From 3954fbe8c0bf1501c6067907c874127109a12457 Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Mon, 22 Jun 2015 14:36:01 +0200
Subject: finishing implementation of #3516

---
 src/mint-lib/mint_api_json.c | 40 ++++++++++++++++++++++++++++++++++------
 src/mint-lib/mint_api_json.h | 11 +++++++++++
 2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/src/mint-lib/mint_api_json.c b/src/mint-lib/mint_api_json.c
index 81511c1c0..e2a73bdd4 100644
--- a/src/mint-lib/mint_api_json.c
+++ b/src/mint-lib/mint_api_json.c
@@ -202,12 +202,40 @@ parse_json (json_t *root,
 
     case MAJ_CMD_EDDSA_SIGNATURE:
       {
-        /* FIXME: parse the JSON signature
-           and the purpose, then check that the
-           signature is valid and the size field
-           is also correct; if all checks out,
-           return the purpose */
-        GNUNET_break (0); // FIXME: implement! #3516
+        struct TALER_CoinSpendSignatureP sig;
+        struct GNUNET_CRYPTO_EccSignaturePurpose *purpose;
+        size_t size;
+        struct MAJ_Specification sig_spec[] = {
+          MAJ_spec_fixed_auto ("eddsa_sig", &sig),
+          MAJ_spec_varsize ("eddsa_val", (void**) &purpose, &size),
+          MAJ_spec_end
+        };
+
+        if (GNUNET_OK !=
+            MAJ_parse_json (pos,
+                            sig_spec))
+        {
+          GNUNET_break_op (0);
+          MAJ_parse_free (sig_spec);
+          return i;
+        }
+        if (size != ntohl (purpose->size))
+        {
+          GNUNET_break_op (0);
+          MAJ_parse_free (sig_spec);
+          return i;
+        }
+        if (GNUNET_OK !=
+            GNUNET_CRYPTO_eddsa_verify (ntohl (purpose->purpose),
+                                        purpose,
+                                        &sig.eddsa_signature,
+                                        spec[i].details.eddsa_signature.pub_key))
+        {
+          GNUNET_break_op (0);
+          MAJ_parse_free (sig_spec);
+          return i;
+        }
+        *spec[i].details.eddsa_signature.purpose_p = purpose;
       }
       break;
 
diff --git a/src/mint-lib/mint_api_json.h b/src/mint-lib/mint_api_json.h
index 91679831d..ec3b63cbc 100644
--- a/src/mint-lib/mint_api_json.h
+++ b/src/mint-lib/mint_api_json.h
@@ -218,6 +218,17 @@ MAJ_parse_free (struct MAJ_Specification *spec);
 #define MAJ_spec_fixed_auto(name,obj) { .cmd = MAJ_CMD_BINARY_FIXED, .field = name, .details.fixed_data.dest = obj, .details.fixed_data.dest_size = sizeof (*obj) }
 
 
+/**
+ * Variable size object (in network byte order, encoded using Crockford
+ * Base32hex encoding).
+ *
+ * @param name name of the JSON field
+ * @param obj_ptr pointer where to write the data (a `void **`)
+ * @param size where to store the number of bytes allocated for @a obj (of type `size_t *`
+ */
+#define MAJ_spec_varsize(name,obj,size) { .cmd = MAJ_CMD_BINARY_VARIABLE, .field = name, .details.variable_data.dest_p = obj, .details.variable_data.dest_size_p = size }
+
+
 /**
  * Absolute time.
  *
-- 
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