Add better support for pub/sub messaging (#5)

grpc.proto

@@ -7,9 +7,19 @@ import "rdf.proto";
 
 // === Pub/Sub ===
 message RdfStreamSubscribe {
+  // The topic to which the client wants to subscribe.
   string topic = 1;
+  // Optional: the stream options requested by the client.
+  // The server should respond with a stream that matches these options.
+  // In case that is not possible, the server must respond with the
+  // INVALID_ARGUMENT error.
+  RdfStreamOptions requested_options = 2;
+}
+
+message RdfStreamReceived {
 }
 
 service RdfStreamService {
-  rpc StreamRdf (RdfStreamSubscribe) returns (stream RdfStreamFrame);
+  rpc SubscribeRdf (RdfStreamSubscribe) returns (stream RdfStreamFrame);
+  rpc PublishRdf (stream RdfStreamFrame) returns (RdfStreamReceived);
 }

rdf.proto

@@ -91,11 +91,15 @@ message RdfDatatypeEntry {
 }
 
 message RdfStreamOptions {
-  RdfStreamType stream_type = 1;
+  // Name of the stream (completely optional).
+  // This may be used for, e.g., topic names in a pub/sub system.
+  string stream_name = 1;
+  // Type of the stream (required)
+  RdfStreamType stream_type = 2;
   // Whether the stream may contain generalized triples, quads, or datasets
-  bool generalized_statements = 2;
+  bool generalized_statements = 3;
   // Whether RdfRepeat will be used
-  bool use_repeat = 3;
+  bool use_repeat = 4;
   // Prefix tables
   uint32 max_name_table_size = 9;
   uint32 max_prefix_table_size = 10;