From 919580a2282d2cccbfd010c7171956dd2eae77c4 Mon Sep 17 00:00:00 2001
From: Yossi Gottlieb <yossigo@gmail.com>
Date: Tue, 18 Aug 2020 17:16:08 +0300
Subject: [PATCH] Modules: expose real client on conn events.

When REDISMODULE_EVENT_CLIENT_CHANGE events are delivered, modules may
want to mutate the client state (e.g. perform authentication).

This change links the module context with the real client rather than a
fake client for these events.

(cherry picked from commit 67b43f75e23ba7a3915bc87e7edaa306fd1eee65)
---
 src/module.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/module.c b/src/module.c
index 65d22b713..afb525dbe 100644
--- a/src/module.c
+++ b/src/module.c
@@ -7263,6 +7263,7 @@ void moduleFireServerEvent(uint64_t eid, int subid, void *data) {
      * cheap if there are no registered modules. */
     if (listLength(RedisModule_EventListeners) == 0) return;
 
+    int real_client_used = 0;
     listIter li;
     listNode *ln;
     listRewind(RedisModule_EventListeners,&li);
@@ -7272,7 +7273,15 @@ void moduleFireServerEvent(uint64_t eid, int subid, void *data) {
             RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
             ctx.module = el->module;
 
-            if (ModulesInHooks == 0) {
+            if (eid == REDISMODULE_EVENT_CLIENT_CHANGE) {
+                /* In the case of client changes, we're pushing the real client
+                 * so the event handler can mutate it if needed. For example,
+                 * to change its authentication state in a way that does not
+                 * depend on specific commands executed later.
+                 */
+                ctx.client = (client *) data;
+                real_client_used = 1;
+            } else if (ModulesInHooks == 0) {
                 ctx.client = moduleFreeContextReusedClient;
             } else {
                 ctx.client = createClient(NULL);
@@ -7325,7 +7334,7 @@ void moduleFireServerEvent(uint64_t eid, int subid, void *data) {
             el->module->in_hook--;
             ModulesInHooks--;
 
-            if (ModulesInHooks != 0) freeClient(ctx.client);
+            if (ModulesInHooks != 0 && !real_client_used) freeClient(ctx.client);
             moduleFreeContext(&ctx);
         }
     }