hello, erasepinf

Author: castaneai

.gitignore

@@ -0,0 +1 @@
+.idea/

README.md

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+# erasepinf
+pinf eraser
+
+```sh
+./erasepinf <mp4 filename>
+```
+
+
+## License
+MIT

erasepinf.go

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+package main
+
+import (
+	"log"
+	"os"
+	"encoding/binary"
+	"encoding/hex"
+	"io"
+	"errors"
+	"fmt"
+)
+
+// atomName => padding size
+var boxAtomPaddings = map[string]int64{
+	"moov": 0,
+	"trak": 0,
+	"mdia": 0,
+	"minf": 0,
+	"stsd": 8,
+	"stbl": 0,
+	"mp4a": 28,
+
+	// --- in pinf
+	"pinf": 0,
+	"schi": 0,
+}
+
+func main() {
+	if len(os.Args) < 2 {
+		log.Fatalf("Usage: ./erasepinf <mp4 filename>")
+	}
+
+	filename := os.Args[1]
+	f, err := os.OpenFile(filename, os.O_RDWR, 0644)
+	defer f.Close()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	atoms, err := readAllAtoms(f)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	pinf, err := searchAtom(atoms, "pinf")
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	dumper := hex.Dumper(os.Stdout)
+	defer dumper.Close()
+
+	data, err := pinf.ReadData(f)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	fmt.Println("-------------before-----------------")
+	dumper.Write(data)
+
+	if err := pinf.destroy(f); err != nil {
+		log.Fatalln(err)
+	}
+
+	data, err = pinf.ReadData(f)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	fmt.Println("-------------after-----------------")
+	dumper.Write(data)
+}
+
+func searchAtom(atoms map[string]*Atom, target string) (*Atom, error) {
+	for name, atom := range atoms {
+		if name == target {
+			return atom, nil
+		}
+		if len(atom.Children) > 0 {
+			return searchAtom(atom.Children, target)
+		}
+	}
+	return nil, errors.New("not found")
+}
+
+type Atom struct {
+	Name string
+	DataStartPos int64
+	DataLen int64
+	Children map[string]*Atom
+}
+
+func (a *Atom) ReadData(r io.ReadSeeker) ([]byte, error) {
+	if _, err := r.Seek(a.DataStartPos, io.SeekStart); err != nil {
+		return nil, err
+	}
+	buf := make([]byte, a.DataLen)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+	return buf, nil
+}
+
+func (a *Atom) destroy(w io.WriteSeeker) (error) {
+	if _, err := w.Seek(a.DataStartPos, io.SeekStart); err != nil {
+		return err
+	}
+	pad := make([]byte, a.DataLen)
+	if _, err := w.Write(pad); err != nil {
+		return err
+	}
+	return nil
+}
+
+func readAllAtoms(r io.ReadSeeker) (map[string]*Atom, error) {
+	atoms := make(map[string]*Atom)
+	for {
+		atom, err := readAtom(r)
+		if err != nil {
+			if err != io.EOF {
+				return nil, err
+			}
+			break
+		}
+		atoms[atom.Name] = atom
+	}
+	return atoms, nil
+}
+
+func readAtom(r io.ReadSeeker) (*Atom, error) {
+	var length uint32
+	if err := binary.Read(r, binary.BigEndian, &length); err != nil {
+		return nil, err
+	}
+
+	nameb := make([]byte, 4)
+	if err := binary.Read(r, binary.BigEndian, &nameb); err != nil {
+		return nil, err
+	}
+	name := string(nameb)
+
+	startPos, err := r.Seek(0, io.SeekCurrent)
+	if err !=  nil {
+		return nil, err
+	}
+	dataLen := int64(length - 8)
+
+	catoms := make(map[string]*Atom)
+	pad, isBox := boxAtomPaddings[name]
+	if isBox {
+		r.Seek(pad, io.SeekCurrent)
+		for {
+			catom, err := readAtom(r)
+			if err != nil {
+				return nil, err
+			}
+			catoms[catom.Name] = catom
+
+			cur, err := r.Seek(0, io.SeekCurrent)
+			if err != nil {
+				return nil, err
+			}
+			if cur >= startPos + dataLen {
+				break
+			}
+		}
+	} else {
+		if _, err := r.Seek(dataLen, io.SeekCurrent); err != nil {
+			return nil, err
+		}
+	}
+
+	return &Atom {
+		Name: name,
+		DataStartPos: startPos,
+		DataLen: dataLen,
+		Children: catoms,
+	}, nil
+}