First commit!

LICENSE

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+Copyright (c) 2016 Albert Nigmatzianov
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

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+# ID3V2
+
+## IMHO
+I think **ID3v2** is a very overwhelmed standard: it does **more than it really should do**. There are a lot of aspects, which developer should take into consideration. And that's why it's pretty complicated to write a **good library**. So if you have some thoughts about writing a **new simply standard** for providing information for digital music tracks, just write me. I think, it's a good time to write an appropriate standard for it 😉
+
+## Information
+**Stable and fast ID3v2 Library written in Go**
+
+This library can only set and write tags, but can't read them. So if you only want to set tags, it fits you. And if there is a tag of version 3 or 4, this library will just delete it.
+
+What it **can** do:
+* Set artist, album, year, genre and **attached pictures** (e.g. album covers) and write all to file
+* Work with only one encoding (UTF-8)
+
+What it **can't** do:
+* Parse tags
+* Work with extended header, flags, padding
+* Work with encodings, except UTF-8
+
+**If you want some functionality, that library can't do, just write an issue. I will implement it as fast as I can**
+
+**And of course, pull requests are welcome!**
+
+## Benchmarks
+
+Set title, artist, album, year, genre and 50KB picture to 4,5MB MP3:
+```
+Benchmark-4	     100	  10209383 ns/op	  383363 B/op	      77 allocs/op
+```
+
+## Installation
+  	$ go get -u github.com/bogem/id3v2
+
+## Usage
+#### Example:
+```go
+package main
+
+import (
+  "github.com/bogem/id3v2"
+  "log"
+)
+
+func main() {
+		tag, err := id3v2.Open("file.mp3")
+		if err != nil {
+			fmt.Println("Error while opening mp3 file: ", err)
+		}
+
+		tag.SetArtist("Artist")
+		tag.SetTitle("Title")
+		tag.SetYear("2016")
+        ...
+
+
+		if err = tag.Close(); err != nil {
+			fmt.Println("Error while closing a tag: ", err)
+		}
+}
+
+```
+
+#### Available functions for setting text frames:
+```go
+tag.SetTitle(string)
+tag.SetArtist(string)
+tag.SetAlbum(string)
+tag.SetYear(string)
+tag.SetGenre(string)
+```
+
+#### Setting a picture
+
+```go
+package main
+
+import (
+  "github.com/bogem/id3v2"
+  "log"
+)
+
+func main() {
+		tag, err := id3v2.Open("file.mp3")
+		if err != nil {
+			log.Fatal("Error while opening mp3 file: ", err)
+		}
+
+		pic := id3v2.NewAttachedPicture()
+		pic.SetMimeType("image/jpeg")
+		pic.SetDescription("Cover")
+		pic.SetPictureType("Cover (front)")
+
+		artwork, err := os.Open("artwork.jpg")
+		if err != nil {
+			log.Fatal("Error while opening an artwork file: ", err)
+		}
+        defer artwork.Close()
+
+		if err = pic.SetPictureFromFile(artwork); err != nil {
+			log.Fatal("Error while setting a picture: ", err)
+		}
+
+		tag.SetAttachedPicture(pic)
+
+		if err = tag.Close(); err != nil {
+			log.Fatal("Error while closing a tag: ", err)
+		}
+}
+
+```
+
+## TODO
+
+* Parse tags
+* Work with other encodings
+* Work with extended header, flags, padding ***(Does somebody really use it?)***
+
+## License
+MIT

bench_test.go

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+package id3v2
+
+import (
+	"os"
+	"testing"
+)
+
+func Benchmark(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		t, err := Open("test.mp3")
+		if err != nil {
+			b.Error("Error while opening mp3 file: ", err)
+		}
+		t.SetTitle("Title")
+		t.SetArtist("Artist")
+		t.SetAlbum("Album")
+		t.SetYear("2016")
+		t.SetGenre("Genre")
+
+		pic := NewAttachedPicture()
+		pic.SetMimeType("image/jpeg")
+		pic.SetDescription("Cover")
+		pic.SetPictureType("Cover (front)")
+
+		artwork, err := os.Open("artwork.jpg")
+		if err != nil {
+			b.Error("Error while opening an artwork file: ", err)
+		}
+
+		if err = pic.SetPictureFromFile(artwork); err != nil {
+			b.Error("Error while setting a picture to picture frame: ", err)
+		}
+		t.SetAttachedPicture(pic)
+		if err = t.Close(); err != nil {
+			b.Error("Error while closing a tag: ", err)
+		}
+		if err = artwork.Close(); err != nil {
+			b.Error("Error while closing an artwork file: ", err)
+		}
+	}
+}

frame/apic_sequence.go

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+package frame
+
+import (
+	"bytes"
+	"errors"
+)
+
+type APICSequencer interface {
+	Framer
+
+	AddPicture(PictureFramer)
+	Picture(picType string) (PictureFramer, error)
+}
+
+// APICSequence stores several APICs and implements interface Framer.
+// Key for APICSequnce is a key for PictureType array,
+// so there is only one picture with the same picture type
+type APICSequence struct {
+	sequence map[int]PictureFramer
+	id       string
+}
+
+func NewAPICSequence() *APICSequence {
+	return &APICSequence{
+		sequence: make(map[int]PictureFramer),
+	}
+}
+
+func (as APICSequence) Form() ([]byte, error) {
+	var b bytes.Buffer
+	for _, pf := range as.sequence {
+		if frame, err := pf.Form(); err != nil {
+			return nil, err
+		} else {
+			b.Write(frame)
+		}
+	}
+	return b.Bytes(), nil
+}
+
+func (as APICSequence) ID() string {
+	return as.id
+}
+
+func (as *APICSequence) SetID(id string) {
+	as.id = id
+}
+
+func (as APICSequence) Size() (size uint32) {
+	for _, pf := range as.sequence {
+		size += pf.Size()
+	}
+	return
+}
+
+func (as *APICSequence) AddPicture(pic PictureFramer) {
+	for k, v := range PictureTypes {
+		if v == pic.PictureType() {
+			as.sequence[k] = pic
+			break
+		}
+	}
+}
+
+func (as APICSequence) Picture(picType string) (PictureFramer, error) {
+	for k, v := range PictureTypes {
+		if v == picType {
+			return as.sequence[k], nil
+		}
+	}
+	return &PictureFrame{}, errors.New("Unsupported picture type")
+}

frame/frame.go

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+package frame
+
+import (
+	"bytes"
+	"github.com/bogem/id3v2/util"
+)
+
+const (
+	FrameHeaderSize  = 10
+	IDSize           = 4
+	BytesInFrameSize = 4
+)
+
+type Framer interface {
+	Form() ([]byte, error)
+	ID() string
+	SetID(string)
+	Size() uint32
+}
+
+type FrameHeader struct {
+	ID        string
+	FrameSize uint32
+}
+
+func FormFrameHeader(f Framer) ([]byte, error) {
+	var b bytes.Buffer
+	b.WriteString(f.ID())
+	if size, err := util.FormSize(f.Size()); err != nil {
+		return nil, err
+	} else {
+		b.Write(size)
+	}
+	b.WriteByte(0)
+	b.WriteByte(0)
+	return b.Bytes(), nil
+}