From c1689166b71f298aec40db877e125c76c178b0ba Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Tue, 16 Oct 2018 16:48:31 +0200
Subject: [PATCH] Streams: rewrite empty streams with XADD MAXLEN 0. Use
 XSETID.

Related to #5426.
---
 src/aof.c | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/src/aof.c b/src/aof.c
index 4877172a..7d31183e 100644
--- a/src/aof.c
+++ b/src/aof.c
@@ -1158,22 +1158,28 @@ int rewriteStreamObject(rio *r, robj *key, robj *o) {
                 if (rioWriteBulkString(r,(char*)value,value_len) == 0) return 0;
             }
         }
-        /* Append XSTREAM SETID after XADD, make sure lastid is correct,
-         * in case of XDEL lastid. */
-        if (rioWriteBulkCount(r,'*',4) == 0) return 0;
-        if (rioWriteBulkString(r,"XSTREAM",7) == 0) return 0;
-        if (rioWriteBulkString(r,"SETID",5) == 0) return 0;
-        if (rioWriteBulkObject(r,key) == 0) return 0;
-        if (rioWriteBulkStreamID(r,&s->last_id) == 0) return 0;
     } else {
-        /* Using XSTREAM CREATE if the stream is empty. */
-        if (rioWriteBulkCount(r,'*',4) == 0) return 0;
-        if (rioWriteBulkString(r,"XSTREAM",7) == 0) return 0;
-        if (rioWriteBulkString(r,"CREATE",6) == 0) return 0;
+        /* Use the XADD MAXLEN 0 trick to generate an empty stream if
+         * the key we are serializing is an empty string, which is possible
+         * for the Stream type. */
+        if (rioWriteBulkCount(r,'*',7) == 0) return 0;
+        if (rioWriteBulkString(r,"XADD",4) == 0) return 0;
         if (rioWriteBulkObject(r,key) == 0) return 0;
-        if (rioWriteBulkStreamID(r,&s->last_id) == 0) return 0;
+        if (rioWriteBulkString(r,"MAXLEN",6) == 0) return 0;
+        if (rioWriteBulkString(r,"0",1) == 0) return 0;
+        if (rioWriteBulkString(r,"*",1) == 0) return 0;
+        if (rioWriteBulkString(r,"x",1) == 0) return 0;
+        if (rioWriteBulkString(r,"y",1) == 0) return 0;
     }
 
+    /* Append XSETID after XADD, make sure lastid is correct,
+     * in case of XDEL lastid. */
+    if (rioWriteBulkCount(r,'*',3) == 0) return 0;
+    if (rioWriteBulkString(r,"XSETID",6) == 0) return 0;
+    if (rioWriteBulkObject(r,key) == 0) return 0;
+    if (rioWriteBulkStreamID(r,&s->last_id) == 0) return 0;
+
+
     /* Create all the stream consumer groups. */
     if (s->cgroups) {
         raxIterator ri;