[age restriction] progress 10/n

More work towards support for extensions:
- Prepared statements and DB-plugin-functions for setting and retrieving
  configurations from the database added.
- primitive "registry" of extensions for age restrictions and peer2peer
  (stub)
- TALER_Extensions now with FP for parsing, setting and converting a
  configuration.
- /management/extensions handler now verifies signature of the (opaque)
  json object for all extensions.
- /management/extensions handler calls the FP in the corrensponding
  TALER_Extension for parsing and setting the configuration of a
  particular extension

More work towards age restriction:
- TALER_Extensions interfaces for config-parser, -setter and converter
  implemented for age restriction
- DB event handler now retrieves config from database, parses it and
  sets it (the age mask) in the global extension.
- load_age_mask now loads age mask from the global extension (and not
  from the config file)
- add age_restricted_denoms to /keys response

1 files changed, 5 insertions, 2 deletions

diff --git a/src/exchange/taler-exchange-httpd.h b/src/exchange/taler-exchange-httpd.h
index fa47af6f..4f04029e 100644
--- a/src/exchange/taler-exchange-httpd.h
+++ b/src/exchange/taler-exchange-httpd.h
@@ -202,9 +202,12 @@ extern volatile bool MHD_terminating;
 extern struct GNUNET_CURL_Context *TEH_curl_ctx;
 
 /**
- * The manifest of the available extensions
+ * The manifest of the available extensions, NULL terminated
  */
-extern const struct TALER_Extension TEH_extensions[TALER_Extension_Max];
+extern struct TALER_Extension **TEH_extensions;
+
+#define TEH_extension_enabled(ext) (0 <= ext && TALER_Extension_Max > ext && \
+                                    NULL != TEH_extensions[ext]->config)
 
 /**
  * @brief Struct describing an URL and the handler for it.