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diff --git a/src/include/anastasis_service.h b/src/include/anastasis_service.h
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+/*
+  This file is part of TALER
+  Copyright (C) 2019-2021 Taler Systems SA
+
+  Anastasis is free software; you can redistribute it and/or modify it under the
+  terms of the GNU Affero General Public License as published by the Free Software
+  Foundation; either version 3, or (at your option) any later version.
+
+  Anastasis 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 Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License along with
+  Anastasis; see the file COPYING.LIB.  If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file include/anastasis_service.h
+ * @brief C interface of libanastasisrest, a C library to use merchant's HTTP API
+ * @author Christian Grothoff
+ * @author Dennis Neufeld
+ * @author Dominik Meister
+ */
+#ifndef ANASTASIS_SERVICE_H
+#define ANASTASIS_SERVICE_H
+
+#include "anastasis_crypto_lib.h"
+#include "anastasis_util_lib.h"
+#include <gnunet/gnunet_curl_lib.h>
+#include <jansson.h>
+
+
+/**
+ * Anastasis authorization method configuration
+ */
+struct ANASTASIS_AuthorizationMethodConfig
+{
+  /**
+   * Type of the method, i.e. "question".
+   */
+  const char *type;
+
+  /**
+   * Fee charged for accessing key share using this method.
+   */
+  struct TALER_Amount usage_fee;
+};
+
+
+/**
+ * @brief Anastasis configuration data.
+ */
+struct ANASTASIS_Config
+{
+  /**
+   * Protocol version supported by the server.
+   */
+  const char *version;
+
+  /**
+   * Business name of the anastasis provider.
+   */
+  const char *business_name;
+
+  /**
+   * Currency used for payments by the server.
+   */
+  const char *currency;
+
+  /**
+   * Array of authorization methods supported by the server.
+   */
+  const struct ANASTASIS_AuthorizationMethodConfig *methods;
+
+  /**
+   * Length of the @e methods array.
+   */
+  unsigned int methods_length;
+
+  /**
+   * Maximum size of an upload in megabytes.
+   */
+  uint32_t storage_limit_in_megabytes;
+
+  /**
+   * Annual fee for an account / policy upload.
+   */
+  struct TALER_Amount annual_fee;
+
+  /**
+   * Fee for a truth upload.
+   */
+  struct TALER_Amount truth_upload_fee;
+
+  /**
+   * Maximum legal liability for data loss covered by the
+   * provider.
+   */
+  struct TALER_Amount liability_limit;
+
+  /**
+   * Server salt.
+   */
+  struct ANASTASIS_CRYPTO_ProviderSaltP salt;
+
+};
+
+
+/**
+ * Function called with the result of a /config request.
+ * Note that an HTTP status of #MHD_HTTP_OK is no guarantee
+ * that @a acfg is non-NULL. @a acfg is non-NULL only if
+ * the server provided an acceptable response.
+ *
+ * @param cls closure
+ * @param http_status the HTTP status
+ * @param acfg configuration obtained, NULL if we could not parse it
+ */
+typedef void
+(*ANASTASIS_ConfigCallback)(void *cls,
+                            unsigned int http_status,
+                            const struct ANASTASIS_Config *acfg);
+
+
+/**
+ * @brief A Config Operation Handle
+ */
+struct ANASTASIS_ConfigOperation;
+
+
+/**
+ * Run a GET /config request against the Anastasis backend.
+ *
+ * @param ctx CURL context to use
+ * @param base_url base URL fo the Anastasis backend
+ * @param cb function to call with the results
+ * @param cb_cls closure for @a cb
+ * @return handle to cancel the operation
+ */
+struct ANASTASIS_ConfigOperation *
+ANASTASIS_get_config (struct GNUNET_CURL_Context *ctx,
+                      const char *base_url,
+                      ANASTASIS_ConfigCallback cb,
+                      void *cb_cls);
+
+
+/**
+ * Cancel ongoing #ANASTASIS_get_config() request.
+ *
+ * @param co configuration request to cancel.
