trafgen: parser: Add TCP header generation function

Add a function 'tcp()' to generate TCP headers from the trafgen
configuration language.

Fields supported:

    sp|sport     TCP source port (default 0)
    dp|dport     TCP destination port (default 0)
    seq          Sequence number (default: 0)
    aseq|ackseq  Acknowledgement number (default 0)
    doff|hlen    Header length/data offset (default: 5)
    cwr          Congestion Window Reduced flag (default: 0)
    ece|ecn      ECN-Echo flag (default: 0)
    urg          Urgent flag (default: 0)
    ack          Acknowledgement flag (default: 0)
    psh          Push flag (default: 0)
    rst          Reset flag (default: 0)
    syn          Synchronize flag (default: 0)
    fin          Finish flag (default: 0)
    win|window   Receive window size (default: 0)
    csum         Checksum field (calculated automatically)
    urgptr       Urgent pointer (default: 0)

Example (SYN on port 80/http):

    { tcp(dport=80, syn, window=5840) }

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

1 files changed, 64 insertions, 0 deletions

diff --git a/trafgen_l4.c b/trafgen_l4.c
index 286e54a..7f80e74 100644
--- a/trafgen_l4.c
+++ b/trafgen_l4.c
@@ -21,6 +21,26 @@ static struct proto_field udp_fields[] = {
 	{ .id = UDP_CSUM,	.len = 2,	.offset = 6 },
 };
 
+static struct proto_field tcp_fields[] = {
+	{ .id = TCP_SPORT,   .len = 2, .offset = 0 },
+	{ .id = TCP_DPORT,   .len = 2, .offset = 2 },
+	{ .id = TCP_SEQ,     .len = 4, .offset = 4 },
+	{ .id = TCP_ACK_SEQ, .len = 4, .offset = 8 },
+	{ .id = TCP_DOFF,    .len = 2, .offset = 12, .shift = 12, .mask = 0xf000 },
+	/* reserved (4 bits) */
+	{ .id = TCP_CWR,     .len = 2, .offset = 12, .shift = 7, .mask = 0x0080 },
+	{ .id = TCP_ECE,     .len = 2, .offset = 12, .shift = 6, .mask = 0x0040 },
+	{ .id = TCP_URG,     .len = 2, .offset = 12, .shift = 5, .mask = 0x0020 },
+	{ .id = TCP_ACK,     .len = 2, .offset = 12, .shift = 4, .mask = 0x0010 },
+	{ .id = TCP_PSH,     .len = 2, .offset = 12, .shift = 3, .mask = 0x0008 },
+	{ .id = TCP_RST,     .len = 2, .offset = 12, .shift = 2, .mask = 0x0004 },
+	{ .id = TCP_SYN,     .len = 2, .offset = 12, .shift = 1, .mask = 0x0002 },
+	{ .id = TCP_FIN,     .len = 2, .offset = 12, .shift = 0, .mask = 0x0001 },
+	{ .id = TCP_WINDOW,  .len = 2, .offset = 14 },
+	{ .id = TCP_CSUM,    .len = 2, .offset = 16 },
+	{ .id = TCP_URG_PTR, .len = 2, .offset = 18 },
+};
+
 static void udp_header_init(struct proto_hdr *hdr)
 {
 	struct proto_hdr *lower;
@@ -65,7 +85,51 @@ static struct proto_hdr udp_hdr = {
 	.packet_finish  = udp_packet_finish,
 };
 
+static void tcp_header_init(struct proto_hdr *hdr)
+{
+	struct proto_hdr *lower;
+
+	proto_lower_default_add(PROTO_IP4);
+
+	lower = proto_current_header();
+
+	if (lower->id == PROTO_IP4)
+		proto_field_set_default_u8(lower, IP4_PROTO, IPPROTO_TCP);
+
+	proto_header_fields_add(hdr, tcp_fields, array_size(tcp_fields));
+
+	proto_field_set_default_be16(hdr, TCP_DOFF, 5);
+}
+
+static void tcp_packet_finish(struct proto_hdr *hdr)
+{
+	struct proto_hdr *lower = proto_lower_header(hdr);
+	struct packet *pkt = current_packet();
+	uint16_t total_len;
+	uint16_t csum;
+
+	if (proto_field_is_set(hdr, TCP_CSUM))
+		return;
+
+	if (!lower || lower->id != PROTO_IP4)
+		return;
+
+	total_len = pkt->len - hdr->pkt_offset;
+	csum = p4_csum((void *) proto_header_ptr(lower), proto_header_ptr(hdr),
+			total_len, IPPROTO_TCP);
+
+	proto_field_set_be16(hdr, TCP_CSUM, bswap_16(csum));
+}
+
+static struct proto_hdr tcp_hdr = {
+	.id		= PROTO_TCP,
+	.layer		= PROTO_L4,
+	.header_init	= tcp_header_init,
+	.packet_finish  = tcp_packet_finish,
+};
+
 void protos_l4_init(void)
 {
 	proto_header_register(&udp_hdr);
+	proto_header_register(&tcp_hdr);
 }