Add function to enable localhost communication only from env var

rmw/CMakeLists.txt

@@ -28,6 +28,7 @@ set(rmw_sources
   "src/allocators.c"
   "src/convert_rcutils_ret_to_rmw_ret.c"
   "src/event.c"
+  "src/host.c"
   "src/init.c"
   "src/init_options.c"
   "src/names_and_types.c"

rmw/include/rmw/host.h

@@ -0,0 +1,52 @@
+// Copyright 2019 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 RMW__IMPL__CPP__HOST_H
+#define RMW__IMPL__CPP__HOST_H
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+#include "rmw/macros.h"
+#include "rmw/types.h"
+
+#define RMW_ENV_VAR_NOT_DEFINED_OR_EMPTY 0
+#define RMW_LOCAL_HOST_ENABLED 1
+#define RMW_INVALID_ALLOWED_HOSTS 2
+
+
+/// Determine if the user provided a list of hosts to communicate to in the
+/**
+ * Checks the allowed hosts declared by the user in the environment variable ROS_ALLOWED_HOSTS.
+ * localhost is the only host supported besides using all network interfaces. Allocates memory for
+ * the list of hosts if it's not empty and supported.
+ * \param[out] allowed_hosts string that contains the list of allowed hosts.
+ * \returns `RMW_ENV_VAR_NOT_DEFINED_OR_EMPTY` if the env var is not defined or is empty.
+ * \returns `RMW_LOCAL_HOST_ENABLED` if the environment variable is localhost
+ * \returns `RMW_INVALID_ALLOWED_HOSTS` when the user provides a non empty string
+ * different than localhost.
+ */
+RMW_PUBLIC
+RMW_WARN_UNUSED
+rmw_ret_t
+rmw_allowed_hosts(
+	char * allowed_hosts);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // RMW__IMPL__CPP__HOST_H

rmw/src/host.c

@@ -0,0 +1,50 @@
+// Copyright 2019 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 <rmw/host.h>
+
+#include <stdlib.h>
+#include <string.h>
+
+rmw_ret_t
+rmw_allowed_hosts(
+	char * allowed_hosts)
+{
+  rmw_ret_t ret = RMW_ENV_VAR_NOT_DEFINED_OR_EMPTY;
+	const char * ros_host_env = "ROS_ALLOWED_HOSTS";
+#ifndef _WIN32
+  const char * ros_host_env_val = getenv(ros_host_env);
+  if (ros_host_env_val != NULL && strlen(ros_host_env_val) > 0) {
+    allowed_hosts = malloc(strlen(ros_host_env_val)+1);
+    strcpy(allowed_hosts, ros_host_env_val);
+  }
+#else
+  size_t ros_host_env_val_size;
+  _dupenv_s(&allowed_hosts, &ros_host_env_val_size, ros_host_env);
+#endif
+  if (allowed_hosts != NULL && strcmp(allowed_hosts, "") != 0) {
+    if (strcmp(allowed_hosts, "localhost") != 0) {
+      ret = RMW_INVALID_ALLOWED_HOSTS;
+      free(allowed_hosts);
+    } else {
+      ret = RMW_LOCAL_HOST_ENABLED;
+    }
+  } else {
+    ret = RMW_ENV_VAR_NOT_DEFINED_OR_EMPTY;
+    if (allowed_hosts != NULL) {
+      free(allowed_hosts);
+    }
+  }
+  return ret;
+}