Backend writers' guide
======================
PowerDNS backends are implemented via a simple yet powerful C++
interface. If your needs are not met by the regular backends, including
the PipeBackend and the RemoteBackend, you may want to write your own.
Before doing any PowerDNS development, please read `this blog
post `__
which has a FAQ and several pictures that help explain what a backend
is.
A backend contains zero DNS logic. It need not look for CNAMEs, it need
not return NS records unless explicitly asked for, etcetera. All DNS
logic is contained within PowerDNS itself - backends should simply
return records matching the description asked for.
.. warning::
However, please note that your backend can get queries in
aNy CAsE! If your database is case sensitive, like most are (with the
notable exception of MySQL), you must make sure that you do find answers
which differ only in case.
.. warning::
PowerDNS may instantiate multiple instances of your
backend, or destroy existing copies and instantiate new ones. Backend
code should therefore be thread-safe with respect to its static data.
Additionally, it is wise if instantiation is a fast operation, with the
possible exception of the first construction.
Notes
-----
Besides regular query types, the DNS also knows the 'ANY' query type.
When a server receives a question for this ANY type, it should reply
with all record types available.
Backends should therefore implement being able to answer 'ANY' queries
in this way, and supply all record types they have when they receive
such an 'ANY' query. This is reflected in the sample script above, which
for every qtype answers if the type matches, or if the query is for
'ANY'.
However, since backends need to implement the ANY query anyhow, PowerDNS
makes use of this. Since almost all DNS queries internally need to be
translated first into a CNAME query and then into the actual query,
possibly followed by a SOA or NS query (this is how DNS works
internally), it makes sense for PowerDNS to speed this up, and just ask
the ANY query of a backend.
When it has done so, it gets the data about SOA, CNAME and NS records in
one go. This speeds things up tremendously.
The upshot of the above is that for any backend, including the PIPE
backend, implementing the ANY query is NOT optional. And in fact, a
backend may see almost exclusively ANY queries. This is not a bug.
Simple read-only native backends
--------------------------------
Implementing a backend consists of inheriting from the DNSBackend class.
For read-only backends, which do not support secondary operation, only the
following methods are relevant:
.. code-block:: cpp
class DNSBackend
{
public:
virtual void lookup(const QType &qtype, const string &qdomain, DNSPacket *pkt_p=0, int zoneId=-1)=0;
virtual bool list(const string &target, int domain_id)=0;
virtual bool get(DNSResourceRecord &r)=0;
virtual bool getSOA(const string &name, SOAData &soadata, DNSPacket *p=0);
};
Note that the first three methods must be implemented. ``getSOA()`` has
a useful default implementation.
The semantics are simple. Each instance of your class only handles one
(1) query at a time. There is no need for locking as PowerDNS guarantees
that your backend will never be called reentrantly.
.. note::
Queries for wildcard names should be answered literally,
without expansion. So, if a backend gets a question for
"\*.powerdns.com", it should only answer with data if there is an actual
"\*.powerdns.com" name
Some examples, a more formal specification is down below. A normal
lookup starts like this:
.. code-block:: cpp
YourBackend yb;
yb.lookup(QType::CNAME,"www.powerdns.com");
Your class should now do everything to start this query. Perform as much
preparation as possible - handling errors at this stage is better for
PowerDNS than doing so later on. A real error should be reported by
throwing an exception.
PowerDNS will then call the ``get()`` method to get
``DNSResourceRecord``\ s back. The following code illustrates a typical
query:
.. code-block:: cpp
yb.lookup(QType::CNAME,"www.powerdns.com");
DNSResourceRecord rr;
while(yb.get(rr))
cout<<"Found cname pointing to '"+rr.content+"'"<getRemote()`` method.
.. note::
Since 4.1.0, 'SOA' lookups are not passed this pointer anymore because
PowerDNS doesn't support tailoring whether a whole zone exists or not based
on who is asking.
Note that **qdomain** can be of any case and that your backend should
make sure it is in effect case insensitive. Furthermore, the case of the
original question should be retained in answers returned by ``get()``!
Finally, the domain_id might also be passed indicating that only
answers from the indicated zone need apply. This can both be used as a
restriction or as a possible speedup, hinting your backend where the
answer might be found.
