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// Copyright (C) 2011-2024 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
#ifndef TSIGRECORD_H
#define TSIGRECORD_H
#include <ostream>
#include <string>
#include <boost/shared_ptr.hpp>
#include <util/buffer.h>
#include <dns/name.h>
#include <dns/rdataclass.h>
namespace isc {
namespace dns {
class AbstractMessageRenderer;
/// TSIG resource record.
///
/// A \c TSIGRecord class object represents a TSIG resource record and is
/// responsible for conversion to and from wire format TSIG record based on
/// the protocol specification (RFC2845).
/// This class is provided so that other classes and applications can handle
/// TSIG without knowing protocol details of TSIG, such as that it uses a
/// fixed constant of TTL.
///
/// \todo So the plan is to eventually provide the "from wire" constructor.
/// It's not yet provided in the current phase of development.
///
/// \note
/// This class could be a derived class of \c AbstractRRset. That way
/// it would be able to be used in a polymorphic way; for example,
/// an application can construct a TSIG RR by itself and insert it to a
/// \c Message object as a generic RRset. On the other hand, it would mean
/// this class would have to implement an \c RdataIterator (even though it
/// can be done via straightforward forwarding) while the iterator is mostly
/// redundant since there should be one and only one RDATA for a valid TSIG
/// RR. Likewise, some methods such as \c setTTL() method wouldn't be well
/// defined due to such special rules for TSIG as using a fixed TTL.
/// Overall, TSIG is a very special RR type that simply uses the compatible
/// resource record format, and it will be unlikely that a user wants to
/// handle it through a generic interface in a polymorphic way.
/// We therefore chose to define it as a separate class. This is also
/// similar to why \c EDNS is a separate class.
class TSIGRecord {
public:
///
/// \name Constructors
///
/// We use the default copy constructor, default copy assignment operator,
/// (and default destructor) intentionally.
//@{
/// Constructor from TSIG key name and RDATA
///
/// \exception std::bad_alloc Resource allocation for copying the name or
/// RDATA fails
TSIGRecord(const Name& key_name, const rdata::any::TSIG& tsig_rdata);
/// Constructor from resource record (RR) parameters.
///
/// This constructor is intended to be used in the context of parsing
/// an incoming DNS message that contains a TSIG. The parser would
/// first extract the owner name, RR type (which is TSIG) class, TTL and
/// the TSIG RDATA from the message. This constructor is expected to
/// be given these RR parameters (except the RR type, because it must be
/// TSIG).
///
/// According to RFC2845, a TSIG RR uses fixed RR class (ANY) and TTL (0).
/// If the RR class or TTL is different from the expected one, this
/// implementation considers it an invalid record and throws an exception
/// of class \c DNSMessageFORMERR.
///
/// \note This behavior is not specified in the protocol specification,
/// but this implementation rejects unexpected values for the following
/// reasons (but in any case, this won't matter much in practice as
/// RFC2848 clearly states these fields always have the fixed values and
/// any sane implementation of TSIG signer will follow that):
/// According to the RFC editor (in a private communication), the intended
/// use of the TSIG TTL field is to signal protocol extensions (currently
/// no such extension is defined), so this field may actually be
/// validly non 0 in future. However, until the implementation supports
/// that extension it may not always be able to handle the extended
/// TSIG as intended; the extension may even affect digest computation.
/// There's a related issue on this point. Different implementations
/// interpret the RFC in different ways on the received TTL when
/// digesting the message: BIND 9 uses the received value (even if
/// it's not 0) as part of the TSIG variables; NLnet Labs' LDNS and NSD
/// always use a fixed constant of 0 regardless of the received TTL value.
/// This means if and when an extension with non 0 TTL is introduced
/// there will be interoperability problems in the form of verification
/// failure. By explicitly rejecting it (and subsequently returning
/// a response with a format error) we can indicate the source of the
/// problem more clearly than a "bad signature" TSIG error, which can
/// happen for various reasons. On the other hand, rejecting unexpected
/// RR classes is mostly for consistency; the RFC lists these two fields
/// in the same way, so it makes more sense to handle them equally.
