It is quite tricky to set field value with a variable length (i.e. DNS query name), to make it possible the field needs to be added to header with 'len=0' in that case there will be no any payload allocation, but only while setting the field value the packet will be appended with a real length bytes and after the field needs to be relocated to the right place.
Signed-off-by: Vadim Kochan <vadi...@gmail.com> --- trafgen_proto.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) diff --git a/trafgen_proto.c b/trafgen_proto.c index 0530032..83a6a7e 100644 --- a/trafgen_proto.c +++ b/trafgen_proto.c @@ -100,6 +100,9 @@ void proto_header_fields_add(struct proto_hdr *hdr, f->pkt_offset = hdr->pkt_offset + fields[i].offset; f->hdr = hdr; + if (!f->len) + continue; + if (f->pkt_offset + f->len > pkt->len) { hdr->len += f->len; set_fill(0, (f->pkt_offset + f->len) - pkt->len); @@ -181,6 +184,45 @@ set_proto: return current; } +static void __proto_field_relocate(struct proto_field *field) +{ + struct proto_hdr *hdr = field->hdr; + struct packet *pkt = packet_get(hdr->pkt_id); + uint8_t *from, *to; + int i; + + /* If this is a last field then just calculate 'pkt_offset' */ + if (field->id == hdr->fields_count - 1) { + field->pkt_offset = hdr->pkt_offset + hdr->len - field->len; + return; + } + + /* Use 'pkt_offset' from the 1st real (len > 0) field after the + * 'target' one */ + for (i = field->id + 1; i < hdr->fields_count; i++) { + if (hdr->fields[i].len == 0) + continue; + + field->pkt_offset = hdr->fields[i].pkt_offset; + break; + } + + /* Move payload of overlapped fields (each after the 'target' field) */ + from = &pkt->payload[field->pkt_offset]; + to = &pkt->payload[field->pkt_offset + field->len]; + memcpy(to, from, hdr->len - field->len); + + /* Recalculate 'pkt_offset' of the rest fields */ + for (; i < hdr->fields_count; i++) { + struct proto_field *tmp = &hdr->fields[i]; + + if (tmp->len == 0) + continue; + + tmp->pkt_offset += field->len; + } +} + static void __proto_field_set_bytes(struct proto_field *field, const uint8_t *bytes, size_t len, bool is_default, bool is_be) @@ -195,6 +237,14 @@ static void __proto_field_set_bytes(struct proto_field *field, if (is_default && field->is_set) return; + if (field->len == 0) { + field->hdr->len += len; + field->len = len; + set_fill(0, len); + + __proto_field_relocate(field); + } + payload = &packet_get(field->hdr->pkt_id)->payload[field->pkt_offset]; if (field->len == 1) { -- 2.11.0 -- You received this message because you are subscribed to the Google Groups "netsniff-ng" group. To unsubscribe from this group and stop receiving emails from it, send an email to netsniff-ng+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.