+ */
+void
+ANASTASIS_config_cancel (struct ANASTASIS_ConfigOperation *co);
+
+
+/****** POLICY API ******/
+
+
+/**
+ * Detailed results from the successful download.
+ */
+struct ANASTASIS_DownloadDetails
+{
+  /**
+   * Signature (already verified).
+   */
+  struct ANASTASIS_AccountSignatureP sig;
+
+  /**
+   * Hash over @e policy and @e policy_size.
+   */
+  struct GNUNET_HashCode curr_policy_hash;
+
+  /**
+   * The backup we downloaded.
+   */
+  const void *policy;
+
+  /**
+   * Number of bytes in @e backup.
+   */
+  size_t policy_size;
+
+  /**
+   * Policy version returned by the service.
+   */
+  uint32_t version;
+};
+
+
+/**
+ * Handle for a GET /policy operation.
+ */
+struct ANASTASIS_PolicyLookupOperation;
+
+
+/**
+ * Callback to process a GET /policy request
+ *
+ * @param cls closure
+ * @param http_status HTTP status code for this request
+ * @param ec anastasis-specific error code
+ * @param obj the response body
+ */
+typedef void
+(*ANASTASIS_PolicyLookupCallback) (void *cls,
+                                   unsigned int http_status,
+                                   const struct ANASTASIS_DownloadDetails *dd);
+
+
+/**
+ * Does a GET /policy.
+ *
+ * @param ctx execution context
+ * @param backend_url base URL of the merchant backend
+ * @param anastasis_pub public key of the user's account
+ * @param cb callback which will work the response gotten from the backend
+ * @param cb_cls closure to pass to the callback
+ * @return handle for this operation, NULL upon errors
+ */
+struct ANASTASIS_PolicyLookupOperation *
+ANASTASIS_policy_lookup (
+  struct GNUNET_CURL_Context *ctx,
+  const char *backend_url,
+  const struct ANASTASIS_CRYPTO_AccountPublicKeyP *anastasis_pub,
+  ANASTASIS_PolicyLookupCallback cb,
+  void *cb_cls);
+
+
+/**
+ * Does a GET /policy for a specific version.
+ *
+ * @param ctx execution context
+ * @param backend_url base URL of the merchant backend
+ * @param anastasis_pub public key of the user's account
+ * @param cb callback which will work the response gotten from the backend
+ * @param cb_cls closure to pass to the callback
+ * @param version version of the policy to be requested
+ * @return handle for this operation, NULL upon errors
+ */
+struct ANASTASIS_PolicyLookupOperation *
+ANASTASIS_policy_lookup_version (
+  struct GNUNET_CURL_Context *ctx,
+  const char *backend_url,
+  const struct ANASTASIS_CRYPTO_AccountPublicKeyP *anastasis_pub,
+  ANASTASIS_PolicyLookupCallback cb,
+  void *cb_cls,
+  unsigned int version);
+
+
+/**
+ * Cancel a GET /policy request.
+ *
+ * @param plo cancel the policy lookup operation
+ */
+void
+ANASTASIS_policy_lookup_cancel (
+  struct ANASTASIS_PolicyLookupOperation *plo);
+
+
+/**
+ * Handle for a POST /policy operation.
+ */
+struct ANASTASIS_PolicyStoreOperation;
+
+
+/**
+ * High-level ways how an upload may conclude.
+ */
+enum ANASTASIS_UploadStatus
+{
+  /**
+   * Backup was successfully made.
+   */
+  ANASTASIS_US_SUCCESS = 0,
+
+  /**
+   * Account expired or payment was explicitly requested
+   * by the client.
+   */
+  ANASTASIS_US_PAYMENT_REQUIRED,
+
+  /**
+   * HTTP interaction failed, see HTTP status.
+   */
+  ANASTASIS_US_HTTP_ERROR,
+
+  /**
+   * We had an internal error (not sure this can happen,
+   * but reserved for HTTP 400 status codes).
+   */
+  ANASTASIS_US_CLIENT_ERROR,
+
+  /**
+   * Server had an internal error.
+   */
+  ANASTASIS_US_SERVER_ERROR,
+
+  /**
+   * Truth already exists. Not applicable for policy uploads.