/// (BIND 9 rejects unexpected RR classes for TSIG, but that is part of
/// general check on RR classes on received RRs; it generally requests
/// all classes are the same, and if the protocol specifies the use of
/// a particular class for a particular type of RR, it requests that
/// class be used).
///
/// Likewise, if \c rdata is not of type \c any::TSIG, an exception of
/// class DNSMessageFORMERR will be thrown. When the caller is a
/// DNS message parser and builds \c rdata from incoming wire format
/// data as described above, this case happens when the RR class is
/// different from ANY (in the implementation, the type check takes place
/// before the explicit check against the RR class explained in the
/// previous paragraph).
///
/// The \c length parameter is intended to be the length of the TSIG RR
/// (from the beginning of the owner name to the end of the RDATA) when
/// the caller is a DNS message parser. Note that it is the actual length
/// for the RR in the format; if the owner name or the algorithm name
/// (in the RDATA) is compressed (although the latter should not be
/// compressed according to RFC3597), the length must be the size of the
/// compressed data. The length is recorded inside the class and will
/// be returned via subsequent calls to \c getLength(). It's intended to
/// be used in the context TSIG verification; in the verify process
/// the MAC computation must be performed for the original data without
/// TSIG, so, to avoid parsing the entire data in the verify process
/// again, it's necessary to record information that can identify the
/// length to be digested for the MAC. This parameter serves for that
/// purpose.
///
/// \note Since the constructor doesn't take the wire format data per se,
/// it doesn't (and cannot) check the validity of \c length, and simply
/// accepts any given value. It even accepts obviously invalid values
/// such as 0. It's caller's responsibility to provide a valid value of
/// length, and, the verifier's responsibility to use the length safely.
///
/// <b>DISCUSSION:</b> this design is fragile in that it introduces
/// a tight coupling between message parsing and TSIG verification via
/// the \c TSIGRecord class. In terms of responsibility decoupling,
/// the ideal way to have \c TSIGRecord remember the entire wire data
/// along with the length of the TSIG. Then in the TSIG verification
/// we could refer to the necessary potion of data solely from a
/// \c TSIGRecord object. However, this approach would require expensive
/// heavy copy of the original data or introduce another kind of coupling
/// between the data holder and this class (if the original data is freed
/// while a \c TSIGRecord object referencing the data still exists, the
/// result will be catastrophic). As a "best current compromise", we
/// use the current design. We may reconsider it if it turns out to
/// cause a big problem or we come up with a better idea.
///
/// \exception DNSMessageFORMERR Given RR parameters are invalid for TSIG.
/// \exception std::bad_alloc Internal resource allocation fails.
///
/// \param name The owner name of the TSIG RR
/// \param rrclass The RR class of the RR. Must be \c RRClass::ANY()
/// (see above)
/// \param ttl The TTL of the RR. Must be 0 (see above)
/// \param rdata The RDATA of the RR. Must be of type \c any::TSIG.
/// \param length The size of the RR (see above)
TSIGRecord(const Name& name, const RRClass& rrclass, const RRTTL& ttl,
const rdata::Rdata& rdata, size_t length);
//@}
/// Return the owner name of the TSIG RR, which is the TSIG key name
///
/// \exception None
const Name& getName() const {
return (key_name_);
}
/// Return the RDATA of the TSIG RR
///
/// \exception None
const rdata::any::TSIG& getRdata() const {
return (rdata_);
}
/// \name Protocol constants and defaults
///
//@{
/// Return the RR class of TSIG
///
/// TSIG always uses the ANY RR class. This static method returns it,
/// when, though unlikely, an application wants to know which class TSIG
/// is supposed to use.
