??

README.md

@@ -4,6 +4,7 @@ Replicated in-memory database and file store.
 
 ## TODO
 
+* [ ] mdb: Tests for using `nil` snapshots ?
 * [ ] mdb: tests for sanitize and validate functions
 * [ ] Test: lib/wal iterator w/ corrupt file (random corruptions)
 * [ ] Test: lib/wal io.go

go.mod

@@ -1,9 +1,10 @@
 module git.crumpington.com/public/jldb
 
-go 1.21.1
+go 1.22
 
 require (
 	github.com/google/btree v1.1.2
+	go.uber.org/goleak v1.3.0
 	golang.org/x/net v0.15.0
 	golang.org/x/sys v0.12.0
 )

go.sum

@@ -1,6 +1,16 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/google/btree v1.1.2 h1:xf4v41cLI2Z6FxbKm+8Bu+m8ifhj15JuZ9sa0jZCMUU=
 github.com/google/btree v1.1.2/go.mod h1:qOPhT0dTNdNzV6Z/lhRX0YXUafgPLFUh+gZMl761Gm4=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.8.0 h1:pSgiaMZlXftHpm5L7V1+rVB+AZJydKsMxsQBIJw4PKk=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
+go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
 golang.org/x/net v0.15.0 h1:ugBLEUaxABaB5AJqW9enI0ACdci2RUd4eP51NTBvuJ8=
 golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
 golang.org/x/sys v0.12.0 h1:CM0HF96J0hcLAwsHPJZjfdNzs0gftsLfgKt57wWHJ0o=
 golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

lib/errs/error.go

@@ -8,26 +8,27 @@ import (
 )
 
 type Error struct {
-	msg        string
+	Code       int64
-	code       int64
+	Msg        string
+	StackTrace string
+
 	collection string
 	index      string
-	stackTrace string
 	err        error // Wrapped error
 }
 
 func NewErr(code int64, msg string) *Error {
 	return &Error{
-		msg:  msg,
+		Code: code,
-		code: code,
+		Msg:  msg,
 	}
 }
 
 func (e *Error) Error() string {
 	if e.collection != "" || e.index != "" {
-		return fmt.Sprintf(`[%d] (%s/%s) %s`, e.code, e.collection, e.index, e.msg)
+		return fmt.Sprintf(`[%d] (%s/%s) %s`, e.Code, e.collection, e.index, e.Msg)
 	} else {
-		return fmt.Sprintf("[%d] %s", e.code, e.msg)
+		return fmt.Sprintf("[%d] %s", e.Code, e.Msg)
 	}
 }
 
@@ -36,11 +37,15 @@ func (e *Error) Is(rhs error) bool {
 	if !ok {
 		return false
 	}
-	return e.code == e2.code
+	return e.Code == e2.Code
+}
+
+func (e *Error) Unwrap() error {
+	return e.err
 }
 
 func (e *Error) WithErr(err error) *Error {
-	if e2, ok := err.(*Error); ok && e2.code == e.code {
+	if e2, ok := err.(*Error); ok && e2.Code == e.Code {
 		return e2
 	}
 
@@ -49,18 +54,11 @@ func (e *Error) WithErr(err error) *Error {
 	return e2
 }
 
-func (e *Error) Unwrap() error {
-	if e.err != nil {
-		return e.err
-	}
-	return e
-}
-
 func (e *Error) WithMsg(msg string, args ...any) *Error {
 	err := *e
-	err.msg += ": " + fmt.Sprintf(msg, args...)
+	err.Msg += ": " + fmt.Sprintf(msg, args...)
-	if len(err.stackTrace) == 0 {
+	if len(err.StackTrace) == 0 {
-		err.stackTrace = string(debug.Stack())
+		err.StackTrace = string(debug.Stack())
 	}
 	return &err
 }
@@ -78,16 +76,16 @@ func (e *Error) WithIndex(s string) *Error {
 }
 
 func (e *Error) msgTruncacted() string {
-	if len(e.msg) > 255 {
+	if len(e.Msg) > 255 {
-		return e.msg[:255]
+		return e.Msg[:255]
 	}
-	return e.msg
+	return e.Msg
 }
 
 func (e *Error) Write(w io.Writer) error {
 	msg := e.msgTruncacted()
 
