X ΔFtail: Rebuild vδE after first track

This is needed to detect where the file was created and indicate with
δF.Epoch=true correspondingly.

wcfs/internal/zdata/δftail.go

@@ -83,7 +83,10 @@ type ΔFtail struct {
 	// ΔFtail merges ΔBtail with history of ZBlk
 	δBtail  *xbtree.ΔBtail
 	fileIdx map[zodb.Oid]setOid      // tree-root -> {} ZBigFile<oid>  as of @head  XXX -> root2file ?
-	byFile  map[zodb.Oid]*_ΔFileTail // file -> δf tail	XXX
+	byFile  map[zodb.Oid]*_ΔFileTail // file -> vδf tail	XXX
+
+	// set of files, which are newly tracked and for which vδE was not yet rebuilt
+	trackNew setOid // {}foid
 
 	trackSetZBlk  map[zodb.Oid]*zblkTrack // zblk -> {} root -> {}blk	as of @head
 }
@@ -137,6 +140,7 @@ func NewΔFtail(at0 zodb.Tid, db *zodb.DB) *ΔFtail {
 		δBtail:        xbtree.NewΔBtail(at0, db),
 		fileIdx:       map[zodb.Oid]setOid{},
 		byFile:        map[zodb.Oid]*_ΔFileTail{},
+		trackNew:      setOid{},
 		trackSetZBlk:  map[zodb.Oid]*zblkTrack{},
 	}
 }
@@ -184,6 +188,7 @@ func (δFtail *ΔFtail) Track(file *ZBigFile, blk int64, path []btree.LONode, zb
 	if !ok {
 		δftail = &_ΔFileTail{root: roid, vδE: nil /*will need to be rebuilt till past*/}
 		δFtail.byFile[foid] = δftail
+		δFtail.trackNew.Add(foid)
 	}
 	if δftail.root != roid {
 		panicf("zfile<%s> changed root from %s -> %s", foid, δftail.root, roid)
@@ -211,6 +216,90 @@ func (δFtail *ΔFtail) Track(file *ZBigFile, blk int64, path []btree.LONode, zb
 	}
 }
 
+// rebuildAll rebuilds vδE for all files from trackNew requests.
+func (δFtail *ΔFtail) rebuildAll() (err error) {
+	defer xerr.Contextf(&err, "ΔFtail rebuildAll")
+	// XXX locking
+
+	for foid := range δFtail.trackNew {
+		delete(δFtail.trackNew, foid)
+		δftail := δFtail.byFile[foid]
+		δBtail := δFtail.δBtail
+		err := δftail.rebuild1(foid, δBtail.ΔZtail(), δBtail.DB())
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// rebuildIfNeeded rebuilds vδE if there is such need.
+//
+// it returns corresponding δftail for convenience.
+// the only case when vδE actually needs to be rebuilt is when the file just started to be tracked.
+func (δFtail *ΔFtail) rebuildIfNeeded(foid zodb.Oid) (_ *_ΔFileTail, err error) {
+	// XXX locking
+
+	δftail := δFtail.byFile[foid]
+	if δftail.vδE != nil {
+		err = nil
+	} else {
+		δBtail := δFtail.δBtail
+		err = δftail.rebuild1(foid, δBtail.ΔZtail(), δBtail.DB())
+	}
+	return δftail, err
+}
+
+// rebuild rebuilds vδE.
+func (δftail *_ΔFileTail) rebuild1(foid zodb.Oid, δZtail *zodb.ΔTail, db *zodb.DB) (err error) {
+	defer xerr.Contextf(&err, "file<%s>: rebuild", foid)
+
+	// XXX locking
+	if δftail.vδE != nil {
+		panic("rebuild: vδE != nil")
+	}
+
+	vδE := []_ΔFileEpoch{}
+	vδZ := δZtail.Data()
+	atPrev := δZtail.Tail()
+	for i := 0; i < len(vδZ); i++ {
+		δZ := vδZ[i]
+
+		fchanged := false
+		for _, oid := range δZ.Changev {
+			if oid == foid {
+				fchanged = true
+				break
+			}
+		}
+		if !fchanged {
+			continue
+		}
+
+		δ, err := zfilediff(db, foid, atPrev, δZ.Rev)
+		if err != nil {
+			return err
+		}
+
+		if δ != nil {
+			δE := _ΔFileEpoch{
+				Rev:             δZ.Rev,
+				oldRoot:         δ.blktabOld,
+				newRoot:         δ.blktabNew,
+				newBlkSize:      δ.blksizeNew,
+				oldTrackSetZBlk: nil, // nothing was tracked
+			}
+			vδE = append(vδE, δE)
+		}
+
+		atPrev = δZ.Rev
+	}
+
+	δftail.vδE = vδE
+	return nil
+}
+
 // Update updates δFtail given raw ZODB changes.
 //
 // It returns change in files space that corresponds to δZ.
@@ -228,6 +317,12 @@ func (δFtail *ΔFtail) Update(δZ *zodb.EventCommit) (_ ΔF, err error) {
 	// XXX verify zhead.At() == δFtail.Head()
 	// XXX locking
 
