Fix SQL error logged on JOIN

Closes: https://todo.sr.ht/~emersion/soju/40

db.go

@@ -46,6 +46,8 @@ type Channel struct {
 	Key  string
 }
 
+var ErrNoSuchChannel = fmt.Errorf("soju: no such channel")
+
 type DB struct {
 	lock sync.RWMutex
 	db   *sql.DB
@@ -265,6 +267,23 @@ func (db *DB) ListChannels(networkID int64) ([]Channel, error) {
 	return channels, nil
 }
 
+func (db *DB) GetChannel(networkID int64, name string) (*Channel, error) {
+	db.lock.RLock()
+	defer db.lock.RUnlock()
+
+	ch := &Channel{Name: name}
+
+	var key *string
+	row := db.db.QueryRow("SELECT id, key FROM Channel WHERE network = ? AND name = ?", networkID, name)
+	if err := row.Scan(&ch.ID, &key); err == sql.ErrNoRows {
+		return nil, ErrNoSuchChannel
+	} else if err != nil {
+		return nil, err
+	}
+	ch.Key = fromStringPtr(key)
+	return ch, nil
+}
+
 func (db *DB) StoreChannel(networkID int64, ch *Channel) error {
 	db.lock.Lock()
 	defer db.lock.Unlock()

downstream.go

@@ -896,12 +896,17 @@ func (dc *downstreamConn) handleMessageRegistered(msg *irc.Message) error {
 				Params:  params,
 			})
 
-			err = dc.srv.db.StoreChannel(uc.network.ID, &Channel{
-				Name: upstreamName,
-				Key:  key,
-			})
-			if err != nil {
-				dc.logger.Printf("failed to create channel %q in DB: %v", upstreamName, err)
+			ch, err := dc.srv.db.GetChannel(uc.network.ID, upstreamName)
+			if err == ErrNoSuchChannel {
+				ch = &Channel{Name: upstreamName}
+			} else if err != nil {
+				return err
+			}
+
+			ch.Key = key
+
+			if err := dc.srv.db.StoreChannel(uc.network.ID, ch); err != nil {
+				return err
 			}
 		}
 	case "PART":