go.crypto/openpgp/packet: Add user attribute packet support.

Supports JPEG images as well as free-form arbitrary subpacket data in
user attributes (RFC 4880, Section 5.12)

R=agl
CC=golang-dev
https://golang.org/cl/12966045

openpgp/packet/opaque.go

@@ -7,6 +7,7 @@ package packet
 import (
 	"bytes"
 	"code.google.com/p/go.crypto/openpgp/errors"
+	"encoding/binary"
 	"io"
 	"io/ioutil"
 )
@@ -83,18 +84,15 @@ func (or *OpaqueReader) Next() (op *OpaquePacket, err error) {
 // OpaqueSubpacket represents an unparsed OpenPGP subpacket,
 // as found in signature and user attribute packets.
 type OpaqueSubpacket struct {
-	Length   uint32
 	SubType  uint8
 	Contents []byte
 }
 
 // OpaqueSubpackets extracts opaque, unparsed OpenPGP subpackets from
 // their byte representation.
-func OpaqueSubpackets(contents []byte) ([]*OpaqueSubpacket, error) {
-	var result []*OpaqueSubpacket
-	var err error
+func OpaqueSubpackets(contents []byte) (result []*OpaqueSubpacket, err error) {
 	var (
-		subHeaderLen uint32
+		subHeaderLen int
 		subPacket    *OpaqueSubpacket
 	)
 	for len(contents) > 0 {
@@ -103,47 +101,64 @@ func OpaqueSubpackets(contents []byte) ([]*OpaqueSubpacket, error) {
 			break
 		}
 		result = append(result, subPacket)
-		contents = contents[subHeaderLen+subPacket.Length:]
+		contents = contents[subHeaderLen+len(subPacket.Contents):]
 	}
-	return result, err
+	return
 }
 
-func nextSubpacket(contents []byte) (subHeaderLen uint32, subPacket *OpaqueSubpacket, err error) {
+func nextSubpacket(contents []byte) (subHeaderLen int, subPacket *OpaqueSubpacket, err error) {
 	// RFC 4880, section 5.2.3.1
+	var subLen uint32
 	if len(contents) < 1 {
 		goto Truncated
 	}
 	subPacket = &OpaqueSubpacket{}
 	switch {
 	case contents[0] < 192:
-		subHeaderLen = 1
-		subPacket.Length = uint32(contents[0])
+		subHeaderLen = 2 // 1 length byte, 1 subtype byte
+		if len(contents) < subHeaderLen {
+			goto Truncated
+		}
+		subLen = uint32(contents[0])
 		contents = contents[1:]
 	case contents[0] < 255:
-		subHeaderLen = 2
-		if len(contents) < 2 {
+		subHeaderLen = 3 // 2 length bytes, 1 subtype
+		if len(contents) < subHeaderLen {
 			goto Truncated
 		}
-		subPacket.Length = uint32(contents[0]-192)<<8 + uint32(contents[1]) + 192
+		subLen = uint32(contents[0]-192)<<8 + uint32(contents[1]) + 192
 		contents = contents[2:]
 	default:
-		subHeaderLen = 5
-		if len(contents) < 5 {
+		subHeaderLen = 6 // 5 length bytes, 1 subtype
+		if len(contents) < subHeaderLen {
 			goto Truncated
 		}
-		subPacket.Length = uint32(contents[1])<<24 |
+		subLen = uint32(contents[1])<<24 |
 			uint32(contents[2])<<16 |
 			uint32(contents[3])<<8 |
 			uint32(contents[4])
 		contents = contents[5:]
 	}
-	if subPacket.Length > uint32(len(contents)) {
+	if subLen > uint32(len(contents)) {
 		goto Truncated
 	}
 	subPacket.SubType = contents[0]
-	subPacket.Contents = contents[1:subPacket.Length]
+	subPacket.Contents = contents[1:subLen]
 	return
 Truncated:
 	err = errors.StructuralError("subpacket truncated")
 	return
 }
+
+func (osp *OpaqueSubpacket) Serialize(w io.Writer) (err error) {
+	buf := make([]byte, 6)
+	buf[0] = 0xff
+	// Header length includes the subtype byte
+	binary.BigEndian.PutUint32(buf[1:5], uint32(len(osp.Contents)+1))
+	buf[5] = osp.SubType
+	if _, err = w.Write(buf); err != nil {
+		return
+	}
+	_, err = w.Write(osp.Contents)
+	return
+}

openpgp/packet/packet.go

@@ -293,6 +293,7 @@ const (
 	packetTypeLiteralData               packetType = 11
 	packetTypeUserId                    packetType = 13
 	packetTypePublicSubkey              packetType = 14
+	packetTypeUserAttribute             packetType = 17
 	packetTypeSymmetricallyEncryptedMDC packetType = 18
 )
 
