Refactor extensions

- Extensions are now compiled as shared libraries and loaded at runtime
  according to the TALER configuration.

- So far, only age restriction is loaded as extension.

- Groundwork for extension auction_brandt started.

7 files changed, 516 insertions, 281 deletions

diff --git a/src/extensions/Makefile.am b/src/extensions/Makefile.am
index 5d4ed128..c867a951 100644
--- a/src/extensions/Makefile.am
+++ b/src/extensions/Makefile.am
@@ -11,7 +11,7 @@ if USE_COVERAGE
 endif
 
 
-# Libraries
+# Basic extension handling library
 
 lib_LTLIBRARIES = \
   libtalerextensions.la
@@ -22,7 +22,7 @@ libtalerextensions_la_LDFLAGS = \
 
 libtalerextensions_la_SOURCES = \
   extensions.c \
-  extension_age_restriction.c
+  age_restriction_helper.c
 
 libtalerextensions_la_LIBADD = \
   $(top_builddir)/src/json/libtalerjson.la \
@@ -31,3 +31,4 @@ libtalerextensions_la_LIBADD = \
   -lgnunetutil \
   -ljansson \
   $(XLIB)
+
diff --git a/src/extensions/age_restriction/Makefile.am b/src/extensions/age_restriction/Makefile.am
new file mode 100644
index 00000000..c81fd0b9
--- /dev/null
+++ b/src/extensions/age_restriction/Makefile.am
@@ -0,0 +1,33 @@
+# This Makefile.am is in the public domain
+
+AM_CPPFLAGS = \
+  -I$(top_srcdir)/src/include \
+  $(LIBGCRYPT_CFLAGS) \
+  $(POSTGRESQL_CPPFLAGS)
+
+if USE_COVERAGE
+  AM_CFLAGS = --coverage -O0
+  XLIB = -lgcov
+endif
+
+# Age restriction as extension library
+
+plugindir = $(libdir)/taler
+
+plugin_LTLIBRARIES = \
+  libtaler_extension_age_restriction.la
+
+libtaler_extension_age_restriction_la_LDFLAGS = \
+  -version-info 0:0:0 \
+  -no-undefined
+
+libtaler_extension_age_restriction_la_SOURCES = \
+  extension_age_restriction.c
+
+libtaler_extension_auctionbrandt_la_LIBADD = \
+  $(top_builddir)/src/json/libtalerjson.la \
+  $(top_builddir)/src/util/libtalerutil.la \
+  -lgnunetjson \
+  -lgnunetutil \
+  -ljansson \
+  $(XLIB)
diff --git a/src/extensions/extension_age_restriction.c b/src/extensions/age_restriction/extension_age_restriction.c
index 00a03841..1399fbc7 100644
--- a/src/extensions/extension_age_restriction.c
+++ b/src/extensions/age_restriction/extension_age_restriction.c
@@ -23,102 +23,6 @@
 #include "taler_extensions.h"
 #include "stdint.h"
 
-/**
- * Carries all the information we need for age restriction
- */
-struct age_restriction_config
-{
-  struct TALER_AgeMask mask;
-  size_t num_groups;
-};
-
-/**
- * Global config for this extension
- */
-static struct age_restriction_config TE_age_restriction_config = {0};
-
-enum GNUNET_GenericReturnValue
-TALER_parse_age_group_string (
-  const char *groups,
-  struct TALER_AgeMask *mask)
-{
-
-  const char *pos = groups;
-  unsigned int prev = 0;
-  unsigned int val = 0;
-  char c;
-
-  while (*pos)
-  {
-    c = *pos++;
-    if (':' == c)
-    {
-      if (prev >= val)
-        return GNUNET_SYSERR;
-
-      mask->bits |= 1 << val;
-      prev = val;
-      val = 0;
-      continue;
-    }
-
-    if ('0'>c || '9'<c)
-      return GNUNET_SYSERR;
-
-    val = 10 * val + c - '0';
-
-    if (0>=val || 32<=val)
-      return GNUNET_SYSERR;
-  }
-
-  if (32<=val || prev>=val)
-    return GNUNET_SYSERR;
-
-  mask->bits |= (1 << val);
-  mask->bits |= 1; // mark zeroth group, too
-
-  return GNUNET_OK;
-}
-
-
-char *
-TALER_age_mask_to_string (
-  const struct TALER_AgeMask *mask)
-{
-  uint32_t bits = mask->bits;
-  unsigned int n = 0;
-  char *buf = GNUNET_malloc (32 * 3); // max characters possible
-  char *pos = buf;
-
-  if (NULL == buf)
-  {
-    return buf;
-  }
-
-  while (bits != 0)
-  {
-    bits >>= 1;
-    n++;
-    if (0 == (bits & 1))
-    {
-      continue;
-    }
-
-    if (n > 9)
-    {
-      *(pos++) = '0' + n / 10;
-    }
-    *(pos++) = '0' + n % 10;
-
-    if (0 != (bits >> 1))
-    {
-      *(pos++) = ':';
-    }
-  }
-  return buf;
-}
-
-
 /* ==================================================
  *
  * Age Restriction  TALER_Extension implementation
@@ -127,6 +31,12 @@ TALER_age_mask_to_string (
  */
 
