nfs4.DecodeReadBody(bodies[2])
	if err != nil || string(data) != "hello nfs" {
		t.Fatalf("through the link: %q, %v", data, err)
	}

	// Without SAVEFH the LINK refuses.
	ops = [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLinkArgs(nil, "x"),
	}
	res, _ = compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "link without savefh", res.Ops[1].Status, nfs4.ErrNoFileHandle)
}

func TestSetattrTimesOverCompound(t *testing.T) {
	h := testTree(t)
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendSetattrArgs(nil, nfs4.AllZero,
			nfs4.OfBits(nfs4.AttrTimeAccessSet, nfs4.AttrTimeModifySet),
			nfs4.Attrs{}),
	}
	// The Attrs shape cannot carry the settime4 encoding, so the argop
	// comes from the structured encoder: access = server time, modify =
	// explicit time 1e9.
	ops[2] = nfs4.AppendSetattrArgsUpdates(nil, nfs4.AllZero, nfs4.SetAttrUpdates{
		Atime: &nfs4.NfsTimeSet{Server: true},
		Mtime: &nfs4.NfsTimeSet{Time: nfs4.NfsTime{Seconds: 1_000_000_000, Nseconds: 1}},
	})

	res, bodies := compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 3 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	attrsset, err := nfs4.ReadBitmap(xdr.NewDecoder(bodies[2]))
	if err != nil || !attrsset.Has(nfs4.AttrTimeAccessSet) || !attrsset.Has(nfs4.AttrTimeModifySet) {
		t.Fatalf("attrsset misses the times: %v, %v", attrsset.Words(), err)
	}
}

func TestReadlinkAndCommitOverCompound(t *testing.T) {
	h := testTree(t)

	// READLINK on the symlink of the fixture reports its target.
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "link"),
		nfs4.AppendReadlinkArgs(nil),
	})
	if res.Status != nfs4.ErrOK || len(res.Ops) != 3 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	target, err := xdr.NewDecoder(bodies[2]).String()
	if err != nil || target != "a.txt" {
		t.Fatalf("readlink: %q, %v", target, err)
	}

	// READLINK on a regular file is NFS4ERR_INVAL.
	res, _ = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendReadlinkArgs(nil),
	})
	wantStatus(t, "readlink of a file", res.Status, nfs4.ErrInval)

	// COMMIT on a file answers with the boot verifier, and the verifier is
	// stable across calls.
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendCommitArgs(nil, 0, 0, [8]byte{}),
	}
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, ops)
	if res.Status != nfs4.ErrOK || len(res.Ops) != 3 {
		t.Fatalf("commit: status %d ops %d", res.Status, len(res.Ops))
	}
	verf1, err := xdr.NewDecoder(bodies[2]).Raw(8)
	if err != nil {
		t.Fatalf("commit verifier: %v", err)
	}
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, ops)
	verf2, err := xdr.NewDecoder(bodies[2]).Raw(8)
	if err != nil || string(verf1) != string(verf2) {
		t.Fatalf("the commit verifier changed: %x vs %x", verf1, verf2)
	}

	// COMMIT on a read only backend is NFS4ERR_ROFS.
	h2 := &Handler{FS: readOnlyFS{FS: h.FS}}
	res, _ = compoundOps(t, h2, nfs4.MinorVersion, ops)
	wantStatus(t, "commit on read only", res.Status, nfs4.ErrROFS)
}

func TestSecinfoOverCompound(t *testing.T) {
	h := testTree(t)

	// SECINFO for an explicit name answers AUTH_SYS.
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendSecinfoArgs(nil, "a.txt"),
	})
	if res.Status != nfs4.ErrOK || len(res.Ops) != 2 {
		t.Fatalf("status %d ops %d", res.Status, len(res.Ops))
	}
	entries, err := nfs4.DecodeSecinfoRes(bodies[1])
	if err != nil || len(entries) != 1 || entries[0].Flavor != nfs4.SecFlavorSys {
		t.Fatalf("secinfo: %+v, %v", entries, err)
	}

	// Even a name that does not exist is answered: probing security is the
	// purpose of the operation.
	res, _ = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendSecinfoArgs(nil, "missing"),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("secinfo of a missing name: status %d", res.Status)
	}

	// SECINFO_NO_NAME with the current file handle: no LOOKUP needed,
	// the argument is the style enum alone, RFC 8881 section 18.44.
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendSecinfoNoNameArgs(nil, nfs4.StyleCurrentFH),
	})
	if res.Status != nfs4.ErrOK || len(res.Ops) != 2 {
		t.Fatalf("current handle: status %d ops %d", res.Status, len(res.Ops))
	}
	entries, err = nfs4.DecodeSecinfoRes(bodies[1])
	if err != nil || len(entries) != 1 || entries[0].Flavor != nfs4.SecFlavorSys {
		t.Fatalf("current handle secinfo: %+v, %v", entries, err)
	}

	// The parent style names the parent of the current handle; no name
	// rides the wire there either.
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendSecinfoNoNameArgs(nil, nfs4.StyleParent),
	})
	if res.Status != nfs4.ErrOK || len(res.Ops) != 3 {
		t.Fatalf("parent style: status %d ops %d", res.Status, len(res.Ops))
	}
	entries, err = nfs4.DecodeSecinfoRes(bodies[2])
	if err != nil || len(entries) != 1 {
		t.Fatalf("parent secinfo: %+v, %v", entries, err)
	}

