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>

4 files changed, 61 insertions, 1 deletions

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