-	if err := binary.Write(w, binary.LittleEndian, e.code); err != nil {
+	if err := binary.Write(w, binary.LittleEndian, e.Code); err != nil {
 		return IO.WithErr(err)
 	}
 
@@ -103,7 +101,7 @@ func (e *Error) Read(r io.Reader) error {
 		size uint8
 	)
 
-	if err := binary.Read(r, binary.LittleEndian, &e.code); err != nil {
+	if err := binary.Read(r, binary.LittleEndian, &e.Code); err != nil {
 		return IO.WithErr(err)
 	}
 
@@ -116,6 +114,6 @@ func (e *Error) Read(r io.Reader) error {
 		return IO.WithErr(err)
 	}
 
-	e.msg = string(msgBuf)
+	e.Msg = string(msgBuf)
 	return nil
 }

lib/errs/fmt.go

@@ -10,12 +10,12 @@ func FmtDetails(err error) string {
 
 	var s string
 	if e.collection != "" || e.index != "" {
-		s = fmt.Sprintf(`[%d] (%s/%s) %s`, e.code, e.collection, e.index, e.msg)
+		s = fmt.Sprintf(`[%d] (%s/%s) %s`, e.Code, e.collection, e.index, e.Msg)
 	} else {
-		s = fmt.Sprintf("[%d] %s", e.code, e.msg)
+		s = fmt.Sprintf("[%d] %s", e.Code, e.Msg)
 	}
-	if len(e.stackTrace) != 0 {
+	if len(e.StackTrace) != 0 {
-		s += "\n\nStack Trace:\n" + e.stackTrace + "\n"
+		s += "\n\nStack Trace:\n" + e.StackTrace + "\n"
 	}
 
 	return s

lib/rep/main_test.go

@@ -0,0 +1,11 @@
+package rep
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}

lib/rep/replicator-walgc.go

@@ -15,7 +15,7 @@ func (rep *Replicator) runWALGC() {
 		select {
 		case <-ticker.C:
 			state := rep.getState()
-			before := time.Now().Unix() - rep.conf.WALSegMaxAgeSec
+			before := time.Now().Unix() - rep.conf.WALSegGCAgeSec
 			if err := rep.wal.DeleteBefore(before, state.SeqNum); err != nil {
 				log.Printf("[WAL-GC] failed to delete wal segments: %v", err)
 			}

lib/rep/replicator.go

@@ -2,6 +2,7 @@ package rep
 
 import (
 	"io"
+	"log"
 	"net"
 	"os"
 	"sync"
@@ -35,8 +36,8 @@ type App struct {
 	// SendState: The primary may need to send storage state to a secondary node.
 	SendState func(conn net.Conn) error
 
-	// (1) RecvState: Secondary nodes may need to load state from the primary if the
+	// (1) RecvState: Secondary nodes may need to load state from the primary if
-	// WAL is too far behind.
+	// the WAL is too far behind.
 	RecvState func(conn net.Conn) error
 
 	// (2) InitStorage: Prepare application storage for possible calls to
@@ -94,41 +95,49 @@ func Open(app App, conf Config) (*Replicator, error) {
 	rep.client = newClient(rep.conf.PrimaryEndpoint, rep.conf.ReplicationPSK, rep.conf.NetTimeout)
 
 	if err := rep.initDirectories(); err != nil {
+		log.Printf("Failed to init directories: %v", err)
 		return nil, err
 	}
 
 	if err := rep.acquireLock(); err != nil {
 		rep.Close()
+		log.Printf("Failed to acquire lock: %v", err)
 		return nil, err
 	}
 
 	if err := rep.loadLocalState(); err != nil {
 		rep.Close()
+		log.Printf("Failed to load local state: %v", err)
 		return nil, err
 	}
 
 	if err := rep.openWAL(); err != nil {
 		rep.Close()
+		log.Printf("Failed to open WAL: %v", err)
 		return nil, err
 	}
 
 	if err := rep.recvStateIfNecessary(); err != nil {
 		rep.Close()
+		log.Printf("Failed to recv state: %v", err)
 		return nil, err
 	}
 
 	if err := rep.app.InitStorage(); err != nil {
 		rep.Close()
+		log.Printf("Failed to init storage: %v", err)
 		return nil, err
 	}
 