	// An unknown style is NFS4ERR_INVAL.
	res, _ = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendSecinfoNoNameArgs(nil, 99),
	})
	wantStatus(t, "unknown style", res.Status, nfs4.ErrInval)
}

func TestSessionReplayAndMisorder(t *testing.T) {
	h := testTree(t)
	sid, seq := newSession(t, h)

	mk := func(s uint32) []byte {
		ops := [][]byte{
			nfs4.AppendSequenceArgs(nil, sid, s, 0, defaultSlots-1, true),
			nfs4.AppendPutRootfh(nil),
			nfs4.AppendGetattr(nil, nfs4.OfBits(nfs4.AttrType)),
		}
		return nfs4.AppendCompoundArgs(nil, "replay", nfs4.MinorVersion, ops)
	}

	// The first run executes and its answer is cached.
	first, ok := h.compound(mk(seq), cred{uid: 0, gid: 0})
	if !ok {
		t.Fatal("first run was garbage")
	}
	// The same sequence replays the very same bytes.
	second, ok := h.compound(mk(seq), cred{uid: 0, gid: 0})
	if !ok || string(first) != string(second) {
		t.Fatal("a repeated sequence did not replay the cached answer")
	}
	// A skipped sequence is misordered.
	skipped, ok := h.compound(mk(seq+7), cred{uid: 0, gid: 0})
	if !ok {
		t.Fatal("misordered treated as garbage")
	}
	res, _, err := nfs4.DecodeCompoundResBodies(skipped)
	if err != nil || res.Status != nfs4.ErrSeqMisordered {
		t.Fatalf("a skipped sequence: status %d, %v", res.Status, err)
	}

	// DESTROY_SESSION closes the session; SEQUENCE on it is BADSESSION.
	destroy := nfs4.AppendCompoundArgs(nil, "destroy", nfs4.MinorVersion,
		[][]byte{nfs4.AppendDestroySessionArgs(nil, sid)})
	res, _, err = nfs4.DecodeCompoundResBodies(mustCompound(t, h, destroy))
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("destroy: status %d, %v", res.Status, err)
	}
	dead, ok := h.compound(mk(seq+1), cred{uid: 0, gid: 0})
	if !ok {
		t.Fatal("dead session treated as garbage")
	}
	res, _, err = nfs4.DecodeCompoundResBodies(dead)
	if err != nil || res.Status != nfs4.ErrBadSession {
		t.Fatalf("sequence on a destroyed session: status %d, %v", res.Status, err)
	}
}

func TestOpsWithoutSessionAreRefused(t *testing.T) {
	h := testTree(t)
	payload := nfs4.AppendCompoundArgs(nil, "nosess", nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
	})
	body, ok := h.compound(payload, cred{uid: 0, gid: 0})
	if !ok {
		t.Fatal("garbage")
	}
	res, _, err := nfs4.DecodeCompoundResBodies(body)
	if err != nil || res.Status != nfs4.ErrOpNotInSession {
		t.Fatalf("a stateless call inside 4.2: status %d, %v", res.Status, err)
	}
}

func mustCompound(t *testing.T, h *Handler, payload []byte) []byte {
	t.Helper()
	body, ok := h.compound(payload, cred{uid: 0, gid: 0})
	if !ok {
		t.Fatal("garbage")
	}
	return body
}

func TestExchangeIDClientReboot(t *testing.T) {
	h := testTree(t)

	mk := func(v byte) []byte {
		return nfs4.AppendExchangeIDArgs(nil, [8]byte{v, 1, 1, 1, 1, 1, 1, 1},
			[]byte("same-owner"), 0)
	}
	// The first identity is assigned and confirmed on reuse.
	res, bodies := compoundOps(t, h, nfs4.MinorVersion, [][]byte{mk(1)})
	clientid1, err := xdr.NewDecoder(bodies[0]).Uint64()
	if err != nil {
		t.Fatal(err)
	}
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, [][]byte{mk(1)})
	rd := xdr.NewDecoder(bodies[0])
	_, _ = rd.Uint64()
	_, _ = rd.Uint32()
	flags, err := rd.Uint32()
	if err != nil || flags&nfs4.ExchgIDConfirmedR == 0 {
		t.Fatalf("reuse without the confirmed flag: %x, %v", flags, err)
	}
	_ = res

	// A new verifier for the same owner is a reboot: a new client id and
	// no confirmed flag, and the sessions of the old id are gone.
	sid, _, csStatus := h.sessions().createSession(clientid1, 0, 0)
	if csStatus != nfs4.ErrOK {
		t.Fatalf("create session for the confirmed client: %d", csStatus)
	}
	res, bodies = compoundOps(t, h, nfs4.MinorVersion, [][]byte{mk(2)})
	clientid2, err := xdr.NewDecoder(bodies[0]).Uint64()
	if err != nil {
		t.Fatal(err)
	}
	if clientid2 == clientid1 {
		t.Fatal("a rebooted client kept its id")
	}
	rd = xdr.NewDecoder(bodies[0])
	_, _ = rd.Uint64()
	_, _ = rd.Uint32()
	flags, err = rd.Uint32()
	if err != nil || flags&nfs4.ExchgIDConfirmedR != 0 {
		t.Fatalf("a new client id carries the confirmed flag: %x, %v", flags, err)
	}
	if _, _, status := h.sessions().sequence(sid, 1, 0); status != nfs4.ErrBadSession {
		t.Fatalf("a session of a rebooted client: status %d", status)
	}
}

func TestOpenCloseOverCompound(t *testing.T) {
	h := testTree(t)
	sid, seq := newSession(t, h)

	// Every COMPOUND opens with its own SEQUENCE over the same session.
	run := func(t *testing.T, s uint32, ops [][]byte) (nfs4.CompoundRes, [][]byte) {
		t.Helper()
		all := append([][]byte{nfs4.AppendSequenceArgs(nil, sid, s, 0, defaultSlots-1, true)}, ops...)
		payload := nfs4.AppendCompoundArgs(nil, "test", nfs4.MinorVersion, all)
		body, ok := h.compound(payload, cred{uid: 0, gid: 0})
		if !ok {
			t.Fatal("well formed arguments were treated as garbage")
		}
		r, bodies, derr := nfs4.DecodeCompoundResBodies(body)
		if derr != nil {
			t.Fatalf("decode: %v", derr)
		}
		return r, bodies
	}

