JDnsShared Class Reference

Abstraction layer on top of QJDns. More...

#include <jdnsshared.h>

List of all members.

Public Types

enum Mode { UnicastInternet, UnicastLocal, Multicast }

Signals

void shutdownFinished ()

Public Member Functions

JDnsShared (Mode mode, QObject *parent=0)

~JDnsShared ()

void setDebug (JDnsSharedDebug *db, const QString &name)

bool addInterface (const QHostAddress &addr)

void removeInterface (const QHostAddress &addr)

void shutdown ()

Static Public Member Functions

static QList< QByteArray > domains ()

static void waitForShutdown (const QList< JDnsShared * > instances)

Friends

class JDnsSharedRequest

Detailed Description

Abstraction layer on top of QJDns.

Note:: Iris users should utilize NetNames for DNS capabilities, not JDnsShared. JDnsShared is provided for non-Iris users (and it is also used internally by NetNames). To use JDnsShared by itself, simply drop the jdnsshared.h and jdnsshared.cpp files, along with JDNS, into your project. It is not a full replacement for Qt's Q3Dns, as some tasks are left to you, but it covers most of it.

QJDns supports everything a typical application should ever need in DNS. However, it is expected that modern applications will need to maintain multiple QJDns instances at the same time, and this is where things can get complicated. For example, most applications will want at least two QJDns instances: one for IPv4 unicast and one for IPv6 unicast.

A single JDnsShared object encapsulates multiple instances of QJDns that are related. For example, an IPv4 unicast instance and an IPv6 unicast instance could be coupled within JDnsShared. Then, when a unicast operation is performed on the JDnsShared object, both underlying instances will be queried as appropriate. The application would not need to perform two resolutions itself, nor deal with any related complexity.

Further, individual operations are performed using a separate class called JDnsSharedRequest, eliminating the need for the application to directly interface with a central QJDns object or track integer handles. This makes it easier for individual parts of the application to "share" the same instance (or set of instances) of QJDns, hence the name.

JDnsShared is a thin abstraction. QJDns subtypes (e.g. QJDns::Type, QJDns::Record, etc) are still used with JDnsShared. Because of the duplication of documentation effort between NetNames and QJDns, there is no formal documentation for QJDns. Users of JDnsShared will need to read qjdns.h, although a basic explanation of the elements can be found below.

Types:

QJDns::Type This is a convenience enumeration for common DNS record types. For example: A, Aaaa, Srv, etc. The values directly map to the integer values of the DNS protocol (e.g. Srv = 33). See qjdns.h for all of the types and values.

QJDns::Record This class holds a DNS record. The main fields are type (integer type, probably something listed in QJDns::Type), rdata (QByteArray of the record value), and haveKnown (boolean to indicate if a decoded form of the record value is also available). See qjdns.h for the possible known fields. You will most-likely always work with known types. Received records that have a type listed in QJDns::Type are guaranteed to be known and will provide a decoded value. If you are creating a record for publishing, you will need to set owner, ttl, and type. If the type to be published is listed in QJDns::Type, then you will need to set haveKnown to true and set the known fields as appropriate, otherwise you need to set rdata. You do not need to supply an encoded form in rdata for known types, it can be left empty in that case.

QJDns::PublishMode This is for Multicast DNS, and can either be Unique or Shared. A shared record can be published by multiple owners (for example, a "_ssh._tcp.local." PTR record might resolve to many different SSH services owned by different machines). A unique record can only have one owner (for example, a "mycomputer.local." A record would resolve to the IP address of the machine that published it). Attempting to publish a record on a network where a unique record is already present will result in a conflict error.

Functions:

QJDns::detectPrimaryMulticast() Detects a multicast interface. Pass QHostAddress::Any or QHostAddress::AnyIPv6, depending on which type of interface is desired.

To use JDnsShared, first create an instance of it, set it up by calling addInterface() as necessary, and then use JDnsSharedRequest to perform operations on it.

