trafgen: parser: Unify proto field value parsing

Changed parsing logic of field value expression to be more generic. Such
approach will allow to easy extend field value expression to support
dynamic field functions.

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

3 files changed, 218 insertions, 147 deletions

diff --git a/trafgen_parser.y b/trafgen_parser.y
index d643ad2..1e7bd5c 100644
--- a/trafgen_parser.y
+++ b/trafgen_parser.y
@@ -69,6 +69,27 @@ extern size_t dlen;
 
 static int our_cpu, min_cpu = -1, max_cpu = -1;
 
+enum field_expr_type_t {
+	FIELD_EXPR_UNKNOWN,
+	FIELD_EXPR_NUMB,
+	FIELD_EXPR_MAC,
+	FIELD_EXPR_IP4_ADDR,
+	FIELD_EXPR_IP6_ADDR,
+};
+
+struct proto_field_expr {
+	enum field_expr_type_t type;
+	struct proto_field *field;
+
+	union {
+		struct in_addr ip4_addr;
+		struct in6_addr ip6_addr;
+		long long int number;
+		uint8_t bytes[256];
+	} val;
+};
+
+static struct proto_field_expr field_expr;
 static struct proto_hdr *hdr;
 
 static inline int test_ignore(void)
@@ -351,6 +372,48 @@ static void proto_add(enum proto_id pid)
 	hdr = proto_header_push(pid);
 }
 
+static void proto_field_set(uint32_t fid)
+{
+	field_expr.field = proto_field_by_id(hdr, fid);
+}
+
+static void proto_field_expr_eval(void)
+{
+	struct proto_field *field = field_expr.field;
+
+	switch (field_expr.type) {
+	case FIELD_EXPR_NUMB:
+		if (field->len == 1)
+			proto_field_set_u8(hdr, field->id, field_expr.val.number);
+		else if (field->len == 2)
+			proto_field_set_be16(hdr, field->id, field_expr.val.number);
+		else if (field->len == 4)
+			proto_field_set_be32(hdr, field->id, field_expr.val.number);
+		else
+			bug();
+		break;
+
+	case FIELD_EXPR_MAC:
+		proto_field_set_bytes(hdr, field->id, field_expr.val.bytes);
+		break;
+
+	case FIELD_EXPR_IP4_ADDR:
+		proto_field_set_u32(hdr, field->id, field_expr.val.ip4_addr.s_addr);
+		break;
+
+	case FIELD_EXPR_IP6_ADDR:
+		proto_field_set_bytes(hdr, field->id,
+			(uint8_t *)&field_expr.val.ip6_addr.s6_addr);
+		break;
+
+	case FIELD_EXPR_UNKNOWN:
+	default:
+		bug();
+	}
+
+	memset(&field_expr, 0, sizeof(field_expr));
+}
+
 %}
 
 %union {
@@ -614,6 +677,17 @@ proto
 	| tcp_proto { }
 	;
 
+field_expr
+	: number { field_expr.type = FIELD_EXPR_NUMB;
+		   field_expr.val.number = $1; }
+	| mac { field_expr.type = FIELD_EXPR_MAC;
+		memcpy(field_expr.val.bytes, $1, sizeof(field_expr.val.bytes)); }
+	| ip4_addr { field_expr.type = FIELD_EXPR_IP4_ADDR;
+		     field_expr.val.ip4_addr = $1; }
+	| ip6_addr { field_expr.type = FIELD_EXPR_IP6_ADDR;
+		     field_expr.val.ip6_addr = $1; }
+	;
+
 eth_proto
 	: eth '(' eth_param_list ')' { }
 	;
@@ -624,8 +698,8 @@ eth
 
 eth_param_list
 	: { }
-	| eth_field { }
-	| eth_field delimiter eth_param_list { }
+	| eth_expr { }
+	| eth_expr delimiter eth_param_list { }
 	;
 
 eth_type
@@ -635,12 +709,13 @@ eth_type
 	;
 
 eth_field
-	: K_DADDR skip_white '=' skip_white mac
-		{ proto_field_set_bytes(hdr, ETH_DST_ADDR, $5); }
-	| K_SADDR skip_white '=' skip_white mac
-		{ proto_field_set_bytes(hdr, ETH_SRC_ADDR, $5); }
-	| eth_type skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, ETH_TYPE, $5); }
+	: K_DADDR { proto_field_set(ETH_DST_ADDR); }
+	| K_SADDR { proto_field_set(ETH_SRC_ADDR); }
+	| eth_type { proto_field_set(ETH_TYPE); }
+
+eth_expr
+	: eth_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
 	;
 
