Try to generate multiple uid before failing

cmd/eksterd/memory.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"bytes"
 	"database/sql"
+	"expvar"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -15,6 +16,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/lib/pq"
 	"p83.nl/go/ekster/pkg/auth"
 	"p83.nl/go/ekster/pkg/fetch"
 	"p83.nl/go/ekster/pkg/microsub"
@@ -26,6 +28,14 @@ import (
 	"willnorris.com/go/microformats"
 )
 
+var (
+	varMicrosub *expvar.Map
+)
+
+func init() {
+	varMicrosub = expvar.NewMap("microsub")
+}
+
 // DefaultPrio is the priority value for new channels
 const DefaultPrio = 9999999
 
@@ -125,27 +135,53 @@ GROUP BY c.id;
 	return channels, nil
 }
 
+func shouldRetryWithNewUID(err error, try int) bool {
+	if err == nil {
+		return false
+	}
+
+	if e, ok := err.(*pq.Error); ok {
+		if e.Code == "23505" && e.Constraint == "channels_uid_key" {
+			if try > 5 {
+				return false
+			}
+			return true
+		}
+	}
+	return false
+}
+
 // ChannelsCreate creates a channels
 func (b *memoryBackend) ChannelsCreate(name string) (microsub.Channel, error) {
-	uid := util.RandStringBytes(24)
+	varMicrosub.Add("ChannelsCreate", 1)
-
+	/*
+	 * try 5 times to generate a uid for a channel.
+	 * If we get a database error we retry.
+	 */
+	try := 0
 	channel := microsub.Channel{
-		UID:    uid,
 		Name:   name,
 		Unread: microsub.Unread{Type: microsub.UnreadCount},
 	}
-
+	for {
-	result, err := b.database.Exec(`insert into "channels" ("uid", "name", "created_at") values($1, $2, DEFAULT)`, channel.UID, channel.Name)
+		varMicrosub.Add("ChannelsCreate.RandStringBytes", 1)
-	if err != nil {
+		channel.UID = util.RandStringBytes(24)
-		return channel, err
+		result, err := b.database.Exec(`insert into "channels" ("uid", "name", "created_at") values($1, $2, DEFAULT)`, channel.UID, channel.Name)
-	}
+		if err != nil {
-
+			log.Println("channels insert", err)
-	if n, err := result.RowsAffected(); err != nil {
+			if !shouldRetryWithNewUID(err, try) {
-		if n > 0 {
+				return channel, err
-			b.broker.Notifier <- sse.Message{Event: "new channel", Object: channelMessage{1, channel}}
+			}
+			try++
+			continue
 		}
+		if n, err := result.RowsAffected(); err != nil {
+			if n > 0 {
+				b.broker.Notifier <- sse.Message{Event: "new channel", Object: channelMessage{1, channel}}
+			}
+		}
+		return channel, nil
 	}
-	return channel, nil
 }
 
 // ChannelsUpdate updates a channels