98 lines
2.4 KiB
Go
98 lines
2.4 KiB
Go
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package resolver
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import (
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"context"
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"errors"
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"io"
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"math"
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"net"
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"time"
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)
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// DialContextFunc is a generic function for dialing a connection.
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type DialContextFunc func(context.Context, string, string) (net.Conn, error)
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// DNSOverTCP is a DNS over TCP/TLS RoundTripper. Use NewDNSOverTCP
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// and NewDNSOverTLS to create specific instances that use plaintext
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// queries or encrypted queries over TLS.
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//
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// As a known bug, this implementation always creates a new connection
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// for each incoming query, thus increasing the response delay.
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type DNSOverTCP struct {
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dial DialContextFunc
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address string
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network string
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requiresPadding bool
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}
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// NewDNSOverTCP creates a new DNSOverTCP transport.
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func NewDNSOverTCP(dial DialContextFunc, address string) DNSOverTCP {
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return DNSOverTCP{
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dial: dial,
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address: address,
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network: "tcp",
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requiresPadding: false,
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}
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}
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// NewDNSOverTLS creates a new DNSOverTLS transport.
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func NewDNSOverTLS(dial DialContextFunc, address string) DNSOverTCP {
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return DNSOverTCP{
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dial: dial,
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address: address,
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network: "dot",
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requiresPadding: true,
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}
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}
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// RoundTrip implements RoundTripper.RoundTrip.
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func (t DNSOverTCP) RoundTrip(ctx context.Context, query []byte) ([]byte, error) {
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if len(query) > math.MaxUint16 {
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return nil, errors.New("query too long")
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}
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conn, err := t.dial(ctx, "tcp", t.address)
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if err != nil {
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return nil, err
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}
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defer conn.Close()
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if err = conn.SetDeadline(time.Now().Add(10 * time.Second)); err != nil {
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return nil, err
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}
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// Write request
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buf := []byte{byte(len(query) >> 8)}
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buf = append(buf, byte(len(query)))
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buf = append(buf, query...)
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if _, err = conn.Write(buf); err != nil {
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return nil, err
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}
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// Read response
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header := make([]byte, 2)
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if _, err = io.ReadFull(conn, header); err != nil {
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return nil, err
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}
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length := int(header[0])<<8 | int(header[1])
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reply := make([]byte, length)
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if _, err = io.ReadFull(conn, reply); err != nil {
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return nil, err
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}
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return reply, nil
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}
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// RequiresPadding returns true for DoT and false for TCP
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// according to RFC8467.
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func (t DNSOverTCP) RequiresPadding() bool {
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return t.requiresPadding
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}
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// Network returns the transport network (e.g., doh, dot)
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func (t DNSOverTCP) Network() string {
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return t.network
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}
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// Address returns the upstream server address.
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func (t DNSOverTCP) Address() string {
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return t.address
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}
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var _ RoundTripper = DNSOverTCP{}
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