Sub domain replace feature

cmd/routedns/config.go

@@ -62,6 +62,7 @@ type group struct {
 	Resolvers  []string
 	Type       string
 	Replace    []rdns.ReplaceOperation // only used by "replace" type
+	Subdomain    []rdns.SubDomainReplaceOperation // only used by "SubDomainReplace" type
 	GCPeriod   int                     `toml:"gc-period"`   // Time-period (seconds) used to expire cached items in the "cache" type
 	ECSOp      string                  `toml:"ecs-op"`      // ECS modifier operation, "add", "delete", "privacy"
 	ECSAddress net.IP                  `toml:"ecs-address"` // ECS address. If empty for "add", uses the client IP. Ignored for "privacy" and "delete"

cmd/routedns/example-config/subdomain-replace.toml

@@ -0,0 +1,31 @@
+
+# into DNS-over-TLS queries to Cloudflare's DNS server.
+[bootstrap-resolver]
+address = "1.1.1.1:853"
+protocol = "dot"
+
+[resolvers.cloudflare-dot]
+address = "gcp.ctptech.dev:853"
+protocol = "dot"
+
+[listeners.local-udp]
+address = ":53"
+protocol = "udp"
+resolver = "sub-domain-replace"
+
+[listeners.local-tcp]
+address = ":53"
+protocol = "tcp"
+resolver = "sub-domain-replace"
+
+# must have dots on both ends to work
+[groups.sub-domain-replace]
+  type = "subdomain-replace"
+  resolvers = [ "cloudflare-dot" ]
+  subdomain = [
+
+    { from = '.ctptech.dev.', to = '.whiskey.software.' },
+    { from = '.whiskey.software.', to = '.charlesp.tech.' },
+    { from = '.whisky.software.', to = '.whiskey.dev.' },
+    { from = '.local.', to = '.' },
+]

cmd/routedns/main.go

@@ -417,7 +417,16 @@ func instantiateGroup(id string, g group, resolvers map[string]rdns.Resolver) er
 		if err != nil {
 			return err
 		}
+	case "subdomain-replace":
+		if len(gr) != 1 {
+			return fmt.Errorf("type replace only supports one resolver in '%s'", id)
+		}
+		resolvers[id], err = rdns.NewSubDomainReplace(id, gr[0], g.Subdomain...)
+		if err != nil {
+			return err
+		}
 	case "ttl-modifier":
+
 		if len(gr) != 1 {
 			return fmt.Errorf("type ttl-modifier only supports one resolver in '%s'", id)
 		}

go.mod

@@ -13,7 +13,7 @@ require (
 	github.com/pkg/errors v0.9.1
 	github.com/quic-go/quic-go v0.33.0
 	github.com/sirupsen/logrus v1.9.0
-	github.com/spf13/cobra v1.6.1
+	github.com/spf13/cobra v1.7.0
 	github.com/stretchr/testify v1.8.1
 	golang.org/x/net v0.7.0
 )
@@ -24,7 +24,7 @@ require (
 	github.com/go-task/slim-sprig v0.0.0-20210107165309-348f09dbbbc0 // indirect
 	github.com/golang/mock v1.6.0 // indirect
 	github.com/google/pprof v0.0.0-20221219190121-3cb0bae90811 // indirect
-	github.com/google/uuid v1.3.0 // indirect
+	github.com/google/uuid v1.1.2 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/kr/pretty v0.3.1 // indirect
 	github.com/onsi/ginkgo/v2 v2.6.1 // indirect

go.sum

@@ -20,12 +20,10 @@ github.com/golang/protobuf v1.5.2 h1:ROPKBNFfQgOUMifHyP+KYbvpjbdoFNs+aK7DXlji0Tw
 github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
 github.com/google/pprof v0.0.0-20221219190121-3cb0bae90811 h1:wORs2YN3R3ona/CXYuTvLM31QlgoNKHvlCNuArCDDCU=
 github.com/google/pprof v0.0.0-20221219190121-3cb0bae90811/go.mod h1:dDKJzRmX4S37WGHujM7tX//fmj1uioxKzKxz3lo4HJo=
+github.com/google/uuid v1.1.2 h1:EVhdT+1Kseyi1/pUmXKaFxYsDNy9RQYkMWRH68J/W7Y=
 github.com/google/uuid v1.1.2/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
-github.com/google/uuid v1.3.0 h1:t6JiXgmwXMjEs8VusXIJk2BXHsn+wx8BZdTaoZ5fu7I=
-github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/heimdalr/dag v1.2.1 h1:XJOMaoWqJK1UKdp+4zaO2uwav9GFbHMGCirdViKMRIQ=
 github.com/heimdalr/dag v1.2.1/go.mod h1:Of/wUB7Yoj4dwiOcGOOYIq6MHlPF/8/QMBKFJpwg+yc=
-github.com/inconshreveable/mousetrap v1.0.1/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
 github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
 github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
 github.com/jtacoma/uritemplates v1.0.0 h1:xwx5sBF7pPAb0Uj8lDC1Q/aBPpOFyQza7OC705ZlLCo=
@@ -67,8 +65,8 @@ github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/f
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=
 github.com/sirupsen/logrus v1.9.0/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
-github.com/spf13/cobra v1.6.1 h1:o94oiPyS4KD1mPy2fmcYYHHfCxLqYjJOhGsCHFZtEzA=
-github.com/spf13/cobra v1.6.1/go.mod h1:IOw/AERYS7UzyrGinqmz6HLUo219MORXGxhbaJUqzrY=
+github.com/spf13/cobra v1.7.0 h1:hyqWnYt1ZQShIddO5kBpj3vu05/++x6tJ6dg8EC572I=
+github.com/spf13/cobra v1.7.0/go.mod h1:uLxZILRyS/50WlhOIKD7W6V5bgeIt+4sICxh6uRMrb0=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
 github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=

