Sending OS information in DoH header

client_info.go

@@ -8,6 +8,7 @@ type ClientInfo struct {
 	Mac      string
 	IP       string
 	Hostname string
+	Self     bool
 }
 
 // LeaseFileFormat specifies the format of DHCP lease file.

cmd/cli/dns_proxy.go

@@ -16,6 +16,7 @@ import (
 	"github.com/miekg/dns"
 	"golang.org/x/sync/errgroup"
 	"tailscale.com/net/interfaces"
+	"tailscale.com/net/netaddr"
 
 	"github.com/Control-D-Inc/ctrld"
 	"github.com/Control-D-Inc/ctrld/internal/dnscache"
@@ -510,6 +511,7 @@ func (p *prog) getClientInfo(remoteIP string, msg *dns.Msg) *ctrld.ClientInfo {
 		ci.IP = p.appCallback.LanIp()
 		ci.Mac = p.appCallback.MacAddress()
 		ci.Hostname = p.appCallback.HostName()
+		ci.Self = true
 		return ci
 	}
 	ci.IP, ci.Mac = ipAndMacFromMsg(msg)
@@ -542,9 +544,36 @@ func (p *prog) getClientInfo(remoteIP string, msg *dns.Msg) *ctrld.ClientInfo {
 	} else {
 		ci.Hostname = p.ciTable.LookupHostname(ci.IP, ci.Mac)
 	}
+	ci.Self = queryFromSelf(ci.IP)
 	return ci
 }
 
+// queryFromSelf reports whether the input IP is from device running ctrld.
+func queryFromSelf(ip string) bool {
+	netIP := netip.MustParseAddr(ip)
+	ifaces, err := interfaces.GetList()
+	if err != nil {
+		mainLog.Load().Warn().Err(err).Msg("could not get interfaces list")
+		return false
+	}
+	for _, iface := range ifaces {
+		addrs, err := iface.Addrs()
+		if err != nil {
+			mainLog.Load().Warn().Err(err).Msgf("could not get interfaces addresses: %s", iface.Name)
+			continue
+		}
+		for _, a := range addrs {
+			switch v := a.(type) {
+			case *net.IPNet:
+				if pfx, ok := netaddr.FromStdIPNet(v); ok && pfx.Addr().Compare(netIP) == 0 {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
 func needRFC1918Listeners(lc *ctrld.ListenerConfig) bool {
 	return lc.IP == "127.0.0.1" && lc.Port == 53
 }

doh.go

@@ -8,6 +8,11 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"runtime"
+	"strings"
+	"sync"
+
+	"github.com/cuonglm/osinfo"
 
 	"github.com/miekg/dns"
 )
@@ -16,9 +21,56 @@ const (
 	dohMacHeader         = "x-cd-mac"
 	dohIPHeader          = "x-cd-ip"
 	dohHostHeader        = "x-cd-host"
+	dohOsHeader          = "x-cd-os"
 	headerApplicationDNS = "application/dns-message"
 )
 
