Optimize encrypt attachment

src/gitlab.com/ProtonMail/go-pm-crypto/internal/packets.go

@@ -0,0 +1,105 @@
+package internal
+
+import (
+	"bytes"
+	"golang.org/x/crypto/openpgp/packet"
+	"gitlab.com/ProtonMail/go-pm-crypto/models"
+	"io"
+			)
+
+func SplitPackets(encryptedReader io.Reader, estimatedLength int) (*models.EncryptedSplit, error){
+	var err error
+
+	//kr *KeyRing, r io.Reader) (key *SymmetricKey, symEncryptedData []byte,
+	packets := packet.NewReader(encryptedReader)
+
+	outSplit := &models.EncryptedSplit{}
+
+	// Save encrypted key and signature apart
+	var ek *packet.EncryptedKey
+	// var decryptErr error
+	for {
+		var p packet.Packet
+		if p, err = packets.Next(); err == io.EOF {
+			err = nil
+			break
+		}
+		switch p := p.(type) {
+		case *packet.EncryptedKey:
+			// We got an encrypted key. Try to decrypt it with each available key
+			if ek != nil && ek.Key != nil {
+				break
+			}
+			ek = p
+			break
+		case *packet.SymmetricallyEncrypted:
+			// The code below is optimized to not
+			var b bytes.Buffer
+			// 128 is an estimation of the size difference between input and output, the size difference is most probably
+			// 16 bytes at a maximum though.
+			b.Grow(128 + estimatedLength)
+			// empty encoded length + start byte
+			b.Write(make([]byte, 6))
+			b.WriteByte(byte(1))
+			actualLength := 1
+			block := make([]byte, 128)
+			for {
+				n, err := p.Contents.Read(block)
+				if err == io.EOF {
+					break
+				}
+				b.Write(block[:n])
+				actualLength += n
+			}
+
+			// quick encoding
+			symEncryptedData := b.Bytes()
+			if actualLength < 192 {
+				symEncryptedData[4] = byte(210)
+				symEncryptedData[5] = byte(actualLength)
+				symEncryptedData = symEncryptedData[4:]
+			} else if actualLength < 8384 {
+				actualLength = actualLength - 192
+				symEncryptedData[3] = byte(210)
+				symEncryptedData[4] = 192+byte(actualLength>>8)
+				symEncryptedData[5] = byte(actualLength)
+				symEncryptedData = symEncryptedData[3:]
+			} else {
+				symEncryptedData[0] = byte(210)
+				symEncryptedData[1] = byte(255)
+				symEncryptedData[2] = byte(actualLength>>24)
+				symEncryptedData[3] = byte(actualLength>>16)
+				symEncryptedData[4] = byte(actualLength>>8)
+				symEncryptedData[5] = byte(actualLength)
+			}
+
+			outSplit.DataPacket = symEncryptedData
+			break
+
+		}
+	}
+
+	var buf bytes.Buffer
+	ek.Serialize(&buf)
+	outSplit.KeyPacket = buf.Bytes()
+
+	return outSplit, err
+}
+
+//encode length based on 4.2.2. in the RFC
+func encodedLength(length int) (b []byte) {
+	if length < 192 {
+		b = append(b, byte(length))
+	} else if length < 8384 {
+		length = length - 192
+		b = append(b, 192+byte(length>>8))
+		b = append(b, byte(length))
+	} else {
+		b = append(b, byte(255))
+		b = append(b, byte(length>>24))
+		b = append(b, byte(length>>16))
+		b = append(b, byte(length>>8))
+		b = append(b, byte(length))
+	}
+	return
+}