 	if err := rep.replay(); err != nil {
 		rep.Close()
+		log.Printf("Failed to replay: %v", err)
 		return nil, err
 	}
 
 	if err := rep.app.LoadFromStorage(); err != nil {
 		rep.Close()
+		log.Printf("Failed to load from storage: %v", err)
 		return nil, err
 	}
 

lib/rep/testapp-harness_test.go

@@ -56,6 +56,7 @@ func (h TestAppHarness) Run(t *testing.T) {
 				WALSegMaxAgeSec: 1,
 				WALSegGCAgeSec:  1,
 			})
+			defer app2.Close()
 
 			val.MethodByName(method.Name).Call([]reflect.Value{
 				reflect.ValueOf(t),

lib/wal/main_test.go

@@ -0,0 +1,11 @@
+package wal
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}

mdb/collection.go

@@ -1,7 +1,6 @@
 package mdb
 
 import (
-	"bytes"
 	"encoding/json"
 	"errors"
 	"hash/crc64"
@@ -25,8 +24,6 @@ type Collection[T any] struct {
 	uniqueIndices []*Index[T]
 
 	ByID *Index[T]
-
-	buf *bytes.Buffer
 }
 
 type CollectionConfig[T any] struct {
@@ -67,7 +64,6 @@ func NewCollection[T any](db *Database, name string, conf *CollectionConfig[T])
 		validate:      conf.Validate,
 		indices:       []*Index[T]{},
 		uniqueIndices: []*Index[T]{},
-		buf:           &bytes.Buffer{},
 	}
 
 	db.addCollection(c.collectionID, c, &collectionState[T]{
@@ -159,6 +155,15 @@ func (c *Collection[T]) Get(tx *Snapshot, id uint64) *T {
 	return c.ByID.Get(tx, item)
 }
 
+func (c *Collection[T]) Has(tx *Snapshot, id uint64) bool {
+	if tx == nil {
+		tx = c.db.Snapshot()
+	}
+	item := new(T)
+	c.setID(item, id)
+	return c.ByID.Has(tx, item)
+}
+
 func (c *Collection[T]) Insert(tx *Snapshot, userItem *T) error {
 	if tx == nil {
 		return c.db.Update(func(tx *Snapshot) error {
@@ -237,6 +242,27 @@ func (c *Collection[T]) update(tx *Snapshot, userItem *T) error {
 	return nil
 }
 
+func (c *Collection[T]) UpdateFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	if tx == nil {
+		return c.db.Update(func(tx *Snapshot) error {
+			return c.updateFunc(tx, id, update)
+		})
+	}
+	return c.updateFunc(tx, id, update)
+}
+
+func (c *Collection[T]) updateFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	item := c.Get(tx, id)
+	if item == nil {
+		return errs.NotFound
+	}
+	if err := update(item); err != nil {
+		return err
+	}
+	c.setID(item, id) // Don't allow the ID to change.
+	return c.update(tx, item)
+}
+
 func (c *Collection[T]) Upsert(tx *Snapshot, item *T) error {
 	if tx == nil {
 		return c.db.Update(func(tx *Snapshot) error {
@@ -257,6 +283,36 @@ func (c *Collection[T]) upsert(tx *Snapshot, item *T) error {
 	return err
 }
 
+func (c *Collection[T]) UpsertFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	if tx == nil {
+		c.db.Update(func(tx *Snapshot) error {
+			return c.upsertFunc(tx, id, update)
+		})
+	}
+	return c.upsertFunc(tx, id, update)
+}
+
+func (c *Collection[T]) upsertFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	insert := false
+
+	item := c.Get(tx, id)
+	if item == nil {
+		item = new(T)
+		insert = true
+	}
+
+	if err := update(item); err != nil {
+		return err
+	}
+
+	c.setID(item, id) // Don't allow the ID to change.
+
+	if insert {
+		return c.insert(tx, item)
+	}
+	return c.update(tx, item)
+}
+
 func (c *Collection[T]) Delete(tx *Snapshot, itemID uint64) error {
 	if tx == nil {
 		return c.db.Update(func(tx *Snapshot) error {
@@ -275,6 +331,9 @@ func (c *Collection[T]) delete(tx *Snapshot, itemID uint64) error {
 }
 
