Update Lego

vendor/github.com/miekg/dns/acceptfunc.go

@@ -0,0 +1,54 @@
+package dns
+
+// MsgAcceptFunc is used early in the server code to accept or reject a message with RcodeFormatError.
+// It returns a MsgAcceptAction to indicate what should happen with the message.
+type MsgAcceptFunc func(dh Header) MsgAcceptAction
+
+// DefaultMsgAcceptFunc checks the request and will reject if:
+//
+// * isn't a request (don't respond in that case).
+// * opcode isn't OpcodeQuery or OpcodeNotify
+// * Zero bit isn't zero
+// * has more than 1 question in the question section
+// * has more than 0 RRs in the Answer section
+// * has more than 0 RRs in the Authority section
+// * has more than 2 RRs in the Additional section
+var DefaultMsgAcceptFunc MsgAcceptFunc = defaultMsgAcceptFunc
+
+// MsgAcceptAction represents the action to be taken.
+type MsgAcceptAction int
+
+const (
+	MsgAccept MsgAcceptAction = iota // Accept the message
+	MsgReject                        // Reject the message with a RcodeFormatError
+	MsgIgnore                        // Ignore the error and send nothing back.
+)
+
+var defaultMsgAcceptFunc = func(dh Header) MsgAcceptAction {
+	if isResponse := dh.Bits&_QR != 0; isResponse {
+		return MsgIgnore
+	}
+
+	// Don't allow dynamic updates, because then the sections can contain a whole bunch of RRs.
+	opcode := int(dh.Bits>>11) & 0xF
+	if opcode != OpcodeQuery && opcode != OpcodeNotify {
+		return MsgReject
+	}
+
+	if isZero := dh.Bits&_Z != 0; isZero {
+		return MsgReject
+	}
+	if dh.Qdcount != 1 {
+		return MsgReject
+	}
+	if dh.Ancount != 0 {
+		return MsgReject
+	}
+	if dh.Nscount != 0 {
+		return MsgReject
+	}
+	if dh.Arcount > 2 {
+		return MsgReject
+	}
+	return MsgAccept
+}