feat: Start implementation of manual header parsing and analysis

cmd/stfs-get-header/main.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"archive/tar"
+	"bytes"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+)
+
+const (
+	blockSize  = 20
+	headerSize = 512
+)
+
+type HeaderInBlock struct {
+	OffsetInBlock int
+	Header        string
+}
+
+func main() {
+	file := flag.String("file", "/dev/nst0", "File (tape drive or tar file) to open")
+
+	flag.Parse()
+
+	fileDescription, err := os.Stat(*file)
+	if err != nil {
+		panic(err)
+	}
+
+	var f *os.File
+	if fileDescription.Mode().IsRegular() {
+		f, err = os.Open(*file)
+		if err != nil {
+			panic(err)
+		}
+	} else {
+		f, err = os.OpenFile(*file, os.O_RDONLY, os.ModeCharDevice)
+		if err != nil {
+			panic(err)
+		}
+	}
+	defer f.Close()
+
+	// Read exactly one block
+	bf := make([]byte, blockSize*headerSize)
+	if _, err := io.ReadFull(f, bf); err != nil {
+		panic(err)
+	}
+
+	// Get the headers from the block
+	headers := []HeaderInBlock{}
+	for i := 0; i < blockSize; i++ {
+		tr := tar.NewReader(bytes.NewReader(bf[headerSize*i : headerSize*(i+1)]))
+		hdr, err := tr.Next()
+		if err != nil {
+			continue
+		}
+
+		headers = append(headers, HeaderInBlock{
+			OffsetInBlock: i,
+			Header:        fmt.Sprintf("%v", hdr),
+		})
+	}
+
+	if len(headers) > 0 {
+		fmt.Println(headers)
+	}
+}