 func (c *Collection[T]) Count(tx *Snapshot) int {
+	if tx == nil {
+		tx = c.db.Snapshot()
+	}
 	return c.ByID.Count(tx)
 }
 

mdb/db-primary.go

@@ -0,0 +1,67 @@
+package mdb
+
+/*
+func (db *Database) openPrimary() (err error) {
+	wal, err := cwal.Open(db.walRootDir, cwal.Config{
+		SegMinCount:  db.conf.WALSegMinCount,
+		SegMaxAgeSec: db.conf.WALSegMaxAgeSec,
+	})
+
+	pFile, err := pfile.Open(db.pageFilePath,
+
+	pFile, err := openPageFileAndReplayWAL(db.rootDir)
+	if err != nil {
+		return err
+	}
+	defer pFile.Close()
+
+	pfHeader, err := pFile.ReadHeader()
+	if err != nil {
+		return err
+	}
+
+	tx := db.Snapshot()
+	tx.seqNum = pfHeader.SeqNum
+	tx.updatedAt = pfHeader.UpdatedAt
+
+	pIndex, err := pagefile.NewIndex(pFile)
+	if err != nil {
+		return err
+	}
+
+	err = pFile.IterateAllocated(pIndex, func(cID, iID uint64, data []byte) error {
+		return db.loadItem(tx, cID, iID, data)
+	})
+	if err != nil {
+		return err
+	}
+
+	w, err := cwal.OpenWriter(db.walRootDir, &cwal.WriterConfig{
+		SegMinCount:  db.conf.WALSegMinCount,
+		SegMaxAgeSec: db.conf.WALSegMaxAgeSec,
+	})
+	if err != nil {
+		return err
+	}
+
+	db.done.Add(1)
+	go txAggregator{
+		Stop:     db.stop,
+		Done:     db.done,
+		ModChan:  db.modChan,
+		W:        w,
+		Index:    pIndex,
+		Snapshot: db.snapshot,
+	}.Run()
+
+	db.done.Add(1)
+	go (&fileWriter{
+		Stop:         db.stop,
+		Done:         db.done,
+		PageFilePath: db.pageFilePath,
+		WALRootDir:   db.walRootDir,
+	}).Run()
+
+	return nil
+}
+*/

mdb/db-rep.go

@@ -99,6 +99,7 @@ func (db *Database) repApply(rec wal.Record) (err error) {
 	}
 	tx.seqNum = rec.SeqNum
 	tx.timestampMS = rec.TimestampMS
+	tx.setReadOnly()
 	db.snapshot.Store(tx)
 	return nil
 }