If initiated successfully, as indicated by returning **true**, answers
should be made available over the ``get()`` method.
Should throw an PDNSException if an error occurred accessing the
database. Returning otherwise indicates that the query was started
successfully. If it is known that no data is available, no exception
should be thrown! An exception indicates that the backend considers
itself broken - not that no answers are available for a question.
It is legal to return here, and have the first call to ``get()`` return
false. This is interpreted as 'no data'.
.. cpp:function:: bool DNSBackend::list(int domain_id, bool include_disabled=false)
Initiates a list of the indicated domain. Records should then be made
available via the ``get()`` method. Need not include the SOA record. If
it is, PowerDNS will not get confused. If include_disabled is given as
true, records that are configured but should not be served to DNS
clients must also be made available.
Should return false if the backend does not consider itself
authoritative for this zone. Should throw an PDNSException if an error
occurred accessing the database. Returning true indicates that data is
or should be available.
.. cpp:function:: bool DNSBackend::get(DNSResourceRecord &rr)
Request a DNSResourceRecord from a query started by ``get()`` of
``list()``. If this functions returns **true**, **rr** has been filled
with data. When it returns false, no more data is available, and **rr**
does not contain new data. A backend should make sure that it either
fills out all fields of the DNSResourceRecord or resets them to their
default values.
The qname field of the DNSResourceRecord should be filled out with the
exact ``qdomain`` passed to lookup, preserving its case. So if a query
for 'CaSe.yourdomain.com' comes in and your database contains data for
'case.yourdomain.com', the qname field of rr should contain
'CaSe.yourdomain.com'!
Should throw an PDNSException in case a database error occurred.
.. cpp:function:: bool DNSBackend::getSOA(const string &name, SOAData &soadata)
If the backend considers itself authoritative over domain ``name``, this
method should fill out the passed **SOAData** structure and return a
positive number. If the backend is functioning correctly, but does not
consider itself authoritative, it should return 0. In case of errors, an
PDNSException should be thrown.
Reporting errors
----------------
To report errors, the Logger class is available which works mostly like
an iostream. Example usage is as shown above in the RandomBackend. Note
that it is very important that each line is ended with **endl** as your
message won't be visible otherwise.
To indicate the importance of an error, the standard syslog errorlevels
are available. They can be set by outputting ``Logger::Critical``,
``Logger::Error``, ``Logger::Warning``, ``Logger::Notice``,
``Logger::Info`` or ``Logger::Debug`` to ``g_log``, in descending order of
graveness.
Declaring and reading configuration details
-------------------------------------------
It is highly likely that a backend needs configuration details. On
launch, these parameters need to be declared with PowerDNS so it knows
it should accept them in the configuration file and on the command line.
Furthermore, they will be listed in the output of ``--help``.
Declaring arguments is done by implementing the member function
``declareArguments()`` in the factory class of your backend. PowerDNS
will call this method after launching the backend.
In the ``declareArguments()`` method, the function ``declare()`` is
available. The exact definitions:
.. cpp:function:: void DNSBackend::declareArguments(const string &suffix="")
This method is called to allow a backend to register configurable
parameters. The suffix is the sub-name of this module. There is no need
to touch this suffix, just pass it on to the declare method.
.. cpp:function:: void DNSBackend::declare(const string &suffix, const string ¶m, const string &explanation, const string &value)
The suffix is passed to your method, and can be passed on to declare.
**param** is the name of your parameter. **explanation** is what will
appear in the output of --help. Furthermore, a default value can be
supplied in the **value** parameter.
A sample implementation:
.. code-block:: cpp
void declareArguments(const string &suffix)
{
declare(suffix,"dbname","Pdns backend database name to connect to","powerdns");
declare(suffix,"user","Pdns backend user to connect as","powerdns");
declare(suffix,"host","Pdns backend host to connect to","");
declare(suffix,"password","Pdns backend password to connect with","");
}
After the arguments have been declared, they can be accessed from your
backend using the ``mustDo()``, ``getArg()`` and ``getArgAsNum()``
methods. The are defined as follows in the DNSBackend class:
.. cpp:function:: void DNSBackend::setArgPrefix(const string &prefix)
Must be called before any of the other accessing functions are used.
