feat: Add seek implementation for file backend

cmd/stfs-seek-file/main.go

@@ -0,0 +1,94 @@
+package main
+
+import (
+	"archive/tar"
+	"bytes"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"os"
+)
+
+const (
+	blockSize = 512
+)
+
+type HeaderInBlock struct {
+	Record int
+	Block  int
+	Header string
+}
+
+func main() {
+	file := flag.String("file", "test.tar", "Tar file to open")
+	recordSize := flag.Int("recordSize", 20, "Amount of 512-bit blocks per record")
+	checkpoint := flag.Int("checkpoint", 0, "Log current record after checkpoint kilobytes have been read")
+	seek := flag.Int("seek", 0, "Record to seek too")
+
+	flag.Parse()
+
+	bytesToSeek := *recordSize * blockSize * *seek
+
+	f, err := os.Open(*file)
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+
+	record := 0
+	for {
+		// Seek to requested record
+		if bytesToSeek > 0 && record < *seek {
+			if _, err := f.Seek(int64(bytesToSeek), 0); err != nil {
+				panic(err)
+			}
+
+			record = *seek
+
+			continue
+		}
+
+		// Lock the current record if requested
+		if *checkpoint > 0 && record%*checkpoint == 0 {
+			log.Println("Checkpoint:", record)
+		}
+
+		// Read exactly one record
+		bf := make([]byte, *recordSize*blockSize)
+		if _, err := io.ReadFull(f, bf); err != nil {
+			if err == io.EOF {
+				break
+			}
+
+			panic(err)
+		}
+
+		// Get the headers from the record
+		headers := []HeaderInBlock{}
+		for i := 0; i < *recordSize; i++ {
+			tr := tar.NewReader(bytes.NewReader(bf[blockSize*i : blockSize*(i+1)]))
+			hdr, err := tr.Next()
+			if err != nil {
+				continue
+			}
+
+			if hdr.Format == tar.FormatUnknown {
+				// EOF
+				break
+			}
+
+			headers = append(headers, HeaderInBlock{
+				Record: record,
+				Block:  i,
+				Header: fmt.Sprintf("%v", hdr),
+			})
+		}
+
+		if len(headers) > 0 {
+			fmt.Println(headers)
+		}
+
+		record++
+	}
+}

go.mod

@@ -2,9 +2,9 @@ module github.com/pojntfx/stfs
 
 go 1.17
 
-require github.com/hanwen/go-fuse/v2 v2.1.0
-
 require (
-	github.com/jacobsa/fuse v0.0.0-20211108140243-7c4418392f94 // indirect
-	golang.org/x/sys v0.0.0-20211112193437-faf0a1b62c6b // indirect
+	github.com/hanwen/go-fuse/v2 v2.1.0
+	github.com/jacobsa/fuse v0.0.0-20211108140243-7c4418392f94
 )
+
+require golang.org/x/sys v0.0.0-20211112193437-faf0a1b62c6b // indirect