 /**
+ * @brief local configuration
+ */
+
+static struct TALER_AgeRestrictionConfig AR_config = {0};
+
+/**
  * @brief implements the TALER_Extension.disable interface.
  *
  * @param ext Pointer to the current extension
@@ -138,6 +48,7 @@ age_restriction_disable (
   if (NULL == ext)
     return;
 
+  ext->enabled = false;
   ext->config = NULL;
 
   if (NULL != ext->config_json)
@@ -146,86 +57,9 @@ age_restriction_disable (
     ext->config_json = NULL;
   }
 
-  TE_age_restriction_config.mask.bits = 0;
-  TE_age_restriction_config.num_groups = 0;
-}
-
-
-/**
- * @brief implements the TALER_Extension.load_taler_config interface.
- *
- * @param ext Pointer to the current extension
- * @param cfg Handle to the GNUNET configuration
- * @return Error if extension for age restriction was set, but age groups were
- *         invalid, OK otherwise.
- */
-static enum GNUNET_GenericReturnValue
-age_restriction_load_taler_config (
-  struct TALER_Extension *ext,
-  const struct GNUNET_CONFIGURATION_Handle *cfg)
-{
-  char *groups = NULL;
-  enum GNUNET_GenericReturnValue ret = GNUNET_SYSERR;
-  struct TALER_AgeMask mask = {0};
-
-  if ((GNUNET_YES !=
-       GNUNET_CONFIGURATION_have_value (cfg,
-                                        TALER_EXTENSION_SECTION_AGE_RESTRICTION,
-                                        "ENABLED"))
-      ||
-      (GNUNET_YES !=
-       GNUNET_CONFIGURATION_get_value_yesno (cfg,
-                                             TALER_EXTENSION_SECTION_AGE_RESTRICTION,
-                                             "ENABLED")))
-  {
-    /* Age restriction is not enabled */
-    ext->config = NULL;
-    ext->config_json = NULL;
-    return GNUNET_OK;
-  }
-
-  /* Age restriction is enabled, extract age groups */
-  if ((GNUNET_YES ==
-       GNUNET_CONFIGURATION_have_value (cfg,
-                                        TALER_EXTENSION_SECTION_AGE_RESTRICTION,
-                                        "AGE_GROUPS"))
-      &&
-      (GNUNET_YES !=
-       GNUNET_CONFIGURATION_get_value_string (cfg,
-                                              TALER_EXTENSION_SECTION_AGE_RESTRICTION,
-                                              "AGE_GROUPS",
-                                              &groups)))
-    return GNUNET_SYSERR;
-
-
-  mask.bits = TALER_EXTENSION_AGE_RESTRICTION_DEFAULT_AGE_MASK;
-  ret = GNUNET_OK;
-
-  if (groups != NULL)
-  {
-    ret = TALER_parse_age_group_string (groups, &mask);
-    if (GNUNET_OK != ret)
-      mask.bits = TALER_EXTENSION_AGE_RESTRICTION_DEFAULT_AGE_MASK;
-  }
-
-  if (GNUNET_OK == ret)
-  {
-    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-                "setting age mask to %x with #groups: %d\n", mask.bits,
-                __builtin_popcount (mask.bits) - 1);
-    TE_age_restriction_config.mask.bits = mask.bits;
-    TE_age_restriction_config.num_groups = __builtin_popcount (mask.bits) - 1; /* no underflow, first bit always set */
-    ext->config = &TE_age_restriction_config;
-
-    /* Note: we do now have TE_age_restriction_config set, however
-     * ext->config_json is NOT set, i.e. the extension is not yet active! For
-     * age restriction to become active, load_json_config must have been
-     * called. */
-  }
-
-
-  GNUNET_free (groups);
-  return ret;
+  AR_config.enabled = false;
+  AR_config.mask.bits = 0;
+  AR_config.num_groups = 0;
 }
 