Typical usage is '``setArgPrefix("mybackend"+suffix)``' in the
constructor of a backend.
.. cpp:function:: bool DNSBackend::mustDo(const string &key)
Returns true if the variable ``key`` is set to anything but 'no'.
.. cpp:function:: const string& DNSBackend::getArg(const string &key)
Returns the exact value of a parameter.
.. cpp:function:: int DNSBackend::getArgAsNum(const string &key)
Returns the numerical value of a parameter. Uses ``atoi()`` internally
Sample usage from the BIND backend: getting the 'check-interval' setting:
.. code-block:: cpp
if(!safeGetBBDomainInfo(i->name, &bbd)) {
bbd.d_id=domain_id++;
bbd.setCheckInterval(getArgAsNum("check-interval"));
bbd.d_lastnotified=0;
bbd.d_loaded=false;
}
.. _rw-slave:
.. _rw-secondary:
Read/write secondary-capable backends
-------------------------------------
The backends above are 'natively capable' in that they contain all data
relevant for a domain and do not pull in data from other nameservers. To
enable storage of information, a backend must be able to do more.
Before diving into the details of the implementation some theory is in
order. Secondary domains are pulled from the primary. PowerDNS needs to know
for which domains it is to be a secondary, and for each secondary domain, what
the IP address of the primary is.
A secondary zone is pulled from a primary, after which it is 'fresh', but
this is only temporary. In the SOA record of a zone there is a field
which specifies the 'refresh' interval. After that interval has elapsed,
the secondary nameserver needs to check at the primary if the serial number
there is higher than what is stored in the backend locally.
If this is the case, PowerDNS dubs the domain 'stale', and schedules a
transfer of data from the remote. This transfer remains scheduled until
the serial numbers remote and locally are identical again.
This theory is implemented by the ``getUnfreshSlaveInfos`` method, which
is called on all backends periodically. This method fills a vector of
**SlaveDomain**\ s with domains that are unfresh and possibly stale.
PowerDNS then retrieves the SOA of those domains remotely and locally
and creates a list of stale domains. For each of these domains, PowerDNS
starts a zone transfer to resynchronise. Because zone transfers can
fail, it is important that the interface to the backend allows for
transaction semantics because a zone might otherwise be left in a
halfway updated situation.
The following excerpt from the DNSBackend shows the relevant functions:
.. code-block:: cpp
class DNSBackend {
public:
/* ... */
virtual bool getDomainInfo(const string &domain, DomainInfo &di);
virtual bool isMaster(const string &name, const string &ip);
virtual bool startTransaction(const string &qname, int id);
virtual bool commitTransaction();
virtual bool abortTransaction();
virtual bool feedRecord(const DNSResourceRecord &rr, string *ordername=0);
virtual void getUnfreshSlaveInfos(vector* domains);
virtual void setFresh(uint32_t id);
/* ... */
}
The mentioned DomainInfo struct looks like this:
.. cpp:class:: DomainInfo
.. cpp:member:: uint32_t DomainInfo::id
ID of this zone within this backend
.. cpp:member:: string DomainInfo::master
IP address of the primary of this domain, if any
.. cpp:member:: uint32_t DomainInfo::serial
Serial number of this zone
.. cpp:member:: uint32_t DomainInfo::notified_serial
Last serial number of this zone that secondaries have seen
.. cpp:member:: time_t DomainInfo::last_check
Last time this zone was checked over at the primary for changes
.. cpp:member:: enum DomainKind DomainInfo::kind
Type of zone
.. cpp:member:: DNSBackend* DomainInfo::backend
Pointer to the backend that feels authoritative for a domain and can act as a secondary
.. cpp:enum:: DomainKind
The kind of domain, one of {Master,Slave,Native}.
These functions all have a default implementation that returns false -
which explains that these methods can be omitted in simple backends.
Furthermore, unlike with simple backends, a secondary capable backend must
make sure that the 'DNSBackend \*db' field of the SOAData record is
filled out correctly - it is used to determine which backend will house
this zone.
.. cpp:function:: bool DomainInfo::isMaster(const string &name, const string &ip)
If a backend considers itself a secondary for the domain **name** and if the
IP address in **ip** is indeed a primary, it should return true. False
otherwise. This is a first line of checks to guard against reloading a
domain unnecessarily.
