bolt12: partial support for minimal offer

Making sure that we are able to fetch the invoice
from an offer without description

E           pyln.client.lightning.RpcError: RPC call failed: method:
offer, payload: {'amount': '2msat'}, error: {'code': -32602, 'message':
'bolt12: Offer does not contain a description: invalid token
\'"lno1qgsqvgnwgcg35z6ee2h3yczraddm72xrfua9uve2rlrm9deu7xyfzrcgqyppvggz953rvg9rtxj8lalh43z8epwydjfrmffn3y3p5qz5cywpu09rr4vs"\''}

Link: #7405
Link: #7404
Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

common/bolt12.c

@@ -211,16 +211,16 @@ struct tlv_offer *offer_decode(const tal_t *ctx,
 	}
 
 	/* BOLT-offers #12:
-	 * - if `offer_description` is not set:
-	 *   - MUST NOT respond to the offer.
-	 * - if `offer_node_id` is not set:
-	 *   - MUST NOT respond to the offer.
+	 *
+	 * - if offer_amount is set and offer_description is not set:
+	 *    - MUST NOT respond to the offer.
 	 */
-	if (!offer->offer_description) {
-		*fail = tal_strdup(ctx, "Offer does not contain a description");
+	if (!offer->offer_description && offer->offer_amount) {
+		*fail = tal_strdup(ctx, "Offer does not contain a description, but contains an amount");
 		return tal_free(offer);
 	}
 
+	/* FIXME(vincenzopalazzo): node id can be null when we use blinded path. */
 	if (!offer->offer_node_id) {
 		*fail = tal_strdup(ctx, "Offer does not contain a node_id");
 		return tal_free(offer);

contrib/msggen/msggen/schema.json

@@ -22996,8 +22996,7 @@
       ],
       "request": {
         "required": [
-          "amount",
-          "description"
+          "amount"
         ],
         "properties": {
           "amount": {

doc/schemas/lightning-offer.json

@@ -12,8 +12,7 @@
   ],
   "request": {
     "required": [
-      "amount",
-      "description"
+      "amount"
     ],
     "properties": {
       "amount": {

lightningd/invoice.c

@@ -1827,16 +1827,15 @@ static struct command_result *json_createinvoice(struct command *cmd,
 			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 					    "Incorrect preimage");
 
-		if (!inv->offer_description)
-			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
-					    "Missing description in invoice");
-
 		if (command_check_only(cmd))
 			return command_check_done(cmd);
 
-		desc = tal_strndup(cmd,
-				   inv->offer_description,
-				   tal_bytelen(inv->offer_description));
+		if (inv->offer_description)
+			desc = tal_strndup(cmd,
+					   inv->offer_description,
+					   tal_bytelen(inv->offer_description));
+		else
+			desc = NULL;
 
 		if (!invoices_create(cmd->ld->wallet->invoices,
 				     &inv_dbid,

plugins/offers.c

@@ -496,19 +496,17 @@ static bool json_add_offer_fields(struct json_stream *js,
 	} else if (offer_amount)
 		json_add_amount_msat(js, "offer_amount_msat",
 				     amount_msat(*offer_amount));
-
 	/* BOLT-offers #12:
-	 * A reader of an offer:
-	 *...
-	 * - if `offer_description` is not set:
-	 *   - MUST NOT respond to the offer.
+	 *
+	 * - if offer_amount is set and offer_description is not set:
+	 *    - MUST NOT respond to the offer.
 	 */
 	if (offer_description)
 		valid &= json_add_utf8(js, "offer_description",
 				       offer_description);
-	else {
+	else if (!offer_description && offer_amount) {
 		json_add_string(js, "warning_missing_offer_description",
-				"offers without a description are invalid");
+				"description is required for the user to know what it was they paid for");
 		valid = false;
 	}
 

plugins/offers_offer.c

@@ -297,7 +297,7 @@ struct command_result *json_offer(struct command *cmd,
 
 	if (!param(cmd, buffer, params,
 		   p_req("amount", param_amount, offer),
-		   p_req("description", param_escaped_string, &desc),
+		   p_opt("description", param_escaped_string, &desc),
 		   p_opt("issuer", param_escaped_string, &issuer),
 		   p_opt("label", param_escaped_string, &offinfo->label),
 		   p_opt("quantity_max", param_u64, &offer->offer_quantity_max),
@@ -357,12 +357,18 @@ struct command_result *json_offer(struct command *cmd,
 						     "needs recurrence");
 	}
 