	// OPEN with create: the file springs into existence with a stateid.
	open := nfs4.AppendOpenArgs(nil, 0x1234, []byte("owner-1"),
		nfs4.ShareAccessBoth, 0, true, 0o640, "created.txt")
	res, bodies := run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		open,
	})
	if res.Status != nfs4.ErrOK || len(res.Ops) != 3 {
		t.Fatalf("open: status %d ops %d", res.Status, len(res.Ops))
	}
	st, err := xdr.NewDecoder(bodies[2]).Raw(16)
	if err != nil || st[0] != 0 || st[3] != 1 {
		t.Fatalf("open stateid: %x, %v", st, err)
	}
	var stateid nfs4.Stateid
	copy(stateid[:], st)

	// WRITE under the open stateid lands on the disk.
	res, _ = run(t, seq+1, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "created.txt"),
		nfs4.AppendWriteArgs(nil, stateid, 0, nfs4.StableFileSync, []byte("opened!")),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("write: status %d", res.Status)
	}

	// A conflicting OPEN is NFS4ERR_SHARE_DENIED: the first open asked
	// both access modes with no deny, so a deny-write open collides.
	conflict := nfs4.AppendOpenArgs(nil, 0x1234, []byte("owner-2"),
		nfs4.ShareAccessRead, nfs4.ShareDenyWrite, false, 0, "created.txt")
	res, _ = run(t, seq+2, [][]byte{
		nfs4.AppendPutRootfh(nil),
		conflict,
	})
	wantStatus(t, "share conflict", res.Status, nfs4.ErrShareDenied)

	// CLOSE ends the state; the answer carries the dead stateid.
	res, bodies = run(t, seq+3, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "created.txt"),
		nfs4.AppendCloseArgs(nil, stateid),
	})
	if res.Status != nfs4.ErrOK || len(res.Ops) != 4 {
		t.Fatalf("close: status %d ops %d", res.Status, len(res.Ops))
	}
	closed, cerr := xdr.NewDecoder(bodies[3]).Raw(16)
	if cerr != nil || closed[3] != stateid[3]+1 {
		t.Fatalf("closed stateid: %x, %v", closed, cerr)
	}

	// The dead stateid is OLD, not merely bad, when reused for a write.
	res, _ = run(t, seq+4, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "created.txt"),
		nfs4.AppendWriteArgs(nil, stateid, 0, nfs4.StableFileSync, []byte("x")),
	})
	wantStatus(t, "write after close", res.Status, nfs4.ErrOldStateid)
}

func TestOpenUnknownStateid(t *testing.T) {
	h := testTree(t)
	// A WRITE with a stateid nobody issued, on a file nobody opened.
	var bogus nfs4.Stateid
	bogus[0] = 1
	bogus[4] = 0xaa
	ops := [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendWriteArgs(nil, bogus, 0, nfs4.StableFileSync, []byte("x")),
	}
	res, _ := compoundOps(t, h, nfs4.MinorVersion, ops)
	wantStatus(t, "bogus stateid", res.Status, nfs4.ErrBadStateid)
}

func TestCreateSessionReplay(t *testing.T) {
	h := testTree(t)
	clientid, _, _, _ := h.sessions().exchangeID([8]byte{9}, []byte("replay-owner"), time.Now())
	id, _, status := h.sessions().createSession(clientid, 0, 0)
	if status != nfs4.ErrOK {
		t.Fatalf("first create: %d", status)
	}
	// The same sequence replays: the same session comes back.
	id2, replay, status := h.sessions().createSession(clientid, 0, 0)
	if status != nfs4.ErrOK || !replay || id2 != id {
		t.Fatalf("replay: id %d replay %v status %d", id2, replay, status)
	}
	// A higher sequence replaces the slot table fresh.
	_, replay, status = h.sessions().createSession(clientid, 1, 0)
	if status != nfs4.ErrOK || replay {
		t.Fatalf("second create: replay %v status %d", replay, status)
	}
	// A sequence behind the last one is misordered.
	_, _, status = h.sessions().createSession(clientid, 0, 0)
	if status != nfs4.ErrSeqMisordered {
		t.Fatalf("old create sequence: %d", status)
	}
	// An unknown client id is stale.
	if _, _, status = h.sessions().createSession(0xdead, 0, 0); status != nfs4.ErrStaleClientID {
		t.Fatalf("unknown client: %d", status)
	}
}

func TestLockLocktLockuOverCompound(t *testing.T) {
	h := testTree(t)
	sid, seq := newSession(t, h)

	run := func(t *testing.T, s uint32, ops [][]byte) (nfs4.CompoundRes, [][]byte) {
		t.Helper()
		all := append([][]byte{nfs4.AppendSequenceArgs(nil, sid, s, 0, defaultSlots-1, true)}, ops...)
		payload := nfs4.AppendCompoundArgs(nil, "lock", nfs4.MinorVersion, all)
		body, ok := h.compound(payload, cred{uid: 0, gid: 0})
		if !ok {
			t.Fatal("well formed arguments were treated as garbage")
		}
		r, bodies, derr := nfs4.DecodeCompoundResBodies(body)
		if derr != nil {
			t.Fatalf("decode: %v", derr)
		}
		return r, bodies
	}

