1 files changed, 33 insertions, 7 deletions

diff --git a/src/networking.c b/src/networking.c
index 3b4f3b0fe..761645cb2 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -135,23 +135,49 @@ redisClient *createClient(int fd) {
  * returns REDIS_OK, and make sure to install the write handler in our event
  * loop so that when the socket is writable new data gets written.
  *
- * If the client should not receive new data, because it is a fake client,
- * a master, a slave not yet online, or because the setup of the write handler
- * failed, the function returns REDIS_ERR.
+ * If the client should not receive new data, because it is a fake client
+ * (used to load AOF in memory), a master or because the setup of the write
+ * handler failed, the function returns REDIS_ERR.
+ *
+ * The function may return REDIS_OK without actually installing the write
+ * event handler in the following cases:
+ *
+ * 1) The event handler should already be installed since the output buffer
+ *    already contained something.
+ * 2) The client is a slave but not yet online, so we want to just accumulate
+ *    writes in the buffer but not actually sending them yet.
  *
  * Typically gets called every time a reply is built, before adding more
  * data to the clients output buffers. If the function returns REDIS_ERR no
  * data should be appended to the output buffers. */
 int prepareClientToWrite(redisClient *c) {
+    /* If it's the Lua client we always return ok without installing any
+     * handler since there is no socket at all. */
     if (c->flags & REDIS_LUA_CLIENT) return REDIS_OK;
+
+    /* Masters don't receive replies, unless REDIS_MASTER_FORCE_REPLY flag
+     * is set. */
     if ((c->flags & REDIS_MASTER) &&
         !(c->flags & REDIS_MASTER_FORCE_REPLY)) return REDIS_ERR;
-    if (c->fd <= 0) return REDIS_ERR; /* Fake client */
+
+    if (c->fd <= 0) return REDIS_ERR; /* Fake client for AOF loading. */
+
+    /* Only install the handler if not already installed and, in case of
+     * slaves, if the client can actually receive writes. */
     if (c->bufpos == 0 && listLength(c->reply) == 0 &&
         (c->replstate == REDIS_REPL_NONE ||
-         c->replstate == REDIS_REPL_ONLINE) && !c->repl_put_online_on_ack &&
-        aeCreateFileEvent(server.el, c->fd, AE_WRITABLE,
-        sendReplyToClient, c) == AE_ERR) return REDIS_ERR;
+         (c->replstate == REDIS_REPL_ONLINE && !c->repl_put_online_on_ack)))
+    {
+        /* Try to install the write handler. */
+        if (aeCreateFileEvent(server.el, c->fd, AE_WRITABLE,
+                sendReplyToClient, c) == AE_ERR)
+        {
+            freeClientAsync(c);
+            return REDIS_ERR;
+        }
+    }
+
+    /* Authorize the caller to queue in the output buffer of this client. */
     return REDIS_OK;
 }