all: add client id preference config param

So client can chose how client id is generated.

client_info.go

@@ -5,10 +5,11 @@ type ClientInfoCtxKey struct{}
 
 // ClientInfo represents ctrld's clients information.
 type ClientInfo struct {
-	Mac      string
-	IP       string
-	Hostname string
-	Self     bool
+	Mac          string
+	IP           string
+	Hostname     string
+	Self         bool
+	ClientIDPref string
 }
 
 // LeaseFileFormat specifies the format of DHCP lease file.

cmd/cli/dns_proxy.go

@@ -67,6 +67,7 @@ func (p *prog) serveDNS(listenerNum string) error {
 		reqId := requestID()
 		remoteIP, _, _ := net.SplitHostPort(w.RemoteAddr().String())
 		ci := p.getClientInfo(remoteIP, m)
+		ci.ClientIDPref = p.cfg.Service.ClientIDPref
 		stripClientSubnet(m)
 		remoteAddr := spoofRemoteAddr(w.RemoteAddr(), ci)
 		fmtSrcToDest := fmtRemoteToLocal(listenerNum, remoteAddr.String(), w.LocalAddr().String())

config.go

@@ -193,6 +193,7 @@ type ServiceConfig struct {
 	DiscoverDHCP          *bool  `mapstructure:"discover_dhcp" toml:"discover_dhcp,omitempty"`
 	DiscoverPtr           *bool  `mapstructure:"discover_ptr" toml:"discover_ptr,omitempty"`
 	DiscoverHosts         *bool  `mapstructure:"discover_hosts" toml:"discover_hosts,omitempty"`
+	ClientIDPref          string `mapstructure:"client_id_preference" toml:"client_id_preference,omitempty" validate:"omitempty,oneof=host mac"`
 	Daemon                bool   `mapstructure:"-" toml:"-"`
 	AllocateIP            bool   `mapstructure:"-" toml:"-"`
 }

config_test.go

@@ -101,6 +101,7 @@ func TestConfigValidation(t *testing.T) {
 		{"lease file format required if lease file exist", configWithExistedLeaseFile(t), true},
 		{"invalid lease file format", configWithInvalidLeaseFileFormat(t), true},
 		{"invalid doh/doh3 endpoint", configWithInvalidDoHEndpoint(t), true},
+		{"invalid client id pref", configWithInvalidClientIDPref(t), true},
 	}
 
 	for _, tc := range tests {
@@ -238,3 +239,9 @@ func configWithInvalidDoHEndpoint(t *testing.T) *ctrld.Config {
 	cfg.Upstream["0"].Type = ctrld.ResolverTypeDOH
 	return cfg
 }
+
+func configWithInvalidClientIDPref(t *testing.T) *ctrld.Config {
+	cfg := defaultConfig(t)
+	cfg.Service.ClientIDPref = "foo"
+	return cfg
+}

docs/config.md

@@ -215,6 +215,17 @@ DHCP leases file format.
 - Valid values: `dnsmasq`, `isc-dhcp`
 - Default: ""
 
+### client_id_preference
+Decide how client ID has is generated.
+
+If `host` -> client id will be a `hash(hostname)`.
+If `mac` -> client id will be `hash(mac)`.
+
+- Type: string
+- Required: no
+- Valid values: `mac`, `host`
+- Default: ""
+
 ## Upstream
 The `[upstream]` section specifies the DNS upstream servers that `ctrld` will forward DNS requests to.
 

doh.go

@@ -18,11 +18,12 @@ import (
 )
 
 const (
-	dohMacHeader         = "x-cd-mac"
-	dohIPHeader          = "x-cd-ip"
-	dohHostHeader        = "x-cd-host"
-	dohOsHeader          = "x-cd-os"
-	headerApplicationDNS = "application/dns-message"
+	dohMacHeader          = "x-cd-mac"
+	dohIPHeader           = "x-cd-ip"
+	dohHostHeader         = "x-cd-host"
+	dohOsHeader           = "x-cd-os"
+	dohClientIDPrefHeader = "x-cd-cpref"
+	headerApplicationDNS  = "application/dns-message"
 )
 
 // EncodeOsNameMap provides mapping from OS name to a shorter string, used for encoding x-cd-os value.
@@ -181,6 +182,12 @@ func addControlDHeaders(req *http.Request, ci *ClientInfo) {
 	if ci.Self {
 		req.Header.Set(dohOsHeader, dohOsHeaderValue())
 	}
+	switch ci.ClientIDPref {
+	case "mac":
+		req.Header.Set(dohClientIDPrefHeader, "1")
+	case "host":
+		req.Header.Set(dohClientIDPrefHeader, "2")
+	}
 }
 
 // addNextDNSHeaders set DoH/Doh3 HTTP request headers for nextdns upstream.