 
@@ -254,24 +88,25 @@ age_restriction_load_json_config (
   if (TALER_Extension_AgeRestriction != ext->type)
     return GNUNET_SYSERR;
 
-  TE_age_restriction_config.mask.bits = mask.bits;
-  TE_age_restriction_config.num_groups = 0;
-
   if (mask.bits > 0)
   {
     /* if the mask is not zero, the first bit MUST be set */
     if (0 == (mask.bits & 1))
       return GNUNET_SYSERR;
 
-    TE_age_restriction_config.num_groups = __builtin_popcount (mask.bits) - 1;
+    AR_config.mask.bits = mask.bits;
+    AR_config.num_groups = __builtin_popcount (mask.bits) - 1;
   }
 
-  ext->config = &TE_age_restriction_config;
+  AR_config.enabled = true;
+  ext->config = &AR_config;
 
   if (NULL != ext->config_json)
     json_decref (ext->config_json);
 
-  ext->config_json = jconfig;
+  ext->enabled = true;
+  ext->config_json = json_copy(jconfig);
+  json_decref(jconfig);
 
   GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
               "loaded new age restriction config with age groups: %s\n",
@@ -296,6 +131,13 @@ age_restriction_config_to_json (
 
   GNUNET_assert (NULL != ext);
 
+  if (! ext->enabled)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "age restriction not enabled");
+    return json_null ();
+  }
+
   if (NULL == ext->config)
   {
     GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
@@ -308,11 +150,13 @@ age_restriction_config_to_json (
     return json_copy (ext->config_json);
   }
 
-  mask_str = TALER_age_mask_to_string (&TE_age_restriction_config.mask);
+  mask_str = TALER_age_mask_to_string (&AR_config.mask);
   conf = GNUNET_JSON_PACK (
     GNUNET_JSON_pack_string ("age_groups", mask_str)
     );
 
+  free(mask_str);
+
   return GNUNET_JSON_PACK (
     GNUNET_JSON_pack_bool ("critical", ext->critical),
     GNUNET_JSON_pack_string ("version", ext->version),
@@ -338,71 +182,119 @@ age_restriction_test_json_config (
 
 
 /* The extension for age restriction */
-struct TALER_Extension TE_age_restriction = {
-  .next = NULL,
+struct TALER_Extension TE_extension_age_restriction = {
   .type = TALER_Extension_AgeRestriction,
   .name = "age_restriction",
   .critical = false,
   .version = "1",
-  .config = NULL,   // disabled per default
+  .enabled = false, /* disabled per default */
+  .config = NULL,
   .config_json = NULL,
   .disable = &age_restriction_disable,
   .test_json_config = &age_restriction_test_json_config,
   .load_json_config = &age_restriction_load_json_config,
   .config_to_json = &age_restriction_config_to_json,
-  .load_taler_config = &age_restriction_load_taler_config,
+  .http_post_handler = NULL,
 };
 
-enum GNUNET_GenericReturnValue
-TALER_extension_age_restriction_register ()
+
+/**
+ * @brief implements the init() function for GNUNET_PLUGIN_load
+ *
+ * @param arg Pointer to the GNUNET_CONFIGURATION_Handle
+ * @return pointer to TALER_Extension on success or NULL otherwise.
+ */
+void *
+libtaler_extension_age_restriction_init (void *arg)
 {
-  return TALER_extensions_add (&TE_age_restriction);
-}
+  const struct GNUNET_CONFIGURATION_Handle *cfg = arg;
+  char *groups = NULL;
+  struct TALER_AgeMask mask = {0};
 
