From c1716d552184d8cd825dc693ab20e47115c689fb Mon Sep 17 00:00:00 2001
From: Xavier Henner <xavier@euclide.org>
Date: Sun, 26 Apr 2015 16:56:26 +0200
Subject: [PATCH 1/3] take into account h.Unsynchronisation and add some sanity
 check

---
 id3v2.go | 40 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/id3v2.go b/id3v2.go
index 32017b9..5d333f1 100644
--- a/id3v2.go
+++ b/id3v2.go
@@ -166,6 +166,12 @@ func readID3v2Frames(r io.Reader, h *ID3v2Header) (map[string]interface{}, error
 		if err != nil {
 			return nil, err
 		}
+		// if size=0, we certainly are in a padding zone. ignore the rest of
+		// the tags. and if size > h.Size, we have a problem
+		if size == 0 || size > h.Size {
+			break
+		}
+
 		offset += headerSize + size
 
 		// Check this stuff out...
@@ -220,6 +226,29 @@ func readID3v2Frames(r io.Reader, h *ID3v2Header) (map[string]interface{}, error
 	return result, nil
 }
 
+type Unsynchroniser struct {
+	orig io.Reader
+}
+
+// filter io.Reader which skip the Unsynchronisation bytes
+func (r *Unsynchroniser) Read(p []byte) (int, error) {
+	nextOk := false
+	for i := 0; i < len(p); i++ {
+		if n, err := r.orig.Read(p[i : i+1]); n == 0 || err != nil {
+			return i, err
+		}
+		if i >= 1 && p[i-1] == 255 && p[i] == 0 && !nextOk {
+			// we must skip this 00
+			i--
+			// but not the next one
+			nextOk = true
+		} else {
+			nextOk = false
+		}
+	}
+	return len(p), nil
+}
+
 // ReadID3v2Tags parses ID3v2.{2,3,4} tags from the io.ReadSeeker into a Metadata, returning
 // non-nil error on failure.
 func ReadID3v2Tags(r io.ReadSeeker) (Metadata, error) {
@@ -232,7 +261,16 @@ func ReadID3v2Tags(r io.ReadSeeker) (Metadata, error) {
 	if err != nil {
 		return nil, err
 	}
-	f, err := readID3v2Frames(r, h)
+
+	var ur io.Reader
+
+	if h.Unsynchronisation {
+		ur = &Unsynchroniser{orig: r}
+	} else {
+		ur = r
+	}
+
+	f, err := readID3v2Frames(ur, h)
 	if err != nil {
 		return nil, err
 	}

From dad1548722e32cabdc898e8c17c2a190e5cf8d22 Mon Sep 17 00:00:00 2001
From: Xavier Henner <xavier@euclide.org>
Date: Thu, 30 Apr 2015 22:07:08 +0200
Subject: [PATCH 2/3] Need to skip Unsynchronisation byte at the boundary
 between 2 Read

---
 id3v2.go | 41 +++++++++++++++++++++++++++++------------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/id3v2.go b/id3v2.go
index 5d333f1..82b4b97 100644
--- a/id3v2.go
+++ b/id3v2.go
@@ -167,8 +167,8 @@ func readID3v2Frames(r io.Reader, h *ID3v2Header) (map[string]interface{}, error
 			return nil, err
 		}
 		// if size=0, we certainly are in a padding zone. ignore the rest of
-		// the tags. and if size > h.Size, we have a problem
-		if size == 0 || size > h.Size {
+		// the tags
+		if size == 0 {
 			break
 		}
 
@@ -227,24 +227,41 @@ func readID3v2Frames(r io.Reader, h *ID3v2Header) (map[string]interface{}, error
 }
 
 type Unsynchroniser struct {
-	orig io.Reader
+	orig      io.Reader
+	prevWasFF bool
 }
 
 // filter io.Reader which skip the Unsynchronisation bytes
 func (r *Unsynchroniser) Read(p []byte) (int, error) {
-	nextOk := false
 	for i := 0; i < len(p); i++ {
-		if n, err := r.orig.Read(p[i : i+1]); n == 0 || err != nil {
+		// there is only one byte to read.
+		if i == len(p)-1 {
+			if n, err := r.orig.Read(p[i : i+1]); n == 0 || err != nil {
+				return i, err
+			}
+			// we need to read this last byte once more
+			if r.prevWasFF && p[i] == 0 {
+				i--
+				r.prevWasFF = false
+			}
+			r.prevWasFF = (p[i] == 255)
+			continue
+		}
+		if n, err := r.orig.Read(p[i : i+2]); n == 0 || err != nil {
 			return i, err
 		}
-		if i >= 1 && p[i-1] == 255 && p[i] == 0 && !nextOk {
-			// we must skip this 00
-			i--
-			// but not the next one
-			nextOk = true
-		} else {
-			nextOk = false
+		if r.prevWasFF && p[i] == 0 {
+			p[i] = p[i+1]
+			r.prevWasFF = false
+			continue
 		}
+		if p[i] == 255 && p[i+1] == 0 {
+			r.prevWasFF = false
+			continue
+		}
+		r.prevWasFF = (p[i+1] == 255)
+		// these 2 bytes are fine, we skip none
+		i++
 	}
 	return len(p), nil
 }

From cac0ed8f5709740950e0ccfa02cedf328a02beb4 Mon Sep 17 00:00:00 2001
From: Xavier Henner <xavier@euclide.org>
Date: Fri, 1 May 2015 00:55:17 +0200
Subject: [PATCH 3/3] now work with 'ff 00 ff 00' in the file

---
 id3v2.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/id3v2.go b/id3v2.go
index 82b4b97..806d23b 100644
--- a/id3v2.go
+++ b/id3v2.go
@@ -252,7 +252,7 @@ func (r *Unsynchroniser) Read(p []byte) (int, error) {
 		}
 		if r.prevWasFF && p[i] == 0 {
 			p[i] = p[i+1]
-			r.prevWasFF = false
+			r.prevWasFF = (p[i+1] == 255)
 			continue
 		}
 		if p[i] == 255 && p[i+1] == 0 {