Fix writing replies to async-closed clients

For some commands such as ACL subcommands, we may firstly close the client that
is being used and want to write reply to it secondly, but we actully can't write
reply to it if we close it even aync. So we add a flag 'CLIENT_CLOSE_AFTER_COMMAND'
to mark the client, this flag means we will close the client after executing commands
and writing entire reply, so that we can write reply to the client when execute
commands and will close it later if it is set to this flag.

src/acl.c

@@ -297,7 +297,13 @@ void ACLFreeUserAndKillClients(user *u) {
              * it in non authenticated mode. */
             c->user = DefaultUser;
             c->authenticated = 0;
-            freeClientAsync(c);
+            /* We will write replies to this client later, so we can't
+             * close it directly even if async. */
+            if (c == server.current_client) {
+                c->flags |= CLIENT_CLOSE_AFTER_COMMAND;
+            } else {
+                freeClientAsync(c);
+            }
         }
     }
     ACLFreeUser(u);

src/module.c

@@ -5530,7 +5530,13 @@ void revokeClientAuthentication(client *c) {
 
     c->user = DefaultUser;
     c->authenticated = 0;
-    freeClientAsync(c);
+    /* We will write replies to this client later, so we can't close it
+     * directly even if async. */
+    if (c == server.current_client) {
+        c->flags |= CLIENT_CLOSE_AFTER_COMMAND;
+    } else {
+        freeClientAsync(c);
+    }
 }
 
 /* Cleanup all clients that have been authenticated with this module. This

src/server.c

@@ -3402,6 +3402,13 @@ void call(client *c, int flags) {
     dirty = server.dirty-dirty;
     if (dirty < 0) dirty = 0;
 
+    /* After executing command, we will close the client after writing entire
+     * reply if it is set 'CLIENT_CLOSE_AFTER_COMMAND' flag. */
+    if (!server.loading && c->flags & CLIENT_CLOSE_AFTER_COMMAND) {
+        c->flags &= ~CLIENT_CLOSE_AFTER_COMMAND;
+        c->flags |= CLIENT_CLOSE_AFTER_REPLY;
+    }
+
     /* When EVAL is called loading the AOF we don't want commands called
      * from Lua to go into the slowlog or to populate statistics. */
     if (server.loading && c->flags & CLIENT_LUA)

src/server.h

@@ -264,6 +264,8 @@ extern int configOOMScoreAdjValuesDefaults[CONFIG_OOM_COUNT];
                                              about writes performed by myself.*/
 #define CLIENT_IN_TO_TABLE (1ULL<<38) /* This client is in the timeout table. */
 #define CLIENT_PROTOCOL_ERROR (1ULL<<39) /* Protocol error chatting with it. */
+#define CLIENT_CLOSE_AFTER_COMMAND (1LL<<40) /* Close after executing commands
+                                              * and writing entire reply. */
 
 /* Client block type (btype field in client structure)
  * if CLIENT_BLOCKED flag is set. */

tests/unit/acl.tcl

@@ -260,6 +260,23 @@ start_server {tags {"acl"}} {
         catch {r ACL help xxx} e
         assert_match "*Unknown subcommand or wrong number of arguments*" $e
     }
+
+    test {Delete a user that the client doesn't use} {
+        r ACL setuser not_used on >passwd
+        assert {[r ACL deluser not_used] == 1}
+        # The client is not closed
+        assert {[r ping] eq {PONG}}
+    }
+
+    test {Delete a user that the client is using} {
+        r ACL setuser using on +acl >passwd
+        r AUTH using passwd
+        # The client will receive reply normally
+        assert {[r ACL deluser using] == 1}
+        # The client is closed
+        catch {[r ping]} e
+        assert_match "*I/O error*" $e
+    }
 }
 
 set server_path [tmpdir "server.acl"]