@@ -333,6 +334,8 @@ func Read(r io.Reader) (p Packet, err error) {
 		p = new(LiteralData)
 	case packetTypeUserId:
 		p = new(UserId)
+	case packetTypeUserAttribute:
+		p = new(UserAttribute)
 	case packetTypeSymmetricallyEncryptedMDC:
 		se := new(SymmetricallyEncrypted)
 		se.MDC = true

openpgp/packet/userattribute.go

@@ -0,0 +1,91 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packet
+
+import (
+	"bytes"
+	"image"
+	"image/jpeg"
+	"io"
+	"io/ioutil"
+)
+
+const UserAttrImageSubpacket = 1
+
+// UserAttribute is capable of storing other types of data about a user
+// beyond name, email and a text comment. In practice, user attributes are typically used
+// to store a signed thumbnail photo JPEG image of the user.
+// See RFC 4880, section 5.12.
+type UserAttribute struct {
+	Contents []*OpaqueSubpacket
+}
+
+// NewUserAttributePhoto creates a user attribute packet
+// containing the given images.
+func NewUserAttributePhoto(photos ...image.Image) (uat *UserAttribute, err error) {
+	uat = new(UserAttribute)
+	for _, photo := range photos {
+		var buf bytes.Buffer
+		// RFC 4880, Section 5.12.1.
+		data := []byte{
+			0x10, 0x00, // Little-endian image header length (16 bytes)
+			0x01,       // Image header version 1
+			0x01,       // JPEG
+			0, 0, 0, 0, // 12 reserved octets, must be all zero.
+			0, 0, 0, 0,
+			0, 0, 0, 0}
+		if _, err = buf.Write(data); err != nil {
+			return
+		}
+		if err = jpeg.Encode(&buf, photo, nil); err != nil {
+			return
+		}
+		uat.Contents = append(uat.Contents, &OpaqueSubpacket{
+			SubType:  UserAttrImageSubpacket,
+			Contents: buf.Bytes()})
+	}
+	return
+}
+
+// NewUserAttribute creates a new user attribute packet containing the given subpackets.
+func NewUserAttribute(contents ...*OpaqueSubpacket) *UserAttribute {
+	return &UserAttribute{Contents: contents}
+}
+
+func (uat *UserAttribute) parse(r io.Reader) (err error) {
+	// RFC 4880, section 5.13
+	b, err := ioutil.ReadAll(r)
+	if err != nil {
+		return
+	}
+	uat.Contents, err = OpaqueSubpackets(b)
+	return
+}
+
+// Serialize marshals the user attribute to w in the form of an OpenPGP packet, including
+// header.
+func (uat *UserAttribute) Serialize(w io.Writer) (err error) {
+	var buf bytes.Buffer
+	for _, sp := range uat.Contents {
+		sp.Serialize(&buf)
+	}
+	if err = serializeHeader(w, packetTypeUserAttribute, buf.Len()); err != nil {
+		return err
+	}
+	_, err = w.Write(buf.Bytes())
+	return
+}
+
+// ImageData returns zero or more byte slices, each containing
+// JPEG File Interchange Format (JFIF), for each photo in the
+// the user attribute packet.
+func (uat *UserAttribute) ImageData() (imageData [][]byte) {
+	for _, sp := range uat.Contents {
+		if sp.SubType == UserAttrImageSubpacket && len(sp.Contents) > 16 {
+			imageData = append(imageData, sp.Contents[16:])
+		}
+	}
+	return
+}

openpgp/packet/userattribute_test.go

@@ -0,0 +1,109 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packet
+
+import (
+	"bytes"
+	"encoding/base64"
+	"image/color"
+	"image/jpeg"
+	"testing"
+)
+
+func TestParseUserAttribute(t *testing.T) {
+	r := base64.NewDecoder(base64.StdEncoding, bytes.NewBufferString(userAttributePacket))
+	for i := 0; i < 2; i++ {
+		p, err := Read(r)
+		if err != nil {
+			t.Fatal(err)
+		}
+		uat := p.(*UserAttribute)
+		imgs := uat.ImageData()
+		if len(imgs) != 1 {
+			t.Errorf("Unexpected number of images in user attribute packet: %d", len(imgs))
+		}
+		if len(imgs[0]) != 3395 {
+			t.Errorf("Unexpected JPEG image size: %d", len(imgs[0]))
+		}
+		img, err := jpeg.Decode(bytes.NewBuffer(imgs[0]))
+		if err != nil {
+			t.Errorf("Error decoding JPEG image: %v", err)
+		}
+		// A pixel in my right eye.
+		pixel := color.NRGBAModel.Convert(img.At(56, 36))
+		ref := color.NRGBA{R: 157, G: 128, B: 124, A: 255}
+		if pixel != ref {
+			t.Errorf("Unexpected pixel color: %v", pixel)
+		}
+		w := bytes.NewBuffer(nil)
+		err = uat.Serialize(w)
+		if err != nil {
+			t.Errorf("Error writing user attribute: %v", err)
+		}
+		r = bytes.NewBuffer(w.Bytes())
+	}
+}
+
+const userAttributePacket = `
+0cyWzJQBEAABAQAAAAAAAAAAAAAAAP/Y/+AAEEpGSUYAAQIAAAEAAQAA/9sAQwAFAwQEBAMFBAQE
+BQUFBgcMCAcHBwcPCgsJDBEPEhIRDxEQExYcFxMUGhUQERghGBocHR8fHxMXIiQiHiQcHh8e/9sA
+QwEFBQUHBgcOCAgOHhQRFB4eHh4eHh4eHh4eHh4eHh4eHh4eHh4eHh4eHh4eHh4eHh4eHh4eHh4e
+Hh4eHh4eHh4e/8AAEQgAZABkAwEiAAIRAQMRAf/EAB8AAAEFAQEBAQEBAAAAAAAAAAABAgMEBQYH
+CAkKC//EALUQAAIBAwMCBAMFBQQEAAABfQECAwAEEQUSITFBBhNRYQcicRQygZGhCCNCscEVUtHw
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