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diff --git a/src/include/taler_templating_lib.h b/src/include/taler_templating_lib.h
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+++ b/src/include/taler_templating_lib.h
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+/*
+  This file is part of TALER
+  Copyright (C) 2020, 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 taler_templating_lib.h
+ * @brief logic to load and complete HTML templates
+ * @author Christian Grothoff
+ */
+#ifndef TALER_TEMPLATING_LIB_H
+#define TALER_TEMPLATING_LIB_H
+
+#include <microhttpd.h>
+#include "taler_mhd_lib.h"
+
+/**
+ * Fill in Mustach template @a tmpl using the data from @a root
+ * and return the result in @a result.
+ *
+ * @param tmpl 0-terminated string with Mustach template
+ * @param root JSON data to fill into the template
+ * @param[out] result where to write the result
+ * @param[out] result_size where to write the length of the result
+ * @return 0 on success, otherwise Mustach-specific error code
+ */
+int
+TALER_TEMPLATING_fill (const char *tmpl,
+                       const json_t *root,
+                       void **result,
+                       size_t *result_size);
+
+
+/**
+ * Load a @a template and substitute using @a root, returning the result in a
+ * @a reply encoded suitable for the @a connection with the given @a
+ * http_status code.  On errors, the @a http_status code
+ * is updated to reflect the type of error encoded in the
+ * @a reply.
+ *
+ * @param connection the connection we act upon
+ * @param[in,out] http_status code to use on success,
+ *           set to alternative code on failure
+ * @param template basename of the template to load
+ * @param instance_id instance ID, used to compute static files URL
+ * @param taler_uri value for "Taler:" header to set, or NULL
+ * @param root JSON object to pass as the root context
+ * @param[out] reply where to write the response object
+ * @return #GNUNET_OK on success (reply queued), #GNUNET_NO if an error was queued,
+ *         #GNUNET_SYSERR on failure (to queue an error)
+ */
+enum GNUNET_GenericReturnValue
+TALER_TEMPLATING_build (struct MHD_Connection *connection,
+                        unsigned int *http_status,
+                        const char *template,
+                        const char *instance_id,
+                        const char *taler_uri,
+                        const json_t *root,
+                        struct MHD_Response **reply);
+
+
+/**
+ * Load a @a template and substitute using @a root, returning
+ * the result to the @a connection with the given
+ * @a http_status code.
+ *
+ * @param connection the connection we act upon
+ * @param http_status code to use on success
+ * @param template basename of the template to load
+ * @param instance_id instance ID, used to compute static files URL
+ * @param taler_uri value for "Taler:" header to set, or NULL
+ * @param root JSON object to pass as the root context
+ * @return #GNUNET_OK on success (reply queued), #GNUNET_NO if an error was queued,
+ *         #GNUNET_SYSERR on failure (to queue an error)
+ */
+enum GNUNET_GenericReturnValue
+TALER_TEMPLATING_reply (struct MHD_Connection *connection,
+                        unsigned int http_status,
+                        const char *template,
+                        const char *instance_id,
+                        const char *taler_uri,
+                        const json_t *root);
+
+
+/**
+ * Load a @a template and substitute an error message based on @a ec and @a
+ * detail, returning the result to the @a connection with the given @a
+ * http_status code.
+ *
+ * @param connection the connection we act upon
+ * @param template_basename basename of the template to load
+ * @param http_status code to use on success
+ * @param ec error code to return
+ * @param detail optional text to add to the template
+ * @return #MHD_YES on success, #MHD_NO to just close the connection
+ */
+MHD_RESULT
+TALER_TEMPLATING_reply_error (struct MHD_Connection *connection,
+                              const char *template_basename,
+                              unsigned int http_status,
+                              enum TALER_ErrorCode ec,
+                              const char *detail);
+
+/**
+ * Preload templates.
+ *
+ * @param subsystem name of the subsystem, "merchant" or "exchange"
+ * @return #GNUNET_OK on success
+ */
+enum GNUNET_GenericReturnValue
+TALER_TEMPLATING_init (const char *subsystem);
+
+
+/**
+ * Nicely shut down templating subsystem.
+ */
+void
+TALER_TEMPLATING_done (void);
+
+#endif