tlvstream: Allow overwriting an already set value

This is necessary in the next commit to override the total_msat that is being
delivered to the destination.

wire/tlvstream.c

@@ -21,14 +21,30 @@ void towire_tlvstream_raw(u8 **pptr, const struct tlv_field *fields)
 	}
 }
 
+static struct tlv_field *tlvstream_get_raw(struct tlv_field *stream, u64 type)
+{
+	for (size_t i=0; i<tal_count(stream); i++)
+		if (stream[i].numtype == type)
+			return &stream[i];
+	return NULL;
+}
+
 void tlvstream_set_raw(struct tlv_field **stream, u64 type, void *value, size_t valuelen)
 {
-	struct tlv_field f;
+	struct tlv_field f, *e = tlvstream_get_raw(*stream, type);
+
+	if (e != NULL) {
+		tal_free(e->value);
+		e->length = valuelen;
+		e->value = tal_dup_arr(*stream, u8, value, e->length, 0);
+	} else {
+		/* If we haven't found it insert it insead. */
 		f.length = valuelen;
 		f.numtype = type;
 		f.value = tal_dup_arr(*stream, u8, value, f.length, 0);
 		tal_arr_expand(stream, f);
 	}
+}
 
 void tlvstream_set_short_channel_id(struct tlv_field **stream, u64 type,
 				    struct short_channel_id *value)
@@ -52,15 +68,6 @@ void tlvstream_set_tu32(struct tlv_field **stream, u64 type, u32 value)
 	tlvstream_set_raw(stream, type, ser, tal_bytelen(ser));
 }
 
-static struct tlv_field *tlvstream_get_raw(struct tlv_field *stream, u64 type)
-{
-	for (size_t i=0; i<tal_count(stream); i++)
-		if (stream[i].numtype == type)
-			return &stream[i];
-	return NULL;
-}
-
-
 bool tlvstream_get_short_channel_id(struct tlv_field *stream, u64 type,
 				    struct short_channel_id *value)
 {