aboutsummaryrefslogtreecommitdiff
path: root/src/lib/exchange_api_refund.c
blob: a9510715bacee8f0b9f98621a61b7dc545c6345d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
/*
  This file is part of TALER
  Copyright (C) 2014-2021 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 lib/exchange_api_refund.c
 * @brief Implementation of the /refund request of the exchange's HTTP API
 * @author Christian Grothoff
 */
#include "platform.h"
#include <jansson.h>
#include <microhttpd.h> /* just for HTTP status codes */
#include <gnunet/gnunet_util_lib.h>
#include <gnunet/gnunet_json_lib.h>
#include <gnunet/gnunet_curl_lib.h>
#include "taler_json_lib.h"
#include "taler_exchange_service.h"
#include "exchange_api_handle.h"
#include "taler_signatures.h"
#include "exchange_api_curl_defaults.h"


/**
 * @brief A Refund Handle
 */
struct TALER_EXCHANGE_RefundHandle
{

  /**
   * The connection to exchange this request handle will use
   */
  struct TALER_EXCHANGE_Handle *exchange;

  /**
   * The url for this request.
   */
  char *url;

  /**
   * Context for #TEH_curl_easy_post(). Keeps the data that must
   * persist for Curl to make the upload.
   */
  struct TALER_CURL_PostContext ctx;

  /**
   * Handle for the request.
   */
  struct GNUNET_CURL_Job *job;

  /**
   * Function to call with the result.
   */
  TALER_EXCHANGE_RefundCallback cb;

  /**
   * Closure for @a cb.
   */
  void *cb_cls;

  /**
   * Information the exchange should sign in response.
   */
  struct TALER_RefundConfirmationPS depconf;

};


/**
 * Verify that the signature on the "200 OK" response
 * from the exchange is valid.
 *
 * @param[in,out] rh refund handle (refund fee added)
 * @param json json reply with the signature
 * @param[out] exchange_pub set to the exchange's public key
 * @param[out] exchange_sig set to the exchange's signature
 * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
 */
static enum GNUNET_GenericReturnValue
verify_refund_signature_ok (struct TALER_EXCHANGE_RefundHandle *rh,
                            const json_t *json,
                            struct TALER_ExchangePublicKeyP *exchange_pub,
                            struct TALER_ExchangeSignatureP *exchange_sig)
{
  const struct TALER_EXCHANGE_Keys *key_state;
  struct GNUNET_JSON_Specification spec[] = {
    GNUNET_JSON_spec_fixed_auto ("exchange_sig",
                                 exchange_sig),
    GNUNET_JSON_spec_fixed_auto ("exchange_pub",
                                 exchange_pub),
    GNUNET_JSON_spec_end ()
  };

  if (GNUNET_OK !=
      GNUNET_JSON_parse (json,
                         spec,
                         NULL, NULL))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  key_state = TALER_EXCHANGE_get_keys (rh->exchange);
  if (GNUNET_OK !=
      TALER_EXCHANGE_test_signing_key (key_state,
                                       exchange_pub))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (GNUNET_OK !=
      GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND,
                                  &rh->depconf,
                                  &exchange_sig->eddsa_signature,
                                  &exchange_pub->eddsa_pub))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * Verify that the information in the "409 Conflict" response
 * from the exchange is valid and indeed shows that the refund
 * amount requested is too high.
 *
 * @param[in,out] rh refund handle (refund fee added)
 * @param json json reply with the coin transaction history
 * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
 */
static enum GNUNET_GenericReturnValue
verify_conflict_history_ok (struct TALER_EXCHANGE_RefundHandle *rh,
                            const json_t *json)
{
  json_t *history;
  struct GNUNET_JSON_Specification spec[] = {
    GNUNET_JSON_spec_json ("history",
                           &history),
    GNUNET_JSON_spec_end ()
  };
  size_t len;
  struct TALER_Amount dtotal;
  bool have_deposit;
  struct TALER_Amount rtotal;
  bool have_refund;

  if (GNUNET_OK !=
      GNUNET_JSON_parse (json,
                         spec,
                         NULL, NULL))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  len = json_array_size (history);
  if (0 == len)
  {
    GNUNET_break_op (0);
    GNUNET_JSON_parse_free (spec);
    return GNUNET_SYSERR;
  }
  have_deposit = false;
  have_refund = false;
  for (size_t off = 0; off<len; off++)
  {
    json_t *transaction;
    struct TALER_Amount amount;
    const char *type;
    struct GNUNET_JSON_Specification spec_glob[] = {
      TALER_JSON_spec_amount_any ("amount",
                                  &amount),
      GNUNET_JSON_spec_string ("type",
                               &type),
      GNUNET_JSON_spec_end ()
    };

