pgp: add attach key command

Add compose command ("attach-key") to attach the public key associated
with the sending account. Public key is attached in ascii armor format,
with the mimetype set according to RFC 3156 ("application/pgp-keys").

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Tested-by: Koni Marti <koni.marti@gmail.com>

7 files changed, 174 insertions, 3 deletions

diff --git a/commands/compose/attach-key.go b/commands/compose/attach-key.go
new file mode 100644
index 0000000..c12df44
--- /dev/null
+++ b/commands/compose/attach-key.go
@@ -0,0 +1,32 @@
+package compose
+
+import (
+	"errors"
+
+	"git.sr.ht/~rjarry/aerc/widgets"
+)
+
+type AttachKey struct{}
+
+func init() {
+	register(AttachKey{})
+}
+
+func (AttachKey) Aliases() []string {
+	return []string{"attach-key"}
+}
+
+func (AttachKey) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
+}
+
+func (AttachKey) Execute(aerc *widgets.Aerc, args []string) error {
+	if len(args) != 1 {
+		return errors.New("Usage: attach-key")
+	}
+
+	composer, _ := aerc.SelectedTab().(*widgets.Composer)
+
+	composer.SetAttachKey(!composer.AttachKey())
+	return nil
+}
diff --git a/doc/aerc.1.scd b/doc/aerc.1.scd
index 3713917..0b33cee 100644
--- a/doc/aerc.1.scd
+++ b/doc/aerc.1.scd
@@ -383,6 +383,9 @@ message list, the message in the message viewer, etc).
 *attach* <path>
 	Attaches the file at the given path to the email.
 
+*attach-key*
+	Attaches the public key for the configured account to the email.
+
 *detach* [path]
 	Detaches the file with the given path from the composed email. If no path is
 	specified, detaches the first attachment instead.
diff --git a/lib/crypto/crypto.go b/lib/crypto/crypto.go
index 54a20e6..3c961ad 100644
--- a/lib/crypto/crypto.go
+++ b/lib/crypto/crypto.go
@@ -21,6 +21,7 @@ type Provider interface {
 	Close()
 	GetSignerKeyId(string) (string, error)
 	GetKeyId(string) (string, error)
+	ExportKey(string) (io.Reader, error)
 }
 
 func New(s string) Provider {
diff --git a/lib/crypto/gpg/gpg.go b/lib/crypto/gpg/gpg.go
index fe32468..00125ba 100644
--- a/lib/crypto/gpg/gpg.go
+++ b/lib/crypto/gpg/gpg.go
@@ -59,6 +59,10 @@ func (m *Mail) GetKeyId(s string) (string, error) {
 	return gpgbin.GetKeyId(s)
 }
 
+func (m *Mail) ExportKey(k string) (io.Reader, error) {
+	return gpgbin.ExportPublicKey(k)
+}
+
 func handleSignatureError(e string) models.SignatureValidity {
 	if e == "gpg: missing public key" {
 		return models.UnknownEntity
diff --git a/lib/crypto/gpg/gpgbin/keys.go b/lib/crypto/gpg/gpgbin/keys.go
index 9c8b233..bef90cf 100644
--- a/lib/crypto/gpg/gpgbin/keys.go
+++ b/lib/crypto/gpg/gpgbin/keys.go
@@ -1,6 +1,12 @@
 package gpgbin
 
-import "fmt"
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os/exec"
+	"strings"
+)
 
 // GetPrivateKeyId runs gpg --list-secret-keys s
 func GetPrivateKeyId(s string) (string, error) {
@@ -21,3 +27,18 @@ func GetKeyId(s string) (string, error) {
 	}
 	return id, nil
 }
+
+// ExportPublicKey exports the public key identified by k in armor format
+func ExportPublicKey(k string) (io.Reader, error) {
+	cmd := exec.Command("gpg", "--export", "--armor", k)
+
+	var outbuf bytes.Buffer
+	var stderr strings.Builder
+	cmd.Stdout = &outbuf
+	cmd.Stderr = &stderr
+	cmd.Run()
+	if strings.Contains(stderr.String(), "gpg") {
+		return nil, fmt.Errorf("gpg: error exporting key")
+	}
+	return &outbuf, nil
+}
diff --git a/lib/crypto/pgp/pgp.go b/lib/crypto/pgp/pgp.go
index f0f3f65..4dbe37c 100644
--- a/lib/crypto/pgp/pgp.go
+++ b/lib/crypto/pgp/pgp.go
@@ -13,6 +13,7 @@ import (
 
 	"git.sr.ht/~rjarry/aerc/models"
 	"github.com/ProtonMail/go-crypto/openpgp"
+	"github.com/ProtonMail/go-crypto/openpgp/armor"
 	"github.com/ProtonMail/go-crypto/openpgp/packet"
 	"github.com/emersion/go-message/mail"
 	"github.com/emersion/go-pgpmail"
@@ -271,6 +272,39 @@ func (m *Mail) GetKeyId(s string) (string, error) {
 	return entity.PrimaryKey.KeyIdString(), nil
 }
 
