bgpd: add set as-path exclude acl-list command

A route-map applied on incoming BGP updates is not able
to replace an unwanted as segments by another one.
unwanted as segment are based on an AS path access-list.

The below configuration illustrates the case:

router bgp 65001

address-family ipv4 unicast
 neighbor 192.168.1.2 route-map rule_2 in
exit-address-family

bgp as-path access-list RULE permit ^65

route-map rule_2 permit 10
 set as-path replace as-path-access-list RULE 6000

```
BGP routing table entry for 10.10.10.10/32, version 13
Paths: (1 available, best #1, table default)
  Advertised to non peer-group peers:
  192.168.10.65
  65000 1 2 3 123
    192.168.10.65 from 192.168.10.65 (10.10.10.11)
      Origin IGP, metric 0, valid, external, best (First path received)
```

After:

```
do show ip bgp 10.10.10.10/32
BGP routing table entry for 10.10.10.10/32, version 15
    Paths: (1 available, best #1, table default)
      Advertised to non peer-group peers:
      192.168.10.65
      6000 1 2 3 123
        192.168.10.65 from 192.168.10.65 (10.10.10.11)
          Origin IGP, metric 0, valid, external, best (First path
          received)
```

Signed-off-by: Francois Dumontet <francois.dumontet@6wind.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/bgpd/bgp_aspath.c b/bgpd/bgp_aspath.c
index 4ea81216bf..2e2248cd72 100644
--- a/bgpd/bgp_aspath.c
+++ b/bgpd/bgp_aspath.c
@@ -1231,6 +1231,46 @@ bool aspath_private_as_check(struct aspath *aspath)
 	return true;
 }
 
+/* Replace all ASN instances of the regex rule with our own ASN  */
+struct aspath *aspath_replace_regex_asn(struct aspath *aspath,
+					struct as_list *acl_list, as_t our_asn)
+{
+	struct aspath *new;
+	struct assegment *cur_seg;
+	struct as_list *cur_as_list;
+	struct as_filter *cur_as_filter;
+	char str_buf[ASPATH_STR_DEFAULT_LEN];
+	uint32_t i;
+
+	new = aspath_dup(aspath);
+	cur_seg = new->segments;
+
+	while (cur_seg) {
+		cur_as_list = acl_list;
+		while (cur_as_list) {
+			cur_as_filter = cur_as_list->head;
+			while (cur_as_filter) {
+				for (i = 0; i < cur_seg->length; i++) {
+					snprintfrr(str_buf,
+						   ASPATH_STR_DEFAULT_LEN,
+						   ASN_FORMAT(new->asnotation),
+						   &cur_seg->as[i]);
+					if (!regexec(cur_as_filter->reg,
+						     str_buf, 0, NULL, 0))
+						cur_seg->as[i] = our_asn;
+				}
+				cur_as_filter = cur_as_filter->next;
+			}
+			cur_as_list = cur_as_list->next;
+		}
+		cur_seg = cur_seg->next;
+	}
+
+	aspath_str_update(new, false);
+	return new;
+}
+
+
 /* Replace all instances of the target ASN with our own ASN */
 struct aspath *aspath_replace_specific_asn(struct aspath *aspath,
 					   as_t target_asn, as_t our_asn)