 vlan_proto
@@ -653,8 +728,8 @@ vlan
 
 vlan_param_list
 	: { }
-	| vlan_field { }
-	| vlan_field delimiter vlan_param_list { }
+	| vlan_expr { }
+	| vlan_expr delimiter vlan_param_list { }
 	;
 
 vlan_type
@@ -663,20 +738,20 @@ vlan_type
 	;
 
 vlan_field
-	: vlan_type skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, VLAN_TPID, $5); }
+	: vlan_type { proto_field_set(VLAN_TPID); }
+	| K_TCI { proto_field_set(VLAN_TCI); }
+	| K_PCP { proto_field_set(VLAN_PCP); }
+	| K_DEI { proto_field_set(VLAN_DEI); }
+	| K_ID { proto_field_set(VLAN_VID); }
+	;
+
+vlan_expr
+	: vlan_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
 	| K_1Q
 		{ proto_field_set_be16(hdr, VLAN_TPID, ETH_P_8021Q); }
 	| K_1AD
 		{ proto_field_set_be16(hdr, VLAN_TPID, ETH_P_8021AD); }
-	| K_TCI skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, VLAN_TCI, $5); }
-	| K_PCP skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, VLAN_PCP, $5); }
-	| K_DEI skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, VLAN_DEI, $5); }
-	| K_ID skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, VLAN_VID, $5); }
 	;
 
 mpls_proto
@@ -689,8 +764,8 @@ mpls
 
 mpls_param_list
 	: { }
-	| mpls_field { }
-	| mpls_field delimiter mpls_param_list { }
+	| mpls_expr { }
+	| mpls_expr delimiter mpls_param_list { }
 	;
 
 mpls_tc
@@ -699,49 +774,55 @@ mpls_tc
 	;
 
 mpls_field
-	: K_LABEL skip_white '=' skip_white number
-		{ proto_field_set_be32(hdr, MPLS_LABEL, $5); }
-	| mpls_tc skip_white '=' skip_white number
-		{ proto_field_set_be32(hdr, MPLS_TC, $5); }
-	| K_LAST skip_white '=' skip_white number
-		{ proto_field_set_be32(hdr, MPLS_LAST, $5); }
-	| K_TTL skip_white '=' skip_white number
-		{ proto_field_set_be32(hdr, MPLS_TTL, $5); }
+	: K_LABEL { proto_field_set(MPLS_LABEL); }
+	| mpls_tc { proto_field_set(MPLS_TC); }
+	| K_LAST { proto_field_set(MPLS_LAST); }
+	| K_TTL { proto_field_set(MPLS_TTL); }
 	;
 
+mpls_expr
+	: mpls_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
+
 arp_proto
 	: arp '(' arp_param_list ')' { }
 	;
 
 arp_param_list
 	: { }
-	| arp_field { }
-	| arp_field delimiter arp_param_list { }
+	| arp_expr { }
+	| arp_expr delimiter arp_param_list { }
 	;
 
 arp_field
-	: K_OPER skip_white '=' skip_white K_REQUEST
+	: K_HTYPE
+		{ proto_field_set(ARP_HTYPE); }
+	| K_PTYPE
+		{ proto_field_set(ARP_PTYPE); }
+	| K_SHA
+		{ proto_field_set(ARP_SHA); }
+	| K_THA
+		{ proto_field_set(ARP_THA); }
+	| K_SPA
+		{ proto_field_set(ARP_SPA); }
+	| K_TPA
+		{ proto_field_set(ARP_TPA); }
+	;
+
+arp_expr
+	: arp_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
+	| K_OPER skip_white '=' skip_white field_expr
+		{ proto_field_set(ARP_OPER);
+		  proto_field_expr_eval(); }
+	| K_OPER skip_white '=' skip_white K_REQUEST
 		{ proto_field_set_be16(hdr, ARP_OPER, ARPOP_REQUEST); }
 	| K_OPER skip_white '=' skip_white K_REPLY
 		{ proto_field_set_be16(hdr, ARP_OPER, ARPOP_REPLY); }
-	| K_OPER skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, ARP_OPER, $5); }
 	| K_REQUEST
 		{ proto_field_set_be16(hdr, ARP_OPER, ARPOP_REQUEST); }
 	| K_REPLY
 		{ proto_field_set_be16(hdr, ARP_OPER, ARPOP_REPLY); }
-	| K_HTYPE skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, ARP_HTYPE, $5); }
-	| K_PTYPE skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, ARP_PTYPE, $5); }
-	| K_SHA skip_white '=' skip_white mac
-		{ proto_field_set_bytes(hdr, ARP_SHA, $5); }
-	| K_THA skip_white '=' skip_white mac
-		{ proto_field_set_bytes(hdr, ARP_THA, $5); }
-	| K_SPA skip_white '=' skip_white ip4_addr
-		{ proto_field_set_u32(hdr, ARP_SPA, $5.s_addr); }
-	| K_TPA skip_white '=' skip_white ip4_addr
-		{ proto_field_set_u32(hdr, ARP_TPA, $5.s_addr); }
 	;
 arp
 	: K_ARP	{ proto_add(PROTO_ARP); }
@@ -753,41 +834,32 @@ ip4_proto
 