+func (m *Mail) ExportKey(k string) (io.Reader, error) {
+	var err error
+	var entity *openpgp.Entity
+	switch strings.Contains(k, "@") {
+	case true:
+		entity, err = m.getSignerEntityByEmail(k)
+		if err != nil {
+			return nil, err
+		}
+	case false:
+		entity, err = m.getSignerEntityByKeyId(k)
+		if err != nil {
+			return nil, err
+		}
+	}
+	pks := bytes.NewBuffer(nil)
+	err = entity.Serialize(pks)
+	if err != nil {
+		return nil, fmt.Errorf("pgp: error exporting key: %v", err)
+	}
+	pka := bytes.NewBuffer(nil)
+	w, err := armor.Encode(pka, "PGP PUBLIC KEY BLOCK", map[string]string{})
+	if err != nil {
+		return nil, fmt.Errorf("pgp: error exporting key: %v", err)
+	}
+	w.Write(pks.Bytes())
+	if err != nil {
+		return nil, fmt.Errorf("pgp: error exporting key: %v", err)
+	}
+	w.Close()
+	return pka, nil
+}
+
 func handleSignatureError(e string) models.SignatureValidity {
 	if e == "openpgp: signature made by unknown entity" {
 		return models.UnknownEntity
diff --git a/widgets/compose.go b/widgets/compose.go
index 49627fc..8830d9d 100644
--- a/widgets/compose.go
+++ b/widgets/compose.go
@@ -51,6 +51,7 @@ type Composer struct {
 	crypto      *cryptoStatus
 	sign        bool
 	encrypt     bool
+	attachKey   bool
 
 	layout    HeaderLayout
 	focusable []ui.MouseableDrawableInteractive
@@ -183,6 +184,16 @@ func (c *Composer) Sent() bool {
 	return c.sent
 }
 
+func (c *Composer) SetAttachKey(attach bool) error {
+	c.attachKey = attach
+	c.resetReview()
+	return nil
+}
+
+func (c *Composer) AttachKey() bool {
+	return c.attachKey
+}
+
 func (c *Composer) SetSign(sign bool) error {
 	c.sign = sign
 	err := c.updateCrypto()
@@ -581,7 +592,7 @@ func (c *Composer) WriteMessage(header *mail.Header, writer io.Writer) error {
 }
 
 func writeMsgImpl(c *Composer, header *mail.Header, writer io.Writer) error {
-	if len(c.attachments) == 0 {
+	if len(c.attachments) == 0 && !c.attachKey {
 		// no attachements
 		return writeInlineBody(header, c.email, writer)
 	} else {
@@ -598,6 +609,12 @@ func writeMsgImpl(c *Composer, header *mail.Header, writer io.Writer) error {
 				return errors.Wrap(err, "writeAttachment")
 			}
 		}
+		if c.attachKey {
+			err := c.writeKeyAttachment(w)
+			if err != nil {
+				return err
+			}
+		}
 		w.Close()
 	}
 	return nil
@@ -1060,6 +1077,9 @@ func newReviewMessage(composer *Composer, err error) *reviewMessage {
 	for i := 0; i < len(composer.attachments)-1; i++ {
 		spec = append(spec, ui.GridSpec{Strategy: ui.SIZE_EXACT, Size: ui.Const(1)})
 	}
+	if composer.attachKey {
+		spec = append(spec, ui.GridSpec{Strategy: ui.SIZE_EXACT, Size: ui.Const(1)})
+	}
 	// make the last element fill remaining space
 	spec = append(spec, ui.GridSpec{Strategy: ui.SIZE_WEIGHT, Size: ui.Const(1)})
 
@@ -1085,7 +1105,12 @@ func newReviewMessage(composer *Composer, err error) *reviewMessage {
 		grid.AddChild(ui.NewText("Attachments:",
 			uiConfig.GetStyle(config.STYLE_TITLE))).At(i, 0)
 		i += 1
-		if len(composer.attachments) == 0 {
+		if composer.attachKey {
+			grid.AddChild(ui.NewText(composer.crypto.signKey+".asc",
+				uiConfig.GetStyle(config.STYLE_DEFAULT))).At(i, 0)
+			i += 1
+		}
+		if len(composer.attachments) == 0 && !composer.attachKey {
 			grid.AddChild(ui.NewText("(none)",
 				uiConfig.GetStyle(config.STYLE_DEFAULT))).At(i, 0)
 		} else {
@@ -1185,3 +1210,54 @@ func (c *Composer) checkEncryptionKeys(_ string) bool {
 	c.updateCrypto()
 	return true
 }
+
+func (c *Composer) writeKeyAttachment(w *mail.Writer) error {
+	// Verify key exists and get keyid
+	cp := c.aerc.Crypto
+	var (
+		err error
+		s   string
+	)
+	if c.crypto.signKey == "" {
+		if c.acctConfig.PgpKeyId != "" {
+			s = c.acctConfig.PgpKeyId
+		} else {
+			s, err = getSenderEmail(c)
+			if err != nil {
+				return err
+			}
+		}
+		c.crypto.signKey, err = cp.GetSignerKeyId(s)
+		if err != nil {
+			return err
+		}
+	}
+	// Get the key in armor format
+	r, err := cp.ExportKey(c.crypto.signKey)
+	if err != nil {
+		c.aerc.PushError(err.Error())
+		return err
+	}
+	filename := c.crypto.signKey + ".asc"
+	mimeType := "application/pgp-keys"
+	params := map[string]string{
+		"charset": "UTF-8",
+		"name":    filename,
+	}
+	// set header fields
+	ah := mail.AttachmentHeader{}
+	ah.SetContentType(mimeType, params)
+	// setting the filename auto sets the content disposition
+	ah.SetFilename(filename)
+
+	aw, err := w.CreateAttachment(ah)
+	if err != nil {
+		return errors.Wrap(err, "CreateKeyAttachment")
+	}
+	defer aw.Close()
+
+	if _, err := io.Copy(aw, r); err != nil {
+		return errors.Wrap(err, "io.Copy")
+	}
+	return nil
+}