From 1fc6cacf34402924268b3bab8351758837d06494 Mon Sep 17 00:00:00 2001
From: David Howden <dhowden@gmail.com>
Date: Wed, 15 Apr 2015 00:06:32 +1000
Subject: [PATCH] Updated ReadFrom to take io.ReadSeeker

---
 id3v1.go | 13 +++++--------
 id3v2.go | 10 ++++++++--
 mp4.go   | 13 +++++++++----
 tag.go   | 26 +++++++++++++-------------
 4 files changed, 35 insertions(+), 27 deletions(-)

diff --git a/id3v1.go b/id3v1.go
index d054cbe..2243e84 100644
--- a/id3v1.go
+++ b/id3v1.go
@@ -5,10 +5,9 @@
 package tag
 
 import (
-	"bytes"
 	"errors"
 	"io"
-	"io/ioutil"
+	"os"
 	"strconv"
 	"strings"
 )
@@ -42,16 +41,14 @@ var id3v1Genres = [...]string{
 // ErrNotID3v1 is an error which is returned when no ID3v1 header is found.
 var ErrNotID3v1 = errors.New("invalid ID3v1 header")
 
-// ReadID3v1Tags reads ID3v1 tags from the given io.Reader.  Returns a non-nil error
-// if there was a problem.
-func ReadID3v1Tags(r io.Reader) (Metadata, error) {
-	b, err := ioutil.ReadAll(r)
+// ReadID3v1Tags reads ID3v1 tags from the io.ReadSeeker.  Returns ErrNotID3v1
+// if there are no ID3v1 tags, otherwise non-nil error if there was a problem.
+func ReadID3v1Tags(r io.ReadSeeker) (Metadata, error) {
+	_, err := r.Seek(-128, os.SEEK_END)
 	if err != nil {
 		return nil, err
 	}
 
-	b = b[len(b)-128 : len(b)]
-	r = bytes.NewReader(b)
 	if tag, err := readString(r, 3); err != nil {
 		return nil, err
 	} else if tag != "TAG" {
diff --git a/id3v2.go b/id3v2.go
index b1c30bf..32017b9 100644
--- a/id3v2.go
+++ b/id3v2.go
@@ -7,6 +7,7 @@ package tag
 import (
 	"fmt"
 	"io"
+	"os"
 	"strings"
 )
 
@@ -219,9 +220,14 @@ func readID3v2Frames(r io.Reader, h *ID3v2Header) (map[string]interface{}, error
 	return result, nil
 }
 
-// ReadID3v2Tags parses ID3v2.{2,3,4} tags from the given io.Reader into a Metadata, returning
+// ReadID3v2Tags parses ID3v2.{2,3,4} tags from the io.ReadSeeker into a Metadata, returning
 // non-nil error on failure.
-func ReadID3v2Tags(r io.Reader) (Metadata, error) {
+func ReadID3v2Tags(r io.ReadSeeker) (Metadata, error) {
+	_, err := r.Seek(0, os.SEEK_SET)
+	if err != nil {
+		return nil, err
+	}
+
 	h, err := readID3v2Header(r)
 	if err != nil {
 		return nil, err
diff --git a/mp4.go b/mp4.go
index 150482d..f18aed1 100644
--- a/mp4.go
+++ b/mp4.go
@@ -8,6 +8,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
+	"os"
 	"strconv"
 )
 
@@ -56,11 +57,15 @@ func (f atomNames) Name(n string) []string {
 // metadataMP4 is the implementation of Metadata for MP4 tag (atom) data.
 type metadataMP4 map[string]interface{}
 
-// ReadAtoms reads MP4 metadata atoms from the reader into a Metadata, returning non-nil
-// error if there was a problem.
-func ReadAtoms(r io.Reader) (Metadata, error) {
+// ReadAtoms reads MP4 metadata atoms from the io.ReadSeeker into a Metadata, returning
+// non-nil error if there was a problem.
+func ReadAtoms(r io.ReadSeeker) (Metadata, error) {
+	_, err := r.Seek(0, os.SEEK_SET)
+	if err != nil {
+		return nil, err
+	}
 	m := make(metadataMP4)
-	err := m.readAtoms(r)
+	err = m.readAtoms(r)
 	return m, err
 }
 
diff --git a/tag.go b/tag.go
index a38aa09..216fd42 100644
--- a/tag.go
+++ b/tag.go
@@ -6,7 +6,6 @@
 package tag
 
 import (
-	"bytes"
 	"errors"
 	"io"
 )
@@ -16,25 +15,26 @@ import (
 var ErrNoTagsFound = errors.New("no tags found")
 
 // ReadFrom parses audio file metadata tags (currently supports ID3v1,2.{2,3,4} and MP4).
-// This method attempts to determine the format of the data provided by the reader, and then
-// chooses ReadAtoms (MP4), ReadID3v2Tags (ID3v2.{2,3,4}) or ReadID3v1Tags as appropriate.
-// Returns non-nil error if the format of the given data could not be determined, or if
-// there was a problem parsing the data.
-func ReadFrom(r io.Reader) (Metadata, error) {
+// This method attempts to determine the format of the data provided by the io.ReadSeeker,
+// and then chooses ReadAtoms (MP4), ReadID3v2Tags (ID3v2.{2,3,4}) or ReadID3v1Tags as
+// appropriate.  Returns non-nil error if the format of the given data could not be determined,
+// or if there was a problem parsing the data.
+func ReadFrom(r io.ReadSeeker) (Metadata, error) {
 	b, err := readBytes(r, 11)
 	if err != nil {
 		return nil, err
 	}
 
-	rr := io.MultiReader(bytes.NewReader(b), r)
-	if string(b[4:11]) == "ftypM4A" {
-		return ReadAtoms(rr)
-	}
-	if string(b[0:3]) == "ID3" {
-		return ReadID3v2Tags(rr)
+	switch {
+
+	case string(b[4:11]) == "ftypM4A":
+		return ReadAtoms(r)
+
+	case string(b[0:3]) == "ID3":
+		return ReadID3v2Tags(r)
 	}
 
-	m, err := ReadID3v1Tags(rr)
+	m, err := ReadID3v1Tags(r)
 	if err != nil {
 		if err == ErrNotID3v1 {
 			err = ErrNoTagsFound