working on fix for #5747

src/exchange/exchange.conf

@@ -15,6 +15,12 @@ REVOCATION_DIR = ${TALER_DATA_HOME}/exchange/revocations/
 # This must be adjusted to your actually installation.
 # MASTER_PUBLIC_KEY = 98NJW3CQHZQGQXTY3K85K531XKPAPAVV4Q5V8PYYRR00NJGZWNVG
 
+# How long do we allow /keys to be cached at most? The actual
+# limit is the minimum of this value and the first expected
+# significant change in /keys based on the expiration times.
+# Used to artifically reduce caching (addresses #5747).
+MAX_KEYS_CACHING = forever
+
 # How to access our database
 DB = postgres
 

src/exchange/taler-exchange-httpd.c

@@ -97,6 +97,11 @@ char *TEH_revocation_directory;
  */
 struct GNUNET_CONFIGURATION_Handle *cfg;
 
+/**
+ * How long is caching /keys allowed at most?
+ */
+struct GNUNET_TIME_Relative max_keys_caching;
+
 /**
  * Master public key (according to the
  * configuration in the exchange directory).
@@ -397,7 +402,6 @@ handle_mhd_request (void *cls,
         "Only POST is allowed", 0,
         &TEH_MHD_handler_send_json_pack_error, MHD_HTTP_METHOD_NOT_ALLOWED },
 #endif
-
       { NULL, NULL, NULL, NULL, 0, 0 }
     };
   static struct TEH_RequestHandler h404 =
@@ -605,6 +609,18 @@ exchange_serve_process_config ()
 {
   char *TEH_master_public_key_str;
 
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (cfg,
+                                           "exchange",
+                                           "MAX_KEYS_CACHING",
+                                           &max_keys_caching))
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               "exchange",
+                               "MAX_KEYS_CACHING",
+                               "valid relative time expected");
+    return GNUNET_SYSERR;
+  }
   if (GNUNET_OK !=
       GNUNET_CONFIGURATION_get_value_filename (cfg,
                                                "exchange",

src/exchange/taler-exchange-httpd.h

@@ -38,6 +38,11 @@ extern char *TEH_exchange_currency_string;
  */
 extern int TEH_exchange_connection_close;
 
+/**
+ * How long is caching /keys allowed at most?
+ */
+extern struct GNUNET_TIME_Relative max_keys_caching;
+
 /**
  * The exchange's configuration.
  */

src/exchange/taler-exchange-httpd_keystate.c

@@ -1166,8 +1166,16 @@ setup_general_response_headers (const struct TEH_KS_StateHandle *key_state,
                                          dat));
   if (0 != key_state->next_reload.abs_value_us)
   {
-    get_date_string (key_state->next_reload,
+    struct GNUNET_TIME_Absolute m;
+
+    m = GNUNET_TIME_relative_to_absolute (max_keys_caching);
+    m = GNUNET_TIME_absolute_min (m,
+                                  key_state->next_reload);
+    get_date_string (m,
                      dat);
+    // FIXME: setting 'm' to FOREVER here exposes
+    // a crash-bug in lib/ where we access /keys
+    // data after it was already free'd!
     GNUNET_break (MHD_YES ==
                   MHD_add_response_header (response,
                                            MHD_HTTP_HEADER_EXPIRES,