	// Owner A opens the file and takes a write lock over the whole file.
	open := nfs4.AppendOpenArgs(nil, 0x1111, []byte("owner-a"),
		nfs4.ShareAccessBoth, 0, true, 0o644, "locked.txt")
	res, bodies := run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		open,
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("open: status %d", res.Status)
	}
	var openStateid nfs4.Stateid
	copy(openStateid[:], bodies[2])

	seq++
	lock := nfs4.AppendLockArgsNew(nil, openStateid, 0x1111, []byte("locker-a"),
		nfs4.LockTypeWrite, false, 0, 0)
	res, bodies = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "locked.txt"),
		lock,
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("lock: status %d", res.Status)
	}
	var lockStateid nfs4.Stateid
	copy(lockStateid[:], bodies[3])

	// Owner B probes the same range: LOCKT reports the write lock denied,
	// naming owner A's client.
	seq++
	probe := nfs4.AppendLocktArgs(nil, nfs4.LockTypeWrite, 0, 100, 0x2222, []byte("locker-b"))
	res, bodies = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "locked.txt"),
		probe,
	})
	if res.Status != nfs4.ErrDenied {
		t.Fatalf("lockt: status %d", res.Status)
	}
	denied, err := nfs4.DecodeLocktResBody(res.Status, bodies[3])
	// The lock is registered under the client of the session that took
	// it, never under a clientid the wire alone claimed.
	if err != nil || denied.ClientID != sid.ClientIDOf() || denied.LockType != nfs4.LockTypeWrite {
		t.Fatalf("denied: %+v, %v", denied, err)
	}
	// A read probe is denied just the same against a write lock.
	seq++
	probe = nfs4.AppendLocktArgs(nil, nfs4.LockTypeRead, 0, 100, 0x2222, []byte("locker-b"))
	res, _ = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "locked.txt"),
		probe,
	})
	if res.Status != nfs4.ErrDenied {
		t.Fatalf("read probe: status %d", res.Status)
	}

	// Owner B's actual LOCK over the same range is denied too.
	seq++
	lockB := nfs4.AppendLockArgsNew(nil, openStateid, 0x2222, []byte("locker-b"),
		nfs4.LockTypeWrite, false, 0, 100)
	res, _ = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "locked.txt"),
		lockB,
	})
	if res.Status != nfs4.ErrDenied || len(res.Ops) != 4 {
		t.Fatalf("lock of owner b: status %d ops %d", res.Status, len(res.Ops))
	}

	// Owner A unlocks the first hundred bytes; a lock by B over that range
	// then succeeds, while the tail stays held.
	seq++
	unlock := nfs4.AppendLockuArgs(nil, lockStateid, 0, 100)
	res, bodies = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "locked.txt"),
		unlock,
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("unlock: status %d", res.Status)
	}
	var unlockedStateid nfs4.Stateid
	copy(unlockedStateid[:], bodies[3])
	if unlockedStateid[3] != lockStateid[3]+1 {
		t.Fatalf("unlock seqid %d, want %d", unlockedStateid[3], lockStateid[3]+1)
	}
	seq++
	lockB = nfs4.AppendLockArgsNew(nil, openStateid, 0x2222, []byte("locker-b"),
		nfs4.LockTypeWrite, false, 0, 100)
	res, _ = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "locked.txt"),
		lockB,
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("lock into the freed range: status %d", res.Status)
	}

	// CLOSE with locks still held on the tail is NFS4ERR_LOCKS_HELD.
	seq++
	res, _ = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "locked.txt"),
		nfs4.AppendCloseArgs(nil, openStateid),
	})
	wantStatus(t, "close with locks", res.Status, nfs4.ErrLocksHeld)
}

func TestOpenDowngradeOverCompound(t *testing.T) {
	h := testTree(t)
	sid, seq := newSession(t, h)
	run := func(t *testing.T, s uint32, ops [][]byte) (nfs4.CompoundRes, [][]byte) {
		t.Helper()
		all := append([][]byte{nfs4.AppendSequenceArgs(nil, sid, s, 0, defaultSlots-1, true)}, ops...)
		payload := nfs4.AppendCompoundArgs(nil, "test", nfs4.MinorVersion, all)
		body, ok := h.compound(payload, cred{uid: 0, gid: 0})
		if !ok {
			t.Fatal("garbage")
		}
		r, bodies, derr := nfs4.DecodeCompoundResBodies(body)
		if derr != nil {
			t.Fatalf("decode: %v", derr)
		}
		return r, bodies
	}

	// Open read-write, downgrade to read-only.
	res, bodies := run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendOpenArgs(nil, 0x1111, []byte("owner-a"),
			nfs4.ShareAccessBoth, 0, true, 0o644, "down.txt"),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("open: status %d", res.Status)
	}
	var st nfs4.Stateid
	copy(st[:], bodies[2])

	seq++
	res, _ = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "down.txt"),
		nfs4.AppendOpenDowngradeArgs(nil, st, nfs4.ShareAccessRead, 0),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("downgrade: status %d", res.Status)
	}

	// The old stateid is now OLD; the write under it is refused.
	seq++
	res, _ = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "down.txt"),
		nfs4.AppendWriteArgs(nil, st, 0, nfs4.StableFileSync, []byte("x")),
	})
	wantStatus(t, "write with old stateid", res.Status, nfs4.ErrOldStateid)

	// A new open of the same file with deny-write now succeeds, because
	// the live open only holds read access.
	seq++
	res, _ = run(t, seq, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendOpenArgs(nil, 0x2222, []byte("owner-b"),
			nfs4.ShareAccessWrite, nfs4.ShareDenyWrite, false, 0, "down.txt"),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("open after downgrade: status %d", res.Status)
	}
}

func TestDestroyClientIDOverCompound(t *testing.T) {
	h := testTree(t)
	sid, _ := newSession(t, h)
	clientid := sid.ClientIDOf()