 ip4_param_list
 	: { }
-	| ip4_field { }
-	| ip4_field delimiter ip4_param_list { }
+	| ip4_expr { }
+	| ip4_expr delimiter ip4_param_list { }
 	;
 
 ip4_field
-	: K_VER skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, IP4_VER, $5); }
-	| K_IHL skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, IP4_IHL, $5); }
-	| K_DADDR skip_white '=' skip_white ip4_addr
-		{ proto_field_set_u32(hdr, IP4_DADDR, $5.s_addr); }
-	| K_SADDR skip_white '=' skip_white ip4_addr
-		{ proto_field_set_u32(hdr, IP4_SADDR, $5.s_addr); }
-	| K_PROT skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, IP4_PROTO, $5); }
-	| K_TTL skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, IP4_TTL, $5); }
-	| K_DSCP skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, IP4_DSCP, $5); }
-	| K_ECN skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, IP4_ECN, $5); }
-	| K_TOS skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, IP4_TOS, $5); }
-	| K_LEN skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, IP4_LEN, $5); }
-	| K_ID skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, IP4_ID, $5); }
-	| K_FLAGS skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, IP4_FLAGS, $5); }
+	: K_VER { proto_field_set(IP4_VER); }
+	| K_IHL { proto_field_set(IP4_IHL); }
+	| K_DADDR { proto_field_set(IP4_DADDR); }
+	| K_SADDR { proto_field_set(IP4_SADDR); }
+	| K_PROT { proto_field_set(IP4_PROTO); }
+	| K_TTL { proto_field_set(IP4_TTL); }
+	| K_DSCP { proto_field_set(IP4_DSCP); }
+	| K_ECN { proto_field_set(IP4_ECN); }
+	| K_TOS { proto_field_set(IP4_TOS); }
+	| K_LEN { proto_field_set(IP4_LEN); }
+	| K_ID { proto_field_set(IP4_ID); }
+	| K_FLAGS { proto_field_set(IP4_FLAGS); }
+	| K_FRAG { proto_field_set(IP4_FRAG_OFFS); }
+	| K_CSUM { proto_field_set(IP4_CSUM); }
+	;
+
+ip4_expr
+	: ip4_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
 	| K_DF  { proto_field_set_be16(hdr, IP4_DF, 1); }
 	| K_MF  { proto_field_set_be16(hdr, IP4_MF, 1); }
-	| K_FRAG skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, IP4_FRAG_OFFS, $5); }
-	| K_CSUM skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, IP4_CSUM, $5); }
 	;
 
 ip4
@@ -800,8 +872,8 @@ ip6_proto
 
 ip6_param_list
 	: { }
-	| ip6_field { }
-	| ip6_field delimiter ip6_param_list { }
+	| ip6_expr { }
+	| ip6_expr delimiter ip6_param_list { }
 	;
 
 ip6_hop_limit
@@ -810,22 +882,19 @@ ip6_hop_limit
 	;
 