+	// rebuild vδE for newly tracked files
+	err = δFtail.rebuildAll()
+	if err != nil {
+		return ΔF{}, err
+	}
+
 	headOld := δFtail.Head()
 
 	δB, err := δFtail.δBtail.Update(δZ)
@@ -466,7 +561,10 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 		return δfTail
 	}
 
-	δftail := δFtail.byFile[zfile.POid()]
+	δftail, err := δFtail.rebuildIfNeeded(zfile.POid())
+	if err != nil {
+		panic(err) // XXX
+	}
 
 	vδZ := δFtail.δBtail.ΔZtail().SliceByRev(lo, hi)
 	iz := len(vδZ) - 1
@@ -631,9 +729,11 @@ func (δFtail *ΔFtail) _LastBlkRev(ctx context.Context, zf *ZBigFile, blk int64
 
 	//fmt.Printf("\nblkrev #%d @%s\n", blk, at)
 	// XXX locking
-	// XXX rebuild
 
-	δftail := δFtail.byFile[zf.POid()]
+	δftail, err := δFtail.rebuildIfNeeded(zf.POid())
+	if err != nil {
+		return zodb.InvalidTid, false, err
+	}
 
 	// find epoch that covers at and associated blktab root/object
 	vδE := δftail.vδE

wcfs/internal/zdata/δftail_test.go

@@ -100,8 +100,6 @@ func TestΔFtail(t *testing.T) {
 		// XXX text
 		{nil, nil},
 
-		// XXX more
-
 		// ---- found by TestΔFtailRandom ----
 
 		{δT{1:a,6:i,7:d,8:e},   δD(a,c,e,f,g,h,i,j)},
@@ -177,11 +175,30 @@ func testΔFtail(t_ *testing.T, testq chan ΔFTestEntry) {
 	t := xbtreetest.NewT(t_)
 	X := exc.Raiseif
 
-	// XXX start δFtail when zfile is not yet exists
-	//     this way we'll verify how ΔFtail rebuilds vδE for started-to-be-tracked file
+	xat := map[zodb.Tid]string{} // tid > "at<i>"
 
+	// start δFtail when zfile does not yet exists
+	// this way we'll verify how ΔFtail rebuilds vδE for started-to-be-tracked file
+	t0 := t.CommitTree("øf")
+	xat[t0.At] = "at0"
+	t.Logf("#   @at0 (%s)", t0.At)
 	δFtail := NewΔFtail(t.Head().At, t.DB)
 