mdb/db-secondary.go

@@ -0,0 +1,129 @@
+package mdb
+
+/*
+func (db *Database) openSecondary() (err error) {
+	if db.shouldLoadFromPrimary() {
+		if err := db.loadFromPrimary(); err != nil {
+			return err
+		}
+	}
+
+	log.Printf("Opening page-file...")
+
+	pFile, err := openPageFileAndReplayWAL(db.rootDir)
+	if err != nil {
+		return err
+	}
+	defer pFile.Close()
+
+	pfHeader, err := pFile.ReadHeader()
+	if err != nil {
+		return err
+	}
+
+	log.Printf("Building page-file index...")
+
+	pIndex, err := pagefile.NewIndex(pFile)
+	if err != nil {
+		return err
+	}
+
+	tx := db.Snapshot()
+	tx.seqNum = pfHeader.SeqNum
+	tx.updatedAt = pfHeader.UpdatedAt
+
+	log.Printf("Loading data into memory...")
+
+	err = pFile.IterateAllocated(pIndex, func(cID, iID uint64, data []byte) error {
+		return db.loadItem(tx, cID, iID, data)
+	})
+	if err != nil {
+		return err
+	}
+
+	log.Printf("Creating writer...")
+
+	w, err := cswal.OpenWriter(db.walRootDir, &cswal.WriterConfig{
+		SegMinCount:  db.conf.WALSegMinCount,
+		SegMaxAgeSec: db.conf.WALSegMaxAgeSec,
+	})
+	if err != nil {
+		return err
+	}
+
+	db.done.Add(1)
+	go (&walFollower{
+		Stop:   db.stop,
+		Done:   db.done,
+		W:      w,
+		Client: NewClient(db.conf.PrimaryURL, db.conf.ReplicationPSK, db.conf.NetTimeout),
+	}).Run()
+
+	db.done.Add(1)
+	go (&follower{
+		Stop:         db.stop,
+		Done:         db.done,
+		WALRootDir:   db.walRootDir,
+		SeqNum:       pfHeader.SeqNum,
+		ApplyChanges: db.applyChanges,
+	}).Run()
+
+	db.done.Add(1)
+	go (&fileWriter{
+		Stop:         db.stop,
+		Done:         db.done,
+		PageFilePath: db.pageFilePath,
+		WALRootDir:   db.walRootDir,
+	}).Run()
+
+	return nil
+}
+
+func (db *Database) shouldLoadFromPrimary() bool {
+	if _, err := os.Stat(db.walRootDir); os.IsNotExist(err) {
+		log.Printf("WAL doesn't exist.")
+		return true
+	}
+	if _, err := os.Stat(db.pageFilePath); os.IsNotExist(err) {
+		log.Printf("Page-file doesn't exist.")
+		return true
+	}
+	return false
+}
+
+func (db *Database) loadFromPrimary() error {
+	client := NewClient(db.conf.PrimaryURL, db.conf.ReplicationPSK, db.conf.NetTimeout)
+	defer client.Disconnect()
+
+	log.Printf("Loading data from primary...")
+
+	if err := os.RemoveAll(db.pageFilePath); err != nil {
+		log.Printf("Failed to remove page-file: %s", err)
+		return errs.IO.WithErr(err) // Caller can retry.
+	}
+
+	if err := os.RemoveAll(db.walRootDir); err != nil {
+		log.Printf("Failed to remove WAL: %s", err)
+		return errs.IO.WithErr(err) // Caller can retry.
+	}
+
+	err := client.DownloadPageFile(db.pageFilePath+".tmp", db.pageFilePath)
+	if err != nil {
+		log.Printf("Failed to get page-file from primary: %s", err)
+		return err // Caller can retry.
+	}
+
+	pfHeader, err := pagefile.ReadHeader(db.pageFilePath)
+	if err != nil {
+		log.Printf("Failed to read page-file sequence number: %s", err)
+		return err // Caller can retry.
+	}
+
+	if err = cswal.CreateEx(db.walRootDir, pfHeader.SeqNum+1); err != nil {
+		log.Printf("Failed to initialize WAL: %s", err)
+		return err // Caller can retry.
+	}
+
+	return nil
+}
+*/

mdb/db-testcases_test.go

@@ -743,29 +743,25 @@ var testDBTestCases = []DBTestCase{{
 
 			first := true
 			pivot := User{Name: "User1"}
-			db.Users.ByName.AscendAfter(tx, &pivot, func(u *User) bool {
+			for u := range db.Users.ByName.AscendAfter(tx, &pivot) {
 				u.Name += "Mod"
 				if err = db.Users.Update(tx, u); err != nil {
-					return false
+					return err
 				}
 				if first {
 					first = false
-					return true
+					continue
 				}
 
 				prev := db.Users.ByID.Get(tx, &User{ID: u.ID - 1})
 				if prev == nil {
-					err = errors.New("Previous user not found")
+					return errors.New("Previous user not found")
-					return false
 				}
 
 				if !strings.HasSuffix(prev.Name, "Mod") {
-					err = errors.New("Incorrect user name: " + prev.Name)
+					return errors.New("Incorrect user name: " + prev.Name)
-					return false
+				}
 			}
-
-				return true
-			})
 			return nil
 		},
 
@@ -801,29 +797,26 @@ var testDBTestCases = []DBTestCase{{
 			}
 
 			first := true
-			db.Users.ByName.DescendAfter(tx, &User{Name: "User5Mod"}, func(u *User) bool {
+			for u := range db.Users.ByName.DescendAfter(tx, &User{Name: "User5Mod"}) {
 				u.Name = strings.TrimSuffix(u.Name, "Mod")
 				if err = db.Users.Update(tx, u); err != nil {
-					return false
+					return err
 				}
 				if first {
 					first = false
-					return true
+					continue
 				}
 
 				prev := db.Users.ByID.Get(tx, &User{ID: u.ID + 1})
 				if prev == nil {
-					err = errors.New("Previous user not found")
+					return errors.New("Previous user not found")
-					return false
 				}
 
 				if strings.HasSuffix(prev.Name, "Mod") {
-					err = errors.New("Incorrect user name: " + prev.Name)
+					return errors.New("Incorrect user name: " + prev.Name)
-					return false
+				}
 			}
 
