Why does hiredis ignore my callback on UNSUBSCRIBE in RESP3?

[stolyaroleh]

When I SUBSCRIBE to a channel with a callback, hiredis calls it with subscribe and message push messages, but not with unsubscribe. Instead, hiredis would send the reply to a push handler. This makes it harder for me to track callback lifetimes in C++, since I no longer have access to void *privdata that I have attached to my subscription.

When running the following modified example-libuv (and manually publishing a message after subscribing), I was expecting the following output:

subscribed
message
unsubscribed

Instead, I get:

subscribed
message
push: unsubscribe

#include <adapters/libuv.h>
#include <async.h>
#include <hiredis.h>

void callback(redisAsyncContext *c, void *r, void *privdata) {
  redisReply *reply = r;
  char *what = reply->element[0]->str;

  if (strcmp(what, "subscribe") == 0) {
    printf("subscribed\n");
    return;
  }

  if (strcmp(what, "message") == 0) {
    printf("message\n");
    redisAsyncCommand(c, NULL, NULL, "UNSUBSCRIBE");
    return;
  }

  if (strcmp(what, "unsubscribe") == 0) {
    printf("unsubscribed\n");
    redisAsyncFree(c);
  }
}

void pushCallback(redisAsyncContext *c, void *r) {
  redisReply *reply = r;
  char *what = reply->element[0]->str;
  printf("push: %s\n", what);
  redisAsyncFree(c);
}

int main(int argc, char **argv) {
  redisAsyncContext *c = redisAsyncConnect("127.0.0.1", 6379);

  if (c->err) {
    printf("Error: %s\n", c->errstr);
    return 1;
  }

  uv_loop_t *loop = uv_default_loop();
  redisLibuvAttach(c, loop);

  redisAsyncSetPushCallback(c, pushCallback);
  redisAsyncCommand(c, NULL, NULL, "HELLO 3");
  redisAsyncCommand(c, callback, NULL, "SUBSCRIBE foo");

  uv_run(loop, UV_RUN_DEFAULT);
  return 0;
}

It appears that this can be fixed with a one line patch:

--- a/async.c
+++ b/async.c
@@ -496,7 +496,8 @@ static int redisIsSubscribeReply(redisReply *reply) {
     len = reply->element[0]->len - off;
 
     return !strncasecmp(str, "subscribe", len) ||
-           !strncasecmp(str, "message", len);
+           !strncasecmp(str, "message", len) ||
+           !strncasecmp(str, "unsubscribe", len);
 
 }

Modified hiredis passes all unit tests and produces the output I expected.

[stolyaroleh]

Probably related: #738
Would you be open to a PR with the change above?

[bjosv]

We have the same problem and I will try-out your proposal a bit, or are there any new revelations regarding this issue?