Add RESET command. (#7982)

Perform full reset of all client connection states, is if the client was
disconnected and re-connected. This affects:

* MULTI state
* Watched keys
* MONITOR mode
* Pub/Sub subscription
* ACL/Authenticated state
* Client tracking state
* Cluster read-only/asking state
* RESP version (reset to 2)
* Selected database
* CLIENT REPLY state

The response is +RESET to make it easily distinguishable from other
responses.

Co-authored-by: Oran Agra <oran@redislabs.com>
Co-authored-by: Itamar Haber <itamar@redislabs.com>

src/networking.c

@@ -97,6 +97,16 @@ void linkClient(client *c) {
     raxInsert(server.clients_index,(unsigned char*)&id,sizeof(id),c,NULL);
 }
 
+/* Initialize client authentication state.
+ */
+static void clientSetDefaultAuth(client *c) {
+    /* If the default user does not require authentication, the user is
+     * directly authenticated. */
+    c->user = DefaultUser;
+    c->authenticated = (c->user->flags & USER_FLAG_NOPASS) &&
+                       !(c->user->flags & USER_FLAG_DISABLED);
+}
+
 client *createClient(connection *conn) {
     client *c = zmalloc(sizeof(client));
 
@@ -130,16 +140,12 @@ client *createClient(connection *conn) {
     c->argv = NULL;
     c->argv_len_sum = 0;
     c->cmd = c->lastcmd = NULL;
-    c->user = DefaultUser;
     c->multibulklen = 0;
     c->bulklen = -1;
     c->sentlen = 0;
     c->flags = 0;
     c->ctime = c->lastinteraction = server.unixtime;
-    /* If the default user does not require authentication, the user is
+    clientSetDefaultAuth(c);
-     * directly authenticated. */
-    c->authenticated = (c->user->flags & USER_FLAG_NOPASS) &&
-                       !(c->user->flags & USER_FLAG_DISABLED);
     c->replstate = REPL_STATE_NONE;
     c->repl_put_online_on_ack = 0;
     c->reploff = 0;
@@ -2257,6 +2263,50 @@ int clientSetNameOrReply(client *c, robj *name) {
     return C_OK;
 }
 
+/* Reset the client state to resemble a newly connected client.
+ */
+void resetCommand(client *c) {
+    listNode *ln;
+
+    /* MONITOR clients are also marked with CLIENT_SLAVE, we need to
+     * distinguish between the two.
+     */
+    if (c->flags & CLIENT_MONITOR) {
+        ln = listSearchKey(server.monitors,c);
+        serverAssert(ln != NULL);
+        listDelNode(server.monitors,ln);
+
+        c->flags &= ~(CLIENT_MONITOR|CLIENT_SLAVE);
+    }
+
+    if (c->flags & (CLIENT_SLAVE|CLIENT_MASTER|CLIENT_MODULE)) {
+        addReplyError(c,"can only reset normal client connections");
+        return;
+    }
+
+    if (c->flags & CLIENT_TRACKING) disableTracking(c);
+    selectDb(c,0);
+    c->resp = 2;
+
+    clientSetDefaultAuth(c);
+    moduleNotifyUserChanged(c);
+    discardTransaction(c);
+
+    pubsubUnsubscribeAllChannels(c,0);
+    pubsubUnsubscribeAllPatterns(c,0);
+
+    if (c->name) {
+        decrRefCount(c->name);
+        c->name = NULL;
+    }
+
+    /* Selectively clear state flags not covered above */
+    c->flags &= ~(CLIENT_ASKING|CLIENT_READONLY|CLIENT_PUBSUB|
+            CLIENT_REPLY_OFF|CLIENT_REPLY_SKIP_NEXT);
+
+    addReplyStatus(c,"RESET");
+}
+
 void clientCommand(client *c) {
     listNode *ln;
     listIter li;

src/server.c

@@ -1036,7 +1036,11 @@ struct redisCommand redisCommandTable[] = {
 
     {"stralgo",stralgoCommand,-2,
      "read-only @string",
-     0,lcsGetKeys,0,0,0,0,0,0}
+     0,lcsGetKeys,0,0,0,0,0,0},
+
+    {"reset",resetCommand,-1,
+     "no-script ok-stale ok-loading fast @connection",
+     0,NULL,0,0,0,0,0,0}
 };
 
