datasource: add environment variable support

api/envoy/config/core/v3/base.proto

@@ -372,7 +372,7 @@ message WatchedDirectory {
   string path = 1 [(validate.rules).string = {min_len: 1}];
 }
 
-// Data source consisting of either a file or an inline value.
+// Data source consisting of a file, an inline value, or an environment variable.
 message DataSource {
   option (udpa.annotations.versioning).previous_message_type = "envoy.api.v2.core.DataSource";
 
@@ -387,6 +387,9 @@ message DataSource {
 
     // String inlined in the configuration.
     string inline_string = 3;
+
+    // Environment variable data source.
+    string environment_variable = 4 [(validate.rules).string = {min_len: 1}];
   }
 }
 

docs/root/version_history/current.rst

@@ -37,6 +37,7 @@ Removed Config or Runtime
 New Features
 ------------
 * api: added support for *xds.type.v3.TypedStruct* in addition to the now-deprecated *udpa.type.v1.TypedStruct* proto message, which is a wrapper proto used to encode typed JSON data in a *google.protobuf.Any* field.
+* config: added :ref:`environment_variable <envoy_v3_api_field_config.core.v3.datasource.environment_variable>` to the :ref:`DataSource <envoy_v3_api_msg_config.core.v3.datasource>`.
 * ext_authz: added :ref:`query_parameters_to_set <envoy_v3_api_field_service.auth.v3.OkHttpResponse.query_parameters_to_set>` and :ref:`query_parameters_to_remove <envoy_v3_api_field_service.auth.v3.OkHttpResponse.query_parameters_to_remove>` for adding and removing query string parameters when using a gRPC authorization server.
 * http: added support for :ref:`retriable health check status codes <envoy_v3_api_field_config.core.v3.HealthCheck.HttpHealthCheck.retriable_statuses>`.
 * thrift_proxy: add upstream response zone metrics in the form ``cluster.cluster_name.zone.local_zone.upstream_zone.thrift.upstream_resp_success``.

source/common/config/datasource.cc

@@ -26,6 +26,15 @@ std::string read(const envoy::config::core::v3::DataSource& source, bool allow_e
   case envoy::config::core::v3::DataSource::SpecifierCase::kInlineString:
     data = source.inline_string();
     break;
+  case envoy::config::core::v3::DataSource::SpecifierCase::kEnvironmentVariable: {
+    const char* environment_variable = std::getenv(source.environment_variable().c_str());
+    if (environment_variable == nullptr) {
+      throw EnvoyException(
+          fmt::format("Environment variable doesn't exist: {}", source.environment_variable()));
+    }
+    data = environment_variable;
+    break;
+  }
   default:
     if (!allow_empty) {
       throw EnvoyException(

test/common/config/datasource_test.cc

@@ -9,6 +9,7 @@
 #include "test/mocks/event/mocks.h"
 #include "test/mocks/init/mocks.h"
 #include "test/mocks/upstream/cluster_manager.h"
+#include "test/test_common/environment.h"
 #include "test/test_common/utility.h"
 
 #include "gtest/gtest.h"
@@ -586,6 +587,73 @@ TEST_F(AsyncDataSourceTest, BaseIntervalTest) {
   EXPECT_THROW(TestUtility::loadFromYamlAndValidate(yaml, config), EnvoyException);
 }
 
+TEST(DataSourceTest, WellKnownEnvironmentVariableTest) {
+  envoy::config::core::v3::DataSource config;
+
+  const std::string yaml = R"EOF(
+    environment_variable:
+      PATH
+  )EOF";
+  TestUtility::loadFromYamlAndValidate(yaml, config);
+
+  EXPECT_EQ(envoy::config::core::v3::DataSource::SpecifierCase::kEnvironmentVariable,
+            config.specifier_case());
+  EXPECT_EQ(config.environment_variable(), "PATH");
+  Api::ApiPtr api = Api::createApiForTest();
+  const auto path_data = DataSource::read(config, false, *api);
+  EXPECT_FALSE(path_data.empty());
+}
+
+TEST(DataSourceTest, MissingEnvironmentVariableTest) {
+  envoy::config::core::v3::DataSource config;
+
+  const std::string yaml = R"EOF(
+    environment_variable:
+      ThisVariableDoesntExist
+  )EOF";
+  TestUtility::loadFromYamlAndValidate(yaml, config);
+
+  EXPECT_EQ(envoy::config::core::v3::DataSource::SpecifierCase::kEnvironmentVariable,
+            config.specifier_case());
+  EXPECT_EQ(config.environment_variable(), "ThisVariableDoesntExist");
+  Api::ApiPtr api = Api::createApiForTest();
+  EXPECT_THROW(DataSource::read(config, false, *api), EnvoyException);
+  EXPECT_THROW(DataSource::read(config, true, *api), EnvoyException);
+}
+
+struct ScopedEnvironmentVariable {
+  ScopedEnvironmentVariable(const std::string& environment_variable, const std::string& value)
+      : environment_variable_(environment_variable) {
+    TestEnvironment::setEnvVar(environment_variable_, value, 1);
+  }
+  ~ScopedEnvironmentVariable() { TestEnvironment::unsetEnvVar(environment_variable_); }
+  const std::string environment_variable_;
+};
+
+TEST(DataSourceTest, EmptyEnvironmentVariableTest) {
+  envoy::config::core::v3::DataSource config;
+  ScopedEnvironmentVariable test_variable("ThisVariableIsEmpty", "");
+
+  const std::string yaml = R"EOF(
+    environment_variable:
+      ThisVariableIsEmpty
+  )EOF";
+  TestUtility::loadFromYamlAndValidate(yaml, config);
+
+  EXPECT_EQ(envoy::config::core::v3::DataSource::SpecifierCase::kEnvironmentVariable,
+            config.specifier_case());
+  EXPECT_EQ(config.environment_variable(), "ThisVariableIsEmpty");
+  Api::ApiPtr api = Api::createApiForTest();
+  EXPECT_THROW(DataSource::read(config, false, *api), EnvoyException);
+#ifdef WIN32
+  // Windows doesn't support empty environment variables.
+  EXPECT_THROW(DataSource::read(config, true, *api), EnvoyException);
+#else
+  const auto environment_variable = DataSource::read(config, true, *api);
+  EXPECT_TRUE(environment_variable.empty());
+#endif
+}
+
 } // namespace
 } // namespace Config
 } // namespace Envoy