Here is an example of how to create and set up a JDnsShared object for typical DNS resolution:

// construct
JDnsShared *dns = new JDnsShared(JDnsShared::UnicastInternet);

// add IPv4 and IPv6 interfaces
dns->addInterface(QHostAddress::Any);
dns->addInterface(QHostAddress::AnyIPv6);

// at this point, the object is ready for operation

Perform a resolution like this:

JDnsSharedRequest *req = new JDnsSharedRequest(dns);
connect(req, SIGNAL(resultsReady()), SLOT(req_resultsReady()));
req->query("psi-im.org", QJDns::A);
...
void req_resultsReady()
{
        if(req->success())
        {
                // print all of the IP addresses obtained
                QList<QJDns::Record> results = req->results();
                foreach(QJDns::Record r, results)
                {
                        if(r.type == QJDns::A)
                                printf("%s\n", qPrintable(r.address.toString());
                }
        }
        else
                printf("Error resolving!\n");
}

It is important to filter the results as shown in the above example. QJDns guarantees at least one record in the results will be of the type queried for, but there may also be CNAME records present (of course, if the query was for a CNAME type, then the results will only be CNAME records). The recommended approach is to simply filter for the record types desired, as shown, rather than single out CNAME specifically.

When you are finished with a JDnsShared object, it should be shut down before deleting:

connect(dns, SIGNAL(shutdownFinished()), SLOT(dns_shutdownFinished()));
dns->shutdown();
...
void dns_shutdownFinished()
{
        delete dns;
}

Setting up JDnsShared for UnicastLocal and Multicast mode is done the same way as with UnicastInternet.

For example, here is how Multicast mode could be set up:

// construct
JDnsShared *dns = new JDnsShared(JDnsShared::Multicast);

// add IPv4 interface
QHostAddress addr = QJDns::detectPrimaryMulticast(QHostAddress::Any);
dns->addInterface(addr);

// at this point, the object is ready for operation

JDnsShared provides a lot of functionality, but certain aspects of DNS are deemed out of its scope. Below are the responsibilities of the user of JDnsShared, if a more complete DNS behavior is desired:

Querying for several "qualified" names. You should first query for the name as provided, and if that fails then query for name + ".domain" (for every domain the computer is in). See domains().
Detecting for ".local" in the name to be queried, and using that to decide whether to query via Multicast/UnicastLocal or UnicastInternet.
For zeroconf/Bonjour, keep in mind that JDnsShared only provides low-level record queries. DNS-SD and any higher layers would be your job.

Using a custom DNS implementation, such as JDnsShared, has the drawback that it is difficult to take advantage of platform-specific features (for example, an OS-wide DNS cache or LDAP integration). An application strategy for normal DNS should probably be:

If an A or AAAA record is desired, use a native lookup.
Else, if the platform has advanced DNS features already (ie, res_query), use those.
Else, use JDnsShared.

For Multicast DNS, awareness of the platform is doubly important. There should only be one Multicast DNS "Responder" per computer, and using JDnsShared in Multicast mode at the same time could result in a conflict. An application strategy for Multicast DNS should be:

If the platform has a Multicast DNS daemon installed already, use it somehow.
Else, use JDnsShared.

See also:: JDnsSharedRequest

Member Enumeration Documentation

enum JDnsShared::Mode

The mode to operate in.

Enumerator:

UnicastInternet For regular DNS resolution. In this mode, lookups are performed on all interfaces, and the first returned result is used.

UnicastLocal Perform regular DNS resolution using the Multicast DNS address. This is used to resolve large and/or known Multicast DNS names without actually multicasting anything.

Multicast Multicast DNS querying and publishing.

Note:
For Multicast mode, JDnsShared supports up to one interface for each IP version (e.g. one IPv4 interface and one IPv6 interface), and expects the default/primary multicast interface for that IP version to be used.

Constructor & Destructor Documentation

JDnsShared::JDnsShared ( Mode mode,

QObject * parent = 0

)

Constructs a new object with the given mode and parent.

JDnsShared::~JDnsShared ( )

Destroys the object.