subdomain-replace.go

@@ -0,0 +1,113 @@
+package rdns
+
+import (
+	"errors"
+	"strings"
+
+	"github.com/miekg/dns"
+)
+
+// Replace is a resolver that modifies queries according to regular expressions
+// and forwards the modified queries to another resolver. Responses are then
+// mapped back to the original query string.
+type SubDomainReplace struct {
+	id       string
+	resolver Resolver
+	exp      subDomainReplaceExpressions
+}
+
+var _ Resolver = &SubDomainReplace{}
+
+type subDomainReplaceExp struct {
+	from string
+	to   string
+}
+
+type subDomainReplaceExpressions []subDomainReplaceExp
+
+func (r subDomainReplaceExp) substitute(qname string) (string, bool) {
+	fromDomain := r.from
+	toDomain := r.to
+	// from {}.ctptech.dev to {}.charlesp.tech
+	// from test.ctptech.dev to test.charlesp.tech
+	if strings.HasSuffix(qname, fromDomain) {
+		str := strings.Replace(qname, fromDomain, toDomain, 1)
+		Log.WithField("qname", qname).Debug("matches: modifying query")
+		return str, true
+	} else {
+		return "", false
+	}
+}
+func (r subDomainReplaceExpressions) apply(qname string) string {
+	for _, e := range r {
+		s, result := e.substitute(qname)
+		if result {
+			return s
+		}
+	}
+	return qname
+}
+
+type SubDomainReplaceOperation struct {
+	From string
+	To   string
+}
+
+// NewReplace returns a new instance of a Replace resolver.
+func NewSubDomainReplace(id string, resolver Resolver, list ...SubDomainReplaceOperation) (*SubDomainReplace, error) {
+	var exp subDomainReplaceExpressions
+	for _, o := range list {
+		if strings.Contains(o.From, "{}") && strings.Contains(o.To, "{}") {
+			exp = append(exp, subDomainReplaceExp{o.From, o.To})
+		} else {
+			return nil, errors.New("{} not found")
+		}
+	}
+	Log.WithField("exp", exp).Debug("exp query")
+	return &SubDomainReplace{id: id, resolver: resolver, exp: exp}, nil
+}
+
+// Resolve a DNS query by first replacing the query string with another
+// sending the query upstream and replace the name in the response with
+// the original query string again.
+func (r *SubDomainReplace) Resolve(q *dns.Msg, ci ClientInfo) (*dns.Msg, error) {
+	if len(q.Question) < 1 {
+		return nil, errors.New("no question in query")
+	}
+
+	oldName := q.Question[0].Name
+	newName := r.exp.apply(oldName)
+	log := logger(r.id, q, ci)
+
+	// if nothing needs modifying, we can stop here and use the original query
+	if newName == oldName {
+		log.Debug("forwarding unmodified query to resolver")
+		return r.resolver.Resolve(q, ci)
+	}
+
+	// Modify the query string
+	q.Question[0].Name = newName
+
+	// Send the query upstream
+	log.WithField("new-qname", newName).WithField("resolver", r.resolver).Debug("forwarding modified query to resolver")
+	a, err := r.resolver.Resolve(q, ci)
+	if err != nil || a == nil {
+		return nil, err
+	}
+
+	// Set the question back to the original name
+	a.Question[0].Name = oldName
+
+	// Now put the original name in all answer records that have the
+	// new name
+	for _, answer := range a.Answer {
+		if answer.Header().Name == newName {
+			answer.Header().Name = oldName
+		}
+	}
+	return a, nil
+}
+
+func (r *SubDomainReplace) String() string {
+	return r.id
+}