.. cpp:function:: void DomainInfo::getUnfreshSlaveInfos(vector\* domains)
When called, the backend should examine its list of secondary domains and
add any unfresh ones to the domains vector.
.. cpp:function:: bool DomainInfo::getDomainInfo(const string &name, DomainInfo & di)
This is like ``getUnfreshSlaveInfos``, but for a specific domain. If the
backend considers itself authoritative for the named zone, ``di`` should
be filled out, and 'true' be returned. Otherwise return false.
.. cpp:function:: bool DomainInfo::startTransaction(const string &qname, int id)
When called, the backend should start a transaction that can be
committed or rolled back atomically later on. In SQL terms, this
function should **BEGIN** a transaction and **DELETE** all records.
.. cpp:function:: bool DomainInfo::feedRecord(const DNSResourceRecord &rr, string *ordername)
Insert this record.
.. cpp:function:: bool DomainInfo::commitTransaction()
Make the changes effective. In SQL terms, execute **COMMIT**.
.. cpp:function:: bool DomainInfo::abortTransaction()
Abort changes. In SQL terms, execute **ABORT**.
.. cpp:function:: bool DomainInfo::setFresh()
Indicate that a domain has either been updated or refreshed without the
need for a retransfer. This causes the domain to vanish from the vector
modified by ``getUnfreshSlaveInfos()``.
PowerDNS will always call ``startTransaction()`` before making calls to
``feedRecord()``. Although it is likely that ``abortTransaction()`` will
be called in case of problems, backends should also be prepared to abort
from their destructor.
The actual code in PowerDNS is currently:
.. code-block:: cpp
Resolver resolver;
resolver.axfr(remote,domain.c_str());
db->startTransaction(domain, domain_id);
g_log<feedRecord(*i);
}
}
db->commitTransaction();
db->setFresh(domain_id);
g_log<&nsset, string *account, DNSBackend **db)
};
This function gets called with the IP address of the potential
autoprimary, the domain it is sending a notification for and the set of
NS records for this domain at that IP address.
Using the supplied data, the backend needs to determine if this is a
bonafide 'supernotification' which should be honoured. If it decides
that it should, the supplied pointer to 'account' needs to be filled
with the configured name of the autoprimary (if accounting is desired),
and the db needs to be filled with a pointer to your backend.
Autoprimary/autosecondary is a complicated concept, if this is all unclear
see the :ref:`autoprimary-operation`
documentation.
Read/write primary-capable backends
-----------------------------------
In order to be a useful primary for a domain, notifies must be sent out
whenever a domain is changed. Periodically, PowerDNS queries backends
for domains that may have changed, and sends out notifications to secondary
nameservers.
In order to do so, PowerDNS calls the ``getUpdatedMasters()`` method.
Like the ``getUnfreshSlaveInfos()`` function mentioned above, this
should add changed domain names to the vector passed.
The following excerpt from the DNSBackend shows the relevant functions:
.. code-block:: cpp
class DNSBackend {
public:
/* ... */
virtual void getUpdatedMasters(vector* domains);
virtual void setNotified(uint32_t id, uint32_t serial);
/* ... */
}
These functions all have a default implementation that returns false -
which explains that these methods can be omitted in simple backends.
Furthermore, unlike with simple backends, a secondary capable backend must
make sure that the 'DNSBackend \*db' field of the SOAData record is
filled out correctly - it is used to determine which backend will house
this zone.
.. cpp:function:: void DNSBackend::getUpdatedMasters(vector* domains)
When called, the backend should examine its list of master domains and
add any changed ones to the :cpp:class:`DomainInfo` vector.
.. cpp:function:: bool DNSBackend::setNotified(uint32_t domain_id, uint32_t serial)
Indicate that notifications have been queued for this domain and that it
need not be considered 'updated' anymore
DNS update support
------------------
To make your backend DNS update compatible, it needs to implement a
number of new functions and functions already used for secondary operation.
The new functions are not DNS update specific and might be used for
other update/remove functionality at a later stage.
