refactor: DNS

dns/transport/local/local.go

@@ -0,0 +1,177 @@
+package local
+
+import (
+	"context"
+	"time"
+
+	"github.com/sagernet/sing-box/adapter"
+	C "github.com/sagernet/sing-box/constant"
+	"github.com/sagernet/sing-box/dns"
+	"github.com/sagernet/sing-box/log"
+	"github.com/sagernet/sing-box/option"
+	"github.com/sagernet/sing/common"
+	"github.com/sagernet/sing/common/buf"
+	E "github.com/sagernet/sing/common/exceptions"
+	M "github.com/sagernet/sing/common/metadata"
+	N "github.com/sagernet/sing/common/network"
+
+	mDNS "github.com/miekg/dns"
+)
+
+func RegisterTransport(registry *dns.TransportRegistry) {
+	dns.RegisterTransport[option.LocalDNSServerOptions](registry, C.DNSTypeLocal, NewTransport)
+}
+
+var _ adapter.DNSTransport = (*Transport)(nil)
+
+type Transport struct {
+	dns.TransportAdapter
+	dialer N.Dialer
+}
+
+func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, options option.LocalDNSServerOptions) (adapter.DNSTransport, error) {
+	transportDialer, err := dns.NewLocalDialer(ctx, options)
+	if err != nil {
+		return nil, err
+	}
+	return &Transport{
+		TransportAdapter: dns.NewTransportAdapterWithLocalOptions(C.DNSTypeTCP, tag, options),
+		dialer:           transportDialer,
+	}, nil
+}
+
+func (t *Transport) Reset() {
+}
+
+func (t *Transport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
+	question := message.Question[0]
+	domain := dns.FqdnToDomain(question.Name)
+	if question.Qtype == mDNS.TypeA || question.Qtype == mDNS.TypeAAAA {
+		addressStrings, _ := lookupStaticHost(domain)
+		if len(addressStrings) > 0 {
+			return dns.FixedResponse(message.Id, question, common.Map(addressStrings, M.ParseAddr), C.DefaultDNSTTL), nil
+		}
+	}
+	systemConfig := getSystemDNSConfig()
+	if systemConfig.singleRequest || !(message.Question[0].Qtype == mDNS.TypeA || message.Question[0].Qtype == mDNS.TypeAAAA) {
+		return t.exchangeSingleRequest(ctx, systemConfig, message, domain)
+	} else {
+		return t.exchangeParallel(ctx, systemConfig, message, domain)
+	}
+}
+
+func (t *Transport) exchangeSingleRequest(ctx context.Context, systemConfig *dnsConfig, message *mDNS.Msg, domain string) (*mDNS.Msg, error) {
+	var lastErr error
+	for _, fqdn := range nameList(systemConfig, domain) {
+		response, err := t.tryOneName(ctx, systemConfig, fqdn, message)
+		if err != nil {
+			lastErr = err
+			continue
+		}
+		return response, nil
+	}
+	return nil, lastErr
+}
+
+func (t *Transport) exchangeParallel(ctx context.Context, systemConfig *dnsConfig, message *mDNS.Msg, domain string) (*mDNS.Msg, error) {
+	returned := make(chan struct{})
+	defer close(returned)
+	type queryResult struct {
+		response *mDNS.Msg
+		err      error
+	}
+	results := make(chan queryResult)
+	startRacer := func(ctx context.Context, fqdn string) {
+		response, err := t.tryOneName(ctx, systemConfig, fqdn, message)
+		select {
+		case results <- queryResult{response, err}:
+		case <-returned:
+		}
+	}
+	queryCtx, queryCancel := context.WithCancel(ctx)
+	defer queryCancel()
+	for _, fqdn := range nameList(systemConfig, domain) {
+		go startRacer(queryCtx, fqdn)
+	}
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case result := <-results:
+		return result.response, result.err
+	}
+}
+
+func (t *Transport) tryOneName(ctx context.Context, config *dnsConfig, fqdn string, message *mDNS.Msg) (*mDNS.Msg, error) {
+	serverOffset := config.serverOffset()
+	sLen := uint32(len(config.servers))
+	var lastErr error
+	for i := 0; i < config.attempts; i++ {
+		for j := uint32(0); j < sLen; j++ {
+			server := config.servers[(serverOffset+j)%sLen]
+			question := message.Question[0]
+			question.Name = fqdn
+			response, err := t.exchangeOne(ctx, M.ParseSocksaddr(server), question, config.timeout, config.useTCP, config.trustAD)
+			if err != nil {
+				lastErr = err
+				continue
+			}
+			return response, nil
+		}
+	}
+	return nil, lastErr
+}
+
+func (t *Transport) exchangeOne(ctx context.Context, server M.Socksaddr, question mDNS.Question, timeout time.Duration, useTCP, ad bool) (*mDNS.Msg, error) {
+	var networks []string
+	if useTCP {
+		networks = []string{N.NetworkTCP}
+	} else {
+		networks = []string{N.NetworkUDP, N.NetworkTCP}
+	}
+	request := &mDNS.Msg{
+		MsgHdr: mDNS.MsgHdr{
+			Id:                uint16(randInt()),
+			RecursionDesired:  true,
+			AuthenticatedData: ad,
+		},
+		Question: []mDNS.Question{question},
+		Compress: true,
+	}
+	request.SetEdns0(maxDNSPacketSize, false)
+	buffer := buf.Get(buf.UDPBufferSize)
+	defer buf.Put(buffer)
+	for _, network := range networks {
+		ctx, cancel := context.WithDeadline(ctx, time.Now().Add(timeout))
+		defer cancel()
+		conn, err := t.dialer.DialContext(ctx, network, server)
+		if err != nil {
+			return nil, err
+		}
+		defer conn.Close()
+		if deadline, loaded := ctx.Deadline(); loaded && !deadline.IsZero() {
+			conn.SetDeadline(deadline)
+		}
+		rawMessage, err := request.PackBuffer(buffer)
+		if err != nil {
+			return nil, E.Cause(err, "pack request")
+		}
+		_, err = conn.Write(rawMessage)
+		if err != nil {
+			return nil, E.Cause(err, "write request")
+		}
+		n, err := conn.Read(buffer)
+		if err != nil {
+			return nil, E.Cause(err, "read response")
+		}
+		var response mDNS.Msg
+		err = response.Unpack(buffer[:n])
+		if err != nil {
+			return nil, E.Cause(err, "unpack response")
+		}
+		if response.Truncated && network == N.NetworkUDP {
+			continue
+		}
+		return &response, nil
+	}
+	panic("unexpected")
+}

