62 lines
1.9 KiB
Go
62 lines
1.9 KiB
Go
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package dns
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// MsgAcceptFunc is used early in the server code to accept or reject a message with RcodeFormatError.
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// It returns a MsgAcceptAction to indicate what should happen with the message.
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type MsgAcceptFunc func(dh Header) MsgAcceptAction
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// DefaultMsgAcceptFunc checks the request and will reject if:
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//
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// * isn't a request (don't respond in that case)
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//
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// * opcode isn't OpcodeQuery or OpcodeNotify
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//
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// * Zero bit isn't zero
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//
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// * does not have exactly 1 question in the question section
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//
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// * has more than 1 RR in the Answer section
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//
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// * has more than 0 RRs in the Authority section
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//
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// * has more than 2 RRs in the Additional section
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var DefaultMsgAcceptFunc MsgAcceptFunc = defaultMsgAcceptFunc
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// MsgAcceptAction represents the action to be taken.
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type MsgAcceptAction int
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// Allowed returned values from a MsgAcceptFunc.
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const (
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MsgAccept MsgAcceptAction = iota // Accept the message
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MsgReject // Reject the message with a RcodeFormatError
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MsgIgnore // Ignore the error and send nothing back.
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MsgRejectNotImplemented // Reject the message with a RcodeNotImplemented
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)
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func defaultMsgAcceptFunc(dh Header) MsgAcceptAction {
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if isResponse := dh.Bits&_QR != 0; isResponse {
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return MsgIgnore
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}
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// Don't allow dynamic updates, because then the sections can contain a whole bunch of RRs.
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opcode := int(dh.Bits>>11) & 0xF
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if opcode != OpcodeQuery && opcode != OpcodeNotify {
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return MsgRejectNotImplemented
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}
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if dh.Qdcount != 1 {
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return MsgReject
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}
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// NOTIFY requests can have a SOA in the ANSWER section. See RFC 1996 Section 3.7 and 3.11.
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if dh.Ancount > 1 {
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return MsgReject
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}
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// IXFR request could have one SOA RR in the NS section. See RFC 1995, section 3.
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if dh.Nscount > 1 {
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return MsgReject
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}
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if dh.Arcount > 2 {
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return MsgReject
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}
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return MsgAccept
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}
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