+  if ((GNUNET_YES !=
+       GNUNET_CONFIGURATION_have_value (cfg,
+                                        TALER_EXTENSION_SECTION_AGE_RESTRICTION,
+                                        "ENABLED"))
+      ||
+      (GNUNET_YES !=
+       GNUNET_CONFIGURATION_get_value_yesno (cfg,
+                                             TALER_EXTENSION_SECTION_AGE_RESTRICTION,
+                                             "ENABLED")))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "[age restriction] no section %s found in configuration\n",
+                TALER_EXTENSION_SECTION_AGE_RESTRICTION);
 
-bool
-TALER_extensions_age_restriction_is_configured ()
-{
-  return (0 != TE_age_restriction_config.mask.bits);
-}
+    return NULL;
+  }
+
+  /* Age restriction is enabled, extract age groups */
+  if ((GNUNET_YES ==
+       GNUNET_CONFIGURATION_have_value (cfg,
+                                        TALER_EXTENSION_SECTION_AGE_RESTRICTION,
+                                        "AGE_GROUPS"))
+      &&
+      (GNUNET_YES !=
+       GNUNET_CONFIGURATION_get_value_string (cfg,
+                                              TALER_EXTENSION_SECTION_AGE_RESTRICTION,
+                                              "AGE_GROUPS",
+                                              &groups)))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "[age restriction] AGE_GROUPS in %s is not a string\n",
+                TALER_EXTENSION_SECTION_AGE_RESTRICTION);
 
+    return NULL;
+  }
 
-struct TALER_AgeMask
-TALER_extensions_age_restriction_ageMask ()
-{
-  return TE_age_restriction_config.mask;
-}
+  mask.bits = TALER_EXTENSION_AGE_RESTRICTION_DEFAULT_AGE_MASK;
 
+  if ((groups != NULL) &&
+      (GNUNET_OK != TALER_parse_age_group_string (groups, &mask)))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "[age restriction] couldn't parse age groups: '%s'\n",
+                groups);
+    return NULL;
+  }
 
-size_t
-TALER_extensions_age_restriction_num_groups ()
-{
-  return TE_age_restriction_config.num_groups;
+  AR_config.mask = mask;
+  AR_config.num_groups = __builtin_popcount (mask.bits) - 1;   /* no underflow, first bit always set */
+  AR_config.enabled = true;
+
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "[age restriction] setting age mask to %s with #groups: %d\n",
+              TALER_age_mask_to_string(&AR_config.mask),
+              __builtin_popcount (AR_config.mask.bits) - 1);
+
+  TE_extension_age_restriction.config = &AR_config;
+  TE_extension_age_restriction.enabled = true;
+
+  /* Note: we do now have TE_age_restriction_config set, however
+   * ext->config_json is NOT set, i.e. the extension is not yet active! For
+   * age restriction to become active, load_json_config must have been
+   * called. */
+
+  GNUNET_free (groups);
+  return &TE_extension_age_restriction;
 }
 
 
-enum GNUNET_GenericReturnValue
-TALER_JSON_parse_age_groups (const json_t *root,
-                             struct TALER_AgeMask *mask)
+/**
+ * @brief implements the done() function for GNUNET_PLUGIN_load
+ *
+ * @param cfg unsued
+ * @return pointer to TALER_Extension on success or NULL otherwise.
+ */
+void *
+libtaler_extension_age_restriction_done (void *arg)
 {
-  enum GNUNET_GenericReturnValue ret;
-  const char *str;
-  struct GNUNET_JSON_Specification spec[] = {
-    GNUNET_JSON_spec_string ("age_groups",
-                             &str),
-    GNUNET_JSON_spec_end ()
-  };
-
-  ret = GNUNET_JSON_parse (root,
-                           spec,
-                           NULL,
-                           NULL);
-  if (GNUNET_OK == ret)
-    TALER_parse_age_group_string (str, mask);
-
-  GNUNET_JSON_parse_free (spec);
-
-  return ret;
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "[age restriction] disabling and unloading");
+  AR_config.enabled = 0;
+  AR_config.mask.bits = 0;
+  AR_config.num_groups = 0;
+  return NULL;
 }
 
