Retry router connection

README.md

@@ -66,28 +66,43 @@ ros2 run demo_nodes_cpp listener
 The listener node should start receiving messages over the `/chatter` topic.
 
 ## Configuration
-`rmw_zenoh` relies on separate configurations files to configure the Zenoh `router` and `session` respectively.
-To understand more about `routers` and `sessions`, see [Zenoh documentation](https://zenoh.io/docs/getting-started/deployment/).
+
+By default, `Zenoh sessions` created by `rmw_zenoh` will attempt to connect to a Zenoh router to receive discovery information.
+To understand more about `Zenoh routers` and `Zenoh sessions`, see [Zenoh documentation](https://zenoh.io/docs/getting-started/deployment/).
+
+### Checking for a Zenoh router.
+The `ZENOH_ROUTER_CHECK_ATTEMPTS` environment variable can be used to configure if and how a `Zenoh session` checks for the presence of a `Zenoh router`.
+The behavior is explained in the table below.
+
+
+| ZENOH_ROUTER_CHECK_ATTEMPTS |                                                 Session behavior                                                 |
+|:---------------------------:|:----------------------------------------------------------------------------------------------------------------:|
+|            unset or 0           |                                                             Indefinitely waits for connection to a Zenoh router. |
+|             < 0            |                                                                                        Skips Zenoh router check. |
+|             > 0             | Attempts to connect to a Zenoh router in `ZENOH_ROUTER_CHECK_ATTEMPTS` attempts with 1 second wait between checks. |
+
+### Session and Router configs
+`rmw_zenoh` relies on separate configurations files to configure the `Zenoh router` and `Zenoh session` respectively.
 For more information on the topology of Zenoh adopted in `rmw_zenoh`, please see [Design](#design).
 Default configuration files are used by `rmw_zenoh` however certain environment variables may be set to provide absolute paths to custom configuration files.
-The table below summarizes the default files and the environment variables for the `router` and `session`.
+The table below summarizes the default files and the environment variables for the `Zenoh router` and `Zenoh session`.
 For a complete list of configurable parameters, see [zenoh/DEFAULT_CONFIG.json5](https://github.com/eclipse-zenoh/zenoh/blob/main/DEFAULT_CONFIG.json5).
 
 |         |                                            Default config                                            |   Envar for custom config  |
 |---------|:----------------------------------------------------------------------------------------------------:|:--------------------------:|
 | Router  |  [DEFAULT_RMW_ZENOH_ROUTER_CONFIG.json5](rmw_zenoh_cpp/config/DEFAULT_RMW_ZENOH_ROUTER_CONFIG.json5)  |  `ZENOH_ROUTER_CONFIG_URI` |
 | Session | [DEFAULT_RMW_ZENOH_SESSION_CONFIG.json5](rmw_zenoh_cpp/config/DEFAULT_RMW_ZENOH_SESSION_CONFIG.json5) | `ZENOH_SESSION_CONFIG_URI` |
 
-For example, to set the path to a custom `router` configuration file,
+For example, to set the path to a custom `Zenoh router` configuration file,
 ```bash
 export ZENOH_ROUTER_CONFIG_URI=$HOME/MY_ZENOH_ROUTER_CONFIG.json5
 ```
 
 ### Connecting multiple hosts
-By default, all discovery traffic is local per host, where the host is the PC running a Zenoh `router`.
-To bridge communications across two hosts, the `router` configuration for one the hosts must be updated to connect to the other `router` at startup.
-This is done by specifying an endpoint in host's `router` configuration file to as seen below.
-In this example, the `router` will connect to the `router` running on a second host with IP address `192.168.1.1` and port `7447`.
+By default, all discovery traffic is local per host, where the host is the PC running a `Zenoh router`.
+To bridge communications across two hosts, the `Zenoh router` configuration for one the hosts must be updated to connect to the other `Zenoh router` at startup.
+This is done by specifying an endpoint in host's `Zenoh router` configuration file to as seen below.
+In this example, the `Zenoh router` will connect to the `Zenoh router` running on a second host with IP address `192.168.1.1` and port `7447`.
 
 ```json
 {
@@ -97,4 +112,4 @@ In this example, the `router` will connect to the `router` running on a second h
 }
 ```
 
-> Note: To connect multiple hosts, include the endpoints of all routers in the network.
+> Note: To connect multiple hosts, include the endpoints of all `Zenoh routers` in the network.

rmw_zenoh_cpp/src/detail/zenoh_config.cpp

@@ -17,6 +17,7 @@
 #include <rcutils/env.h>
 #include <rcutils/logging_macros.h>
 
+#include <limits>
 #include <string>
 
 #include <ament_index_cpp/get_package_share_directory.hpp>
@@ -35,6 +36,8 @@ static const std::unordered_map<ConfigurableEntity,
   {ConfigurableEntity::Router, {"ZENOH_ROUTER_CONFIG_URI", "DEFAULT_RMW_ZENOH_ROUTER_CONFIG.json5"}}
 };
 
