add external data source public API for description (#14438)

Author: jepett0

ydb/public/api/grpc/ydb_table_v1.proto

@@ -10,7 +10,7 @@ service TableService {
     // Create new session. Implicit session creation is forbidden,
     // so user must create new session before execute any query,
     // otherwise BAD_SESSION status will be returned.
-    // Simultaneous execution of requests are forbiden.
+    // Simultaneous execution of requests are forbidden.
     // Sessions are volatile, can be invalidated by server, for example in case
     // of fatal errors. All requests with this session will fail with BAD_SESSION status.
     // So, client must be able to handle BAD_SESSION status.
@@ -85,4 +85,10 @@ service TableService {
 
     // Executes scan query with streaming result.
     rpc StreamExecuteScanQuery(Table.ExecuteScanQueryRequest) returns (stream Table.ExecuteScanQueryPartialResponse);
+
+    // Returns information about a given external data source.
+    rpc DescribeExternalDataSource(Table.DescribeExternalDataSourceRequest) returns (Table.DescribeExternalDataSourceResponse);
+
+    // Returns information about a given external table.
+    rpc DescribeExternalTable(Table.DescribeExternalTableRequest) returns (Table.DescribeExternalTableResponse);
 }

ydb/public/api/protos/ydb_table.proto

@@ -1294,3 +1294,43 @@ message ExecuteScanQueryPartialResult {
     // collects additional diagnostics about query compilation, including query plan and scheme
     string query_full_diagnostics = 7;
 }
+
+// Returns information about an external data source with a given path.
+message DescribeExternalDataSourceRequest {
+    Ydb.Operations.OperationParams operation_params = 1;
+    string path = 2;
+}
+
+message DescribeExternalDataSourceResponse {
+    // Holds DescribeExternalDataSourceResult in case of a successful call.
+    Ydb.Operations.Operation operation = 1;
+}
+
+message DescribeExternalDataSourceResult {
+    // Description of a generic scheme object.
+    Ydb.Scheme.Entry self = 1;
+    optional string source_type = 2;
+    optional string location = 3;
+    map<string, string> properties = 4;
+}
+
+// Returns information about an external table with a given path.
+message DescribeExternalTableRequest {
+    Ydb.Operations.OperationParams operation_params = 1;
+    string path = 2;
+}
+
+message DescribeExternalTableResponse {
+    // Holds DescribeExternalTableResult in case of a successful call.
+    Ydb.Operations.Operation operation = 1;
+}
+
+message DescribeExternalTableResult {
+    // Description of a generic scheme object.
+    Ydb.Scheme.Entry self = 1;
+    optional string source_type = 2;
+    optional string data_source_path = 3;
+    optional string location = 4;
+    repeated ColumnMeta columns = 5;
+    map<string, string> content = 6;
+}