 
diff --git a/src/extensions/age_restriction_helper.c b/src/extensions/age_restriction_helper.c
new file mode 100644
index 00000000..2cd77515
--- /dev/null
+++ b/src/extensions/age_restriction_helper.c
@@ -0,0 +1,74 @@
+/*
+   This file is part of TALER
+   Copyright (C) 2022- Taler Systems SA
+
+   TALER is free software; you can redistribute it and/or modify it under the
+   terms of the GNU General Public License as published by the Free Software
+   Foundation; either version 3, or (at your option) any later version.
+
+   TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+   A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License along with
+   TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+/**
+ * @file age_restriction_helper.c
+ * @brief Helper functions for age restriction
+ * @author Özgür Kesim
+ */
+
+#include "platform.h"
+#include "taler_util.h"
+#include "taler_signatures.h"
+#include "taler_extensions.h"
+#include "stdint.h"
+
+
+const struct TALER_AgeRestrictionConfig *
+TALER_extensions_get_age_restriction_config ()
+{
+  const struct TALER_Extension *ext;
+
+  ext = TALER_extensions_get_by_type (TALER_Extension_AgeRestriction);
+  if (NULL == ext)
+    return NULL;
+
+  return ext->config;
+}
+
+
+bool
+TALER_extensions_is_age_restriction_enabled ()
+{
+  const struct TALER_Extension *ext;
+
+  ext = TALER_extensions_get_by_type (TALER_Extension_AgeRestriction);
+  if (NULL == ext)
+    return false;
+
+  return ext->enabled;
+}
+
+
+struct TALER_AgeMask
+TALER_extensions_get_age_restriction_mask ()
+{
+  const struct TALER_Extension *ext;
+  const struct TALER_AgeRestrictionConfig *conf;
+
+  ext = TALER_extensions_get_by_type (TALER_Extension_AgeRestriction);
+
+  if ((NULL == ext) ||
+      (NULL == ext->config) ||
+      (! ext->enabled))
+    return (struct TALER_AgeMask) {0}
+  ;
+
+  conf = ext->config;
+  return conf->mask;
+}
+
+
+/* end age_restriction_helper.c */
diff --git a/src/extensions/auction_brandt/Makefile.am b/src/extensions/auction_brandt/Makefile.am
new file mode 100644
index 00000000..f616c164
--- /dev/null
+++ b/src/extensions/auction_brandt/Makefile.am
@@ -0,0 +1,34 @@
+# This Makefile.am is in the public domain
+
+AM_CPPFLAGS = \
+  -I$(top_srcdir)/src/include \
+  $(LIBGCRYPT_CFLAGS) \
+  $(POSTGRESQL_CPPFLAGS)
+
+if USE_COVERAGE
+  AM_CFLAGS = --coverage -O0
+  XLIB = -lgcov
+endif
+
+
+# Auction of Brandt type as extension library
+
+plugindir = $(libdir)/taler
+
+plugin_LTLIBRARIES = \
+  libtaler_extension_auction_brandt.la
+
+libtaler_extension_auction_brandt_la_LDFLAGS = \
+  -version-info 0:0:0 \
+  -no-undefined
+
+libtaler_extension_auction_brandt_la_SOURCES = \
+  extension_auction_brandt.c
+
+libtaler_extension_auction_brandt_la_LIBADD = \
+  $(top_builddir)/src/json/libtalerjson.la \
+  $(top_builddir)/src/util/libtalerutil.la \
+  -lgnunetjson \
+  -lgnunetutil \
+  -ljansson \
+  $(XLIB)
diff --git a/src/extensions/auction_brandt/extension_auction_brandt.c b/src/extensions/auction_brandt/extension_auction_brandt.c
new file mode 100644
index 00000000..a6efd94b
--- /dev/null
+++ b/src/extensions/auction_brandt/extension_auction_brandt.c
@@ -0,0 +1,182 @@
+/*
+   This file is part of TALER
+   Copyright (C) 2021-2022 Taler Systems SA
+
+   TALER is free software; you can redistribute it and/or modify it under the
+   terms of the GNU General Public License as published by the Free Software
+   Foundation; either version 3, or (at your option) any later version.
+
+   TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+   A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License along with
+   TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+/**
+ * @file extension_auction_brandt.c
+ * @brief Extension for replay of auctions of type brandt
+ * @author Özgür Kesim
+ */
+#include "platform.h"
+#include "taler_util.h"
+#include "taler_extensions.h"
+#include "../../exchange/taler-exchange-httpd.h"
+#include "taler_mhd_lib.h"
+#include "stdint.h"
