More efficient Table reading

low/inode.go

@@ -7,7 +7,9 @@ import (
 	"github.com/CalebQ42/squashfs/low/inode"
 )
 
-func (r Reader) InodeFromRef(ref uint64) (inode.Inode, error) {
+type InodeRef = uint64
+
+func (r Reader) InodeFromRef(ref InodeRef) (inode.Inode, error) {
 	offset, meta := (ref>>16)+r.Superblock.InodeTableStart, ref&0xFFFF
 	rdr := metadata.NewReader(toreader.NewReader(r.r, int64(offset)), r.d)
 	defer rdr.Close()

low/reader.go

@@ -34,7 +34,7 @@ type Reader struct {
 	d           decompress.Decompressor
 	fragTable   *Table[fragEntry]
 	idTable     *Table[uint32]
-	exportTable *Table[uint64]
+	exportTable *Table[InodeRef]
 }
 
 func NewReader(r io.ReaderAt) (rdr Reader, err error) {
@@ -78,12 +78,42 @@ func NewReader(r io.ReaderAt) (rdr Reader, err error) {
 	if err != nil {
 		return rdr, errors.Join(errors.New("failed to read root directory"), err)
 	}
-	rdr.fragTable = NewTable[fragEntry](&rdr, rdr.Superblock.FragTableStart, rdr.Superblock.FragCount)
-	rdr.idTable = NewTable[uint32](&rdr, rdr.Superblock.IdTableStart, uint32(rdr.Superblock.IdCount))
-	rdr.exportTable = NewTable[uint64](&rdr, rdr.Superblock.ExportTableStart, rdr.Superblock.InodeCount)
+	rdr.fragTable = NewTable(&rdr, rdr.Superblock.FragTableStart, rdr.Superblock.FragCount, readFrag)
+	rdr.idTable = NewTable(&rdr, rdr.Superblock.IdTableStart, uint32(rdr.Superblock.IdCount), readId)
+	rdr.exportTable = NewTable(&rdr, rdr.Superblock.ExportTableStart, rdr.Superblock.InodeCount, readRef)
 	return
 }
 
+func readFrag(r io.Reader) (fragEntry, error) {
+	dat := make([]byte, 16)
+	_, err := r.Read(dat)
+	if err != nil {
+		return fragEntry{}, err
+	}
+	return fragEntry{
+		Start: binary.LittleEndian.Uint64(dat[0:8]),
+		Size:  binary.LittleEndian.Uint32(dat[8:12]),
+	}, nil
+}
+
+func readId(r io.Reader) (uint32, error) {
+	dat := make([]byte, 4)
+	_, err := r.Read(dat)
+	if err != nil {
+		return 0, err
+	}
+	return binary.LittleEndian.Uint32(dat), nil
+}
+
+func readRef(r io.Reader) (InodeRef, error) {
+	dat := make([]byte, 8)
+	_, err := r.Read(dat)
+	if err != nil {
+		return 0, err
+	}
+	return binary.LittleEndian.Uint64(dat), nil
+}
+
 // Get a uid/gid at the given index. Lazily populates the reader's Id table as necessary.
 func (r *Reader) Id(i uint16) (uint32, error) {
 	return r.idTable.Get(uint32(i))
@@ -95,7 +125,7 @@ func (r *Reader) fragEntry(i uint32) (fragEntry, error) {
 }
 
 // Get an inode reference at the given index. Lazily populates the reader's export table as necessary.
-func (r *Reader) inodeRef(i uint32) (uint64, error) {
+func (r *Reader) inodeRef(i uint32) (InodeRef, error) {
 	return r.exportTable.Get(i)
 }
 

low/superblock.go

@@ -14,7 +14,7 @@ type superblock struct {
 	IdCount          uint16
 	VerMaj           uint16
 	VerMin           uint16
-	RootInodeRef     uint64
+	RootInodeRef     InodeRef
 	Size             uint64
 	IdTableStart     uint64
 	XattrTableStart  uint64

low/table.go

@@ -3,6 +3,7 @@ package squashfslow
 import (
 	"encoding/binary"
 	"errors"
+	"io"
 	"sync"
 
 	"github.com/CalebQ42/squashfs/internal/metadata"
@@ -13,6 +14,8 @@ var errOutOfBounds = errors.New("out of bounds")
 var errUnexpectedOutOfBounds = errors.New("unexpected out of bounds")
 var errNilCollection = errors.New("nil collection")
 
+type CreateFunction[T any] = func(io.Reader) (T, error)
+
 type Table[T any] struct {
 	totalItems    uint32
 	itemsPerBlock uint32
@@ -20,9 +23,10 @@ type Table[T any] struct {
 	mut           sync.RWMutex
 	currentItems  []T
 	rdr           *Reader
+	createFunc    CreateFunction[T]
 }
 
-func NewTable[T any](rdr *Reader, start uint64, totalItems uint32) *Table[T] {
+func NewTable[T any](rdr *Reader, start uint64, totalItems uint32, createFunc CreateFunction[T]) *Table[T] {
 	var zero T
 	return &Table[T]{
 		totalItems:    totalItems,
@@ -30,6 +34,7 @@ func NewTable[T any](rdr *Reader, start uint64, totalItems uint32) *Table[T] {
 		offset:        start,
 		mut:           sync.RWMutex{},
 		rdr:           rdr,
+		createFunc:    createFunc,
 	}
 }
 
@@ -65,14 +70,16 @@ func (t *Table[T]) fillAndGet(requestedItemIndex uint32) (T, error) {
 		}
 		t.offset += 8
 		toRead = min(t.itemsPerBlock, t.totalItems-uint32(len(t.currentItems)))
-		new := make([]T, toRead)
+		oldLen := uint32(len(t.currentItems))
+		t.currentItems = append(t.currentItems, make([]T, toRead)...)
 		metaRdr = metadata.NewReader(toreader.NewReader(t.rdr.r, int64(offset)), t.rdr.d)
-		err = binary.Read(&metaRdr, binary.LittleEndian, new)
-		if err != nil {
-			var zero T
-			return zero, err
+		for i := range toRead {
+			t.currentItems[oldLen+i], err = t.createFunc(&metaRdr)
+			if err != nil {
+				var zero T
+				return zero, err
+			}
 		}
-		t.currentItems = append(t.currentItems, new...)
 	}
 	return t.currentItems[requestedItemIndex], nil
 }