KDNSSD::ServiceBrowser Class

class KDNSSD::ServiceBrowser

Browses for network services advertised over DNS-SD. More...

Header: #include <KDNSSD/ServiceBrowser>
CMake: find_package(KF6 REQUIRED COMPONENTS DNSSD)
target_link_libraries(mytarget PRIVATE KF6::DNSSD)

Public Types

enum State { Working, Stopped, Unsupported }

Public Functions

ServiceBrowser(const QString &type, bool autoResolve = false, const QString &domain = QString(), const QString &subtype = QString())
bool isAutoResolving() const
QList<KDNSSD::RemoteService::Ptr> services() const
virtual void startBrowse()

Signals

void finished()
void serviceAdded(KDNSSD::RemoteService::Ptr service)
void serviceRemoved(KDNSSD::RemoteService::Ptr service)

Static Public Members

QString getLocalHostName()
KDNSSD::ServiceBrowser::State isAvailable()
QHostAddress resolveHostName(const QString &hostname)

Detailed Description

This is the central class in the KDNSSD library for applications that want to discover services on network.

Suppose that you need list of web servers running. Then you might do something like:

 KDNSSD::ServiceBrowser *browser = new KDNSSD::ServiceBrowser(QStringLiteral("_http._tcp"));
 connect(browser, &KDNSSD::ServiceBrowser::serviceAdded,
         this, [](KDNSSD::RemoteService::Ptr service) {
         });
 connect(browser, &KDNSSD::ServiceBrowser::serviceRemoved,
         this, [](KDNSSD::RemoteService::Ptr service) {
         });
 browser->startBrowse();

In above example addService() will be called for every web server already running and for every web service that subsequently appears on the network and delService() will be called when a server previously advertised is stopped.

Because no domain was passed to constructor, the default domain will be searched. To find other domains to browse for services on, use DomainBrowser.

Member Type Documentation

enum ServiceBrowser::State

Availability of DNS-SD services.

ConstantValueDescription
KDNSSD::ServiceBrowser::Working0The DNS-SD services are available.
KDNSSD::ServiceBrowser::Stopped1Not available because mDnsd or Avahi daemon is not running.
KDNSSD::ServiceBrowser::Unsupported2Not available because KDE was compiled without DNS-SD support.

Member Function Documentation

[explicit] ServiceBrowser::ServiceBrowser(const QString &type, bool autoResolve = false, const QString &domain = QString(), const QString &subtype = QString())

Creates a ServiceBrowser for a particular service type.

DomainBrowser can be used to find other domains to browse on. If no domain is given, the default domain is used.

The service type is the high-level protocol type, followed by a dot, followed by the transport protocol type (_tcp or _udp). The DNS-SD website maintains a full list of service types.

The subtype parameter allows you to do more fine-grained filtering on the services you are interested in. So you might request only FTP servers that allow anonymous access by passing "_ftp._tcp" as the type and "_anon" as the subtype. Subtypes are particularly important for types like _soap and _upnp, which are far too generic for most applications. In these cases, the subtype can be used to specify the particular SOAP or UPnP protocol they want.

Warning: Enabling autoResolve will increase network usage by resolving all services, so this feature should be used only when necessary.

type is the service type to browse for (example: "_http._tcp")

autoResolve if true, discovered services will be resolved before being reported with the serviceAdded() signal

domain is the domain to search on instead of the default one

subtype if not an empty string, only browse for a specific subtype

See also startBrowse() and isAvailable().

[signal] void ServiceBrowser::finished()

Emitted when the list of published services has settled.

Note: This signal is emitted once after startBrowse() is called when all the services of the requested type that are currently published have been reported (even if none are available or the DNS-SD service is not available). It is emitted again when a new batch of services become available or disappear.

For example, if a new host is connected to network and announces some services watched for by this ServiceBrowser, they will be reported by one or more serviceAdded() signals and the whole batch will be concluded by finished().

