Add SORT_RO command (#9299)

Add a readonly variant of the STORE command, so it can be used on
read-only workloads (replica, ACL, etc)

src/server.c

@@ -789,6 +789,10 @@ struct redisCommand redisCommandTable[] = {
      "write use-memory @list @set @sortedset @dangerous",
      0,sortGetKeys,1,1,1,0,0,0},
 
+    {"sort_ro",sortroCommand,-2,
+     "read-only @list @set @sortedset @dangerous",
+     0,NULL,1,1,1,0,0,0},
+
     {"info",infoCommand,-1,
      "ok-loading ok-stale random @dangerous",
      0,NULL,0,0,0,0,0,0},

src/server.h

@@ -2606,6 +2606,7 @@ void syncCommand(client *c);
 void flushdbCommand(client *c);
 void flushallCommand(client *c);
 void sortCommand(client *c);
+void sortroCommand(client *c);
 void lremCommand(client *c);
 void lposCommand(client *c);
 void rpoplpushCommand(client *c);

src/sort.c

@@ -189,7 +189,7 @@ int sortCompare(const void *s1, const void *s2) {
 
 /* The SORT command is the most complex command in Redis. Warning: this code
  * is optimized for speed and a bit less for readability */
-void sortCommand(client *c) {
+void sortCommandGeneric(client *c, int readonly) {
     list *operations;
     unsigned int outputlen = 0;
     int desc = 0, alpha = 0;
@@ -226,7 +226,7 @@ void sortCommand(client *c) {
                 break;
             }
             j+=2;
-        } else if (!strcasecmp(c->argv[j]->ptr,"store") && leftargs >= 1) {
+        } else if (readonly == 0 && !strcasecmp(c->argv[j]->ptr,"store") && leftargs >= 1) {
             storekey = c->argv[j+1];
             j++;
         } else if (!strcasecmp(c->argv[j]->ptr,"by") && leftargs >= 1) {
@@ -595,3 +595,12 @@ void sortCommand(client *c) {
     }
     zfree(vector);
 }
+
+/* SORT wrapper function for read-only mode. */
+void sortroCommand(client *c) {
+    sortCommandGeneric(c, 1);
+}
+
+void sortCommand(client *c) {
+    sortCommandGeneric(c, 0);
+}

tests/unit/sort.tcl

@@ -263,6 +263,18 @@ start_server {
         r lrange testb 0 -1
     } {5 3 4} {cluster:skip}
 
+    test "SORT_RO - Successful case" {
+        r del mylist
+        r lpush mylist a
+        r set x:a 100
+        r sort_ro mylist by nosort get x:*->
+    } {100} {cluster:skip}
+
+    test "SORT_RO - Cannot run with STORE arg" {
+        catch {r sort_ro foolist STORE bar} e
+        set e
+    } {ERR syntax error}
+
     tags {"slow"} {
         set num 100
         set res [create_random_dataset $num lpush]