-				return true
-			})
 			return nil
 		},
 

mdb/db-testlist_test.go

@@ -123,7 +123,7 @@ func TestDBList(t *testing.T) {
 	for _, tc := range cases {
 		t.Run(tc.Name, func(t *testing.T) {
 			tx := db.Snapshot()
-			l := db.UserData.ByName.List(tx, &tc.Args, nil)
+			l := db.UserData.ByName.List(tx, tc.Args, nil)
 			if len(l) != len(tc.Expected) {
 				t.Fatal(tc.Name, l)
 			}

mdb/db-testrunner_test.go

@@ -72,7 +72,7 @@ func testRunner_testCase(t *testing.T, testCase DBTestCase) {
 	}
 
 	// TODO: Why is this necessary?
-	time.Sleep(time.Second)
+	//time.Sleep(time.Second)
 	finalStep := testCase.Steps[len(testCase.Steps)-1]
 
 	secondarySnapshot := db2.Snapshot()

mdb/db.go

@@ -73,6 +73,10 @@ type Database struct {
 }
 
 func New(conf Config) *Database {
+	if conf.NetTimeout <= 0 {
+		conf.NetTimeout = time.Minute
+	}
+
 	if conf.MaxConcurrentUpdates <= 0 {
 		conf.MaxConcurrentUpdates = 32
 	}

mdb/equality_test.go

@@ -1,7 +1,6 @@
 package mdb
 
 import (
-	"fmt"
 	"reflect"
 	"testing"
 )
@@ -20,18 +19,16 @@ func (i Index[T]) AssertEqual(t *testing.T, tx1, tx2 *Snapshot) {
 	}
 
 	errStr := ""
-	i.Ascend(tx1, func(item1 *T) bool {
+	iter := i.Ascend(tx1)
+	for item1 := range iter {
 		item2 := i.Get(tx2, item1)
 		if item2 == nil {
-			errStr = fmt.Sprintf("Indices don't match. %v not found.", item1)
+			t.Fatalf("Indices don't match. %v not found.", item1)
-			return false
 		}
 		if !reflect.DeepEqual(item1, item2) {
-			errStr = fmt.Sprintf("%v != %v", item1, item2)
+			t.Fatalf("%v != %v", item1, item2)
-			return false
+		}
 	}
-		return true
-	})
 
 	if errStr != "" {
 		t.Fatal(errStr)

mdb/index.go

@@ -1,6 +1,7 @@
 package mdb
 
 import (
+	"iter"
 	"unsafe"
 
 	"github.com/google/btree"
@@ -111,85 +112,40 @@ func (i *Index[T]) Max(tx *Snapshot) *T {
 	return nil
 }
 
-func (i *Index[T]) Ascend(tx *Snapshot, each func(*T) bool) {
+func (i *Index[T]) Ascend(tx *Snapshot) iter.Seq[*T] {
 	tx = i.ensureSnapshot(tx)
+	return func(yield func(*T) bool) {
 		i.btreeForIter(tx).Ascend(func(t *T) bool {
-		return each(i.copy(t))
+			return yield(i.copy(t))
 		})
 	}
+}
 
-func (i *Index[T]) AscendAfter(tx *Snapshot, after *T, each func(*T) bool) {
+func (i *Index[T]) AscendAfter(tx *Snapshot, after *T) iter.Seq[*T] {
 	tx = i.ensureSnapshot(tx)
+	return func(yield func(*T) bool) {
 		i.btreeForIter(tx).AscendGreaterOrEqual(after, func(t *T) bool {
-		return each(i.copy(t))
+			return yield(i.copy(t))
 		})
 	}
+}
 
-func (i *Index[T]) Descend(tx *Snapshot, each func(*T) bool) {
+func (i *Index[T]) Descend(tx *Snapshot) iter.Seq[*T] {
 	tx = i.ensureSnapshot(tx)
+	return func(yield func(*T) bool) {
 		i.btreeForIter(tx).Descend(func(t *T) bool {
-		return each(i.copy(t))
+			return yield(i.copy(t))
 		})
 	}
+}
 
