lib: rework printfrr extensions to output directly

Allowing printfrr extensions to directly write to the output buffer has
a few advantages:
- there is no arbitrary length limit imposed (previously 64)
- the output doesn't need to be copied another time
- the extension can directly use bprintfrr() to put together pieces

The downside is that the theoretical length (regardless of available
buffer space) must be computed correctly.

Extended unit tests to test these paths a bit more thoroughly.

Signed-off-by: David Lamparter <equinox@diac24.net>

1 files changed, 53 insertions, 34 deletions

diff --git a/lib/nexthop.c b/lib/nexthop.c
index 17ef95c687..64b4f3adb1 100644
--- a/lib/nexthop.c
+++ b/lib/nexthop.c
@@ -730,80 +730,99 @@ int nexthop_str2backups(const char *str, int *num_backups,
  *		nexthop2str()
  */
 printfrr_ext_autoreg_p("NH", printfrr_nh)
-static ssize_t printfrr_nh(char *buf, size_t bsz, const char *fmt,
+static ssize_t printfrr_nh(struct fbuf *buf, const char **fmt,
 			   int prec, const void *ptr)
 {
 	const struct nexthop *nexthop = ptr;
-	struct fbuf fb = { .buf = buf, .pos = buf, .len = bsz - 1 };
 	bool do_ifi = false;
-	const char *s, *v_is = "", *v_via = "", *v_viaif = "via ";
-	ssize_t ret = 3;
+	const char *v_is = "", *v_via = "", *v_viaif = "via ";
+	ssize_t ret = 0;
 
-	/* NULL-check */
-	if (nexthop == NULL) {
-		if (fmt[2] == 'v' && fmt[3] == 'v')
-			ret++;
-
-		strlcpy(buf, "NULL", bsz);
-
-		return ret;
-	}
-
-	switch (fmt[2]) {
+	switch (**fmt) {
 	case 'v':
-		if (fmt[3] == 'v') {
+		(*fmt)++;
+		if (**fmt == 'v') {
 			v_is = "is ";
 			v_via = "via ";
 			v_viaif = "";
-			ret++;
+			(*fmt)++;
 		}
 
+		if (!nexthop)
+			return bputs(buf, "NULL");
+
 		switch (nexthop->type) {
 		case NEXTHOP_TYPE_IPV4:
 		case NEXTHOP_TYPE_IPV4_IFINDEX:
-			bprintfrr(&fb, "%s%pI4", v_via, &nexthop->gate.ipv4);
+			ret += bprintfrr(buf, "%s%pI4", v_via,
+					 &nexthop->gate.ipv4);
 			do_ifi = true;
 			break;
 		case NEXTHOP_TYPE_IPV6:
 		case NEXTHOP_TYPE_IPV6_IFINDEX:
-			bprintfrr(&fb, "%s%pI6", v_via, &nexthop->gate.ipv6);
+			ret += bprintfrr(buf, "%s%pI6", v_via,
+					 &nexthop->gate.ipv6);
 			do_ifi = true;
 			break;
 		case NEXTHOP_TYPE_IFINDEX:
-			bprintfrr(&fb, "%sdirectly connected, %s", v_is,
-				ifindex2ifname(nexthop->ifindex,
-					       nexthop->vrf_id));
+			ret += bprintfrr(buf, "%sdirectly connected, %s", v_is,
+					 ifindex2ifname(nexthop->ifindex,
+							nexthop->vrf_id));
 			break;
 		case NEXTHOP_TYPE_BLACKHOLE:
+			ret += bputs(buf, "unreachable");
+
 			switch (nexthop->bh_type) {
 			case BLACKHOLE_REJECT:
-				s = " (ICMP unreachable)";
+				ret += bputs(buf, " (ICMP unreachable)");
 				break;
 			case BLACKHOLE_ADMINPROHIB:
-				s = " (ICMP admin-prohibited)";
+				ret += bputs(buf, " (ICMP admin-prohibited)");
 				break;
 			case BLACKHOLE_NULL:
-				s = " (blackhole)";
+				ret += bputs(buf, " (blackhole)");
 				break;
 			default:
-				s = "";
 				break;
 			}
-			bprintfrr(&fb, "unreachable%s", s);
 			break;
 		default:
 			break;
 		}
 		if (do_ifi && nexthop->ifindex)
-			bprintfrr(&fb, ", %s%s", v_viaif, ifindex2ifname(
-					nexthop->ifindex,
-					nexthop->vrf_id));
+			ret += bprintfrr(buf, ", %s%s", v_viaif,
+					 ifindex2ifname(nexthop->ifindex,
+							nexthop->vrf_id));
 
-		*fb.pos = '\0';
 		return ret;
 	case 's':
-		nexthop2str(nexthop, buf, bsz);
-		return 3;
+		(*fmt)++;
+
+		if (!nexthop)
+			return bputs(buf, "NULL");
+
+		switch (nexthop->type) {
+		case NEXTHOP_TYPE_IFINDEX:
+			ret += bprintfrr(buf, "if %u", nexthop->ifindex);
+			break;
+		case NEXTHOP_TYPE_IPV4:
+		case NEXTHOP_TYPE_IPV4_IFINDEX:
+			ret += bprintfrr(buf, "%pI4 if %u", &nexthop->gate.ipv4,
+					 nexthop->ifindex);
+			break;
+		case NEXTHOP_TYPE_IPV6:
+		case NEXTHOP_TYPE_IPV6_IFINDEX:
+			ret += bprintfrr(buf, "%pI6 if %u", &nexthop->gate.ipv6,
+					 nexthop->ifindex);
+			break;
+		case NEXTHOP_TYPE_BLACKHOLE:
+			ret += bputs(buf, "blackhole");
+			break;
+		default:
+			ret += bputs(buf, "unknown");
+			break;
+		}
+		return ret;
 	}
-	return 0;
+	return -1;
 }