+static const char * router_check_attempts_envar = "ZENOH_ROUTER_CHECK_ATTEMPTS";
+
 rmw_ret_t _get_z_config(
   const char * envar_name,
   const char * default_uri,
@@ -89,3 +92,34 @@ rmw_ret_t get_z_config(const ConfigurableEntity & entity, z_owned_config_t * con
 
   return _get_z_config(envar_map_it->second.first, default_config_path.c_str(), config);
 }
+
+///==============================================================================
+std::optional<uint64_t> zenoh_router_check_attempts()
+{
+  const char * envar_value;
+  // The default value is to check indefinitely.
+  uint64_t default_value = std::numeric_limits<uint64_t>::max();
+
+  if (NULL != rcutils_get_env(router_check_attempts_envar, &envar_value)) {
+    // NULL is returned if everything is ok.
+    RCUTILS_LOG_ERROR_NAMED(
+      "rmw_zenoh_cpp", "Envar %s cannot be read. Report this bug.",
+      router_check_attempts_envar);
+    return default_value;
+  }
+  // If the environment variable contains a value, handle it accordingly.
+  if (envar_value[0] != '\0') {
+    const auto read_value = std::strtol(envar_value, nullptr, 10);
+    if (read_value > 0) {
+      return read_value;
+    } else if (read_value < 0) {
+      // If less than 0, we skip the check.
+      return std::nullopt;
+    }
+    // If the value is 0, check indefinitely.
+    return default_value;
+  }
+
+  // If unset, check indefinitely.
+  return default_value;
+}

rmw_zenoh_cpp/src/detail/zenoh_config.hpp

@@ -17,6 +17,7 @@
 
 #include <zenoh.h>
 
+#include <optional>
 #include <unordered_map>
 #include <utility>
 
@@ -43,4 +44,15 @@ enum class ConfigurableEntity : uint8_t
 [[nodiscard]]
 rmw_ret_t get_z_config(const ConfigurableEntity & entity, z_owned_config_t * config);
 
+///==============================================================================
+/// Get the number of times rmw_init should try to connect to a zenoh router
+/// based on the environment variable ZENOH_ROUTER_CHECK_ATTEMPTS.
+/// @details The behavior is as follows:
+///   - If not set or 0, the max value is returned.
+///   - If less than 0, std::nullopt is returned.
+///   - Else value of environemnt variable is returned.
+/// @return The number of times to try connecting to a zenoh router and
+///   std::nullopt if establishing a connection to a router is not required.
+std::optional<uint64_t> zenoh_router_check_attempts();
+
 #endif  // DETAIL__ZENOH_CONFIG_HPP_

rmw_zenoh_cpp/src/detail/zenoh_router_check.cpp

@@ -21,32 +21,38 @@
 #include <sstream>
 #include <string>
 
+#include "liveliness_utils.hpp"
 
+///=============================================================================
 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 = liveliness::zid_to_str(*id);
+      RCUTILS_LOG_INFO_NAMED(
+        "rmw_zenoh_cpp",
+        "Successfully connected to a Zenoh router 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<void>(id);
       (*(static_cast<int *>(ctx)))++;
     };
 
   rmw_ret_t ret = RMW_RET_OK;
   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");
+      "rmw_zenoh_cpp",
+      "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");
+        "rmw_zenoh_cpp",
+        "Unable to connect to a Zenoh router. "
+        "Have you started a router with `ros2 run rmw_zenoh_cpp rmw_zenohd`?");
       ret = RMW_RET_ERROR;
     }
   }

rmw_zenoh_cpp/src/rmw_init.cpp

@@ -16,6 +16,7 @@
 
 #include <new>
 #include <string>
+#include <thread>
 
 #include "detail/guard_condition.hpp"
 #include "detail/identifier.hpp"
@@ -175,10 +176,24 @@ rmw_init(const rmw_init_options_t * options, rmw_context_t * context)
   z_id_t zid = z_info_zid(z_loan(context->impl->session));
   context->impl->graph_cache = std::make_unique<GraphCache>(zid);
 
-  // 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;
+  // Verify if the zenoh router is running if configured.
+  const std::optional<uint64_t> configured_connection_attempts = zenoh_router_check_attempts();
+  if (configured_connection_attempts.has_value()) {
+    ret = RMW_RET_ERROR;
+    uint64_t connection_attempts = 0;
+    // Retry until the connection is successful.
+    while (ret != RMW_RET_OK && connection_attempts < configured_connection_attempts.value()) {
+      if ((ret = zenoh_router_check(z_loan(context->impl->session))) != RMW_RET_OK) {
+        ++connection_attempts;
+      }
+      std::this_thread::sleep_for(std::chrono::seconds(1));
+    }
+    if (ret != RMW_RET_OK) {
+      RMW_SET_ERROR_MSG_WITH_FORMAT_STRING(
+        "Unable to connect to a Zenoh router after %zu retries.",
+        configured_connection_attempts.value());
+      return ret;
+    }
   }
 
   // Initialize the shm manager if shared_memory is enabled in the config.

rmw_zenoh_cpp/src/rmw_zenoh.cpp

@@ -2277,7 +2277,7 @@ rmw_send_request(
   opts.target = Z_QUERY_TARGET_ALL_COMPLETE;
   // The default timeout for a z_get query is 10 seconds and if a response is not received within
   // this window, the queryable will return an invalid reply. However, it is common for actions,
-  // which are implemented using services, to take an extended duration to complete.Hence, we set
+  // which are implemented using services, to take an extended duration to complete. Hence, we set
   // the timeout_ms to the largest supported value to account for most realistic scenarios.
   opts.timeout_ms = std::numeric_limits<uint64_t>::max();
   // Latest consolidation guarantees unicity of replies for the same key expression,