-func (i *Index[T]) DescendAfter(tx *Snapshot, after *T, each func(*T) bool) {
+func (i *Index[T]) DescendAfter(tx *Snapshot, after *T) iter.Seq[*T] {
 	tx = i.ensureSnapshot(tx)
+	return func(yield func(*T) bool) {
 		i.btreeForIter(tx).DescendLessOrEqual(after, func(t *T) bool {
-		return each(i.copy(t))
+			return yield(i.copy(t))
 		})
 	}
-
-type ListArgs[T any] struct {
-	Desc  bool          // True for descending order, otherwise ascending.
-	After *T            // If after is given, iterate after (and including) the value.
-	While func(*T) bool // Continue iterating until While is false.
-	Limit int           // Maximum number of items to return. 0 => All.
-}
-
-func (i *Index[T]) List(tx *Snapshot, args *ListArgs[T], out []*T) []*T {
-	tx = i.ensureSnapshot(tx)
-	if args == nil {
-		args = &ListArgs[T]{}
-	}
-
-	if args.Limit < 0 {
-		return nil
-	}
-
-	if args.While == nil {
-		args.While = func(*T) bool { return true }
-	}
-
-	size := args.Limit
-	if size == 0 {
-		size = 32 // Why not?
-	}
-
-	items := out[:0]
-
-	each := func(item *T) bool {
-		if !args.While(item) {
-			return false
-		}
-		items = append(items, item)
-		return args.Limit == 0 || len(items) < args.Limit
-	}
-
-	if args.Desc {
-		if args.After != nil {
-			i.DescendAfter(tx, args.After, each)
-		} else {
-			i.Descend(tx, each)
-		}
-	} else {
-		if args.After != nil {
-			i.AscendAfter(tx, args.After, each)
-		} else {
-			i.Ascend(tx, each)
-		}
-	}
-
-	return items
 }
 
 func (i *Index[T]) Count(tx *Snapshot) int {

mdb/index_test.go

@@ -1,9 +1,8 @@
 package mdb
 
 func (i Index[T]) Dump(tx *Snapshot) (l []T) {
-	i.Ascend(tx, func(t *T) bool {
+	for t := range i.Ascend(tx) {
 		l = append(l, *t)
-		return true
+	}
-	})
 	return l
 }

mdb/main_test.go

@@ -0,0 +1,11 @@
+package mdb
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}

mdb/pfile/freelist.go

@@ -51,6 +51,10 @@ func (f *freeList) Push(pages ...uint64) {
 	}
 }
 
+func (f *freeList) SetNextPage(nextPage uint64) {
+	f.nextPage = nextPage
+}
+
 func (f *freeList) Pop(count int, out []uint64) []uint64 {
 	out = out[:0]
 

mdb/pfile/index.go

@@ -13,14 +13,19 @@ type Index struct {
 }
 
 func NewIndex(f *File) (*Index, error) {
+	firstPage, err := f.pageCount()
+	if err != nil {
+		return nil, err
+	}
+
 	idx := &Index{
-		fList: newFreeList(0),
+		fList: newFreeList(firstPage),
 		aList: *newAllocList(),
 		seen:  map[[2]uint64]struct{}{},
 		mask:  []bool{},
 	}
 
-	err := f.iterate(func(pageID uint64, page dataPage) error {
+	err = f.iterate(func(pageID uint64, page dataPage) error {
 		header := page.Header()
 		switch header.PageType {
 		case pageTypeHead:

mdb/pfile/pagefile.go

@@ -134,6 +134,21 @@ func (pf *File) writePage(page dataPage, id uint64) error {
 // Reading
 // ----------------------------------------------------------------------------
 
+func (pf *File) pageCount() (uint64, error) {
+	fi, err := pf.f.Stat()
+	if err != nil {
+		return 0, errs.IO.WithErr(err)
+	}
+
+	fileSize := fi.Size()
+	if fileSize%pageSize != 0 {
+		return 0, errs.Corrupt.WithMsg("File size isn't a multiple of page size.")
+	}
+
+	maxPage := uint64(fileSize / pageSize)
+	return maxPage, nil
+}
+
 func (pf *File) iterate(each func(pageID uint64, page dataPage) error) error {
 	pf.lock.RLock()
 	defer pf.lock.RUnlock()