invoice: Allow "any" msatoshi, for amountless invoices.

Fixes: #534

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: 09/06/2016
+.\"      Date: 01/10/2018
 .\"    Manual: \ \&
 .\"    Source: \ \&
 .\"  Language: English
 .\"
-.TH "LIGHTNING\-INVOICE" "7" "09/06/2016" "\ \&" "\ \&"
+.TH "LIGHTNING\-INVOICE" "7" "01/10/2018" "\ \&" "\ \&"
 .\" -----------------------------------------------------------------
 .\" * Define some portability stuff
 .\" -----------------------------------------------------------------
@@ -36,10 +36,12 @@ lightning-invoice \- Protocol for accepting payments\&.
 .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\&.
 .sp
+The \fImsatoshi\fR can be the string "any", which creates an invoice that can be paid with any amount\&.
+.sp
 The \fIlabel\fR must be unique; it is never revealed to other nodes on the lightning network, but it can be used to query the status of this invoice\&.
 .SH "RETURN VALUE"
 .sp
-On success, a hash is returned as \fIrhash\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 getinvoice(7) to query whether this invoice was created or not\&.
+On success, a hash is returned as \fIrhash\fR to be given to the payer\&. 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 getinvoice(7) to query whether this invoice was created or not\&.
 .SH "AUTHOR"
 .sp
 Rusty Russell <rusty@rustcorp\&.com\&.au> is mainly responsible\&.

doc/lightning-invoice.7.txt

@@ -16,6 +16,9 @@ The *invoice* 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.
 
+The 'msatoshi' can be the string "any", which creates an invoice
+that can be paid with any amount.
+
 The 'label' must be unique; it is never revealed to other nodes on
 the lightning network, but it can be used to query the status of this
 invoice.
@@ -24,6 +27,8 @@ RETURN VALUE
 ------------
 
 On success, a hash is returned as 'rhash' to be given to the payer.
+It also returns a BOLT11 invoice as 'bolt11' 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
 getinvoice(7) to query whether this invoice was created or not.

lightningd/invoice.c

@@ -197,13 +197,18 @@ static void json_invoice(struct command *cmd,
 
 	sha256(&invoice->rhash, invoice->r.r, sizeof(invoice->r.r));
 
-	invoice->msatoshi = tal(invoice, u64);
-	if (!json_tok_u64(buffer, msatoshi, invoice->msatoshi)
-	    || *invoice->msatoshi == 0) {
-		command_fail(cmd, "'%.*s' is not a valid positive number",
-			     msatoshi->end - msatoshi->start,
-			     buffer + msatoshi->start);
-		return;
+	if (json_tok_streq(buffer, msatoshi, "any"))
+		invoice->msatoshi = NULL;
+	else {
+		invoice->msatoshi = tal(invoice, u64);
+		if (!json_tok_u64(buffer, msatoshi, invoice->msatoshi)
+		    || *invoice->msatoshi == 0) {
+			command_fail(cmd,
+				     "'%.*s' is not a valid positive number",
+				     msatoshi->end - msatoshi->start,
+				     buffer + msatoshi->start);
+			return;
+		}
 	}
 
 	invoice->label = tal_strndup(invoice, buffer + label->start,