nostrdb/block: add bolt11 invoice encoding/decoding

Signed-off-by: William Casarin <jb55@jb55.com>

nostrdb/src/invoice.c

@@ -0,0 +1,69 @@
+
+#include "cursor.h"
+#include "invoice.h"
+#include "bolt11/bolt11.h"
+#include "bolt11/amount.h"
+
+int ndb_encode_invoice(struct cursor *cur, struct bolt11 *invoice) {
+	if (!invoice->description && !invoice->description_hash)
+		return 0;
+
+	if (!cursor_push_byte(cur, 1))
+		return 0;
+
+	// TODO: make cursor_cursor_push_varint uint64_t
+	if (!cursor_push_varint(cur, invoice->msat->millisatoshis))
+		return 0;
+
+	if (!cursor_push_varint(cur, invoice->timestamp))
+		return 0;
+
+	if (!cursor_push_varint(cur, invoice->expiry))
+		return 0;
+
+	if (invoice->description) {
+		if (!cursor_push_byte(cur, 1))
+			return 0;
+		if (!cursor_push_c_str(cur, invoice->description))
+			return 0;
+	} else {
+		if (!cursor_push_byte(cur, 2))
+			return 0;
+		if (!cursor_push(cur, invoice->description_hash->u.u8, 32))
+			return 0;
+	}
+
+	return 1;
+}
+
+int ndb_decode_invoice(struct cursor *cur, struct ndb_invoice *invoice)
+{
+	unsigned char desc_type;
+	if (!cursor_pull_byte(cur, &invoice->version))
+		return 0;
+
+	if (!cursor_pull_varint(cur, &invoice->amount))
+		return 0;
+
+	if (!cursor_pull_varint(cur, &invoice->timestamp))
+		return 0;
+
+	if (!cursor_pull_varint(cur, &invoice->expiry))
+		return 0;
+
+	if (!cursor_pull_byte(cur, &desc_type))
+		return 0;
+
+	if (desc_type == 1) {
+		if (!cursor_pull_c_str(cur, (const char**)&invoice->description))
+			return 0;
+	} else if (desc_type == 2) {
+		invoice->description_hash = cur->p;
+		if (!cursor_skip(cur, 32))
+			return 0;
+	} else {
+		return 0;
+	}
+
+	return 1;
+}