    transaction = json_array_get (history,
                                  off);
    if (GNUNET_OK !=
        GNUNET_JSON_parse (transaction,
                           spec_glob,
                           NULL, NULL))
    {
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
    if (0 == strcasecmp (type,
                         "DEPOSIT"))
    {
      struct TALER_Amount deposit_fee;
      struct TALER_MerchantWireHash h_wire;
      struct TALER_PrivateContractHash h_contract_terms;
      struct TALER_AgeCommitmentHash h_age_commitment = {{{0}}};
      // struct TALER_ExtensionContractHash h_extensions; // FIXME!
      struct TALER_DenominationHash h_denom_pub;
      struct GNUNET_TIME_Timestamp wallet_timestamp;
      struct TALER_MerchantPublicKeyP merchant_pub;
      struct GNUNET_TIME_Timestamp refund_deadline;
      struct TALER_CoinSpendSignatureP sig;
      struct GNUNET_JSON_Specification ispec[] = {
        GNUNET_JSON_spec_fixed_auto ("coin_sig",
                                     &sig),
        GNUNET_JSON_spec_fixed_auto ("h_contract_terms",
                                     &h_contract_terms),
        GNUNET_JSON_spec_fixed_auto ("h_wire",
                                     &h_wire),
        GNUNET_JSON_spec_fixed_auto ("h_denom_pub",
                                     &h_denom_pub),
        GNUNET_JSON_spec_mark_optional (
          GNUNET_JSON_spec_fixed_auto ("h_age_commitment",
                                       &h_age_commitment)),
        GNUNET_JSON_spec_timestamp ("timestamp",
                                    &wallet_timestamp),
        GNUNET_JSON_spec_timestamp ("refund_deadline",
                                    &refund_deadline),
        TALER_JSON_spec_amount_any ("deposit_fee",
                                    &deposit_fee),
        GNUNET_JSON_spec_fixed_auto ("merchant_pub",
                                     &merchant_pub),
        GNUNET_JSON_spec_end ()
      };

      if (GNUNET_OK !=
          GNUNET_JSON_parse (transaction,
                             ispec,
                             NULL, NULL))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (GNUNET_OK !=
          TALER_wallet_deposit_verify (&amount,
                                       &deposit_fee,
                                       &h_wire,
                                       &h_contract_terms,
                                       &h_age_commitment,
                                       NULL /* h_extensions! */,
                                       &h_denom_pub,
                                       wallet_timestamp,
                                       &merchant_pub,
                                       refund_deadline,
                                       &rh->depconf.coin_pub,
                                       &sig))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if ( (0 != GNUNET_memcmp (&rh->depconf.h_contract_terms,
                                &h_contract_terms)) ||
           (0 != GNUNET_memcmp (&rh->depconf.merchant,
                                &merchant_pub)) )
      {
        /* deposit information is about a different merchant/contract */
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (have_deposit)
      {
        /* this cannot really happen, but we conservatively support it anyway */
        if (GNUNET_YES !=
            TALER_amount_cmp_currency (&amount,
                                       &dtotal))
        {
          GNUNET_break_op (0);
          GNUNET_JSON_parse_free (spec);
          return GNUNET_SYSERR;
        }
        GNUNET_break (0 <=
                      TALER_amount_add (&dtotal,
                                        &dtotal,
                                        &amount));
      }
      else
      {
        dtotal = amount;
        have_deposit = true;
      }
    }
    else if (0 == strcasecmp (type,
                              "REFUND"))
    {
      struct TALER_MerchantSignatureP sig;
      struct TALER_Amount refund_fee;
      struct TALER_Amount sig_amount;
      struct TALER_PrivateContractHash h_contract_terms;
      uint64_t rtransaction_id;
      struct TALER_MerchantPublicKeyP merchant_pub;
      struct GNUNET_JSON_Specification ispec[] = {
        TALER_JSON_spec_amount_any ("refund_fee",
                                    &refund_fee),
        GNUNET_JSON_spec_fixed_auto ("merchant_sig",
                                     &sig),
        GNUNET_JSON_spec_fixed_auto ("h_contract_terms",
                                     &h_contract_terms),
        GNUNET_JSON_spec_fixed_auto ("merchant_pub",
                                     &merchant_pub),
        GNUNET_JSON_spec_uint64 ("rtransaction_id",
                                 &rtransaction_id),
        GNUNET_JSON_spec_end ()
      };

