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constructor.go
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constructor.go
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package proxy
import "github.com/miekg/dns"
// MessageConstructor creates DNS messages.
type MessageConstructor interface {
// NewMsgNXDOMAIN creates a new response message replying to req with the
// NXDOMAIN code.
NewMsgNXDOMAIN(req *dns.Msg) (resp *dns.Msg)
// NewMsgSERVFAIL creates a new response message replying to req with the
// SERVFAIL code.
NewMsgSERVFAIL(req *dns.Msg) (resp *dns.Msg)
// NewMsgNOTIMPLEMENTED creates a new response message replying to req with
// the NOTIMPLEMENTED code.
NewMsgNOTIMPLEMENTED(req *dns.Msg) (resp *dns.Msg)
}
// defaultMessageConstructor is a default implementation of MessageConstructor.
type defaultMessageConstructor struct{}
// type check
var _ MessageConstructor = defaultMessageConstructor{}
// NewMsgNXDOMAIN implements the [MessageConstructor] interface for
// defaultMessageConstructor.
func (defaultMessageConstructor) NewMsgNXDOMAIN(req *dns.Msg) (resp *dns.Msg) {
return reply(req, dns.RcodeNameError)
}
// NewMsgSERVFAIL implements the [MessageConstructor] interface for
// defaultMessageConstructor.
func (defaultMessageConstructor) NewMsgSERVFAIL(req *dns.Msg) (resp *dns.Msg) {
return reply(req, dns.RcodeServerFailure)
}
// NewMsgNOTIMPLEMENTED implements the [MessageConstructor] interface for
// defaultMessageConstructor.
func (defaultMessageConstructor) NewMsgNOTIMPLEMENTED(req *dns.Msg) (resp *dns.Msg) {
resp = reply(req, dns.RcodeNotImplemented)
// Most of the Internet and especially the inner core has an MTU of at least
// 1500 octets. Maximum DNS/UDP payload size for IPv6 on MTU 1500 ethernet
// is 1452 (1500 minus 40 (IPv6 header size) minus 8 (UDP header size)).
//
// See appendix A of https://datatracker.ietf.org/doc/draft-ietf-dnsop-avoid-fragmentation/17.
const maxUDPPayload = 1452
// NOTIMPLEMENTED without EDNS is treated as 'we don't support EDNS', so
// explicitly set it.
resp.SetEdns0(maxUDPPayload, false)
return resp
}
// reply creates a new response message replying to req with the given code.
func reply(req *dns.Msg, code int) (resp *dns.Msg) {
resp = (&dns.Msg{}).SetRcode(req, code)
resp.RecursionAvailable = true
return resp
}