submission: Add support for module contexts to client.

src/submission/submission-client.c

@@ -44,6 +44,8 @@
 static const struct smtp_server_callbacks smtp_callbacks;
 static const struct submission_client_vfuncs submission_client_vfuncs;
 
+struct submission_module_register submission_module_register = { 0 };
+
 struct client *submission_clients;
 unsigned int submission_client_count;
 
@@ -225,6 +227,8 @@ struct client *client_create(int fd_in, int fd_out,
 
 	client_parse_backend_capabilities(client);
 
+	p_array_init(&client->module_contexts, client->pool, 5);
+
 	client->conn = smtp_server_connection_create(smtp_server,
 		fd_in, fd_out, user->conn.remote_ip, user->conn.remote_port,
 		FALSE, &smtp_set, &smtp_callbacks, client);

src/submission/submission-client.h

@@ -79,13 +79,26 @@ struct client {
 	struct submission_backend *backends;
 	unsigned int backends_count;
 
+	/* Module-specific contexts. */
+	ARRAY(union submission_module_context *) module_contexts;
+
 	bool standalone:1;
 	bool disconnected:1;
 	bool destroyed:1;
 	bool anvil_sent:1;
 	bool backend_capabilities_configured:1;
 };
 
+struct submission_module_register {
+	unsigned int id;
+};
+
+union submission_module_context {
+	struct submission_client_vfuncs super;
+	struct submission_module_register *reg;
+};
+extern struct submission_module_register submission_module_register;
+
 extern struct client *submission_clients;
 extern unsigned int submission_client_count;