invoice: Support providing preimage when making invoice.

contrib/pylightning/lightning/lightning.py

@@ -150,7 +150,7 @@ class LightningRpc(UnixDomainSocketRpc):
         }
         return self.call("listchannels", payload)
 
-    def invoice(self, msatoshi, label, description, expiry=None, fallbacks=None):
+    def invoice(self, msatoshi, label, description, expiry=None, fallbacks=None, preimage=None):
         """
         Create an invoice for {msatoshi} with {label} and {description} with
         optional {expiry} seconds (default 1 hour)
@@ -160,7 +160,8 @@ class LightningRpc(UnixDomainSocketRpc):
             "label": label,
             "description": description,
             "expiry": expiry,
-            "fallbacks": fallbacks
+            "fallbacks": fallbacks,
+            "preimage": preimage
         }
         return self.call("invoice", payload)
 

doc/lightning-invoice.7

@@ -2,12 +2,12 @@
 .\"     Title: lightning-invoice
 .\"    Author: [see the "AUTHOR" section]
 .\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
-.\"      Date: 04/06/2018
+.\"      Date: 04/23/2018
 .\"    Manual: \ \&
 .\"    Source: \ \&
 .\"  Language: English
 .\"
-.TH "LIGHTNING\-INVOICE" "7" "04/06/2018" "\ \&" "\ \&"
+.TH "LIGHTNING\-INVOICE" "7" "04/23/2018" "\ \&" "\ \&"
 .\" -----------------------------------------------------------------
 .\" * Define some portability stuff
 .\" -----------------------------------------------------------------
@@ -31,7 +31,7 @@
 lightning-invoice \- Protocol for accepting payments\&.
 .SH "SYNOPSIS"
 .sp
-\fBinvoice\fR \fImsatoshi\fR \fIlabel\fR \fIdescription\fR [\fIexpiry\fR] [\fIfallbacks\fR]
+\fBinvoice\fR \fImsatoshi\fR \fIlabel\fR \fIdescription\fR [\fIexpiry\fR] [\fIfallbacks\fR] [\fIpreimage\fR]
 .SH "DESCRIPTION"
 .sp
 The \fBinvoice\fR RPC command creates the expectation of a payment of a given amount of milli\-satoshi: it returns a unique token which another lightning daemon can use to pay this invoice\&.
@@ -45,6 +45,8 @@ The \fIdescription\fR is a short description of purpose of payment, e\&.g\&. \fI
 The \fIexpiry\fR is optionally the number of seconds the invoice is valid for\&. If no value is provided the default of 3600 (1 Hour) is used\&.
 .sp
 The \fIfallbacks\fR array is one or more fallback addresses to include in the invoice (in order from most\-preferred to least): note that these arrays are not currently tracked to fulfill the invoice\&.
+.sp
+The \fIpreimage\fR is a 64\-digit hex string to be used as payment preimage for the created invoice\&. By default, if unspecified, lightningd will generate a secure pseudorandom preimage seeded from an appropriate entropy source on your system\&. \fBIMPORTANT\fR: if you specify the \fIpreimage\fR, you are responsible, to ensure appropriate care for generating using a secure pseudorandom generator seeded with sufficient entropy, and keeping the preimage secret\&. This parameter is an advanced feature intended for use with cutting\-edge cryptographic protocols and should not be used unless explicitly needed\&.
 .SH "RETURN VALUE"
 .sp
 On success, a hash is returned as \fIpayment_hash\fR to be given to the payer, and the \fIexpiry_time\fR as a UNIX timestamp\&. It also returns a BOLT11 invoice as \fIbolt11\fR to be given to the payer\&. On failure, an error is returned and no invoice is created\&. If the lightning process fails before responding, the caller should use lightning\-listinvoice(7) to query whether this invoice was created or not\&.

doc/lightning-invoice.7.txt

@@ -8,7 +8,7 @@ lightning-invoice - Protocol for accepting payments.
 
 SYNOPSIS
 --------
-*invoice* 'msatoshi' 'label' 'description' ['expiry'] ['fallbacks']
+*invoice* 'msatoshi' 'label' 'description' ['expiry'] ['fallbacks'] ['preimage']
 
 DESCRIPTION
 -----------
@@ -36,6 +36,18 @@ The 'fallbacks' array is one or more fallback addresses to include in
 the invoice (in order from most-preferred to least): note that these
 arrays are not currently tracked to fulfill the invoice.
 
+The 'preimage' is a 64-digit hex string to be used as payment preimage
+for the created invoice.
+By default, if unspecified, lightningd will generate a secure
+pseudorandom preimage seeded from an appropriate entropy source on
+your system.
+*IMPORTANT*: if you specify the 'preimage', you are responsible, to
+ensure appropriate care for generating using a secure pseudorandom
+generator seeded with sufficient entropy, and keeping the preimage
+secret.
+This parameter is an advanced feature intended for use with cutting-edge
+cryptographic protocols and should not be used unless explicitly needed.
+
 RETURN VALUE
 ------------
 

lightningd/invoice.c

@@ -156,6 +156,7 @@ static void json_invoice(struct command *cmd,
 	struct invoice invoice;
 	struct invoice_details details;
 	jsmntok_t *msatoshi, *label, *desctok, *exp, *fallback, *fallbacks;
+	jsmntok_t *preimagetok;
 	u64 *msatoshi_val;
 	const struct json_escaped *label_val, *desc;
 	const char *desc_val;
@@ -174,6 +175,7 @@ static void json_invoice(struct command *cmd,
 			     "?expiry", &exp,
 			     "?fallback", &fallback,
 			     "?fallbacks", &fallbacks,
+			     "?preimage", &preimagetok,
 			     NULL)) {
 		return;
 	}
@@ -281,8 +283,18 @@ static void json_invoice(struct command *cmd,
 	struct preimage r;
 	struct sha256 rhash;
 
-	/* Generate random secret preimage and hash. */
-	randombytes_buf(r.r, sizeof(r.r));
+	if (preimagetok) {
+		/* Get secret preimage from user. */
+		if (!hex_decode(buffer + preimagetok->start,
+				preimagetok->end - preimagetok->start,
+				r.r, sizeof(r.r))) {
+			command_fail(cmd, "preimage must be 64 hex digits");
+			return;
+		}
+	} else
+		/* Generate random secret preimage. */
+		randombytes_buf(r.r, sizeof(r.r));
+	/* Generate preimage hash. */
 	sha256(&rhash, r.r, sizeof(r.r));
 
 	/* Construct bolt11 string. */

tests/test_lightningd.py

@@ -445,6 +445,23 @@ class LightningDTests(BaseLightningDTests):
         assert len(l1.rpc.listinvoices('inv1')['invoices']) == 0
         assert len(l1.rpc.listinvoices('inv2')['invoices']) == 0
 
+    def test_invoice_preimage(self):
+        """Test explicit invoice 'preimage'.
+        """
+        l1, l2 = self.connect()
+        self.fund_channel(l1, l2, 10**6)
+
+        # I promise the below number is randomly generated
+        invoice_preimage = "17b08f669513b7379728fc1abcea5eaf3448bc1eba55a68ca2cd1843409cdc04"
+
+        # Make invoice and pay it
+        inv = l2.rpc.invoice(msatoshi=123456, label="inv", description="?", preimage=invoice_preimage)
+        payment = l1.rpc.pay(inv['bolt11'])
+
+        # Check preimage was given.
+        payment_preimage = payment['payment_preimage']
+        assert invoice_preimage == payment_preimage
+
     def test_invoice(self):
         l1 = self.node_factory.get_node()
         l2 = self.node_factory.get_node()