.. code-block:: cpp
class DNSBackend {
public:
/* ... */
virtual bool startTransaction(const string &qname, int id);
virtual bool commitTransaction();
virtual bool abortTransaction();
virtual bool feedRecord(const DNSResourceRecord &rr, string *ordername);
virtual bool replaceRRSet(uint32_t domain_id, const string& qname, const QType& qt, const vector& rrset)
virtual bool listSubZone(const string &zone, int domain_id);
/* ... */
}
.. cpp:function:: virtual bool DNSBackend::startTransaction(const string &qname, int id)
See :cpp:func:`above `. Please
note that this function now receives a negative number (-1), which
indicates that the current zone data should NOT be deleted.
.. cpp:function:: virtual bool DNSBackend::commitTransaction()
See :cpp:func:`above `.
.. cpp:function:: virtual bool DNSBackend::abortTransaction()
See cpp:func:`above `. Method is called when an
exception is received.
.. cpp:function:: virtual bool DNSBackend::feedRecord(const DNSResourceRecord &rr, string *ordername)
See :cpp:func:`above `.
Please keep in mind that the zone is not empty because
``startTransaction()`` was called different.
.. cpp:function:: virtual bool DNSBackend::listSubZone(const string &name, int domain_id)
This method is needed for rectification of a zone after NS-records have
been added. For DNSSEC, we need to know which records are below the
currently added record. ``listSubZone()`` is used like ``list()`` which
means PowerDNS will call ``get()`` after this method. The default SQL
query looks something like this::
// First %s is 'sub.zone.com', second %s is '*.sub.zone.com'
select content,ttl,prio,type,domain_id,name from records where (name='%s' OR name like '%s') and domain_id=%d
The method is not only used when adding records, but also to correct
ENT-records in powerdns. Make sure it returns every record in the tree
below the given record.
.. cpp:function:: virtual bool DNSBackend::replaceRRSet(uint32_t domain_id, const string& qname, const QType& qt, const vector& rrset)
This method should remove all the records with ``qname`` of type ``qt``.
``qt`` might also be ANY, which means all the records with that
``qname`` need to be removed. After removal, the records in ``rrset``
must be added to the zone. ``rrset`` can be empty in which case the
method is used to remove a RRset.
Domain metadata support
-----------------------
As described in :doc:`../domainmetadata`, each served zone can have “metadata”. Such metadata determines how this zone behaves in certain circumstances.
In order for a backend to support domain metadata, the following operations have to be implemented:
.. code-block:: cpp
class DNSBackend {
public:
/* ... */
virtual bool getAllDomainMetadata(const DNSName& name, std::map >& meta);
virtual bool getDomainMetadata(const DNSName& name, const std::string& kind, std::vector& meta);
virtual bool setDomainMetadata(const DNSName& name, const std::string& kind, const std::vector& meta);
/* ... */
}
.. cpp:function:: virtual bool getAllDomainMetadata(const DNSName& name, std::map >& meta)
Fills 'meta' with the value(s) of all kinds for zone 'name'. Returns true if the domain metadata operation are supported, regardless
of whether there is any data for this zone.
.. cpp:function:: virtual bool getDomainMetadata(const DNSName& name, const std::string& kind, std::vector& meta)
Fills 'meta' with the value(s) of the specified kind for zone 'name'. Returns true if the domain metadata operation are supported, regardless
of whether there is any data of this kind for this zone.
.. cpp:function:: virtual bool setDomainMetadata(const DNSName& name, const std::string& kind, const std::vector& meta)
Store the values from 'meta' for the specified kind for zone 'name', discarding existing values if any. An empty meta is equivalent to a deletion request.
Returns true if the values have been correctly stored, and false otherwise.