+   */
+  ANASTASIS_US_CONFLICTING_TRUTH
+};
+
+
+/**
+ * Result of an upload.
+ */
+struct ANASTASIS_UploadDetails
+{
+  /**
+   * High level status of the upload operation. Determines @e details.
+   */
+  enum ANASTASIS_UploadStatus us;
+
+  /**
+   * HTTP status code.
+   */
+  unsigned int http_status;
+
+  /**
+   * Taler error code.
+   */
+  enum TALER_ErrorCode ec;
+
+  union
+  {
+
+    struct
+    {
+      /**
+       * Hash of the stored recovery data, returned if
+       * @e us is #ANASTASIS_US_SUCCESS.
+       */
+      const struct GNUNET_HashCode *curr_backup_hash;
+
+      /**
+       * At what time is the provider set to forget this
+       * policy (because the account expires)?
+       */
+      struct GNUNET_TIME_Absolute policy_expiration;
+
+      /**
+       * Version number of the resulting policy.
+       */
+      unsigned long long policy_version;
+
+    } success;
+
+    /**
+     * Details about required payment.
+     */
+    struct
+    {
+      /**
+       * A taler://pay/-URI with a request to pay the annual fee for
+       * the service.  Returned if @e us is #ANASTASIS_US_PAYMENT_REQUIRED.
+       */
+      const char *payment_request;
+
+      /**
+       * The payment secret (aka order ID) extracted from the @e payment_request.
+       */
+      struct ANASTASIS_PaymentSecretP ps;
+    } payment;
+
+  } details;
+};
+
+
+/**
+ * Callback to process a POST /policy request
+ *
+ * @param cls closure
+ * @param http_status HTTP status code for this request
+ * @param obj the decoded response body
+ */
+typedef void
+(*ANASTASIS_PolicyStoreCallback) (void *cls,
+                                  const struct ANASTASIS_UploadDetails *up);
+
+
+/**
+ * Store policies, does a POST /policy/$ACCOUNT_PUB
+ *
+ * @param ctx the CURL context used to connect to the backend
+ * @param backend_url backend's base URL, including final "/"
+ * @param anastasis_priv private key of the user's account
+ * @param recovery_data policy data to be stored
+ * @param recovery_data_size number of bytes in @a recovery_data
+ * @param payment_years_requested for how many years would the client like the service to store the truth?
+ * @param paid_order_id payment identifier of last payment
+ * @param payment_timeout how long to wait for the payment, use
+ *           #GNUNET_TIME_UNIT_ZERO to let the server pick
+ * @param cb callback processing the response from /policy
+ * @param cb_cls closure for cb
+ * @return handle for the operation
+ */
+struct ANASTASIS_PolicyStoreOperation *
+ANASTASIS_policy_store (
+  struct GNUNET_CURL_Context *ctx,
+  const char *backend_url,
+  const struct ANASTASIS_CRYPTO_AccountPrivateKeyP *anastasis_priv,
+  const void *recovery_data,
+  size_t recovery_data_size,
+  uint32_t payment_years_requested,
+  const struct ANASTASIS_PaymentSecretP *payment_secret,
+  struct GNUNET_TIME_Relative payment_timeout,
+  ANASTASIS_PolicyStoreCallback cb,
+  void *cb_cls);
+
+
+/**
+ * Cancel a POST /policy request.
+ *
+ * @param pso the policy store operation to cancel
+ */
+void
+ANASTASIS_policy_store_cancel (
+  struct ANASTASIS_PolicyStoreOperation *pso);
+
+
+/****** TRUTH API ******/
+
+
+/**
+ * Operational status.
+ */
+enum ANASTASIS_KeyShareDownloadStatus
+{
+  /**
+   * We got the encrypted key share.
+   */
+  ANASTASIS_KSD_SUCCESS = 0,
+
+  /**
+   * Payment is needed to proceed with the recovery.
+   */
+  ANASTASIS_KSD_PAYMENT_REQUIRED,
+
+  /**
+   * The provided answer was wrong or missing. Instructions for
+   * getting a good answer may be provided.