      if (GNUNET_OK !=
          GNUNET_JSON_parse (transaction,
                             ispec,
                             NULL, NULL))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (0 >
          TALER_amount_add (&sig_amount,
                            &refund_fee,
                            &amount))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (GNUNET_OK !=
          TALER_merchant_refund_verify (&rh->depconf.coin_pub,
                                        &h_contract_terms,
                                        rtransaction_id,
                                        &sig_amount,
                                        &merchant_pub,
                                        &sig))
      {
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if ( (0 != GNUNET_memcmp (&rh->depconf.h_contract_terms,
                                &h_contract_terms)) ||
           (0 != GNUNET_memcmp (&rh->depconf.merchant,
                                &merchant_pub)) )
      {
        /* refund is about a different merchant/contract */
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
      if (rtransaction_id == rh->depconf.rtransaction_id)
      {
        /* Eh, this shows either a dependency failure or idempotency,
           but must not happen in a conflict reply. Fail! */
        GNUNET_break_op (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }

      if (have_refund)
      {
        if (GNUNET_YES !=
            TALER_amount_cmp_currency (&amount,
                                       &rtotal))
        {
          GNUNET_break_op (0);
          GNUNET_JSON_parse_free (spec);
          return GNUNET_SYSERR;
        }
        GNUNET_break (0 <=
                      TALER_amount_add (&rtotal,
                                        &rtotal,
                                        &amount));
      }
      else
      {
        rtotal = amount;
        have_refund = true;
      }
    }
    else
    {
      /* unexpected type, new version on server? */
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  "Unexpected type `%s' in response for exchange refund\n",
                  type);
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
  }

  {
    struct TALER_Amount amount;

    TALER_amount_ntoh (&amount,
                       &rh->depconf.refund_amount);
    if (have_refund)
    {
      if (0 >
          TALER_amount_add (&rtotal,
                            &rtotal,
                            &amount))
      {
        GNUNET_break (0);
        GNUNET_JSON_parse_free (spec);
        return GNUNET_SYSERR;
      }
    }
    else
    {
      rtotal = amount;
    }
  }
  if (-1 == TALER_amount_cmp (&dtotal,
                              &rtotal))
  {
    /* dtotal < rtotal: good! */
    GNUNET_JSON_parse_free (spec);
    return GNUNET_OK;
  }
  /* this fails to prove a conflict */
  GNUNET_break_op (0);
  GNUNET_JSON_parse_free (spec);
  return GNUNET_SYSERR;
}


/**
 * Verify that the information on the "412 Dependency Failed" response
 * from the exchange is valid and indeed shows that there is a refund
 * transaction ID reuse going on.
 *
 * @param[in,out] rh refund handle (refund fee added)
 * @param json json reply with the signature
 * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
 */
static enum GNUNET_GenericReturnValue
verify_failed_dependency_ok (struct TALER_EXCHANGE_RefundHandle *rh,
                             const json_t *json)
{
  json_t *h;
  json_t *e;
  struct GNUNET_JSON_Specification spec[] = {
    GNUNET_JSON_spec_json ("history",
                           &h),
    GNUNET_JSON_spec_end ()
  };

  if (GNUNET_OK !=
      GNUNET_JSON_parse (json,
                         spec,
                         NULL, NULL))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if ( (! json_is_array (h)) ||
       (1 != json_array_size (h) ) )
  {
    GNUNET_break_op (0);
    GNUNET_JSON_parse_free (spec);
    return GNUNET_SYSERR;
  }
  e = json_array_get (h, 0);
  {
    struct TALER_Amount amount;
    struct TALER_Amount depconf_amount;
    const char *type;
    struct TALER_MerchantSignatureP sig;
    struct TALER_Amount refund_fee;
    struct TALER_PrivateContractHash h_contract_terms;
    uint64_t rtransaction_id;
    struct TALER_MerchantPublicKeyP merchant_pub;
    struct GNUNET_JSON_Specification ispec[] = {
      TALER_JSON_spec_amount_any ("amount",
                                  &amount),
      GNUNET_JSON_spec_string ("type",
                               &type),
      TALER_JSON_spec_amount_any ("refund_fee",
                                  &refund_fee),
      GNUNET_JSON_spec_fixed_auto ("merchant_sig",
                                   &sig),
      GNUNET_JSON_spec_fixed_auto ("h_contract_terms",
                                   &h_contract_terms),
      GNUNET_JSON_spec_fixed_auto ("merchant_pub",
                                   &merchant_pub),
      GNUNET_JSON_spec_uint64 ("rtransaction_id",
                               &rtransaction_id),
      GNUNET_JSON_spec_end ()
    };