 /*============================ Utility functions ============================ */
@@ -3740,7 +3744,8 @@ int processCommand(client *c) {
          * set. */
         if (c->flags & CLIENT_MULTI &&
             c->cmd->proc != execCommand &&
-            c->cmd->proc != discardCommand) {
+            c->cmd->proc != discardCommand &&
+            c->cmd->proc != resetCommand) {
             reject_cmd_on_oom = 1;
         }
 
@@ -3806,10 +3811,11 @@ int processCommand(client *c) {
         c->cmd->proc != subscribeCommand &&
         c->cmd->proc != unsubscribeCommand &&
         c->cmd->proc != psubscribeCommand &&
-        c->cmd->proc != punsubscribeCommand) {
+        c->cmd->proc != punsubscribeCommand &&
+        c->cmd->proc != resetCommand) {
         rejectCommandFormat(c,
             "Can't execute '%s': only (P)SUBSCRIBE / "
-            "(P)UNSUBSCRIBE / PING / QUIT are allowed in this context",
+            "(P)UNSUBSCRIBE / PING / QUIT / RESET are allowed in this context",
             c->cmd->name);
         return C_OK;
     }
@@ -3860,7 +3866,8 @@ int processCommand(client *c) {
     /* Exec the command */
     if (c->flags & CLIENT_MULTI &&
         c->cmd->proc != execCommand && c->cmd->proc != discardCommand &&
-        c->cmd->proc != multiCommand && c->cmd->proc != watchCommand)
+        c->cmd->proc != multiCommand && c->cmd->proc != watchCommand &&
+        c->cmd->proc != resetCommand)
     {
         queueMultiCommand(c);
         addReply(c,shared.queued);

src/server.h

@@ -2493,6 +2493,7 @@ void xtrimCommand(client *c);
 void lolwutCommand(client *c);
 void aclCommand(client *c);
 void stralgoCommand(client *c);
+void resetCommand(client *c);
 
 #if defined(__GNUC__)
 void *calloc(size_t count, size_t size) __attribute__ ((deprecated));

tests/unit/other.tcl

@@ -249,6 +249,57 @@ start_server {tags {"other"}} {
         waitForBgsave r
         r save
     } {OK}
+
+    test {RESET clears client state} {
+        r client setname test-client
+        r client tracking on
+
+        assert_equal [r reset] "RESET"
+        set client [r client list]
+        assert_match {*name= *} $client
+        assert_match {*flags=N *} $client
+    }
+
+    test {RESET clears MONITOR state} {
+        set rd [redis_deferring_client]
+        $rd monitor
+        assert_equal [$rd read] "OK"
+
+        $rd reset
+
+        # skip reset ouptut
+        $rd read
+        assert_equal [$rd read] "RESET"
+
+        assert_no_match {*flags=O*} [r client list]
+    }
+
+    test {RESET clears and discards MULTI state} {
+        r multi
+        r set key-a a
+
+        r reset
+        catch {r exec} err
+        assert_match {*EXEC without MULTI*} $err
+    }
+
+    test {RESET clears Pub/Sub state} {
+        r subscribe channel-1
+        r reset
+
+        # confirm we're not subscribed by executing another command
+        r set key val
+    }
+
+    test {RESET clears authenticated state} {
+        r acl setuser user1 on >secret +@all
+        r auth user1 secret
+        assert_equal [r acl whoami] user1
+
+        r reset
+
+        assert_equal [r acl whoami] default
+    }
 }
 
 start_server {tags {"other"}} {