///
/// \exception None
static const RRClass& getClass();
/// Return the TTL value of TSIG
///
/// TSIG always uses 0 TTL. This static method returns it,
/// when, though unlikely, an application wants to know the TTL TSIG
/// is supposed to use.
///
/// \exception None
static const RRTTL& getTTL();
//@}
/// Return the length of the TSIG record
///
/// When constructed from the key name and RDATA, it is the length of
/// the record when it is rendered by the \c toWire() method.
///
/// \note When constructed "from wire", that will mean the length of
/// the wire format data for the TSIG RR. The length will be necessary
/// to verify the message once parse is completed.
///
/// \exception None
size_t getLength() const {
return (length_);
}
/// \brief Render the \c TSIG RR in the wire format.
///
/// This method renders the TSIG record as a form of a DNS TSIG RR
/// via \c renderer, which encapsulates output buffer and other rendering
/// contexts.
///
/// Normally this version of \c toWire() method tries to compress the
/// owner name of the RR whenever possible, but this method intentionally
/// skips owner name compression. This is due to a report that some
/// Windows clients refuse a TSIG if its owner name is compressed
/// (See http://marc.info/?l=bind-workers&m=126637138430819&w=2).
/// Reportedly this seemed to be specific to GSS-TSIG, but this
/// implementation skip compression regardless of the algorithm.
///
/// If by adding the TSIG RR the message size would exceed the limit
/// maintained in \c renderer, this method skips rendering the RR
/// and returns 0 and mark \c renderer as "truncated" (so that a
/// subsequent call to \c isTruncated() on \c renderer will result in
/// \c true); otherwise it returns 1, which is the number of RR
/// rendered.
///
/// \note If the caller follows the specification of adding TSIG
/// as described in RFC2845, this should not happen; the caller is
/// generally expected to leave a sufficient room in the message for
/// the TSIG. But this method checks the unexpected case nevertheless.
///
/// \exception std::bad_alloc Internal resource allocation fails (this
/// should be rare).
///
/// \param renderer DNS message rendering context that encapsulates the
/// output buffer and name compression information.
/// \return 1 if the TSIG RR fits in the message size limit; otherwise 0.
uint32_t toWire(AbstractMessageRenderer& renderer) const;
/// \brief Render the \c TSIG RR in the wire format.
///
/// This method is same as \c toWire(AbstractMessageRenderer&)const
/// except it renders the RR in an \c OutputBuffer and therefore
/// does not care about message size limit.
/// As a consequence it always returns 1.
uint32_t toWire(isc::util::OutputBuffer& buffer) const;
/// Convert the TSIG record to a string.
///
/// The output format is the same as the result of \c toText() for
/// other normal types of RRsets (with always using the same RR class
/// and TTL). It also ends with a newline.
///
/// \exception std::bad_alloc Internal resource allocation fails (this
/// should be rare).
///
/// \return A string representation of \c TSIG record
std::string toText() const;
/// The TTL value to be used in TSIG RRs.
static const uint32_t TSIG_TTL = 0;
//@}
private:
const Name key_name_;
const rdata::any::TSIG rdata_;
const size_t length_;
};
/// A pointer-like type pointing to a \c TSIGRecord object.
typedef boost::shared_ptr<TSIGRecord> TSIGRecordPtr;
/// A pointer-like type pointing to an immutable \c TSIGRecord object.
typedef boost::shared_ptr<const TSIGRecord> ConstTSIGRecordPtr;
/// Insert the \c TSIGRecord as a string into stream.
///
/// This method convert \c record into a string and inserts it into the
/// output stream \c os.
///
/// \param os A \c std::ostream object on which the insertion operation is
/// performed.
/// \param record A \c TSIGRecord object output by the operation.
/// \return A reference to the same \c std::ostream object referenced by
/// parameter \c os after the insertion operation.
std::ostream& operator<<(std::ostream& os, const TSIGRecord& record);
}
}
#endif // TSIGRECORD_H
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