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>

1 files changed, 20 insertions, 0 deletions

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
+}