    if (GNUNET_OK !=
        GNUNET_JSON_parse (e,
                           ispec,
                           NULL, NULL))
    {
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
    if (GNUNET_OK !=
        TALER_merchant_refund_verify (&rh->depconf.coin_pub,
                                      &h_contract_terms,
                                      rtransaction_id,
                                      &amount,
                                      &merchant_pub,
                                      &sig))
    {
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
    TALER_amount_ntoh (&depconf_amount,
                       &rh->depconf.refund_amount);
    if ( (rtransaction_id != rh->depconf.rtransaction_id) ||
         (0 != GNUNET_memcmp (&rh->depconf.h_contract_terms,
                              &h_contract_terms)) ||
         (0 != GNUNET_memcmp (&rh->depconf.merchant,
                              &merchant_pub)) ||
         (0 == TALER_amount_cmp (&depconf_amount,
                                 &amount)) )
    {
      GNUNET_break_op (0);
      GNUNET_JSON_parse_free (spec);
      return GNUNET_SYSERR;
    }
  }
  GNUNET_JSON_parse_free (spec);
  return GNUNET_OK;
}


/**
 * Function called when we're done processing the
 * HTTP /refund request.
 *
 * @param cls the `struct TALER_EXCHANGE_RefundHandle`
 * @param response_code HTTP response code, 0 on error
 * @param response parsed JSON result, NULL on error
 */
static void
handle_refund_finished (void *cls,
                        long response_code,
                        const void *response)
{
  struct TALER_EXCHANGE_RefundHandle *rh = cls;
  struct TALER_ExchangePublicKeyP exchange_pub;
  struct TALER_ExchangeSignatureP exchange_sig;
  struct TALER_ExchangePublicKeyP *ep = NULL;
  struct TALER_ExchangeSignatureP *es = NULL;
  const json_t *j = response;
  struct TALER_EXCHANGE_HttpResponse hr = {
    .reply = j,
    .http_status = (unsigned int) response_code
  };

  rh->job = NULL;
  switch (response_code)
  {
  case 0:
    hr.ec = TALER_EC_GENERIC_INVALID_RESPONSE;
    break;
  case MHD_HTTP_OK:
    if (GNUNET_OK !=
        verify_refund_signature_ok (rh,
                                    j,
                                    &exchange_pub,
                                    &exchange_sig))
    {
      GNUNET_break_op (0);
      hr.http_status = 0;
      hr.ec = TALER_EC_EXCHANGE_REFUND_INVALID_SIGNATURE_BY_EXCHANGE;
    }
    else
    {
      ep = &exchange_pub;
      es = &exchange_sig;
    }
    break;
  case MHD_HTTP_BAD_REQUEST:
    /* This should never happen, either us or the exchange is buggy
       (or API version conflict); also can happen if the currency
       differs (which we should obviously never support).
       Just pass JSON reply to the application */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_FORBIDDEN:
    /* Nothing really to verify, exchange says one of the signatures is
       invalid; as we checked them, this should never happen, we
       should pass the JSON reply to the application */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_NOT_FOUND:
    /* Nothing really to verify, this should never
       happen, we should pass the JSON reply to the application */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_CONFLICT:
    /* Requested total refunds exceed deposited amount */
    if (GNUNET_OK !=
        verify_conflict_history_ok (rh,
                                    j))
    {
      GNUNET_break (0);
      hr.http_status = 0;
      hr.ec = TALER_EC_EXCHANGE_REFUND_INVALID_FAILURE_PROOF_BY_EXCHANGE;
      hr.hint = "conflict information provided by exchange is invalid";
      break;
    }
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_GONE:
    /* Kind of normal: the money was already sent to the merchant
       (it was too late for the refund). */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_PRECONDITION_FAILED:
    if (GNUNET_OK !=
        verify_failed_dependency_ok (rh,
                                     j))
    {
      GNUNET_break (0);
      hr.http_status = 0;
      hr.ec = TALER_EC_EXCHANGE_REFUND_INVALID_FAILURE_PROOF_BY_EXCHANGE;
      hr.hint = "failed precondition proof returned by exchange is invalid";
      break;
    }
    /* Two different refund requests were made about the same deposit, but
       carrying identical refund transaction ids.  */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  case MHD_HTTP_INTERNAL_SERVER_ERROR:
    /* Server had an internal issue; we should retry, but this API
       leaves this to the application */
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    break;
  default:
    /* unexpected response code */
    GNUNET_break_op (0);
    hr.ec = TALER_JSON_get_error_code (j);
    hr.hint = TALER_JSON_get_error_hint (j);
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Unexpected response code %u/%d for exchange refund\n",
                (unsigned int) response_code,
                hr.ec);
    break;
  }
  rh->cb (rh->cb_cls,
          &hr,
          ep,
          es);
  TALER_EXCHANGE_refund_cancel (rh);
}


