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
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