+#include <microhttpd.h>
+
+#define EXTENSION_NAME "auction_brandt"
+
+/* Path to the replay program. */
+static char *replay_program;
+
+/**
+ * @brief implements the TALER_Extension.disable interface.
+ *
+ * @param ext Pointer to the current extension
+ */
+static void
+auction_disable (
+  struct TALER_Extension *ext)
+{
+  ext->enabled = false;
+}
+
+
+/**
+ * @brief implements the TALER_Extension.test_json_config interface.
+ *
+ * @param config configuration as json_t* to test
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR otherwise.
+ */
+static enum GNUNET_GenericReturnValue
+auction_test_json_config (
+  const json_t *config)
+{
+  /* This extension has no configuration */
+  return GNUNET_OK;
+}
+
+
+/**
+ * @brief implements the TALER_Extension.config_to_json interface.
+ *
+ * @param ext if NULL, only tests the configuration
+ * @return configuration as json_t* object, maybe NULL
+ */
+static json_t *
+auction_config_to_json (
+  const struct TALER_Extension *ext)
+{
+  /* This extension has no configuration */
+  return json_null ();
+}
+
+
+/**
+ * @brief implements the TALER_Extension.load_json_config interface.
+ *
+ * @param ext if NULL, only tests the configuration
+ * @param jconfig the configuration as json
+ */
+static enum GNUNET_GenericReturnValue
+auction_load_json_config (
+  struct TALER_Extension *ext,
+  json_t *jconfig)
+{
+  /* This extension has no configuration */
+  ext->enabled = true;
+  return GNUNET_OK;
+}
+
+
+/**
+ * @brief implements the TALER_Extension.http_post_handler
+ */
+
+static MHD_RESULT
+auction_http_post_handler (
+  struct MHD_Connection *connection,
+  const json_t *root,
+  const char *const args[])
+{
+  /* TODO */
+  GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+              "auction_http_post_handler not implemented yet");
+  return MHD_HTTP_NOT_IMPLEMENTED;
+}
+
+
+/* The extension struct for auctions of brandt-style */
+struct TALER_Extension TE_auction_brandt = {
+  .type = 0x0815, /* TODO: where do we get this from? */
+  .name = EXTENSION_NAME,
+  .critical = false,
+  .version = "0",
+  .enabled = false, /* disabled per default */
+  .config = NULL,
+  .config_json = NULL,
+  .disable = &auction_disable,
+  .test_json_config = &auction_test_json_config,
+  .load_json_config = &auction_load_json_config,
+  .config_to_json = &auction_config_to_json,
+  .http_post_handler = &auction_http_post_handler,
+};
+
+
+/* TODO: sql handler */
+
+/**
+ * ===========================================
+ *  Handler for GNUNET_PLUGIN_load and _unload
+ * ===========================================
+ */
+
+/**
+ * @brief Initialization function for the extension.
+ *        Will be called by GNUNET_PLUGIN_load.
+ *
+ * @param arg Configuration - ptr to GNUNET_CONFIGURATION_Handle
+ * @return Pointer to TE_auction_brandt
+ */
+struct TALER_Extension *
+init (void *arg)
+{
+  const struct GNUNET_CONFIGURATION_Handle *cfg = arg;
+
+  if (GNUNET_SYSERR ==
+      GNUNET_CONFIGURATION_get_value_string (cfg,
+                                             "extension_" EXTENSION_NAME,
+                                             "replay_program",
+                                             &replay_program))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "extension_" EXTENSION_NAME,
+                               "replay_program");
+    return NULL;
+  }
+
+  return &TE_auction_brandt;
+}
+
+/**
+ * @brief Tear-down function for the extension.
+ *        Will be called by GNUNET_PLUGIN_unload.
+ *
+ * @param ignored
+ * @return null
+ */
+void *
+done (void *arg)
+{
+	auction_disable(&TE_auction_brandt);
+	GNUNET_free(replay_program);
+	replay_program=NULL;
+
+	return NULL;
+}
+
+
+
+/* end of extension_auction_brandt.c */
diff --git a/src/extensions/extensions.c b/src/extensions/extensions.c
index 0df0bae3..95fb8cf0 100644
--- a/src/extensions/extensions.c
+++ b/src/extensions/extensions.c
@@ -24,21 +24,22 @@
 #include "taler_extensions.h"
 #include "stdint.h"
 
