Resp3 oob push support (#841)

Proper support for RESP3 PUSH messages.

By default, PUSH messages are now intercepted and the reply memory freed.  
This means existing code should work unchanged when connecting to Redis
>= 6.0.0 even if `CLIENT TRACKING` were then enabled.

Additionally, we define two callbacks users can configure if they wish to handle
these messages in a custom way:

void redisPushFn(void *privdata, void *reply);
void redisAsyncPushFn(redisAsyncContext *ac, void *reply);

See #825

2 files changed, 121 insertions, 0 deletions

diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index dd3a313..1d5bc56 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -44,3 +44,6 @@ ENDIF()
 
 ADD_EXECUTABLE(example example.c)
 TARGET_LINK_LIBRARIES(example hiredis)
+
+ADD_EXECUTABLE(example-push example-push.c)
+TARGET_LINK_LIBRARIES(example-push hiredis)
diff --git a/examples/example-push.c b/examples/example-push.c
new file mode 100644
index 0000000..d8b41f9
--- /dev/null
+++ b/examples/example-push.c
@@ -0,0 +1,118 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <hiredis.h>
+#include <win32.h>
+
+#define KEY_COUNT 5
+
+#define panicAbort(fmt, ...) \
+    do { \
+        fprintf(stderr, "%s:%d:%s(): " fmt, __FILE__, __LINE__, __func__, __VA_ARGS__); \
+        exit(-1); \
+    } while (0)
+
+static void assertReplyAndFree(redisContext *context, redisReply *reply, int type) {
+    if (reply == NULL)
+        panicAbort("NULL reply from server (error: %s)", context->errstr);
+
+    if (reply->type != type) {
+        if (reply->type == REDIS_REPLY_ERROR)
+            fprintf(stderr, "Redis Error: %s\n", reply->str);
+
+        panicAbort("Expected reply type %d but got type %d", type, reply->type);
+    }
+
+    freeReplyObject(reply);
+}
+
+/* Switch to the RESP3 protocol and enable client tracking */
+static void enableClientTracking(redisContext *c) {
+    redisReply *reply = redisCommand(c, "HELLO 3");
+    if (reply == NULL || c->err) {
+        panicAbort("NULL reply or server error (error: %s)", c->errstr);
+    }
+
+    if (reply->type != REDIS_REPLY_MAP) {
+        fprintf(stderr, "Error: Can't send HELLO 3 command.  Are you sure you're ");
+        fprintf(stderr, "connected to redis-server >= 6.0.0?\nRedis error: %s\n",
+                        reply->type == REDIS_REPLY_ERROR ? reply->str : "(unknown)");
+        exit(-1);
+    }
+
+    freeReplyObject(reply);
+
+    /* Enable client tracking */
+    reply = redisCommand(c, "CLIENT TRACKING ON");
+    assertReplyAndFree(c, reply, REDIS_REPLY_STATUS);
+}
+
+void pushReplyHandler(void *privdata, void *r) {
+    redisReply *reply = r;
+    int *invalidations = privdata;
+
+    /* Sanity check on the invalidation reply */
+    if (reply->type != REDIS_REPLY_PUSH || reply->elements != 2 ||
+        reply->element[1]->type != REDIS_REPLY_ARRAY ||
+        reply->element[1]->element[0]->type != REDIS_REPLY_STRING)
+    {
+        panicAbort("%s", "Can't parse PUSH message!");
+    }
+
+    /* Increment our invalidation count */
+    *invalidations += 1;
+
+    printf("pushReplyHandler(): INVALIDATE '%s' (invalidation count: %d)\n",
+           reply->element[1]->element[0]->str, *invalidations);
+
+    freeReplyObject(reply);
+}
+
+int main(int argc, char **argv) {
+    unsigned int j, invalidations = 0;
+    redisContext *c;
+    redisReply *reply;
+
+    const char *hostname = (argc > 1) ? argv[1] : "127.0.0.1";
+    int port = (argc > 2) ? atoi(argv[2]) : 6379;
+
+    redisOptions o = {0};
+    REDIS_OPTIONS_SET_TCP(&o, hostname, port);
+
+    /* Set our custom PUSH message handler */
+    o.push_cb = pushReplyHandler;
+
+    c = redisConnectWithOptions(&o);
+    if (c == NULL || c->err)
+        panicAbort("Connection error:  %s", c ? c->errstr : "OOM");
+
+    /* Enable RESP3 and turn on client tracking */
+    enableClientTracking(c);
+
+    /* Set our context privdata to the address of our invalidation counter.  Each
+     * time our PUSH handler is called, hiredis will pass the privdata for context */
+    c->privdata = &invalidations;
+
+    /* Set some keys and then read them back.  Once we do that, Redis will deliver
+     * invalidation push messages whenever the key is modified */
+    for (j = 0; j < KEY_COUNT; j++) {
+        reply = redisCommand(c, "SET key:%d initial:%d", j, j);
+        assertReplyAndFree(c, reply, REDIS_REPLY_STATUS);
+
+        reply = redisCommand(c, "GET key:%d", j);
+        assertReplyAndFree(c, reply, REDIS_REPLY_STRING);
+    }
+
+    /* Trigger invalidation messages by updating keys we just read */
+    for (j = 0; j < KEY_COUNT; j++) {
+        printf("            main(): SET key:%d update:%d\n", j, j);
+        reply = redisCommand(c, "SET key:%d update:%d", j, j);
+        assertReplyAndFree(c, reply, REDIS_REPLY_STATUS);
+        printf("            main(): SET REPLY OK\n");
+    }
+
+    printf("\nTotal detected invalidations: %d, expected: %d\n", invalidations, KEY_COUNT);
+
+    /* PING server */
+    redisFree(c);
+}