invoice: add deschashonly parameter.

LNURL wants this so they can include images etc in descriptions.

Replaces: #4892
Changelog-Added: JSON-RPC: `invoice` has a new parameter `deschashonly` to put hash of description in bolt11.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/bolt11.c

@@ -1119,11 +1119,16 @@ char *bolt11_encode_(const tal_t *ctx,
 	/* Thus we do built-in fields, then extras last. */
 	encode_p(&data, &b11->payment_hash);
 
-	if (b11->description)
-		encode_d(&data, b11->description);
-
+	/* BOLT #11:
+	 * A writer:
+	 *...
+	 *    - MUST include either exactly one `d` or exactly one `h` field.
+	 */
+	/* We sometimes keep description around (to put in db), so prefer hash */
 	if (b11->description_hash)
 		encode_h(&data, b11->description_hash);
+	else if (b11->description)
+		encode_d(&data, b11->description);
 
 	if (n_field)
 		encode_n(&data, &b11->receiver_id);

contrib/pyln-client/pyln/client/lightning.py

@@ -828,7 +828,7 @@ def help(self, command=None):
         return self.call("help", payload)
 
     def invoice(self, msatoshi, label, description, expiry=None, fallbacks=None,
-                preimage=None, exposeprivatechannels=None, cltv=None):
+                preimage=None, exposeprivatechannels=None, cltv=None, deschashonly=None):
         """
         Create an invoice for {msatoshi} with {label} and {description} with
         optional {expiry} seconds (default 1 week).
@@ -842,6 +842,7 @@ def invoice(self, msatoshi, label, description, expiry=None, fallbacks=None,
             "preimage": preimage,
             "exposeprivatechannels": exposeprivatechannels,
             "cltv": cltv,
+            "deschashonly": deschashonly,
         }
         return self.call("invoice", payload)
 

doc/lightning-invoice.7.md

@@ -5,7 +5,7 @@ SYNOPSIS
 --------
 
 **invoice** *msatoshi* *label* *description* [*expiry*]
-[*fallbacks*] [*preimage*] [*exposeprivatechannels*] [*cltv*]
+[*fallbacks*] [*preimage*] [*exposeprivatechannels*] [*cltv*] [*deschashonly*]
 
 DESCRIPTION
 -----------
@@ -29,8 +29,9 @@ of this invoice.
 
 The *description* is a short description of purpose of payment, e.g. *1
 cup of coffee*. This value is encoded into the BOLT11 invoice and is
-viewable by any node you send this invoice to. It must be UTF-8, and
-cannot use *\\u* JSON escape codes.
+viewable by any node you send this invoice to (unless *deschashonly* is
+true as described below). It must be UTF-8, and cannot use *\\u* JSON 
+escape codes.
 
 The *expiry* is optionally the time the invoice is valid for; without a
 suffix it is interpreted as seconds, otherwise suffixes *s*, *m*, *h*,
@@ -68,6 +69,11 @@ payment.
 If specified, *cltv* sets the *min_final_cltv_expiry* for the invoice.
 Otherwise, it's set to the parameter **cltv-final**.
 
+If *deschash* is true (default false), then the bolt11 returned
+contains a hash of the *description*, rather than the *description*
+itself: this allows much longer descriptions, but they must be
+communicated via some other mechanism.
+
 RETURN VALUE
 ------------
 

lightningd/invoice.c

@@ -1135,6 +1135,7 @@ static struct command_result *json_invoice(struct command *cmd,
 	u32 *cltv;
 	struct jsonrpc_request *req;
 	struct plugin *plugin;
+	bool *hashonly;
 #if DEVELOPER
 	const jsmntok_t *routes;
 #endif
@@ -1153,6 +1154,7 @@ static struct command_result *json_invoice(struct command *cmd,
 			 &info->chanhints),
 		   p_opt_def("cltv", param_number, &cltv,
 			     cmd->ld->config.cltv_final),
+		   p_opt_def("deschashonly", param_bool, &hashonly, false),
 #if DEVELOPER
 		   p_opt("dev-routes", param_array, &routes),
 #endif
@@ -1165,7 +1167,7 @@ static struct command_result *json_invoice(struct command *cmd,
 				    INVOICE_MAX_LABEL_LEN);
 	}
 
-	if (strlen(desc_val) > BOLT11_FIELD_BYTE_LIMIT) {
+	if (strlen(desc_val) > BOLT11_FIELD_BYTE_LIMIT && !*hashonly) {
 		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 				    "Descriptions greater than %d bytes "
 				    "not yet supported "
@@ -1207,7 +1209,18 @@ static struct command_result *json_invoice(struct command *cmd,
 	info->b11->min_final_cltv_expiry = *cltv;
 	info->b11->expiry = *expiry;
 	info->b11->description = tal_steal(info->b11, desc_val);
-	info->b11->description_hash = NULL;
+	/* BOLT #11:
+	 * * `h` (23): `data_length` 52. 256-bit description of purpose of payment (SHA256).
+	 *...
+	 * A writer:
+	 *...
+	 *    - MUST include either exactly one `d` or exactly one `h` field.
+	 */
+	if (*hashonly) {
+		info->b11->description_hash = tal(info->b11, struct sha256);
+		sha256(info->b11->description_hash, desc_val, strlen(desc_val));
+	} else
+		info->b11->description_hash = NULL;
 	info->b11->payment_secret = tal_dup(info->b11, struct secret,
 					    &payment_secret);
 	info->b11->features = tal_dup_talarr(info->b11, u8,

tests/test_invoices.py

@@ -712,3 +712,24 @@ def match(node, query, invoice):
     for q in queries:
         r = l1.rpc.listinvoices(**q)
         assert len(r['invoices']) == 0
+
+
+def test_invoice_deschash(node_factory, chainparams):
+    l1, l2 = node_factory.line_graph(2)
+
+    # BOLT #11:
+    # * `h`: tagged field: hash of description
+    #  * `p5`: `data_length` (`p` = 1, `5` = 20; 1 * 32 + 20 == 52)
+    #  * `8yjmdan79s6qqdhdzgynm4zwqd5d7xmw5fk98klysy043l2ahrqs`: SHA256 of 'One piece of chocolate cake, one icecream cone, one pickle, one slice of swiss cheese, one slice of salami, one lollypop, one piece of cherry pie, one sausage, one cupcake, and one slice of watermelon'
+    inv = l2.rpc.invoice(42, 'label', 'One piece of chocolate cake, one icecream cone, one pickle, one slice of swiss cheese, one slice of salami, one lollypop, one piece of cherry pie, one sausage, one cupcake, and one slice of watermelon', deschashonly=True)
+    assert '8yjmdan79s6qqdhdzgynm4zwqd5d7xmw5fk98klysy043l2ahrqs' in inv['bolt11']
+
+    b11 = l2.rpc.decodepay(inv['bolt11'])
+    assert 'description' not in b11
+    assert b11['description_hash'] == '3925b6f67e2c340036ed12093dd44e0368df1b6ea26c53dbe4811f58fd5db8c1'
+
+    listinv = only_one(l2.rpc.listinvoices()['invoices'])
+    assert listinv['description'] == 'One piece of chocolate cake, one icecream cone, one pickle, one slice of swiss cheese, one slice of salami, one lollypop, one piece of cherry pie, one sausage, one cupcake, and one slice of watermelon'
+
+    # Make sure we can pay it!
+    l1.rpc.pay(inv['bolt11'])