This signal can be used by applications that just want to get a list of the currently available services (similar to a directory listing) and do not care about adding or removing services that appear or disappear later.

Warning: There is no guarantee any RemoteService pointers received by serviceAdded() will be valid by the time this signal is emitted, so you should either do all your work involving them in the slot receiving the serviceAdded() signal, or you should listen to serviceRemoved() as well.

See also serviceAdded() and serviceRemoved().

[static] QString ServiceBrowser::getLocalHostName()

The mDNS hostname of the local machine.

Usually this will return the same as QHostInfo::localHostName(), but it may be changed to something different in the Avahi configuration file (if using the Avahi backend).

Returns the hostname, or an empty string on failure

bool ServiceBrowser::isAutoResolving() const

Whether discovered services are resolved before being reported.

Returns the value of the autoResolve parameter passed to the constructor.

[static] KDNSSD::ServiceBrowser::State ServiceBrowser::isAvailable()

Checks availability of DNS-SD services.

Note: Although this method is part of ServiceBrowser, none of the classes in this library will be able to perform their intended function if this method does not return Working.

If this method does not return Working, it is still safe to call any of the methods in this library. However, no services will be found or published and no domains will be found.

If you use this function to report an error to the user, below is a suggestion on how to word the errors when publishing a service. The first line of each error message can also be used for reporting errors when browsing for services.

 switch(KDNSSD::ServiceBrowser::isAvailable()) {
 case KDNSSD::ServiceBrowser::Working:
     return "";
 case KDNSSD::ServiceBrowser::Stopped:
     return i18n("<p>The Zeroconf daemon is not running. See the Service"
                 " Discovery Handbook for more information.<br/>"
                 "Other users will not see the services provided by this
                 " system when browsing the network via zeroconf, but "
                 " normal access will still work.</p>");
 case KDNSSD::ServiceBrowser::Unsupported:
     return i18n("<p>Zeroconf support is not available in this version of KDE."
                 " See the Service Discovery Handbook for more information.<br/>"
                 "Other users will not see the services provided by this
                 " application when browsing the network via zeroconf, but "
                 " normal access will still work.</p>");
 default:
     return i18n("<p>Unknown error with Zeroconf.<br/>"
                 "Other users will not see the services provided by this
                 " application when browsing the network via zeroconf, but "
                 " normal access will still work.</p>");
 }
 

Returns the mDNS-SD service state.

[static] QHostAddress ServiceBrowser::resolveHostName(const QString &hostname)

Resolves an mDNS hostname into an IP address.

Note: This function is very rarely useful, since a properly configured system is able to resolve an mDNS-based host name using the system resolver (ie: you can just pass the mDNS hostname to KIO or other library).

hostname the hostname to be resolved

Returns a QHostAddress containing the IP address, or QHostAddress() if resolution failed

[signal] void ServiceBrowser::serviceAdded(KDNSSD::RemoteService::Ptr service)

Emitted when new service is discovered.

If isAutoResolving() returns true, this will not be emitted until the service has been resolved.

service is a RemoteService object describing the service

See also serviceRemoved() and finished().

[signal] void ServiceBrowser::serviceRemoved(KDNSSD::RemoteService::Ptr service)

Emitted when a service is no longer published over DNS-SD.

The RemoteService object is removed from the services() list and deleted immediately after this signal returns.

Warning: Do not use a delayed connection with this signal.

service a RemoteService object describing the service

See also serviceAdded() and finished().

QList<KDNSSD::RemoteService::Ptr> ServiceBrowser::services() const

The currently known services of the specified type.

Returns a list of RemoteService pointers

See also serviceAdded() and serviceRemoved().

[virtual] void ServiceBrowser::startBrowse()

Starts browsing for services.

Note: Only the first call to this function will have any effect.

Browsing stops when the ServiceBrowser object is destroyed.

Warning: The serviceAdded() signal may be emitted before this function returns.

See also serviceAdded(), serviceRemoved(), and finished().