97 lines
2.3 KiB
Go
97 lines
2.3 KiB
Go
package udp
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import (
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"errors"
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"net"
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"github.com/apernet/OpenGFW/modifier"
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"github.com/google/gopacket"
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"github.com/google/gopacket/layers"
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)
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var _ modifier.Modifier = (*DNSModifier)(nil)
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var (
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errInvalidIP = errors.New("invalid ip")
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errNotValidDNSResponse = errors.New("not a valid dns response")
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errEmptyDNSQuestion = errors.New("empty dns question")
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)
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type DNSModifier struct{}
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func (m *DNSModifier) Name() string {
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return "dns"
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}
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func (m *DNSModifier) New(args map[string]interface{}) (modifier.Instance, error) {
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i := &dnsModifierInstance{}
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aStr, ok := args["a"].(string)
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if ok {
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a := net.ParseIP(aStr).To4()
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if a == nil {
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return nil, &modifier.ErrInvalidArgs{Err: errInvalidIP}
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}
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i.A = a
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}
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aaaaStr, ok := args["aaaa"].(string)
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if ok {
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aaaa := net.ParseIP(aaaaStr).To16()
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if aaaa == nil {
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return nil, &modifier.ErrInvalidArgs{Err: errInvalidIP}
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}
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i.AAAA = aaaa
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}
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return i, nil
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}
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var _ modifier.UDPModifierInstance = (*dnsModifierInstance)(nil)
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type dnsModifierInstance struct {
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A net.IP
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AAAA net.IP
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}
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func (i *dnsModifierInstance) Process(data []byte) ([]byte, error) {
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dns := &layers.DNS{}
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err := dns.DecodeFromBytes(data, gopacket.NilDecodeFeedback)
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if err != nil {
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return nil, &modifier.ErrInvalidPacket{Err: err}
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}
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if !dns.QR || dns.ResponseCode != layers.DNSResponseCodeNoErr {
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return nil, &modifier.ErrInvalidPacket{Err: errNotValidDNSResponse}
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}
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if len(dns.Questions) == 0 {
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return nil, &modifier.ErrInvalidPacket{Err: errEmptyDNSQuestion}
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}
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// In practice, most if not all DNS clients only send one question
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// per packet, so we don't care about the rest for now.
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q := dns.Questions[0]
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switch q.Type {
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case layers.DNSTypeA:
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if i.A != nil {
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dns.Answers = []layers.DNSResourceRecord{{
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Name: q.Name,
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Type: layers.DNSTypeA,
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Class: layers.DNSClassIN,
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IP: i.A,
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}}
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}
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case layers.DNSTypeAAAA:
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if i.AAAA != nil {
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dns.Answers = []layers.DNSResourceRecord{{
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Name: q.Name,
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Type: layers.DNSTypeAAAA,
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Class: layers.DNSClassIN,
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IP: i.AAAA,
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}}
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}
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}
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buf := gopacket.NewSerializeBuffer() // Modifiers must be safe for concurrent use, so we can't reuse the buffer
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err = gopacket.SerializeLayers(buf, gopacket.SerializeOptions{
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FixLengths: true,
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ComputeChecksums: true,
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}, dns)
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return buf.Bytes(), err
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}
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