TSIG keys
---------
In order for a backend to support the storage of TSIG keys, the following operations have to be implemented:
.. code-block:: cpp
class DNSBackend {
public:
/* ... */
virtual bool getTSIGKey(const DNSName& name, DNSName* algorithm, string* content);
virtual bool setTSIGKey(const DNSName& name, const DNSName& algorithm, const string& content);
virtual bool deleteTSIGKey(const DNSName& name);
virtual bool getTSIGKeys(std::vector< struct TSIGKey > &keys);
/* ... */
}
DNSSEC support
--------------
In order for a backend to support DNSSEC, quite a few number of additional operations have to be implemented:
.. code-block:: cpp
struct KeyData {
std::string content;
unsigned int id;
unsigned int flags;
bool active;
bool published;
};
class DNSBackend {
public:
/* ... */
virtual bool doesDNSSEC();
virtual bool getBeforeAndAfterNamesAbsolute(uint32_t id, const DNSName& qname, DNSName& unhashed, DNSName& before, DNSName& after);
/* update operations */
virtual bool updateDNSSECOrderNameAndAuth(uint32_t domain_id, const DNSName& qname, const DNSName& ordername, bool auth, const uint16_t qtype=QType::ANY);
virtual bool updateEmptyNonTerminals(uint32_t domain_id, set& insert, set& erase, bool remove);
virtual bool feedEnts(int domain_id, map &nonterm);
virtual bool feedEnts3(int domain_id, const DNSName &domain, map &nonterm, const NSEC3PARAMRecordContent& ns3prc, bool narrow);
/* keys management */
virtual bool getDomainKeys(const DNSName& name, std::vector& keys);
virtual bool removeDomainKey(const DNSName& name, unsigned int id);
virtual bool addDomainKey(const DNSName& name, const KeyData& key, int64_t& id);
virtual bool activateDomainKey(const DNSName& name, unsigned int id);
virtual bool deactivateDomainKey(const DNSName& name, unsigned int id);
virtual bool publishDomainKey(const DNSName& name, unsigned int id);
virtual bool unpublishDomainKey(const DNSName& name, unsigned int id);
/* ... */
}
.. cpp:function:: virtual bool doesDNSSEC()
Returns true if that backend supports DNSSEC.
.. cpp:function:: virtual bool getBeforeAndAfterNamesAbsolute(uint32_t id, const DNSName& qname, DNSName& unhashed, DNSName& before, DNSName& after)
Asks the names before and after qname for NSEC and NSEC3. The qname will be hashed when using NSEC3. Care must be taken to handle wrap-around when qname is the first or last in the ordered list of zone names.
.. cpp:function:: virtual bool updateDNSSECOrderNameAndAuth(uint32_t domain_id, const DNSName& qname, const DNSName& ordername, bool auth, const uint16_t qtype=QType::ANY)
Updates the ordername and auth fields.
.. cpp:function:: virtual bool updateEmptyNonTerminals(uint32_t domain_id, set& insert, set& erase, bool remove)
Updates ENT after a zone has been rectified. If 'remove' is false, 'erase' contains a list of ENTs to remove from the zone before adding any. Otherwise all ENTs should be removed from the zone before adding any. 'insert' contains the list of ENTs to add to the zone after the removals have been done.
.. cpp:function:: virtual bool feedEnts(int domain_id, map &nonterm)
This method is used by ``pdnsutil rectify-zone`` to populate missing non-terminals. This is used when you have, say, record like _sip._upd.example.com, but no _udp.example.com. PowerDNS requires that there exists a non-terminal in between, and this instructs you to add one.
.. cpp:function:: virtual bool feedEnts3(int domain_id, const DNSName &domain, map &nonterm, const NSEC3PARAMRecordContent& ns3prc, bool narrow)
Same as feedEnts, but provides NSEC3 hashing parameters.
.. cpp:function:: virtual bool getDomainKeys(const DNSName& name, std::vector& keys)
Retrieves all DNSSEC keys. Content must be valid key record in format that PowerDNS understands.
.. cpp:function:: virtual bool removeDomainKey(const DNSName& name, unsigned int id)
Removes this key.
.. cpp:function:: virtual bool addDomainKey(const DNSName& name, const KeyData& key, int64_t& id)
Adds a new DNSSEC key for this domain.
.. cpp:function:: virtual bool activateDomainKey(const DNSName& name, unsigned int id)
Activates an inactive DNSSEC key for this domain.
.. cpp:function:: virtual bool deactivateDomainKey(const DNSName& name, unsigned int id)
Deactivates an active DNSSEC key for this domain.
.. cpp:function:: virtual bool publishDomainKey(const DNSName& name, unsigned int id)
Publishes a previously hidden DNSSEC key for this domain.
.. cpp:function:: virtual bool unpublishDomainKey(const DNSName& name, unsigned int id)
Hides a DNSSEC key for this domain. Hidden DNSSEC keys are used for signing but do not appear in the actual zone,
and are useful for rollover operations.
