Fix all lint errors

obfuscated2/frame.go

@@ -9,7 +9,6 @@ import (
 	"github.com/juju/errors"
 )
 
-// https://blog.susanka.eu/how-telegram-obfuscates-its-mtproto-traffic/
 // [frameOffsetFirst:frameOffsetKey:frameOffsetIV:frameOffsetMagic:frameOffsetDC:frameOffsetEnd]
 const (
 	frameLenKey   = 32
@@ -30,23 +29,34 @@ const (
 
 var tgMagicBytes = []byte{tgMagicByte, tgMagicByte, tgMagicByte, tgMagicByte}
 
+// Frame represents handshake frame. Telegram sends 64 bytes of obfuscated2
+// initialization data first.
+// https://blog.susanka.eu/how-telegram-obfuscates-its-mtproto-traffic/
 type Frame []byte
 
+// Key returns AES encryption key.
 func (f Frame) Key() []byte {
 	return f[frameOffsetFirst:frameOffsetKey]
 }
 
+// IV returns AES encryption initialization vector
 func (f Frame) IV() []byte {
 	return f[frameOffsetKey:frameOffsetIV]
 }
 
+// Magic returns magic bytes from last 8 bytes of frame. Telegram checks
+// for values there. If after decryption magic is not as expected,
+// connection considered as failed.
 func (f Frame) Magic() []byte {
 	return f[frameOffsetIV:frameOffsetMagic]
 }
 
+// DC returns number of datacenter IP client wants to use.
 func (f Frame) DC() (n int16) {
 	buf := bytes.NewReader(f[frameOffsetMagic:frameOffsetDC])
-	binary.Read(buf, binary.LittleEndian, &n)
+	if err := binary.Read(buf, binary.LittleEndian, &n); err != nil {
+		n = 1
+	}
 
 	if n < 0 {
 		n = -n
@@ -57,10 +67,13 @@ func (f Frame) DC() (n int16) {
 	return n - 1
 }
 
+// Valid checks that *decrypted* frame is valid. Only magic bytes are checked.
 func (f Frame) Valid() bool {
 	return bytes.Equal(f.Magic(), tgMagicBytes)
 }
 
+// Invert inverts frame for extracting encryption keys. Pkease check that link:
+// https://blog.susanka.eu/how-telegram-obfuscates-its-mtproto-traffic/
 func (f Frame) Invert() Frame {
 	reversed := make(Frame, FrameLen)
 	copy(reversed, f)
@@ -72,6 +85,7 @@ func (f Frame) Invert() Frame {
 	return reversed
 }
 
+// ExtractFrame extracts exact obfuscated2 handshake frame from given reader.
 func ExtractFrame(conn io.Reader) (Frame, error) {
 	buf := &bytes.Buffer{}
 	if _, err := io.CopyN(buf, conn, FrameLen); err != nil {

obfuscated2/obfuscated2.go

@@ -8,35 +8,43 @@ import (
 	"github.com/juju/errors"
 )
 
+// Obfuscated2 contains AES CTR encryption and decryption streams
+// for telegram connection.
 type Obfuscated2 struct {
 	decryptor cipher.Stream
 	encryptor cipher.Stream
 }
 
+// Encrypt encrypts given data.
 func (o *Obfuscated2) Encrypt(data []byte) []byte {
 	buf := make([]byte, len(data))
 	o.encryptor.XORKeyStream(buf, data)
 	return buf
 }
 
+// Decrypt decrypts given data.
 func (o *Obfuscated2) Decrypt(data []byte) []byte {
 	buf := make([]byte, len(data))
 	o.decryptor.XORKeyStream(buf, data)
 	return buf
 }
 
+// ParseObfuscated2ClientFrame parses client frame. Please check this link for
+// details: http://telegra.ph/telegram-blocks-wtf-05-26
+//
+// Beware, link above is in russian.
 func ParseObfuscated2ClientFrame(secret, data []byte) (*Obfuscated2, int16, error) {
 	frame := Frame(data)
 
 	decHasher := sha256.New()
-	decHasher.Write(frame.Key())
-	decHasher.Write(secret)
+	decHasher.Write(frame.Key()) // nolint: errcheck
+	decHasher.Write(secret)      // nolint: errcheck
 	decryptor := makeStreamCipher(decHasher.Sum(nil), frame.IV())
 
 	invertedFrame := frame.Invert()
 	encHasher := sha256.New()
-	encHasher.Write(invertedFrame.Key())
-	encHasher.Write(secret)
+	encHasher.Write(invertedFrame.Key()) // nolint: errcheck
+	encHasher.Write(secret)              // nolint: errcheck
 	encryptor := makeStreamCipher(encHasher.Sum(nil), invertedFrame.IV())
 
 	decryptedFrame := make(Frame, FrameLen)
@@ -53,6 +61,9 @@ func ParseObfuscated2ClientFrame(secret, data []byte) (*Obfuscated2, int16, erro
 	return obfs, decryptedFrame.DC(), nil
 }
 
+// MakeTelegramObfuscated2Frame creates new handshake frame to send to
+// Telegram.
+// https://blog.susanka.eu/how-telegram-obfuscates-its-mtproto-traffic/
 func MakeTelegramObfuscated2Frame() (*Obfuscated2, Frame) {
 	frame := generateFrame()
 

obfuscated2/obfuscated2_test.go

@@ -2,7 +2,6 @@ package obfuscated2
 
 import (
 	"crypto/sha256"
-	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"