Verify a zenoh router is available for the session

rmw_zenoh_cpp/CMakeLists.txt

@@ -35,6 +35,7 @@ add_library(rmw_zenoh_cpp SHARED
   src/detail/type_support.cpp
   src/detail/type_support_common.cpp
   src/detail/zenoh_config.cpp
+  src/detail/zenoh_router_check.cpp
   src/rmw_event.cpp
   src/rmw_get_network_flow_endpoints.cpp
   src/rmw_get_node_info_and_types.cpp

rmw_zenoh_cpp/src/detail/zenoh_router_check.cpp

@@ -0,0 +1,89 @@
+// Copyright 2023 Open Source Robotics Foundation, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "zenoh_router_check.hpp"
+
+#include <rcutils/env.h>
+#include <rcutils/logging_macros.h>
+
+#include <iomanip>
+#include <sstream>
+#include <string>
+
+namespace
+{
+
+// Convert a Zenoh Id to a string
+// Zenoh IDs are LSB-first 128bit unsigned and non-zero integers in hexadecimal lowercase.
+// @param pid Zenoh Id to convert
+std::string zid_to_str(const z_id_t & pid)
+{
+  std::stringstream ss;
+  int len = 0;
+  for (size_t i = 0; i < sizeof(pid.id); ++i) {
+    if (pid.id[i]) {
+      len = static_cast<int>(i) + 1;
+    }
+  }
+  if (!len) {
+    ss << "";
+  } else {
+    for (int i = len - 1; i >= 0; --i) {
+      ss << std::hex << std::setfill('0') << std::setw(2) << static_cast<int>(pid.id[i]);
+    }
+  }
+  return ss.str();
+}
+
+}  // namespace
+
+rmw_ret_t zenoh_router_check(z_session_t session)
+{
+  // Initialize context for callback
+  int context = 0;
+
+  // Define callback
+  auto callback = [](const struct z_id_t * id, void * ctx) {
+      const std::string id_str = zid_to_str(*id);
+      RCUTILS_LOG_INFO_NAMED(
+        "ZenohRouterCheck",
+        "A Zenoh router connected to the session with id '%s'", id_str.c_str());
+      // Note: Callback is guaranteed to never be called
+      // concurrently according to z_info_routers_zid docstring
+      (*(static_cast<int *>(ctx)))++;
+    };
+
+  rmw_ret_t ret;
+  z_owned_closure_zid_t router_callback = z_closure(callback, nullptr /* drop */, &context);
+  if (z_info_routers_zid(session, z_move(router_callback))) {
+    RCUTILS_LOG_ERROR_NAMED(
+      "ZenohRouterCheck",
+      "Failed to evaluate if Zenoh routers are connected to the session");
+    ret = RMW_RET_ERROR;
+  } else {
+    if (context == 0) {
+      RCUTILS_LOG_ERROR_NAMED(
+        "ZenohRouterCheck",
+        "No Zenoh router connected to the session");
+      ret = RMW_RET_ERROR;
+    } else {
+      RCUTILS_LOG_INFO_NAMED(
+        "ZenohRouterCheck",
+        "There are %d Zenoh routers connected to the session", context);
+      ret = RMW_RET_OK;
+    }
+  }
+
+  return ret;
+}

rmw_zenoh_cpp/src/detail/zenoh_router_check.hpp

@@ -0,0 +1,27 @@
+// Copyright 2023 Open Source Robotics Foundation, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef DETAIL__ZENOH_ROUTER_CHECK_HPP_
+#define DETAIL__ZENOH_ROUTER_CHECK_HPP_
+
+#include <zenoh.h>
+
+#include "rmw/ret_types.h"
+
+/// Check if a Zenoh router is connected to the session.
+/// @param session Zenoh session to check.
+/// @return RMW_RET_OK if a Zenoh router is connected to the session.
+rmw_ret_t zenoh_router_check(z_session_t session);
+
+#endif  // DETAIL__ZENOH_ROUTER_CHECK_HPP_

rmw_zenoh_cpp/src/rmw_init.cpp

@@ -20,6 +20,7 @@
 #include "detail/identifier.hpp"
 #include "detail/rmw_data_types.hpp"
 #include "detail/zenoh_config.hpp"
+#include "detail/zenoh_router_check.hpp"
 
 #include "rcutils/env.h"
 #include "rcutils/logging_macros.h"
@@ -173,6 +174,12 @@ rmw_init(const rmw_init_options_t * options, rmw_context_t * context)
       z_close(z_move(context->impl->session));
     });
 
+  // Verify if the zenoh router is running.
+  if ((ret = zenoh_router_check(z_loan(context->impl->session))) != RMW_RET_OK) {
+    RMW_SET_ERROR_MSG("Error while checking for Zenoh router");
+    return ret;
+  }
+
   // Initialize the shm manager if shared_memory is enabled in the config.
   if (shm_enabled._cstr != nullptr &&
     strcmp(shm_enabled._cstr, "true") == 0)