Adds strip-wildcards

strip-wildcards/.gitignore

@@ -0,0 +1,2 @@
+testdata
+strip-wildcards

strip-wildcards/main.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"math/rand"
+	"net"
+	"os"
+	"strings"
+	"time"
+)
+
+var globalRandString string
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+	globalRandString = randString(16)
+}
+
+func main() {
+	sc := bufio.NewScanner(os.Stdin)
+	r := &resolver{cache: make(map[string]bool)}
+
+	for sc.Scan() {
+		name := strings.ToLower(sc.Text())
+
+		if !r.containsWildcard(name) {
+			fmt.Println(name)
+		}
+	}
+}
+
+type resolver struct {
+	cache map[string]bool
+}
+
+func (r *resolver) isWildcard(name string) bool {
+	if r.cache[name] {
+		return true
+	}
+
+	check := fmt.Sprintf("%s.%s", globalRandString, name)
+	_, err := net.LookupHost(check)
+	r.cache[name] = err == nil
+	return err == nil
+}
+
+func (r *resolver) containsWildcard(name string) bool {
+
+	parts := strings.Split(name, ".")
+
+	// Given one.two.target.com
+	// Start from the right hand side, check:
+	//   $rand.com
+	//   $rand.target.com
+	//   $rand.two.target.com
+	// Do not check $rand.one.two.target.com otherwise
+	// we'd just be resolving every line of input which
+	// is what we're trying to avoid doing.
+	for i := len(parts) - 1; i > 1; i-- {
+		candidate := strings.Join(parts[i-1:len(parts)], ".")
+		if r.isWildcard(candidate) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func randString(length int) string {
+	chars := []byte("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
+	out := bytes.Buffer{}
+
+	for i := 0; i < length; i++ {
+		out.WriteByte(chars[rand.Intn(len(chars))])
+	}
+
+	return out.String()
+}