From 1a17cdfadf43ae6179dc7556caae579436066a2f Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Fri, 30 Nov 2018 16:31:02 +0100
Subject: [PATCH] RESP3: addReplyNullArray() added for better RESP2 compat.

---
 src/networking.c | 12 ++++++++++++
 src/server.h     |  1 +
 2 files changed, 13 insertions(+)

diff --git a/src/networking.c b/src/networking.c
index 72f44f07..8be22629 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -611,6 +611,18 @@ void addReplyNull(client *c) {
     }
 }
 
+/* A null array is a concept that no longer exists in RESP3. However
+ * RESP2 had it, so API-wise we have this call, that will emit the correct
+ * RESP2 protocol, however for RESP3 the reply will always be just the
+ * Null type "_\r\n". */
+void addReplyNullArray(client *c) {
+    if (c->resp == 2) {
+        addReplyString(c,"*-1\r\n",5);
+    } else {
+        addReplyString(c,"_\r\n",3);
+    }
+}
+
 /* Create the length prefix of a bulk reply, example: $2234 */
 void addReplyBulkLen(client *c, robj *obj) {
     size_t len;
diff --git a/src/server.h b/src/server.h
index 2958c635..d4558df5 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1438,6 +1438,7 @@ void acceptTcpHandler(aeEventLoop *el, int fd, void *privdata, int mask);
 void acceptUnixHandler(aeEventLoop *el, int fd, void *privdata, int mask);
 void readQueryFromClient(aeEventLoop *el, int fd, void *privdata, int mask);
 void addReplyNull(client *c);
+void addReplyNullArray(client *c);
 void addReplyString(client *c, const char *s, size_t len);
 void addReplyBulk(client *c, robj *obj);
 void addReplyBulkCString(client *c, const char *s);