struct TALER_EXCHANGE_RefundHandle *
TALER_EXCHANGE_refund (struct TALER_EXCHANGE_Handle *exchange,
                       const struct TALER_Amount *amount,
                       const struct TALER_PrivateContractHash *h_contract_terms,
                       const struct TALER_CoinSpendPublicKeyP *coin_pub,
                       uint64_t rtransaction_id,
                       const struct TALER_MerchantPrivateKeyP *merchant_priv,
                       TALER_EXCHANGE_RefundCallback cb,
                       void *cb_cls)
{
  struct TALER_MerchantPublicKeyP merchant_pub;
  struct TALER_MerchantSignatureP merchant_sig;
  struct TALER_EXCHANGE_RefundHandle *rh;
  struct GNUNET_CURL_Context *ctx;
  json_t *refund_obj;
  CURL *eh;
  char arg_str[sizeof (struct TALER_CoinSpendPublicKeyP) * 2 + 32];

  GNUNET_assert (GNUNET_YES ==
                 TEAH_handle_is_ready (exchange));
  GNUNET_CRYPTO_eddsa_key_get_public (&merchant_priv->eddsa_priv,
                                      &merchant_pub.eddsa_pub);
  TALER_merchant_refund_sign (coin_pub,
                              h_contract_terms,
                              rtransaction_id,
                              amount,
                              merchant_priv,
                              &merchant_sig);
  {
    char pub_str[sizeof (struct TALER_CoinSpendPublicKeyP) * 2];
    char *end;

    end = GNUNET_STRINGS_data_to_string (
      coin_pub,
      sizeof (struct TALER_CoinSpendPublicKeyP),
      pub_str,
      sizeof (pub_str));
    *end = '\0';
    GNUNET_snprintf (arg_str,
                     sizeof (arg_str),
                     "/coins/%s/refund",
                     pub_str);
  }
  refund_obj = GNUNET_JSON_PACK (
    TALER_JSON_pack_amount ("refund_amount",
                            amount),
    GNUNET_JSON_pack_data_auto ("h_contract_terms",
                                h_contract_terms),
    GNUNET_JSON_pack_uint64 ("rtransaction_id",
                             rtransaction_id),
    GNUNET_JSON_pack_data_auto ("merchant_pub",
                                &merchant_pub),
    GNUNET_JSON_pack_data_auto ("merchant_sig",
                                &merchant_sig));
  rh = GNUNET_new (struct TALER_EXCHANGE_RefundHandle);
  rh->exchange = exchange;
  rh->cb = cb;
  rh->cb_cls = cb_cls;
  rh->url = TEAH_path_to_url (exchange,
                              arg_str);
  if (NULL == rh->url)
  {
    json_decref (refund_obj);
    GNUNET_free (rh);
    return NULL;
  }
  rh->depconf.purpose.size = htonl (sizeof (struct TALER_RefundConfirmationPS));
  rh->depconf.purpose.purpose = htonl (TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND);
  rh->depconf.h_contract_terms = *h_contract_terms;
  rh->depconf.coin_pub = *coin_pub;
  rh->depconf.merchant = merchant_pub;
  rh->depconf.rtransaction_id = GNUNET_htonll (rtransaction_id);
  TALER_amount_hton (&rh->depconf.refund_amount,
                     amount);

  eh = TALER_EXCHANGE_curl_easy_get_ (rh->url);
  if ( (NULL == eh) ||
       (GNUNET_OK !=
        TALER_curl_easy_post (&rh->ctx,
                              eh,
                              refund_obj)) )
  {
    GNUNET_break (0);
    if (NULL != eh)
      curl_easy_cleanup (eh);
    json_decref (refund_obj);
    GNUNET_free (rh->url);
    GNUNET_free (rh);
    return NULL;
  }
  json_decref (refund_obj);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "URL for refund: `%s'\n",
              rh->url);
  ctx = TEAH_handle_to_context (exchange);
  rh->job = GNUNET_CURL_job_add2 (ctx,
                                  eh,
                                  rh->ctx.headers,
                                  &handle_refund_finished,
                                  rh);
  return rh;
}


void
TALER_EXCHANGE_refund_cancel (struct TALER_EXCHANGE_RefundHandle *refund)
{
  if (NULL != refund->job)
  {
    GNUNET_CURL_job_cancel (refund->job);
    refund->job = NULL;
  }
  GNUNET_free (refund->url);
  TALER_curl_easy_post_finished (&refund->ctx);
  GNUNET_free (refund);
}


/* end of exchange_api_refund.c */