+	if (desc)
+		offer->offer_description
+			= tal_dup_arr(offer, char, desc, strlen(desc), 0);
+
 	/* BOLT-offers #12:
-	 * - MUST set `offer_description` to a complete description of the
-	 *   purpose of the payment.
+	 *
+	 * - if offer_amount is set and offer_description is not set:
+	 *    - MUST NOT respond to the offer.
 	 */
-	offer->offer_description
-		= tal_dup_arr(offer, char, desc, strlen(desc), 0);
+	if (!offer->offer_description && offer->offer_amount)
+		return command_fail_badparam(cmd, "description", buffer, params,
+					     "description is required for the user to know what it was they paid for");
 
 	/* BOLT-offers #12:
 	 * - if it sets `offer_issuer`:
@@ -414,7 +420,7 @@ struct command_result *json_invoicerequest(struct command *cmd,
 
 	if (!param(cmd, buffer, params,
 		   p_req("amount", param_msat, &msat),
-		   p_req("description", param_escaped_string, &desc),
+		   p_opt("description", param_escaped_string, &desc),
 		   p_opt("issuer", param_escaped_string, &issuer),
 		   p_opt("label", param_escaped_string, &label),
 		   p_opt("absolute_expiry", param_u64,
@@ -429,15 +435,20 @@ struct command_result *json_invoicerequest(struct command *cmd,
 
 	/* BOLT-offers #12:
 	 * - otherwise (not responding to an offer):
-	 *   - MUST set (or not set) `offer_description`, `offer_absolute_expiry`, `offer_paths` and `offer_issuer` as it would for an offer.
-	 *   - MUST set `invreq_payer_id` as it would set `offer_node_id` for an offer.
-	 *   - MUST NOT include `signature`, `offer_metadata`, `offer_chains`, `offer_amount`, `offer_currency`, `offer_features`, `offer_quantity_max` or `offer_node_id`
+	 *   - MUST set offer_description to a complete description of the purpose of the payment.
+	 *   - MUST set (or not set) offer_absolute_expiry and offer_issuer as it would for an offer.
+	 *   - MUST set invreq_payer_id (as it would set offer_node_id for an offer).
+	 *   - MUST set invreq_paths as it would set (or not set) offer_paths for an offer.
+	 *   - MUST NOT include signature, offer_metadata, offer_chains, offer_amount, offer_currency, offer_features, offer_quantity_max, offer_paths or offer_node_id
 	 *   - if the chain for the invoice is not solely bitcoin:
-	 *     - MUST specify `invreq_chain` the offer is valid for.
-	 *   - MUST set `invreq_amount`.
+	 *     - MUST pecify invreq_chain the offer is valid for.
+	 *     - MUST set invreq_amount.
 	 */
-	invreq->offer_description
-		= tal_dup_arr(invreq, char, desc, strlen(desc), 0);
+	if (desc)
+		invreq->offer_description = tal_dup_arr(invreq, char, desc, strlen(desc), 0);
+	else
+		invreq->offer_description = NULL;
+
 	if (issuer) {
 		invreq->offer_issuer
 			= tal_dup_arr(invreq, char, issuer, strlen(issuer), 0);

tests/test_pay.py

@@ -5721,3 +5721,35 @@ def test_onionmessage_ratelimit(node_factory):
     # It will recover though!
     time.sleep(0.250)
     l1.rpc.fetchinvoice(offer['bolt12'])
+
+
+def test_fetch_no_description_offer(node_factory):
+    """Reproducing the issue: https://github.com/ElementsProject/lightning/issues/7405"""
+    l1, l2 = node_factory.line_graph(2, opts={'experimental-offers': None,
+                                              'allow-deprecated-apis': True})
+
+    # Deprecated fields make schema checker upset.
+    offer = l2.rpc.call('offer', {'amount': 'any'})
+    inv = l1.rpc.call('fetchinvoice', {'offer': offer['bolt12'], 'amount_msat': '2sat'})
+
+    # Deprecated fields make schema checker upset.
+    l1.rpc.jsonschemas = {}
+    offer_decode = l1.rpc.decode(offer['bolt12'])
+    assert offer_decode['type'] == 'bolt12 offer', f'No possible to decode the offer `{offer}`'
+
+    l1.rpc.pay(inv['invoice'])
+
+
+def test_fetch_no_description_with_amount(node_factory):
+    """Reproducing the issue: https://github.com/ElementsProject/lightning/issues/7405"""
+    l1, l2 = node_factory.line_graph(2, opts={'experimental-offers': None,
+                                              'allow-deprecated-apis': True})
+
+    # Deprecated fields make schema checker upset.
+    # BOLT-offers #12:
+    #
+    # - if offer_amount is set and offer_description is not set:
+    #   - MUST NOT respond to the offer.
+    err = r'description is required for the user to know what it was they paid for'
+    with pytest.raises(RpcError, match=err) as err:
+        _ = l2.rpc.call('offer', {'amount': '2msat'})