From 94f1e2f000dc79cbb1ef57202f5e6fc354205a21 Mon Sep 17 00:00:00 2001
From: Kevin Wallace <doof@doof.net>
Date: Fri, 25 Jun 2021 23:04:34 -0700
Subject: add -asn flag to look up ASN info

---
 main.go | 42 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/main.go b/main.go
index ca024a9..01401d4 100644
--- a/main.go
+++ b/main.go
@@ -10,6 +10,10 @@ import (
 
 var (
 	txt = flag.Bool("txt", false, "also look up TXT records")
+	asn = flag.Bool("asn", false, "also look up ASN info from -asn-zone4/-asn-zone6 reverse zones")
+
+	asnZone4 = flag.String("asn-zone4", "origin.asn.cymru.com", "v4 reverse zone for -asn")
+	asnZone6 = flag.String("asn-zone6", "origin6.asn.cymru.com", "v6 reverse zone for -asn")
 )
 
 func main() {
@@ -20,6 +24,16 @@ func main() {
 		} else {
 			fmt.Printf("# %s\n", arg)
 			for _, ipnet := range ipnets {
+				if *asn {
+					asnInfos, err := lookupAsnInfo(ipnet)
+					if err != nil {
+						printErr(ipnet, "ASN", err)
+					} else {
+						for _, asnInfo := range asnInfos {
+							fmt.Printf("# %s\n", asnInfo)
+						}
+					}
+				}
 				ip := ipnet.IP
 				for ipnet.Contains(ip) {
 					if names, err := net.LookupAddr(ip.String()); err != nil {
@@ -44,12 +58,12 @@ func main() {
 	}
 }
 
-func printErr(ip net.IP, rrtype string, err error) {
+func printErr(what interface{}, rrtype string, err error) {
 	// the error types here are awful and this feels like it might
 	// accidentally catch some non-NXDOMAIN errors
 	if !strings.HasSuffix(err.Error(), "no such host") &&
 		!strings.HasSuffix(err.Error(), "nodename nor servname provided, or not known") {
-		fmt.Fprintf(os.Stderr, "%s\t# %s error: %s\n", ip, rrtype, err)
+		fmt.Fprintf(os.Stderr, "%s\t# %s error: %s\n", what, rrtype, err)
 	}
 }
 
@@ -126,6 +140,9 @@ func resolveArg(arg string) ([]net.IPNet, error) {
 				ipnets[i] = *ipnet
 			}
 		} else {
+			if ip4 := ip.To4(); ip4 != nil {
+				ip = ip4
+			}
 			ipnets[i].IP = ip
 			ipnets[i].Mask = net.CIDRMask(len(ip)*8, len(ip)*8)
 		}
@@ -143,3 +160,24 @@ func resolveHost(host string, canLookup bool) ([]net.IP, error) {
 	}
 	return nil, fmt.Errorf("can't parse IP")
 }
+
+func lookupAsnInfo(ipnet net.IPNet) ([]string, error) {
+	ones, bits := ipnet.Mask.Size()
+	if bits == 0 {
+		return nil, fmt.Errorf("invalid netmask in %s", ipnet)
+	}
+	var name string
+	if ip4 := ipnet.IP.To4(); ip4 != nil {
+		for b := (ones-1)/8; b >= 0; b-- {
+			name += fmt.Sprintf("%d.", ip4[b])
+		}
+		name += *asnZone4
+	} else {
+		ip6 := ipnet.IP
+		for n := (ones-1)/4; n >= 0; n-- {
+			name += fmt.Sprintf("%x.", (ip6[n/2] >> (4-4*(n%2))) & 0xf)
+		}
+		name += *asnZone6
+	}
+	return net.LookupTXT(name)
+}
-- 
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