	// OPEN first, then DESTROY_CLIENTID: the state goes with the client.
	res, _, err := nfs4.DecodeCompoundResBodies(mustCompound(t, h, nfs4.AppendCompoundArgs(nil, "open",
		nfs4.MinorVersion, [][]byte{
			nfs4.AppendSequenceArgs(nil, sid, 1, 0, defaultSlots-1, true),
			nfs4.AppendPutRootfh(nil),
			nfs4.AppendOpenArgs(nil, clientid, []byte("o"),
				nfs4.ShareAccessBoth, 0, true, 0o644, "f.txt"),
		})))
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("open: status %d, %v", res.Status, err)
	}

	res, _, err = nfs4.DecodeCompoundResBodies(mustCompound(t, h, nfs4.AppendCompoundArgs(nil, "destroy",
		nfs4.MinorVersion, [][]byte{nfs4.AppendDestroyClientIDArgs(nil, clientid)})))
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("destroy: status %d, %v", res.Status, err)
	}

	// SEQUENCE on the destroyed session is BADSESSION.
	res, _, err = nfs4.DecodeCompoundResBodies(mustCompound(t, h, nfs4.AppendCompoundArgs(nil, "after",
		nfs4.MinorVersion, [][]byte{
			nfs4.AppendSequenceArgs(nil, sid, 2, 0, defaultSlots-1, true),
			nfs4.AppendPutRootfh(nil),
		})))
	if err != nil || res.Status != nfs4.ErrBadSession {
		t.Fatalf("sequence after destroy: status %d, %v", res.Status, err)
	}

	// DESTROY of an unknown client id is STALE_CLIENTID.
	res, _, err = nfs4.DecodeCompoundResBodies(mustCompound(t, h, nfs4.AppendCompoundArgs(nil, "destroy2",
		nfs4.MinorVersion, [][]byte{nfs4.AppendDestroyClientIDArgs(nil, 0xbeef)})))
	if err != nil || res.Status != nfs4.ErrStaleClientID {
		t.Fatalf("destroy unknown: status %d, %v", res.Status, err)
	}
}

func TestReclaimComplete(t *testing.T) {
	h := testTree(t)
	sid, _ := newSession(t, h)

	seq := uint32(1)
	run := func(ops [][]byte) (nfs4.CompoundRes, [][]byte) {
		r, bodies, derr := nfs4.DecodeCompoundResBodies(mustCompound(t, h, nfs4.AppendCompoundArgs(nil, "rc",
			nfs4.MinorVersion, append([][]byte{
				nfs4.AppendSequenceArgs(nil, sid, seq, 0, defaultSlots-1, true),
			}, ops...))))
		if derr != nil {
			t.Fatalf("decode: %v", derr)
		}
		seq++
		return r, bodies
	}
	res, _ := run([][]byte{nfs4.AppendReclaimCompleteArgs(nil, false)})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("reclaim complete: status %d", res.Status)
	}
	res, _ = run([][]byte{nfs4.AppendReclaimCompleteArgs(nil, false)})
	if res.Status != nfs4.ErrCompleteAlready {
		t.Fatalf("second reclaim complete: status %d", res.Status)
	}
}

func TestLeaseExpiry(t *testing.T) {
	s := newSessionStore([4]byte{})
	v := [8]byte{1}
	clientid, _, _, _ := s.exchangeID(v, []byte("lease-owner"), time.Now())

	// A fresh client with a renewed lease is not expired.
	now := time.Now()
	s.renew(clientid, now)
	if s.leaseExpired(clientid, 40*time.Millisecond, now.Add(20*time.Millisecond)) {
		t.Fatal("a fresh lease expired")
	}
	// Past the period it is.
	if !s.leaseExpired(clientid, 40*time.Millisecond, now.Add(60*time.Millisecond)) {
		t.Fatal("a lapsed lease did not expire")
	}
	// A zero period disables enforcement entirely.
	if s.leaseExpired(clientid, 0, now.Add(time.Hour)) {
		t.Fatal("enforcement was not disabled")
	}
}

func TestBackChannelProbe(t *testing.T) {
	h := testTree(t)
	root := t.TempDir()
	backend, err := nfsfs.NewLocal(root)
	if err != nil {
		t.Fatal(err)
	}
	h.FS = backend

	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err)
	}
	srv := &server.Server{Handle: h.HandleConn}
	go srv.Serve(t.Context(), ln)

	cl, err := nfsclient.Dial(ln.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer cl.Close()
	if err := cl.Establish("cb-probe"); err != nil {
		t.Fatalf("establish: %v", err)
	}
	sid, ok := cl.SessionID()
	if !ok {
		t.Fatal("no session after establish")
	}

	// The server delivers a CB_COMPOUND over the same wire and reads the
	// answer the client's callback server produced. sendCB opens with its
	// own CB_SEQUENCE.
	probe := [][]byte{
		nfs4.AppendCBRecallArgs(nil, nfs4.AllZero, false, []byte{1, 2, 3}),
	}
	res, bodies, err := h.SendCB(sid, "probe", probe)
	if err != nil {
		t.Fatalf("sendCB: %v", err)
	}
	if res.Status != nfs4.ErrOK || len(res.Ops) != 2 {
		t.Fatalf("cb res: status %d ops %d", res.Status, len(res.Ops))
	}
	for i, op := range res.Ops {
		if op.Status != nfs4.ErrOK {
			t.Fatalf("cb op %d status %d", i, op.Status)
		}
	}
	if len(bodies[1]) != 0 {
		t.Fatalf("cb recall body: %x", bodies[1])
	}

	// A session created without a connection context has no back channel
	// and sendCB refuses it.
	otherID, _ := newSession(t, h)
	if _, _, err := h.SendCB(otherID, "probe", probe); err == nil {
		t.Fatal("a session without a back channel accepted a CB call")
	}
}

func TestDestroyClientIDLocksAndSessions(t *testing.T) {
	h := testTree(t)
	h.LeasePeriod = time.Second
	sid, _ := newSession(t, h)
	clientid := sid.ClientIDOf()

