lib: add function to obtain Message-ID hostname

Make the function already present in app/compose.go reusable while also
changing its signature for it not to require involvement of a Composer
instance.

Signed-off-by: Karel Balej <balejk@matfyz.cz>
Acked-by: Robin Jarry <robin@jarry.cc>

2 files changed, 30 insertions, 21 deletions

diff --git a/app/compose.go b/app/compose.go
index be8e5563..c71c7013 100644
--- a/app/compose.go
+++ b/app/compose.go
@@ -5,7 +5,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"math/rand"
 	"net/textproto"
 	"os"
 	"os/exec"
@@ -24,6 +23,7 @@ import (
 	"git.sr.ht/~rjarry/aerc/config"
 	"git.sr.ht/~rjarry/aerc/lib"
 	"git.sr.ht/~rjarry/aerc/lib/format"
+	"git.sr.ht/~rjarry/aerc/lib/send"
 	"git.sr.ht/~rjarry/aerc/lib/state"
 	"git.sr.ht/~rjarry/aerc/lib/templates"
 	"git.sr.ht/~rjarry/aerc/lib/ui"
@@ -820,7 +820,15 @@ func (c *Composer) PrepareHeader() (*mail.Header, error) {
 	// control headers not normally set by the user
 	// repeated calls to PrepareHeader should be a noop
 	if !c.header.Has("Message-Id") {
-		hostname, err := getMessageIdHostname(c)
+		froms, err := c.header.AddressList("from")
+		if err != nil {
+			return nil, err
+		}
+		if len(froms) == 0 {
+			return nil, fmt.Errorf("no valid From address found")
+		}
+		hostname, err := send.GetMessageIdHostname(
+			c.acctConfig.SendWithHostname, froms[0])
 		if err != nil {
 			return nil, err
 		}
@@ -839,25 +847,6 @@ func (c *Composer) PrepareHeader() (*mail.Header, error) {
 	return c.header, nil
 }
 
-func getMessageIdHostname(c *Composer) (string, error) {
-	if c.acctConfig.SendWithHostname {
-		return os.Hostname()
-	}
-	addrs, err := c.header.AddressList("from")
-	if err != nil {
-		return "", err
-	}
-	if len(addrs) == 0 {
-		// no from address present, generate a random hostname
-		return strings.ToUpper(strconv.FormatInt(rand.Int63(), 36)), nil
-	}
-	_, domain, found := strings.Cut(addrs[0].Address, "@")
-	if !found {
-		return "", fmt.Errorf("Invalid address %q", addrs[0])
-	}
-	return domain, nil
-}
-
 func (c *Composer) parseEmbeddedHeader() (*mail.Header, error) {
 	_, err := c.email.Seek(0, io.SeekStart)
 	if err != nil {
diff --git a/lib/send/parse.go b/lib/send/parse.go
index 460e91dc..d1088ee2 100644
--- a/lib/send/parse.go
+++ b/lib/send/parse.go
@@ -2,8 +2,13 @@ package send
 
 import (
 	"fmt"
+	"math/rand"
 	"net/url"
+	"os"
+	"strconv"
 	"strings"
+
+	"github.com/emersion/go-message/mail"
 )
 
 func parseScheme(uri *url.URL) (protocol string, auth string, err error) {
@@ -30,3 +35,18 @@ func parseScheme(uri *url.URL) (protocol string, auth string, err error) {
 	}
 	return protocol, auth, nil
 }
+
+func GetMessageIdHostname(sendWithHostname bool, from *mail.Address) (string, error) {
+	if sendWithHostname {
+		return os.Hostname()
+	}
+	if from == nil {
+		// no from address present, generate a random hostname
+		return strings.ToUpper(strconv.FormatInt(rand.Int63(), 36)), nil
+	}
+	_, domain, found := strings.Cut(from.Address, "@")
+	if !found {
+		return "", fmt.Errorf("Invalid address %q", from)
+	}
+	return domain, nil
+}