Miscellaneous
-------------
ENT (Empty Non-Terminal)
~~~~~~~~~~~~~~~~~~~~~~~~
You are expected to reply with a DNSResourceRecord having ``qtype = 0``,
``ttl = 0`` and ``content`` should be empty string (string length 0)
Storage classes
~~~~~~~~~~~~~~~
You may have noticed that PowerDNS has several C++ classes for holding DNS data.
Some use presentation format, some use the wire format.
Some just hold content, some hold a whole record.
Below, we'll show the class definitions of each (with some details omitted, but with some useful words added) to help you find your way.
.. code-block:: cpp
struct DNSZoneRecord
{
int domain_id{-1};
uint8_t scopeMask{0};
int signttl{0};
DNSName wildcardname;
bool auth{true};
bool disabled{false};
DNSRecord dr;
};
``DNSZoneRecord`` holds a record in the context of a zone.
It is a wrapper around ``DNSRecord`` with some extra fields that PowerDNS might need to handle DNSSEC and ECS correctly.
.. code-block:: cpp
struct DNSRecord
{
DNSRecord() : d_type(0), d_class(QClass::IN), d_ttl(0), d_clen(0), d_place(DNSResourceRecord::ANSWER)
{}
explicit DNSRecord(const DNSResourceRecord& rr);
DNSName d_name;
std::shared_ptr d_content;
uint16_t d_type;
uint16_t d_class;
uint32_t d_ttl;
uint16_t d_clen;
DNSResourceRecord::Place d_place;
// this orders by name/type/class/ttl/lowercased zone representation
bool operator<(const DNSRecord& rhs);
// this orders in canonical order and keeps the SOA record on top
static bool prettyCompare(const DNSRecord& a, const DNSRecord& b);
bool operator==(const DNSRecord& rhs) const
};
``DNSRecord`` holds a DNS record.
It has name, type, class, TTL, content length, and a content object of type ``DNSRecordContent``.
.. code-block:: cpp
class DNSRecordContent
{
public:
static std::shared_ptr mastermake(...);
virtual std::string getZoneRepresentation(bool noDot=false) const = 0;
virtual void toPacket(DNSPacketWriter& pw)=0;
virtual string serialize(const DNSName& qname, bool canonic=false, bool lowerCase=false);
virtual bool operator==(const DNSRecordContent& rhs); // compares presentation format
static shared_ptr deserialize(const DNSName& qname, uint16_t qtype, const string& serialized);
void doRecordCheck(const struct DNSRecord&){}
virtual uint16_t getType() const = 0;
};
``DNSRecordContent`` holds DNS content, in individual fields for the various contents of record types.
It is subclassed for all supported types:
.. code-block:: cpp
class SRVRecordContent : public DNSRecordContent
{
public:
SRVRecordContent(uint16_t preference, uint16_t weight, uint16_t port, DNSName target);
includeboilerplate(SRV)
uint16_t d_weight, d_port;
DNSName d_target;
uint16_t d_preference;
};
.. code-block:: cpp
class DNSResourceRecord
{
public:
DNSResourceRecord() : last_modified(0), ttl(0), signttl(0), domain_id(-1), qclass(1), scopeMask(0), auth(1), disabled(0) {};
static DNSResourceRecord fromWire(const DNSRecord& d);
void setContent(const string& content);
string getZoneRepresentation(bool noDot=false) const;
DNSName qname; //!< the name of this record, for example: www.powerdns.com
DNSName ordername;
DNSName wildcardname;
string content; //!< what this record points to. Example: 10.1.2.3
uint32_t ttl; //!< Time To Live of this record
uint32_t signttl; //!< If non-zero, use this TTL as original TTL in the RRSIG
int domain_id; //!< If a backend implements this, the domain_id of the zone this record is in
QType qtype; //!< qtype of this record, ie A, CNAME, MX etc
uint16_t qclass; //!< class of this record
uint8_t scopeMask;
bool auth;
bool disabled;
bool operator==(const DNSResourceRecord& rhs);
bool operator<(const DNSResourceRecord &b);
``DNSResourceRecord`` holds a DNS record with content in presentation format, as a string.