+	// load dataTab
+	dataTab  := map[string]string{}               // ZBlk<name> -> data
+	for /*oid*/_, zblki := range t.Head().ZBlkTab {
+		dataTab[zblki.Name] = zblki.Data
+	}
+
+	// create zfile, but do not track it yet
+	t1 := t.CommitTree(fmt.Sprintf("t0:a D%s", dataTabTxt(dataTab)))
+	xat[t1.At] = "at1"
+	t.Logf("# → @at1 (%s)  %s\t; not-yet-tracked", t1.At, t1.Tree)
+	δF, err := δFtail.Update(t1.ΔZ);  X(err)
+	if !(δF.Rev == t1.At && len(δF.ByFile) == 0) {
+		t.Errorf("wrong δF:\nhave {%s, %v}\nwant: {%s, ø}", δF.Rev, δF.ByFile, t1.At)
+	}
+
 	// load zfile via root['treegen/file']
 	txn, ctx := transaction.New(context.Background())
 	zconn, err := t.DB.Open(ctx, &zodb.ConnOptions{At: t.Head().At, NoPool: true});  X(err)
@@ -199,28 +216,31 @@ func testΔFtail(t_ *testing.T, testq chan ΔFTestEntry) {
 	}
 	zfile.PDeactivate()
 
+	// start track zfile[0,∞) from the beginning
+	// this should make ΔFtail to see all zfile changes
+	size, path, err := zfile.Size(ctx);  X(err)
+	δFtail.Track(zfile, /*blk*/-1, path, /*zblk*/nil)
+	if sizeOK := 1*blksize; size != sizeOK { // NOTE maches t1 commit
+		t.Fatalf("BUG: zfile size: have %d  ; want %d", size, sizeOK)
+	}
 
 	// data built via applying changes from testv
-	vδf      := []*ΔFile{}                        // (rev↑, {}blk)
-	//vδE      := []_ΔFileEpoch{}                   // (rev↑, EPOCH)
-	var vδE []_ΔFileEpoch // FIXME change to !nil (^^^) after ΔFtail.rebuild is added
-	blkTab   := map[int64]string{}                // #blk -> ZBlk<name>
-	dataTab  := map[string]string{}               // ZBlk<name> -> data
+	vδf      := []*ΔFile{                         // (rev↑, {}blk)
+			{Rev: t1.At, Epoch: true},
+		    }
+	vδE      := []_ΔFileEpoch{                    // (rev↑, EPOCH)
+			{
+				Rev:             t1.At,
+				oldRoot:         zodb.InvalidOid,
+				newRoot:         blktabOid,
+				newBlkSize:      blksize,
+				oldTrackSetZBlk: nil,
+			},
+		    }
+	blkTab   := map[int64]string{0:"a"}           // #blk -> ZBlk<name>
 	Zinblk   := map[string]setI64{}               // ZBlk<name> -> which #blk refer to it
 	blkRevAt := map[zodb.Tid]map[int64]zodb.Tid{} // {} at -> {} #blk -> rev
 
-	// initialize dataTab from root['treegen/values']
-	for /*oid*/_, zblki := range t.Head().ZBlkTab {
-		dataTab[zblki.Name] = zblki.Data
-	}
-
-	// track zfile[-∞,∞) from the beginning
-	// this should make ΔFtail to see all zfile changes
-	size, path, err := zfile.Size(ctx);  X(err)
-	δFtail.Track(zfile, /*blk*/-1, path, /*zblk*/nil)
-	if size != 0 {
-		t.Fatalf("BUG: zfile is not initially empty:  size=%d", size)
-	}
 	// retrack should be called after new epoch to track zfile[-∞,∞) again
 	retrack := func() {
 		for blk := range blkTab {
@@ -229,11 +249,8 @@ func testΔFtail(t_ *testing.T, testq chan ΔFTestEntry) {
 		}
 	}
 
-	xat := map[zodb.Tid]string{} // tid > "at<i>"
-	xat[δFtail.Head()] = "at0"
-	t.Logf("#   @at0 (%s)", δFtail.Head())
 
-	epochv := []zodb.Tid{0}
+	epochv := []zodb.Tid{t0.At, t1.At}
 
 	// δfstr/vδfstr converts δf/vδf to string taking xat into account
 	δfstr := func(δf *ΔFile) string {
@@ -255,7 +272,7 @@ func testΔFtail(t_ *testing.T, testq chan ΔFTestEntry) {
 	}
 
 
-	i := 0
+	i := 1 // matches t1
 	delfilePrev := false
 	for test := range testq {
 		i++