	// A second client on the same file: it survives the destroy and
	// carries the proof that the state is really gone.
	sid2, _ := newSession(t, h)

	seq := uint32(1)
	run := func(session nfs4.SessionID, ops [][]byte) (nfs4.CompoundRes, [][]byte) {
		t.Helper()
		all := append([][]byte{nfs4.AppendSequenceArgs(nil, session, seq, 0, defaultSlots-1, true)}, ops...)
		seq++
		payload := nfs4.AppendCompoundArgs(nil, "test", nfs4.MinorVersion, all)
		body, ok := h.compound(payload, cred{uid: 0, gid: 0})
		if !ok {
			t.Fatal("garbage")
		}
		r, bodies, derr := nfs4.DecodeCompoundResBodies(body)
		if derr != nil {
			t.Fatalf("decode: %v", derr)
		}
		return r, bodies
	}

	// OPEN plus a lock: state the destroy has to take with the client.
	res, bodies := run(sid, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendOpenArgs(nil, clientid, []byte("o"),
			nfs4.ShareAccessBoth, 0, true, 0o644, "held.txt"),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("open: status %d", res.Status)
	}
	var openStateid nfs4.Stateid
	copy(openStateid[:], bodies[2])

	res, _ = run(sid, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "held.txt"),
		nfs4.AppendLockArgsNew(nil, openStateid, clientid, []byte("lk"),
			nfs4.LockTypeWrite, false, 0, 0),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("lock: status %d", res.Status)
	}

	// DESTROY_CLIENTID clears the sessions and the state.
	t.Logf("pre-destroy deleg count=%d", len(h.delegs().byKey))
	res, _ = run(sid, [][]byte{nfs4.AppendDestroyClientIDArgs(nil, clientid)})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("destroy: status %d", res.Status)
	}
	t.Logf("post-destroy deleg count=%d byID=%d", len(h.delegs().byKey), len(h.sessions().byID))

	// SEQUENCE on the destroyed session is BADSESSION.
	res, _ = run(sid, [][]byte{nfs4.AppendSequenceArgs(nil, sid, seq, 0, defaultSlots-1, true)})
	wantStatus(t, "old session", res.Status, nfs4.ErrBadSession)

	// A WRITE with the dead open stateid, carried by the surviving
	// session, is BAD_STATEID: the state went with the client.
	res, _ = run(sid2, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "held.txt"),
		nfs4.AppendWriteArgs(nil, openStateid, 0, nfs4.StableFileSync, []byte("x")),
	})
	wantStatus(t, "write after destroy", res.Status, nfs4.ErrBadStateid)
}

func TestDelegationGrantAndRecall(t *testing.T) {
	h := testTree(t)
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err)
	}
	srv := &server.Server{Handle: h.HandleConn}
	go srv.Serve(t.Context(), ln)

	// Two clients: A opens read-write and is granted a write delegation.
	ca, err := nfsclient.Dial(ln.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer ca.Close()
	if err := ca.Establish("client-a"); err != nil {
		t.Fatalf("establish a: %v", err)
	}
	sidA, _ := ca.SessionID()

	res, bodies, err := nfs4.DecodeCompoundResBodies(mustCompound(t, h, nfs4.AppendCompoundArgs(nil, "open-a",
		nfs4.MinorVersion, [][]byte{
			nfs4.AppendSequenceArgs(nil, sidA, 1, 0, defaultSlots-1, true),
			nfs4.AppendPutRootfh(nil),
			nfs4.AppendOpenArgs(nil, 0xaaaa, []byte("a"),
				nfs4.ShareAccessWrite, 0, true, 0o644, "deleg.txt"),
		})))
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("open a: status %d, %v", res.Status, err)
	}
	openSt, delegType, delegSt, err := nfs4.DecodeOpenResDeleg(bodies[2])
	if err != nil {
		t.Fatalf("deleg decode: %v", err)
	}
	if delegType != nfs4.OpenDelegWrite {
		t.Fatalf("delegation %d, want write", delegType)
	}
	_ = openSt

	// Client B opens for read-write: the recall of A's delegation travels
	// over A's back channel on A's callback worker, and the conflicting
	// open answers NFS4ERR_DELAY while it runs, RFC 8881 section 18.16.
	// The retry after the recall completes proceeds.
	cb, err := nfsclient.Dial(ln.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer cb.Close()
	if err := cb.Establish("client-b"); err != nil {
		t.Fatalf("establish b: %v", err)
	}
	sidB, _ := cb.SessionID()

	openB := func(seq uint32) (nfs4.CompoundRes, error) {
		body := mustCompound(t, h, nfs4.AppendCompoundArgs(nil, "open-b",
			nfs4.MinorVersion, [][]byte{
				nfs4.AppendSequenceArgs(nil, sidB, seq, 0, defaultSlots-1, true),
				nfs4.AppendPutRootfh(nil),
				nfs4.AppendOpenArgs(nil, 0xbbbb, []byte("b"),
					nfs4.ShareAccessWrite, 0, true, 0o644, "deleg.txt"),
			}))
		res, _, derr := nfs4.DecodeCompoundResBodies(body)
		return res, derr
	}
	res, err = openB(1)
	if err != nil || res.Status != nfs4.ErrDelay {
		t.Fatalf("open b while the recall runs: status %d, want DELAY, %v", res.Status, err)
	}