+   */
+  ANASTASIS_KSD_INVALID_ANSWER,
+
+  /**
+   * To answer the challenge, the client should be redirected to
+   * the given URL.
+   */
+  ANASTASIS_KSD_REDIRECT_FOR_AUTHENTICATION,
+
+  /**
+   * The provider had an error.
+   */
+  ANASTASIS_KSD_SERVER_ERROR,
+
+  /**
+   * The provider claims we made an error.
+   */
+  ANASTASIS_KSD_CLIENT_FAILURE,
+
+  /**
+   * The provider does not know this truth.
+   */
+  ANASTASIS_KSD_TRUTH_UNKNOWN,
+
+  /**
+   * Too many attempts to solve the challenge were made in a short
+   * time. Try again laster.
+   */
+  ANASTASIS_KSD_RATE_LIMIT_EXCEEDED
+
+};
+
+
+/**
+ * Detailed results from the successful download.
+ */
+struct ANASTASIS_KeyShareDownloadDetails
+{
+
+  /**
+   * Operational status.
+   */
+  enum ANASTASIS_KeyShareDownloadStatus status;
+
+  /**
+   * Anastasis URL that returned the @e status.
+   */
+  const char *server_url;
+
+  /**
+   * Details depending on @e status.
+   */
+  union
+  {
+
+    /**
+     * The encrypted key share (if @e status is #ANASTASIS_KSD_SUCCESS).
+     */
+    struct ANASTASIS_CRYPTO_EncryptedKeyShareP eks;
+
+    /**
+     * Response if the challenge still needs to be answered, and the
+     * instructions are provided inline (no redirection).
+     */
+    struct
+    {
+
+      /**
+       * HTTP status returned by the server.  #MHD_HTTP_ALREADY_REPORTED
+       * if the server did already send the challenge to the user,
+       * #MHD_HTTP_FORBIDDEN if the answer was wrong (or missing).
+       */
+      unsigned int http_status;
+
+      /**
+       * Response with server-side reply containing instructions for the user
+       */
+      const char *body;
+
+      /**
+       * Content-type: mime type of @e body, NULL if server did not provide any.
+       */
+      const char *content_type;
+
+      /**
+       * Number of bytes in @e body.
+       */
+      size_t body_size;
+
+    } open_challenge;
+
+    /**
+     * URL with instructions for the user to satisfy the challenge, if
+     * @e status is #ANASTASIS_KSD_REDIRECT_FOR_AUTHENTICATION.
+     */
+    const char *redirect_url;
+
+    /**
+     * Response with instructions for how to pay, if
+     * @e status is #ANASTASIS_KSD_PAYMENT_REQUIRED.
+     */
+    struct
+    {
+
+      /**
+       * "taler://pay" URL with details how to pay for the challenge.
+       */
+      const char *taler_pay_uri;
+
+      /**
+       * The order ID from @e taler_pay_uri.
+       */
+      struct ANASTASIS_PaymentSecretP payment_secret;
+
+    } payment_required;
+
+
+    /**
+     * Response with details about a server-side failure, if
+     * @e status is #ANASTASIS_KSD_SERVER_FAILURE,
+     * #ANASTASIS_KSD_CLIENT_FAILURE or #ANASTASIS_KSD_TRUTH_UNKNOWN.
+     */
+    struct
+    {
+
+      /**
+       * HTTP status returned by the server.
+       */
+      unsigned int http_status;
+
+      /**
+       * Taler-specific error code.
+       */
+      enum TALER_ErrorCode ec;
+
+    } server_failure;
+
+  } details;
+};
+
+
+/**
+ * Handle for a GET /truth operation.
+ */
+struct ANASTASIS_KeyShareLookupOperation;
+
+
+/**
+ * Callback to process a GET /truth request
+ *
+ * @param cls closure
+ * @param http_status HTTP status code for this request
+ * @param kdd details about the key share
+ */
+typedef void
+(*ANASTASIS_KeyShareLookupCallback) (
+  void *cls,
+  const struct ANASTASIS_KeyShareDownloadDetails *kdd);
+
+
+/**
+ * Does a GET /truth.