dns/transport/local/local_badlinkname.go

@@ -0,0 +1,19 @@
+//go:build badlinkname
+
+package local
+
+import (
+	_ "unsafe"
+)
+
+//go:linkname getSystemDNSConfig net.getSystemDNSConfig
+func getSystemDNSConfig() *dnsConfig
+
+//go:linkname nameList net.(*dnsConfig).nameList
+func nameList(c *dnsConfig, name string) []string
+
+//go:linkname lookupStaticHost net.lookupStaticHost
+func lookupStaticHost(host string) ([]string, string)
+
+//go:linkname splitHostZone net.splitHostZone
+func splitHostZone(s string) (host, zone string)

dns/transport/local/local_linkname.go

@@ -0,0 +1,44 @@
+package local
+
+import (
+	"sync/atomic"
+	"time"
+	_ "unsafe"
+)
+
+const (
+	// net.maxDNSPacketSize
+	maxDNSPacketSize = 1232
+)
+
+type dnsConfig struct {
+	servers       []string      // server addresses (in host:port form) to use
+	search        []string      // rooted suffixes to append to local name
+	ndots         int           // number of dots in name to trigger absolute lookup
+	timeout       time.Duration // wait before giving up on a query, including retries
+	attempts      int           // lost packets before giving up on server
+	rotate        bool          // round robin among servers
+	unknownOpt    bool          // anything unknown was encountered
+	lookup        []string      // OpenBSD top-level database "lookup" order
+	err           error         // any error that occurs during open of resolv.conf
+	mtime         time.Time     // time of resolv.conf modification
+	soffset       uint32        // used by serverOffset
+	singleRequest bool          // use sequential A and AAAA queries instead of parallel queries
+	useTCP        bool          // force usage of TCP for DNS resolutions
+	trustAD       bool          // add AD flag to queries
+	noReload      bool          // do not check for config file updates
+}
+
+func (c *dnsConfig) serverOffset() uint32 {
+	if c.rotate {
+		return atomic.AddUint32(&c.soffset, 1) - 1 // return 0 to start
+	}
+	return 0
+}
+
+//go:linkname runtime_rand runtime.rand
+func runtime_rand() uint64
+
+func randInt() int {
+	return int(uint(runtime_rand()) >> 1) // clear sign bit
+}

dns/transport/local/local_notbadlinkname.go

@@ -0,0 +1,19 @@
+//go:build !badlinkname
+
+package local
+
+func getSystemDNSConfig() *dnsConfig {
+	panic("stub")
+}
+
+func nameList(c *dnsConfig, name string) []string {
+	panic("stub")
+}
+
+func lookupStaticHost(host string) ([]string, string) {
+	panic("stub")
+}
+
+func splitHostZone(s string) (host, zone string) {
+	panic("stub")
+}