fix: used to fail sdk rpc in case target was self

src/plugin/rpc/client.rs

@@ -389,8 +389,8 @@ fn resolve_rpc_target(
         // XXX: this shouldn't be a problem if replicasets aren't too big,
         // but if they are we might want to construct a HashSet from candidates
         for instance_id in replicas {
-            if my_instance_id == instance_id {
-                // Don't want to call self
+            if my_instance_id == instance_id && candidates.len() > 1 {
+                // Prefer someone else instead of self
                 continue;
             }
             if candidates.contains(&instance_id) {
@@ -406,8 +406,8 @@ fn resolve_rpc_target(
         // TODO: find a better strategy then just the random one
         let random_index = rand::random::<usize>() % candidates.len();
         let mut instance_id = std::mem::take(&mut candidates[random_index]);
-        if instance_id == my_instance_id {
-            // Don't want to call self
+        if instance_id == my_instance_id && candidates.len() > 1 {
+            // Prefer someone else instead of self
             let index = (random_index + 1) % candidates.len();
             instance_id = std::mem::take(&mut candidates[index]);
         }

test/int/test_plugin.py

@@ -2477,6 +2477,36 @@ cluster:
     # TODO: check calling to poisoned service
 
 
+def test_plugin_rpc_sdk_single_instance(cluster: Cluster):
+    i1 = cluster.add_instance(wait_online=True, init_replication_factor=1)
+
+    plugin_name = _PLUGIN_W_SDK
+    service_name = SERVICE_W_RPC
+    install_and_enable_plugin(i1, plugin_name, [service_name], migrate=True)
+
+    # Check sending request with `master = false` when there's ony one instance
+    context = make_context()
+    input = dict(
+        service_info=(plugin_name, service_name, _PLUGIN_VERSION_1),
+        path="/ping",
+        input="by-bucket-id",
+        bucket_id=13,
+        to_master=False,
+    )
+    i1.call(".proc_rpc_dispatch", "/proxy", msgpack.dumps(input), context)
+
+    # Check sending request with `master = false` when there's ony one instance
+    context = make_context()
+    input = dict(
+        service_info=(plugin_name, service_name, _PLUGIN_VERSION_1),
+        path="/ping",
+        input="by-replicaset-id",
+        replicaset_id=i1.call(".proc_instance_info")["replicaset_id"],
+        to_master=False,
+    )
+    i1.call(".proc_rpc_dispatch", "/proxy", msgpack.dumps(input), context)
+
+
 def test_sdk_internal(cluster: Cluster):
     [i1] = cluster.deploy(instance_count=1)