+ *
+ * @param ctx execution context
+ * @param backend_url base URL of the merchant backend
+ * @param truth_public_key identification of the Truth
+ * @param truth_key Key used to Decrypt the Truth on the Server
+ * @param payment_secret secret from the previously done payment NULL to trigger payment
+ * @param payment_timeout how long to wait for the payment, use
+ *           #GNUNET_TIME_UNIT_ZERO to let the server pick
+ * @param hashed_answer hashed answer to the challenge
+ * @param cb callback which will work the response gotten from the backend
+ * @param cb_cls closure to pass to the callback
+ * @return handle for this operation, NULL upon errors
+ */
+struct ANASTASIS_KeyShareLookupOperation *
+ANASTASIS_keyshare_lookup (
+  struct GNUNET_CURL_Context *ctx,
+  const char *backend_url,
+  const struct ANASTASIS_CRYPTO_TruthUUIDP *truth_uuid,
+  const struct ANASTASIS_CRYPTO_TruthKeyP *truth_key,
+  const struct ANASTASIS_PaymentSecretP *payment_secret,
+  struct GNUNET_TIME_Relative timeout,
+  const struct GNUNET_HashCode *hashed_answer,
+  ANASTASIS_KeyShareLookupCallback cb,
+  void *cb_cls);
+
+
+/**
+ * Cancel a GET /truth request.
+ *
+ * @param tlo cancel the truth lookup operation
+ */
+void
+ANASTASIS_keyshare_lookup_cancel (
+  struct ANASTASIS_KeyShareLookupOperation *kslo);
+
+
+/**
+ * Handle for a POST /truth operation.
+ */
+struct ANASTASIS_TruthStoreOperation;
+
+
+/**
+ * Callback to process a POST /truth request
+ *
+ * @param cls closure
+ * @param obj the response body
+ */
+typedef void
+(*ANASTASIS_TruthStoreCallback) (void *cls,
+                                 const struct ANASTASIS_UploadDetails *up);
+
+
+/**
+ * Store Truth, does a POST /truth/$UUID
+ *
+ * @param ctx the CURL context used to connect to the backend
+ * @param backend_url backend's base URL, including final "/"
+ * @param uuid unique identfication of the Truth Upload
+ * @param prev_truth_data_hash hash of the previous truth upload, NULL for the first upload ever
+ * @param type type of the authorization method
+ * @param encrypted_keyshare key material to return to the client upon authorization
+ * @param truth_mime mime type of @e encrypted_truth (after decryption)
+ * @param encrypted_truth_size number of bytes in @e encrypted_truth
+ * @param encrypted_truth contains the @a type-specific authorization data
+ * @param payment_years_requested for how many years would the client like the service to store the truth?
+ * @param payment_timeout how long to wait for the payment, use
+ *           #GNUNET_TIME_UNIT_ZERO to let the server pick
+ * @param cb callback processing the response from /truth
+ * @param cb_cls closure for cb
+ * @return handle for the operation
+ */
+struct ANASTASIS_TruthStoreOperation *
+ANASTASIS_truth_store (
+  struct GNUNET_CURL_Context *ctx,
+  const char *backend_url,
+  const struct ANASTASIS_CRYPTO_TruthUUIDP *uuid,
+  const char *type,
+  const struct ANASTASIS_CRYPTO_EncryptedKeyShareP *encrypted_keyshare,
+  const char *truth_mime,
+  size_t encrypted_truth_size,
+  const void *encrypted_truth,
+  uint32_t payment_years_requested,
+  struct GNUNET_TIME_Relative payment_timeout,
+  ANASTASIS_TruthStoreCallback cb,
+  void *cb_cls);
+
+
+/**
+ * Cancel a POST /truth request.
+ *
+ * @param tso the truth store operation
+ */
+void
+ANASTASIS_truth_store_cancel (
+  struct ANASTASIS_TruthStoreOperation *tso);
+
+
+#endif  /* _ANASTASIS_SERVICE_H */