+// EncodeOsNameMap provides mapping from OS name to a shorter string, used for encoding x-cd-os value.
+var EncodeOsNameMap = map[string]string{
+	"windows": "1",
+	"darwin":  "2",
+	"linux":   "3",
+	"freebsd": "4",
+}
+
+// DecodeOsNameMap provides mapping from encoded OS name to real value, used for decoding x-cd-os value.
+var DecodeOsNameMap = map[string]string{}
+
+// EncodeArchNameMap provides mapping from OS arch to a shorter string, used for encoding x-cd-os value.
+var EncodeArchNameMap = map[string]string{
+	"amd64":  "1",
+	"arm64":  "2",
+	"arm":    "3",
+	"386":    "4",
+	"mips":   "5",
+	"mipsle": "6",
+	"mips64": "7",
+}
+
+// DecodeArchNameMap provides mapping from encoded OS arch to real value, used for decoding x-cd-os value.
+var DecodeArchNameMap = map[string]string{}
+
+func init() {
+	for k, v := range EncodeOsNameMap {
+		DecodeOsNameMap[v] = k
+	}
+	for k, v := range EncodeArchNameMap {
+		DecodeArchNameMap[v] = k
+	}
+}
+
+// TODO: use sync.OnceValue when upgrading to go1.21
+var xCdOsValueOnce sync.Once
+var xCdOsValue string
+
+func dohOsHeaderValue() string {
+	xCdOsValueOnce.Do(func() {
+		oi := osinfo.New()
+		xCdOsValue = strings.Join([]string{EncodeOsNameMap[runtime.GOOS], EncodeArchNameMap[runtime.GOARCH], oi.Dist}, "-")
+	})
+	return xCdOsValue
+}
+
 func newDohResolver(uc *UpstreamConfig) *dohResolver {
 	r := &dohResolver{
 		endpoint:          uc.u,
@@ -97,6 +149,8 @@ func (r *dohResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, erro
 func addHeader(ctx context.Context, req *http.Request, sendClientInfo bool) {
 	req.Header.Set("Content-Type", headerApplicationDNS)
 	req.Header.Set("Accept", headerApplicationDNS)
+	req.Header.Set(dohOsHeader, dohOsHeaderValue())
+
 	printed := false
 	if sendClientInfo {
 		if ci, ok := ctx.Value(ClientInfoCtxKey{}).(*ClientInfo); ok && ci != nil {
@@ -110,6 +164,9 @@ func addHeader(ctx context.Context, req *http.Request, sendClientInfo bool) {
 			if ci.Hostname != "" {
 				req.Header.Set(dohHostHeader, ci.Hostname)
 			}
+			if ci.Self {
+				req.Header.Set(dohOsHeader, dohOsHeaderValue())
+			}
 		}
 	}
 	if printed {

doh_test.go

@@ -0,0 +1,23 @@
+package ctrld
+
+import (
+	"runtime"
+	"testing"
+)
+
+func Test_dohOsHeaderValue(t *testing.T) {
+	val := dohOsHeaderValue()
+	if val == "" {
+		t.Fatalf("empty %s", dohOsHeader)
+	}
+	t.Log(val)
+
+	encodedOs := EncodeOsNameMap[runtime.GOOS]
+	if encodedOs == "" {
+		t.Fatalf("missing encoding value for: %q", runtime.GOOS)
+	}
+	decodedOs := DecodeOsNameMap[encodedOs]
+	if decodedOs == "" {
+		t.Fatalf("missing decoding value for: %q", runtime.GOOS)
+	}
+}

go.mod

@@ -4,7 +4,7 @@ go 1.20
 
 require (
 	github.com/coreos/go-systemd/v22 v22.5.0
-	github.com/cuonglm/osinfo v0.0.0-20230329055532-c513f836da19
+	github.com/cuonglm/osinfo v0.0.0-20230921071424-e0e1b1e0bbbf
 	github.com/frankban/quicktest v1.14.5
 	github.com/fsnotify/fsnotify v1.6.0
 	github.com/go-playground/validator/v10 v10.11.1

go.sum

@@ -57,6 +57,8 @@ github.com/cpuguy83/go-md2man/v2 v2.0.2/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46t
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/cuonglm/osinfo v0.0.0-20230329055532-c513f836da19 h1:7P/f19Mr0oa3ug8BYt4JuRe/Zq3dF4Mrr4m8+Kw+Hcs=
 github.com/cuonglm/osinfo v0.0.0-20230329055532-c513f836da19/go.mod h1:G45410zMgmnSjLVKCq4f6GpbYAzoP2plX9rPwgx6C24=
+github.com/cuonglm/osinfo v0.0.0-20230921071424-e0e1b1e0bbbf h1:40DHYsri+d1bnroFDU2FQAeq68f3kAlOzlQ93kCf26Q=
+github.com/cuonglm/osinfo v0.0.0-20230921071424-e0e1b1e0bbbf/go.mod h1:G45410zMgmnSjLVKCq4f6GpbYAzoP2plX9rPwgx6C24=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=