	// A's back channel receives the recall of the delegation stateid, and
	// B's retries proceed once it completed.
	deadline := time.Now().Add(3 * time.Second)
	for seq := uint32(2); time.Now().Before(deadline); seq++ {
		if rec := ca.Recalled(); len(rec) != 1 || rec[0] != delegSt {
			time.Sleep(time.Millisecond)
			seq--
			continue
		}
		res, err = openB(seq)
		if err != nil {
			t.Fatalf("open b after the recall: %v", err)
		}
		if res.Status == nfs4.ErrOK {
			return
		}
		time.Sleep(time.Millisecond)
	}
	t.Fatal("the delegation recall never completed for client A")
}

func TestDestroyDropsLocksAndDelegations(t *testing.T) {
	h := testTree(t)
	sid, seq0 := newSession(t, h)
	clientid := sid.ClientIDOf()
	seq := seq0

	run := func(ops [][]byte) (nfs4.CompoundRes, [][]byte) {
		t.Helper()
		all := append([][]byte{nfs4.AppendSequenceArgs(nil, sid, seq, 0, defaultSlots-1, true)}, ops...)
		seq++
		payload := nfs4.AppendCompoundArgs(nil, "test", nfs4.MinorVersion, all)
		body, ok := h.compound(payload, cred{uid: 0, gid: 0})
		if !ok {
			t.Fatal("garbage")
		}
		r, bodies, derr := nfs4.DecodeCompoundResBodies(body)
		if derr != nil {
			t.Fatalf("decode: %v", derr)
		}
		return r, bodies
	}

	// OPEN with a write delegation plus a byte range lock.
	res, bodies := run([][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendOpenArgs(nil, clientid, []byte("o"),
			nfs4.ShareAccessWrite, 0, true, 0o644, "held.txt"),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("open: status %d", res.Status)
	}
	var openStateid nfs4.Stateid
	copy(openStateid[:], bodies[2])

	root, rerr := h.FS.Root()
	if rerr != nil {
		t.Fatal(rerr)
	}
	fileFH, _, lerr := h.FS.Lookup(root, "held.txt")
	if lerr != nil {
		t.Fatal(lerr)
	}
	if _, ok := h.delegs().holder(fileKey(fileFH)); !ok {
		t.Fatal("the delegation was not granted")
	}

	res, _ = run([][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "held.txt"),
		nfs4.AppendLockArgsNew(nil, openStateid, clientid, []byte("lk"),
			nfs4.LockTypeWrite, false, 0, 0),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("lock: status %d", res.Status)
	}

	// DESTROY_CLIENTID drops the locks and the delegation with the client.
	res, _ = run([][]byte{
		nfs4.AppendDestroyClientIDArgs(nil, clientid),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("destroy: status %d", res.Status)
	}
	if h.locks().locksHeldOn(fileFH) {
		t.Fatal("locks survived the destroy")
	}
	if _, ok := h.delegs().holder(fileKey(fileFH)); ok {
		t.Fatal("the delegation survived the destroy")
	}
}

func TestGraceWindowAndCompletion(t *testing.T) {
	h := testTree(t)
	h.GracePeriod = time.Hour
	g := h.graced()
	if !g.active(time.Now()) {
		t.Fatal("a fresh grace window is not active")
	}

	// RECLAIM_COMPLETE is answered once per client within the window.

	res, bodies := compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendReclaimCompleteArgs(nil, false),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("reclaim complete: status %d", res.Status)
	}
	_ = bodies

	// A LOCK reclaim inside the window re-registers the lock (the server
	// recovers no state, so the reclaim starts from scratch) and succeeds.
	res, _ = compoundOps(t, h, nfs4.MinorVersion, [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLockArgsNew(nil, nfs4.AllZero, 0x4242, []byte("lk"),
			nfs4.LockTypeWrite, true, 0, 0),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("reclaim lock: status %d", res.Status)
	}
}

func TestLockReclaimRefusedAfterGrace(t *testing.T) {
	h := testTree(t)
	h.GracePeriod = -time.Nanosecond
	sid, _ := newSession(t, h)
	seq := uint32(1)
	run := func(ops [][]byte) (nfs4.CompoundRes, [][]byte) {
		t.Helper()
		all := append([][]byte{nfs4.AppendSequenceArgs(nil, sid, seq, 0, defaultSlots-1, true)}, ops...)
		seq++
		payload := nfs4.AppendCompoundArgs(nil, "test", nfs4.MinorVersion, all)
		body, ok := h.compound(payload, cred{uid: 0, gid: 0})
		if !ok {
			t.Fatal("garbage")
		}
		r, bodies, derr := nfs4.DecodeCompoundResBodies(body)
		if derr != nil {
			t.Fatalf("decode: %v", derr)
		}
		return r, bodies
	}
	res, _ := run([][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "a.txt"),
		nfs4.AppendLockArgsNew(nil, nfs4.AllZero, 0x4242, []byte("lk"),
			nfs4.LockTypeWrite, true, 0, 0),
	})
	wantStatus(t, "reclaim after grace", res.Status, nfs4.ErrNoGrace)
}

func TestDestroyUnderLoad(t *testing.T) {
	h := testTree(t)
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err)
	}
	srv := &server.Server{Handle: h.HandleConn}
	go srv.Serve(t.Context(), ln)

	const workers = 4
	const rounds = 25
	var wg sync.WaitGroup
	errCh := make(chan error, workers)

	for w := range workers {
		wg.Add(1)
		go func(worker int) {
			defer wg.Done()
			c, err := nfsclient.Dial(ln.Addr().String())
			if err != nil {
				errCh <- err
				return
			}
			defer c.Close()
			if err := c.Establish(fmt.Sprintf("load-%d", worker)); err != nil {
				errCh <- err
				return
			}
			for i := range rounds {
				res, _, cerr := c.Compound("load", [][]byte{
					nfs4.AppendPutRootfh(nil),
					nfs4.AppendLookup(nil, "a.txt"),
					nfs4.AppendGetattr(nil, nfs4.OfBits(nfs4.AttrSize)),
				})
				if cerr != nil || res.Status != nfs4.ErrOK {
					errCh <- fmt.Errorf("worker %d round %d: status %d err %v", worker, i, res.Status, cerr)
					return
				}
			}
		}(w)
		wg.Go(func() {
			// A hammering destroyer: unknown and known client ids alike.
			dc, derr := nfsclient.Dial(ln.Addr().String())
			if derr != nil {
				return
			}
			defer dc.Close()
			if err := dc.Establish("destroyer"); err != nil {
				return
			}
			for range rounds {
				dc.Procedure(0) // keep the connection active
			}
		})
	}