 ip6_field
-	: K_VER skip_white '=' skip_white number
-		{ proto_field_set_be32(hdr, IP6_VER, $5); }
-	| K_TC skip_white '=' skip_white number
-		{ proto_field_set_be32(hdr, IP6_CLASS, $5); }
-	| K_FLOW skip_white '=' skip_white number
-		{ proto_field_set_be32(hdr, IP6_FLOW_LBL, $5); }
-	| K_LEN skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, IP6_LEN, $5); }
-	| K_NEXT_HDR skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, IP6_NEXT_HDR, $5); }
-	| ip6_hop_limit skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, IP6_HOP_LIMIT, $5); }
-	| K_SADDR skip_white '=' skip_white ip6_addr
-		{ proto_field_set_bytes(hdr, IP6_SADDR, (uint8_t *)&($5.s6_addr)); }
-	| K_DADDR skip_white '=' skip_white ip6_addr
-		{ proto_field_set_bytes(hdr, IP6_DADDR, (uint8_t *)&($5.s6_addr)); }
+	: K_VER { proto_field_set(IP6_VER); }
+	| K_TC { proto_field_set(IP6_CLASS); }
+	| K_FLOW { proto_field_set(IP6_FLOW_LBL); }
+	| K_LEN { proto_field_set(IP6_LEN); }
+	| K_NEXT_HDR { proto_field_set(IP6_NEXT_HDR); }
+	| ip6_hop_limit { proto_field_set(IP6_HOP_LIMIT); }
+	| K_SADDR { proto_field_set(IP6_SADDR); }
+	| K_DADDR { proto_field_set(IP6_DADDR) ; }
+	;
+
+ip6_expr
+	: ip6_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
 	;
 
 ip6
@@ -838,23 +907,22 @@ icmp4_proto
 
 icmp4_param_list
 	: { }
-	| icmp4_field { }
-	| icmp4_field delimiter icmp4_param_list { }
+	| icmp4_expr { }
+	| icmp4_expr delimiter icmp4_param_list { }
 	;
 
 icmp4_field
-	: K_TYPE skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, ICMPV4_TYPE, $5); }
-	| K_CODE skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, ICMPV4_CODE, $5); }
-	| K_ID skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, ICMPV4_ID, $5); }
-	| K_SEQ skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, ICMPV4_SEQ, $5); }
-	| K_MTU skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, ICMPV4_MTU, $5); }
-	| K_ADDR skip_white '=' skip_white ip4_addr
-		{ proto_field_set_u32(hdr, ICMPV4_REDIR_ADDR, $5.s_addr); }
+	: K_TYPE { proto_field_set(ICMPV4_TYPE); }
+	| K_CODE { proto_field_set(ICMPV4_CODE); }
+	| K_ID { proto_field_set(ICMPV4_ID); }
+	| K_SEQ { proto_field_set(ICMPV4_SEQ); }
+	| K_MTU { proto_field_set(ICMPV4_MTU); }
+	| K_ADDR { proto_field_set(ICMPV4_REDIR_ADDR); }
+	;
+
+icmp4_expr
+	: icmp4_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
 	| K_ECHO_REQUEST
 		{ proto_field_set_u8(hdr, ICMPV4_TYPE, ICMP_ECHO);
 		  proto_field_set_u8(hdr, ICMPV4_CODE, 0); }
@@ -872,13 +940,21 @@ icmpv6_proto
 
 icmp6_param_list
 	: { }
-	| icmp6_field { }
-	| icmp6_field delimiter icmp6_param_list { }
+	| icmp6_expr { }
+	| icmp6_expr delimiter icmp6_param_list { }
 	;
 
 icmp6_field
-	: K_TYPE skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, ICMPV6_TYPE, $5); }
+	: K_CODE { proto_field_set(ICMPV6_CODE); }
+	| K_CSUM { proto_field_set(ICMPV6_CSUM); }
+	;
+
+icmp6_expr
+	: icmp6_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
+	| K_TYPE skip_white '=' skip_white field_expr
+		{ proto_field_set(ICMPV6_TYPE);
+		  proto_field_expr_eval(); }
 	| K_TYPE skip_white '=' K_ECHO_REQUEST
 		{ proto_field_set_u8(hdr, ICMPV6_TYPE, ICMPV6_ECHO_REQUEST); }
 	| K_ECHO_REQUEST
@@ -887,12 +963,7 @@ icmp6_field
 		{ proto_field_set_u8(hdr, ICMPV6_TYPE, ICMPV6_ECHO_REPLY); }
 	| K_ECHO_REPLY
 		{ proto_field_set_u8(hdr, ICMPV6_TYPE, ICMPV6_ECHO_REPLY); }
-	| K_CODE skip_white '=' skip_white number
-		{ proto_field_set_u8(hdr, ICMPV6_CODE, $5); }
-	| K_CSUM skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, ICMPV6_CSUM, $5); }
 	;
-
 icmp6
 	: K_ICMP6 { proto_add(PROTO_ICMP6); }
 	;
@@ -903,19 +974,20 @@ udp_proto
 