Member Function Documentation

bool JDnsShared::addInterface ( const QHostAddress & addr )

Adds an interface to operate on.
For UnicastInternet and UnicastLocal, these will almost always be QHostAddress::Any or QHostAddress::AnyIPv6 (operate on the default interface for IPv4 or IPv6, respectively).
For Multicast, it is expected that the default/primary multicast interface will be used here. Do not pass QHostAddress::Any (or AnyIPv6) with Multicast mode.
Returns true if the interface was successfully added, otherwise returns false.

static QList<QByteArray> JDnsShared::domains ( ) [static]

The domains to search in.
You should perform a separate resolution for every domain configured on this machine.

void JDnsShared::removeInterface ( const QHostAddress & addr )

Removes a previously-added interface.

void JDnsShared::setDebug ( JDnsSharedDebug * db,

const QString & name

)

Sets the debug object to report to.
If a debug object is set using this function, then JDnsShared will send output text to it, prefixing each line with name.

void JDnsShared::shutdown ( )

Shuts down the object.
This operation primarily exists for Multicast mode, so that any published records have a chance to be unpublished. If the JDnsShared object is simply deleted without performing a shutdown, then published records will linger on the network until their TTLs expire.
When shutdown is complete, the shutdownFinished() signal will be emitted.

void JDnsShared::shutdownFinished ( ) [signal]

Indicates the object has been shut down.

static void JDnsShared::waitForShutdown ( const QList< JDnsShared * > instances ) [static]

Performs a blocking shutdown of many JDnsShared instances.
This function is a convenient way to shutdown multiple JDnsShared instances synchronously. The internal shutdown procedure uses no more than a few cycles of the eventloop, so it should be safe to call without worry of the application being overly stalled. This function takes ownership of the instances passed to it, and will delete them upon completion.
It is worth noting that this function is implemented without the use of a nested eventloop. All of the JDnsShared instances are moved into a temporary thread to perform the shutdown procedure, which should not cause any unexpected behavior in the current thread.

QList<JDnsShared*> list; list += jdnsShared_unicast; list += jdnsShared_multicast; JDnsShared::waitForShutdown(list); // collect remaining debug information QStringList finalDebugLines = jdnsSharedDebug.readDebugLines();

The documentation for this class was generated from the following file:

jdnsshared.h

Generated on Sun Mar 18 17:58:50 2007 for IrisNet by

1.4.6


Public Types
enum	Mode { UnicastInternet, UnicastLocal, Multicast }
Signals
void	shutdownFinished ()
Public Member Functions
	JDnsShared (Mode mode, QObject *parent=0)
	~JDnsShared ()
void	setDebug (JDnsSharedDebug *db, const QString &name)
bool	addInterface (const QHostAddress &addr)
void	removeInterface (const QHostAddress &addr)
void	shutdown ()
Static Public Member Functions
static QList< QByteArray >	domains ()
static void	waitForShutdown (const QList< JDnsShared * > instances)
Friends
class	JDnsSharedRequest

QJDns::Type	This is a convenience enumeration for common DNS record types. For example: A, Aaaa, Srv, etc. The values directly map to the integer values of the DNS protocol (e.g. Srv = 33). See qjdns.h for all of the types and values.
QJDns::Record	This class holds a DNS record. The main fields are type (integer type, probably something listed in QJDns::Type), rdata (QByteArray of the record value), and haveKnown (boolean to indicate if a decoded form of the record value is also available). See qjdns.h for the possible known fields. You will most-likely always work with known types. Received records that have a type listed in QJDns::Type are guaranteed to be known and will provide a decoded value. If you are creating a record for publishing, you will need to set owner, ttl, and type. If the type to be published is listed in QJDns::Type, then you will need to set haveKnown to true and set the known fields as appropriate, otherwise you need to set rdata. You do not need to supply an encoded form in rdata for known types, it can be left empty in that case.
QJDns::PublishMode	This is for Multicast DNS, and can either be Unique or Shared. A shared record can be published by multiple owners (for example, a "_ssh._tcp.local." PTR record might resolve to many different SSH services owned by different machines). A unique record can only have one owner (for example, a "mycomputer.local." A record would resolve to the IP address of the machine that published it). Attempting to publish a record on a network where a unique record is already present will result in a conflict error.