-
 /* head of the list of all registered extensions */
-static struct TALER_Extension *TE_extensions = NULL;
-
+static struct TALER_Extensions TE_extensions = {
+  .next = NULL,
+  .extension = NULL,
+};
 
-const struct TALER_Extension *
+const struct TALER_Extensions *
 TALER_extensions_get_head ()
 {
-  return TE_extensions;
+  return &TE_extensions;
 }
 
 
-enum GNUNET_GenericReturnValue
-TALER_extensions_add (
-  struct TALER_Extension *extension)
+static enum GNUNET_GenericReturnValue
+add_extension (
+  const struct TALER_Extension *extension)
 {
   /* Sanity checks */
   if ((NULL == extension) ||
@@ -47,28 +48,30 @@ TALER_extensions_add (
       (NULL == extension->disable) ||
       (NULL == extension->test_json_config) ||
       (NULL == extension->load_json_config) ||
-      (NULL == extension->config_to_json) ||
-      (NULL == extension->load_taler_config))
+      (NULL == extension->config_to_json))
   {
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                 "invalid extension\n");
     return GNUNET_SYSERR;
   }
 
-  if (NULL == TE_extensions) /* first extension ?*/
-    TE_extensions = (struct TALER_Extension *) extension;
+  if (NULL == TE_extensions.extension) /* first extension ?*/
+    TE_extensions.extension = extension;
   else
   {
-    struct TALER_Extension *iter;
-    struct TALER_Extension *last;
+    struct TALER_Extensions *iter;
+    struct TALER_Extensions *last;
 
     /* Check for collisions */
-    for (iter = TE_extensions; NULL != iter; iter = iter->next)
+    for (iter = &TE_extensions;
+         NULL != iter && NULL != iter->extension;
+         iter = iter->next)
     {
+      const struct TALER_Extension *ext = iter->extension;
       last = iter;
-      if (extension->type == iter->type ||
+      if (extension->type == ext->type ||
           0 == strcasecmp (extension->name,
-                           iter->name))
+                           ext->name))
       {
         GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                     "extension collision for `%s'\n",
@@ -78,7 +81,11 @@ TALER_extensions_add (
     }
 
     /* No collisions found, so add this extension to the list */
-    last->next = extension;
+    {
+      struct TALER_Extensions *extn = GNUNET_new (struct TALER_Extensions);
+      extn->extension = extension;
+      last->next = extn;
+    }
   }
 
   return GNUNET_OK;
@@ -89,12 +96,12 @@ const struct TALER_Extension *
 TALER_extensions_get_by_type (
   enum TALER_Extension_Type type)
 {
-  for (const struct TALER_Extension *it = TE_extensions;
-       NULL != it;
+  for (const struct TALER_Extensions *it = &TE_extensions;
+       NULL != it && NULL != it->extension;
        it = it->next)
   {
-    if (it->type == type)
-      return it;
+    if (it->extension->type == type)
+      return it->extension;
   }
 
   /* No extension found. */
@@ -109,8 +116,7 @@ TALER_extensions_is_enabled_type (
   const struct TALER_Extension *ext =
     TALER_extensions_get_by_type (type);
 