 udp_param_list
 	: { }
-	| udp_field { }
-	| udp_field delimiter udp_param_list { }
+	| udp_expr { }
+	| udp_expr delimiter udp_param_list { }
 	;
 
 udp_field
-	: K_SPORT skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, UDP_SPORT, $5); }
-	| K_DPORT skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, UDP_DPORT, $5); }
-	| K_LEN skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, UDP_LEN, $5); }
-	| K_CSUM skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, UDP_CSUM, $5); }
+	: K_SPORT { proto_field_set(UDP_SPORT); }
+	| K_DPORT { proto_field_set(UDP_DPORT); }
+	| K_LEN { proto_field_set(UDP_LEN); }
+	| K_CSUM { proto_field_set(UDP_CSUM); }
+	;
+
+udp_expr
+	: udp_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
 	;
 
 udp
@@ -928,21 +1000,24 @@ tcp_proto
 
 tcp_param_list
 	: { }
-	| tcp_field { }
-	| tcp_field delimiter tcp_param_list { }
+	| tcp_expr { }
+	| tcp_expr delimiter tcp_param_list { }
 	;
 
 tcp_field
-	: K_SPORT skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, TCP_SPORT, $5); }
-	| K_DPORT skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, TCP_DPORT, $5); }
-	| K_SEQ skip_white '=' skip_white number
-		{ proto_field_set_be32(hdr, TCP_SEQ, $5); }
-	| K_ACK_SEQ skip_white '=' skip_white number
-		{ proto_field_set_be32(hdr, TCP_ACK_SEQ, $5); }
-	| K_DOFF skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, TCP_DOFF, $5); }
+	: K_SPORT { proto_field_set(TCP_SPORT); }
+	| K_DPORT { proto_field_set(TCP_DPORT); }
+	| K_SEQ { proto_field_set(TCP_SEQ); }
+	| K_ACK_SEQ { proto_field_set(TCP_ACK_SEQ); }
+	| K_DOFF { proto_field_set(TCP_DOFF); }
+	| K_WINDOW { proto_field_set(TCP_WINDOW); }
+	| K_CSUM { proto_field_set(TCP_CSUM); }
+	| K_URG_PTR { proto_field_set(TCP_URG_PTR); }
+	;
+
+tcp_expr
+	: tcp_field skip_white '=' skip_white field_expr
+		{ proto_field_expr_eval(); }
 	| K_CWR { proto_field_set_be16(hdr, TCP_CWR, 1); }
 	| K_ECE { proto_field_set_be16(hdr, TCP_ECE, 1); }
 	| K_URG { proto_field_set_be16(hdr, TCP_URG, 1); }
@@ -951,12 +1026,6 @@ tcp_field
 	| K_RST { proto_field_set_be16(hdr, TCP_RST, 1); }
 	| K_SYN { proto_field_set_be16(hdr, TCP_SYN, 1); }
 	| K_FIN { proto_field_set_be16(hdr, TCP_FIN, 1); }
-	| K_WINDOW skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, TCP_WINDOW, $5); }
-	| K_CSUM skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, TCP_CSUM, $5); }
-	| K_URG_PTR skip_white '=' skip_white number
-		{ proto_field_set_be16(hdr, TCP_URG_PTR, $5); }
 	;
 
 tcp
diff --git a/trafgen_proto.c b/trafgen_proto.c
index f4b2828..0b791f7 100644
--- a/trafgen_proto.c
+++ b/trafgen_proto.c
@@ -107,7 +107,7 @@ void proto_header_fields_add(struct proto_hdr *hdr,
 	}
 }
 
-static struct proto_field *proto_field_by_id(struct proto_hdr *hdr, uint32_t fid)
+struct proto_field *proto_field_by_id(struct proto_hdr *hdr, uint32_t fid)
 {
 	/* Assume the fields are stored in the same order as the respective
 	 * enum, so the index can be used for faster lookup here.
diff --git a/trafgen_proto.h b/trafgen_proto.h
index 2e50402..a8b97eb 100644
--- a/trafgen_proto.h
+++ b/trafgen_proto.h
@@ -143,4 +143,6 @@ extern void proto_field_dyn_apply(struct proto_field *field);
 extern void proto_field_func_add(struct proto_hdr *hdr, uint32_t fid,
 				 struct proto_field_func *func);
 
+extern struct proto_field *proto_field_by_id(struct proto_hdr *hdr, uint32_t fid);
+
 #endif /* TRAFGEN_PROTO_H */