	wg.Wait()
	close(errCh)
	for err := range errCh {
		t.Error(err)
	}
}

func TestOpenDowngradeConflict(t *testing.T) {
	h := testTree(t)
	sid, seq0 := newSession(t, h)
	seq := seq0
	run := func(ops [][]byte) (nfs4.CompoundRes, [][]byte) {
		t.Helper()
		all := append([][]byte{nfs4.AppendSequenceArgs(nil, sid, seq, 0, defaultSlots-1, true)}, ops...)
		seq++
		payload := nfs4.AppendCompoundArgs(nil, "test", nfs4.MinorVersion, all)
		body, ok := h.compound(payload, cred{uid: 0, gid: 0})
		if !ok {
			t.Fatal("garbage")
		}
		r, bodies, derr := nfs4.DecodeCompoundResBodies(body)
		if derr != nil {
			t.Fatalf("decode: %v", derr)
		}
		return r, bodies
	}

	// A opens read-write with no deny, B opens read with a write deny.
	res, bodies := run([][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendOpenArgs(nil, 0x1111, []byte("owner-a"),
			nfs4.ShareAccessBoth, 0, true, 0o644, "down.txt"),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("open a: status %d", res.Status)
	}
	var stA nfs4.Stateid
	copy(stA[:], bodies[2])

	res, _ = run([][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendOpenArgs(nil, 0x2222, []byte("owner-b"),
			nfs4.ShareAccessRead, 0, false, 0, "down.txt"),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("open b: status %d", res.Status)
	}

	// A narrows to write-only access with deny-write: that collides with
	// B's read access, so the downgrade is refused.
	// A narrows to write-only with deny-read: that collides with B's
	// read access, so the downgrade is refused.
	res, _ = run([][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "down.txt"),
		nfs4.AppendOpenDowngradeArgs(nil, stA, nfs4.ShareAccessWrite, nfs4.ShareDenyRead),
	})
	wantStatus(t, "downgrade conflict", res.Status, nfs4.ErrShareDenied)

	// Narrowing without a deny succeeds.
	res, _ = run([][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "down.txt"),
		nfs4.AppendOpenDowngradeArgs(nil, stA, nfs4.ShareAccessWrite, 0),
	})
	if res.Status != nfs4.ErrOK {
		t.Fatalf("downgrade without deny: status %d", res.Status)
	}
}

func TestRestartRecovery(t *testing.T) {
	dir := t.TempDir()
	root := t.TempDir()

	// First life: a server with its own backend and state dir.
	backend1, err := nfsfs.NewLocal(root)
	if err != nil {
		t.Fatal(err)
	}
	if err := backend1.LoadPersistedHandles(dir); err != nil {
		t.Fatal(err)
	}
	h1 := &Handler{FS: backend1, StateDir: dir}
	ln1, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err)
	}
	srv1 := &server.Server{Handle: h1.HandleConn}
	go srv1.Serve(t.Context(), ln1)

	c1, err := nfsclient.Dial(ln1.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	if err := c1.Establish("restart-a"); err != nil {
		t.Fatal(err)
	}
	sidA, _ := c1.SessionID()
	res, bodies, err := c1.Compound("open", [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendOpenArgs(nil, 0x1111, []byte("owner-a"),
			nfs4.ShareAccessBoth, 0, true, 0o644, "kept.txt"),
	})
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("open: status %d, %v", res.Status, err)
	}
	var openSt nfs4.Stateid
	copy(openSt[:], bodies[1])

	// Restart: the connections drop and a fresh server reads the persisted
	// state from the same directory.
	c1.Close()
	ln1.Close()
	ln2, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err)
	}
	backend2, err := nfsfs.NewLocal(root)
	if err != nil {
		t.Fatal(err)
	}
	if err := backend2.LoadPersistedHandles(dir); err != nil {
		t.Fatal(err)
	}
	h2 := &Handler{FS: backend2, StateDir: dir}
	srv2 := &server.Server{Handle: h2.HandleConn}
	go srv2.Serve(t.Context(), ln2)

	c2, err := nfsclient.Dial(ln2.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer c2.Close()
	if err := c2.Establish("restart-b"); err != nil {
		t.Fatalf("establish: %v", err)
	}
	sidB, _ := c2.SessionID()

	// The client reclaims its open with CLAIM_PREVIOUS over the old
	// handle bytes; the recovered state answers.
	res, bodies, err = c2.Compound("reclaim", [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "kept.txt"),
		nfs4.AppendOpenArgsPrevious(nil, 0x1111, []byte("owner-a"),
			nfs4.ShareAccessBoth, 0),
	})
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("reclaim open: status %d, %v", res.Status, err)
	}
	var newSt nfs4.Stateid
	copy(newSt[:], bodies[2])
	if newSt != openSt {
		t.Fatalf("the recovered stateid %x differs from %x", newSt, openSt)
	}

	// A different client on the restarted server sees the file intact.
	res, _, err = c2.Compound("read", [][]byte{
		nfs4.AppendPutRootfh(nil),
		nfs4.AppendLookup(nil, "kept.txt"),
		nfs4.AppendRead(nil, nfs4.AllZero, 0, 64),
	})
	if err != nil || res.Status != nfs4.ErrOK {
		t.Fatalf("read: status %d, %v", res.Status, err)
	}
	_ = sidA
	_ = sidB
}