-  return (NULL != ext &&
-          TALER_extensions_is_enabled (ext));
+  return (NULL != ext && ext->enabled);
 }
 
 
@@ -118,14 +124,15 @@ const struct TALER_Extension *
 TALER_extensions_get_by_name (
   const char *name)
 {
-  for (const struct TALER_Extension *it = TE_extensions;
+  for (const struct TALER_Extensions *it = &TE_extensions;
        NULL != it;
        it = it->next)
   {
-    if (0 == strcasecmp (name, it->name))
-      return it;
+    if (0 == strcasecmp (name, it->extension->name))
+      return it->extension;
   }
-  /* No extension found. */
+  /* No extension found, try to load it. */
+
   return NULL;
 }
 
@@ -178,7 +185,8 @@ configure_extension (
 {
   struct LoadConfClosure *col = cls;
   const char *name;
-  const struct TALER_Extension *extension;
+  char *lib_name;
+  struct TALER_Extension *extension;
 
   if (GNUNET_OK != col->error)
     return;
@@ -190,33 +198,49 @@ configure_extension (
 
   name = section + sizeof(TALER_EXTENSION_SECTION_PREFIX) - 1;
 
-  if (NULL ==
-      (extension = TALER_extensions_get_by_name (name)))
+
+  /* Load the extension library */
+  GNUNET_asprintf (&lib_name,
+                   "libtaler_extension_%s",
+                   name);
+  extension = GNUNET_PLUGIN_load (
+    lib_name,
+    (void *) col->cfg);
+  if (NULL == extension)
   {
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "Unsupported extension `%s` (section [%s]).\n", name,
+                "Couldn't load extension library to `%s` (section [%s]).\n",
+                name,
                 section);
     col->error = GNUNET_SYSERR;
     return;
   }
 
-  if (GNUNET_OK !=
-      extension->load_taler_config (
-        (struct TALER_Extension *) extension,
-        col->cfg))
+
+  if (GNUNET_OK != add_extension (extension))
   {
+    /* TODO: Ignoring return values here */
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "Couldn't parse configuration for extension `%s` (section [%s]).\n",
+                "Couldn't add extension `%s` (section [%s]).\n",
                 name,
                 section);
     col->error = GNUNET_SYSERR;
+    GNUNET_PLUGIN_unload (
+      lib_name,
+      (void *) col->cfg);
     return;
   }
+
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "extension library '%s' loaded\n",
+              lib_name);
 }
 
 
+static bool extensions_loaded = false;
+
 enum GNUNET_GenericReturnValue
-TALER_extensions_load_taler_config (
+TALER_extensions_load (
   const struct GNUNET_CONFIGURATION_Handle *cfg)
 {
   struct LoadConfClosure col = {
@@ -224,9 +248,16 @@ TALER_extensions_load_taler_config (
     .error = GNUNET_OK,
   };
 
+  if (extensions_loaded)
+    return GNUNET_OK;
+
   GNUNET_CONFIGURATION_iterate_sections (cfg,
                                          &configure_extension,
                                          &col);
+
+  if (GNUNET_OK == col.error)
+    extensions_loaded = true;
+
   return col.error;
 }
 
@@ -309,28 +340,16 @@ TALER_extensions_load_json_config (
   }
 
   /* make sure to disable all extensions that weren't mentioned in the json */
-  for (const struct TALER_Extension *it = TALER_extensions_get_head ();
+  for (const struct TALER_Extensions *it = TALER_extensions_get_head ();
        NULL != it;
        it = it->next)
   {
-    if (NULL == json_object_get (extensions, it->name))
-      it->disable ((struct TALER_Extension *) it);
+    if (NULL == json_object_get (extensions, it->extension->name))
+      it->extension->disable ((struct TALER_Extension *) it);
   }
 
   return GNUNET_OK;
 }
 
 
-bool
-TALER_extensions_age_restriction_is_enabled ()
-{
-  const struct TALER_Extension *age =
-    TALER_extensions_get_by_type (TALER_Extension_AgeRestriction);
-
-  return (NULL != age &&
-          NULL != age->config_json &&
-          TALER_extensions_age_restriction_is_configured ());
-}
-
-
 /* end of extensions.c */