Fix the wrong woff when execute WAIT / WAITAOF in script (valkey-io#776)

When executing the script, the client passed in is a fake
client, and its woff is always 0.

This results in woff always being 0 when executing wait/waitaof
in the script, and the command returns a wrong number.

---------

Signed-off-by: Binbin <[email protected]>

src/replication.c

@@ -3400,6 +3400,18 @@ void replicationRequestAckFromReplicas(void) {
     server.get_ack_from_replicas = 1;
 }
 
+/* This function return client woff. If the script is currently running,
+ * returns the actual client woff */
+long long getClientWriteOffset(client *c) {
+    if (scriptIsRunning()) {
+        /* If a script is currently running, the client passed in is a fake
+         * client, and its woff is always 0. */
+        serverAssert(scriptGetClient() == c);
+        c = scriptGetCaller();
+    }
+    return c->woff;
+}
+
 /* Return the number of replicas that already acknowledged the specified
  * replication offset. */
 int replicationCountAcksByOffset(long long offset) {
@@ -3439,7 +3451,7 @@ int replicationCountAOFAcksByOffset(long long offset) {
 void waitCommand(client *c) {
     mstime_t timeout;
     long numreplicas, ackreplicas;
-    long long offset = c->woff;
+    long long offset = getClientWriteOffset(c);
 
     if (server.primary_host) {
         addReplyError(
@@ -3453,7 +3465,7 @@ void waitCommand(client *c) {
     if (getTimeoutFromObjectOrReply(c, c->argv[2], &timeout, UNIT_MILLISECONDS) != C_OK) return;
 
     /* First try without blocking at all. */
-    ackreplicas = replicationCountAcksByOffset(c->woff);
+    ackreplicas = replicationCountAcksByOffset(offset);
     if (ackreplicas >= numreplicas || c->flag.deny_blocking) {
         addReplyLongLong(c, ackreplicas);
         return;
@@ -3489,9 +3501,11 @@ void waitaofCommand(client *c) {
         return;
     }
 
+    long long offset = getClientWriteOffset(c);
+
     /* First try without blocking at all. */
-    ackreplicas = replicationCountAOFAcksByOffset(c->woff);
-    acklocal = server.fsynced_reploff >= c->woff;
+    ackreplicas = replicationCountAOFAcksByOffset(offset);
+    acklocal = server.fsynced_reploff >= offset;
     if ((ackreplicas >= numreplicas && acklocal >= numlocal) || c->flag.deny_blocking) {
         addReplyArrayLen(c, 2);
         addReplyLongLong(c, acklocal);
@@ -3501,7 +3515,7 @@ void waitaofCommand(client *c) {
 
     /* Otherwise block the client and put it into our list of clients
      * waiting for ack from replicas. */
-    blockClientForReplicaAck(c, timeout, c->woff, numreplicas, numlocal);
+    blockClientForReplicaAck(c, timeout, offset, numreplicas, numlocal);
 
     /* Make sure that the server will send an ACK request to all the replicas
      * before returning to the event loop. */

tests/unit/scripting.tcl

@@ -294,7 +294,7 @@ start_server {tags {"scripting"}} {
     } {0}
 
     test {EVAL - Scripts do not block on waitaof} {
-        run_script {redis.call('incr', 'x') return redis.pcall('waitaof','0','1','0')} 0
+        run_script {return redis.pcall('waitaof','0','1','0')} 0
     } {* 0}
 
     test {EVAL - Scripts do not block on XREAD with BLOCK option} {

tests/unit/wait.tcl

@@ -98,6 +98,35 @@ start_server {} {
         $rd close
         $rd2 close
     }
+
+    start_server {} {
+        test {Setup a new replica} {
+            r replicaof $master_host $master_port
+            wait_for_ofs_sync $master r
+            wait_for_ofs_sync $master $slave
+        }
+
+        test {WAIT in script will work} {
+            # Pause the old replica so it can not catch up the offset.
+            pause_process $slave_pid
+
+            # Primary set a new key and wait the new replica catch up the offset.
+            $master set foo bar
+            wait_for_ofs_sync $master r
+
+            # Wait for the new replica to report the acked offset to the primary.
+            # Because the old replica is paused, so the WAIT can only return 1.
+            # In an earlier version it returned 2, because the fake client's woff
+            # is always 0 so WAIT counted all the replicas.
+            wait_for_condition 50 100 {
+                [$master eval "return server.call('wait', '2', '0')" 0] eq 1
+            } else {
+                fail "WAIT in script does not work as expected."
+            }
+
+            resume_process $slave_pid
+        }
+    }
 }}