No reuse of the previous reply callback

When multiple replies are parsed from a socket in one read
a previously found callback might get reused when the current
reply has no known callback.

This can be triggered by the added testcase which unsubscribe to
subscribed (A,B) and a non-subscribed channel (X).
Without this correction a callback for wrong channel is called.
-  In 'unsubscribe B X A', B's callback is called when handling X.
-  Now this is not done, i.e. there is no callback called for X.

async.c

@@ -508,7 +508,6 @@ static int redisIsSubscribeReply(redisReply *reply) {
 
 void redisProcessCallbacks(redisAsyncContext *ac) {
     redisContext *c = &(ac->c);
-    redisCallback cb = {NULL, NULL, 0, NULL};
     void *reply = NULL;
     int status;
 
@@ -524,6 +523,7 @@ void redisProcessCallbacks(redisAsyncContext *ac) {
 
             /* If monitor mode, repush callback */
             if(c->flags & REDIS_MONITORING) {
+                redisCallback cb = {NULL, NULL, 0, NULL};
                 __redisPushCallback(&ac->replies,&cb);
             }
 
@@ -547,6 +547,7 @@ void redisProcessCallbacks(redisAsyncContext *ac) {
 
         /* Even if the context is subscribed, pending regular
          * callbacks will get a reply before pub/sub messages arrive. */
+        redisCallback cb = {NULL, NULL, 0, NULL};
         if (__redisShiftCallback(&ac->replies,&cb) != REDIS_OK) {
             /*
              * A spontaneous reply in a not-subscribed context can be the error

test.c

@@ -1711,6 +1711,98 @@ static void test_command_timeout_during_pubsub(struct config config) {
     /* Verify test checkpoints */
     test_cond(state.checkpoint == 5);
 }
+
+/* Subscribe callback for test_pubsub_multiple_channels */
+void subscribe_channel_a_cb(redisAsyncContext *ac, void *r, void *privdata) {
+    redisReply *reply = r;
+    TestState *state = privdata;
+
+    assert(reply != NULL && reply->type == REDIS_REPLY_ARRAY &&
+           reply->elements == 3);
+
+    if (strcmp(reply->element[0]->str,"subscribe") == 0) {
+        assert(strcmp(reply->element[1]->str,"A") == 0);
+        publish_msg(state->options,"A","Hello!");
+        state->checkpoint++;
+    } else if (strcmp(reply->element[0]->str,"message") == 0) {
+        assert(strcmp(reply->element[1]->str,"A") == 0 &&
+               strcmp(reply->element[2]->str,"Hello!") == 0);
+        state->checkpoint++;
+
+        /* Unsubscribe to channels, including a channel X which we don't subscribe to */
+        redisAsyncCommand(ac,unexpected_cb,
+                          (void*)"unsubscribe should not call unexpected_cb()",
+                          "unsubscribe B X A");
+        /* Send a regular command after unsubscribing, then disconnect */
+        state->disconnect = 1;
+        redisAsyncCommand(ac,integer_cb,state,"LPUSH mylist foo");
+    } else if (strcmp(reply->element[0]->str,"unsubscribe") == 0) {
+        assert(strcmp(reply->element[1]->str,"A") == 0);
+        state->checkpoint++;
+    } else {
+        printf("Unexpected pubsub command: %s\n", reply->element[0]->str);
+        exit(1);
+    }
+}
+
+/* Subscribe callback for test_pubsub_multiple_channels */
+void subscribe_channel_b_cb(redisAsyncContext *ac, void *r, void *privdata) {
+    redisReply *reply = r;
+    TestState *state = privdata;
+
+    assert(reply != NULL && reply->type == REDIS_REPLY_ARRAY &&
+           reply->elements == 3);
+
+    if (strcmp(reply->element[0]->str,"subscribe") == 0) {
+        assert(strcmp(reply->element[1]->str,"B") == 0);
+        state->checkpoint++;
+    } else if (strcmp(reply->element[0]->str,"unsubscribe") == 0) {
+        assert(strcmp(reply->element[1]->str,"B") == 0);
+        state->checkpoint++;
+    } else {
+        printf("Unexpected pubsub command: %s\n", reply->element[0]->str);
+        exit(1);
+    }
+}
+
+/* Test handling of multiple channels
+ * - subscribe to channel A and B
+ * - a published message on A triggers an unsubscribe of channel B, X and A
+ *   where channel X is not subscribed to.
+ * - a command sent after unsubscribe triggers a disconnect */
+static void test_pubsub_multiple_channels(struct config config) {
+    test("Subscribe to multiple channels: ");
+    /* Setup event dispatcher with a testcase timeout */
+    base = event_base_new();
+    struct event *timeout = evtimer_new(base,timeout_cb,NULL);
+    assert(timeout != NULL);
+
+    evtimer_assign(timeout,base,timeout_cb,NULL);
+    struct timeval timeout_tv = {.tv_sec = 10};
+    evtimer_add(timeout,&timeout_tv);
+
+    /* Connect */
+    redisOptions options = get_redis_tcp_options(config);
+    redisAsyncContext *ac = redisAsyncConnectWithOptions(&options);
+    assert(ac != NULL && ac->err == 0);
+    redisLibeventAttach(ac,base);
+
+    /* Not expecting any push messages in this test */
+    redisAsyncSetPushCallback(ac,unexpected_push_cb);
+
+    /* Start subscribing to two channels */
+    TestState state = {.options = &options};
+    redisAsyncCommand(ac,subscribe_channel_a_cb,&state,"subscribe A");
+    redisAsyncCommand(ac,subscribe_channel_b_cb,&state,"subscribe B");
+
+    /* Start event dispatching loop */
+    assert(event_base_dispatch(base) == 0);
+    event_free(timeout);
+    event_base_free(base);
+
+    /* Verify test checkpoints */
+    test_cond(state.checkpoint == 6);
+}
 #endif /* HIREDIS_TEST_ASYNC */
 
 int main(int argc, char **argv) {
@@ -1841,6 +1933,7 @@ int main(int argc, char **argv) {
     disconnect(c, 0);
 
     test_pubsub_handling(cfg);
+    test_pubsub_multiple_channels(cfg);
     if (major >= 6) {
         test_pubsub_handling_resp3(cfg);
         test_command_timeout_during_pubsub(cfg);