At the Core Foundation level we have the CFNetServices API which supports the registration and discovery of services using DNS/mDNS.
1.0 CFNetServiceBrowser
A CFNetServiceBrowser is the CFNetServices equivalent of an NSNetServiceBrowser.
2.0 CFNetService
A CFNetService is the CFNetServices equivalent of an NSNetService.
3.0 Synchronous vs. Aynchronous
Unlike the NSNetServiceBrowser and NSNetService methods the equivalent CFNetServiceBrowser and CFNetService functions can be used synchronously or asynchronously.
By default the functions are synchronous.
To make them asynchronous for a given CFNetServiceBrowser or CFNetService it must be added to a CFRunLoop.
4.0 Searching For Services Asynchronously
To search for services of a given type using the CFNetworkServices API we need to
-
create a
CFNetServiceBrowser -
make it asynchronous
-
start the search
4.1 CFNetServiceBrowserCreate
We can create a CFNetServiceBrowser using the function CFNetServiceBrowserCreate which is declared like this
CFNetServiceBrowserRef CFNetServiceBrowserCreate (
CFAllocatorRef alloc,
CFNetServiceBrowserClientCallBack clientCB,
CFNetServiceClientContext* clientContext);
The alloc argument is a reference to an allocator to use when creating the CFNetServiceBrowser or more likely the constant
kCFAllocatorDefault4.1.1 The clientCB Argument
The clientCB argument is a pointer to a function of type CFNetServiceBrowserClientCallBack.
This function will be invoked when a service is found or if an error occurs.
The function type CFNetServiceBrowserClientCallBack is declared like this
typedef void (*CFNetServiceBrowserClientCallBack) (
CFNetServiceBrowserRef browser,
CFOptionFlags flags,
CFTypeRef domainOrService,
CFStreamError* error,
void* info);;
The browser argument is the CFNetServiceBrowserRef that was returned from the call to CFNetServiceBrowserCreate.
The callback function is also invoked when searching for domains so the flags argument is used to distinguish between the two uses.
It is also used to distinguish between the discovery of a service and the disappearance of a previously discovered service.
When a service is discovered the value of the flags argument will be zero (0).
When a previously discovered service disappears the value of the flags argument will be
kCFNetServiceFlagRemove
When being invoked on the discovery or disappearance of a service the domainOrService argument will be a
CFNetServiceRef.
If an error has occurred, the error and domain fields of error argument will be set.
The info argument is the value of the info field of the CFNetServiceClientContext passed to the call to CFNetServiceBrowserCreate.
4.1.2 The clientContext Argument
The clientContext argument is a pointer to a CFNetServiceClientContext which is declared like this.
struct CFNetServiceClientContext {
CFIndex version;
void* info;
CFAllocatorRetainCallBack retain;
CFAllocatorReleaseCallBack release;
CFAllocatorCopyDescriptionCallBack copyDescription;
};
typedef struct CFNetServiceClientContext CFNetServiceClientContext;
The info field can be used to store a pointer to an ‘object’ which will be passed to the callback function passed via the clientCB argument.
If the retain and release fields are not NULL then the functions specified will be invoked when the implementation wishes to retain and release the ‘object’ specified in the info field.
It is not clear from the documentation whether the contents of the CFNetServiceClientContext are copied.
A const qualifier is sometimes a clue, but a little experimentation shows that they are, so it is safe to stack allocate.
4.2 CFNetServiceBrowserScheduleWithRunLoop
We can add our newly created CFNetServiceBrowser to a CFRunLoop using the function CFNetServiceBrowserScheduleWithRunLoop which is declared like this
void CFNetServiceBrowserScheduleWithRunLoop(
CFNetServiceBrowserRef browser,
CFRunLoopRef runLoop,
CFStringRef runLoopMode);
The easiest way to use this is to add the CFNetServiceBrowser to the main CFRunLoop in the default mode like so
CFNetServiceBrowserScheduleWithRunLoop(
browser,
CFRunLoopGetMain(),
kCFRunLoopDefaultMode);4.3 CFNetServiceBrowserSearchForServices
Once we have made our CFNetServiceBrowse asynchronous we can start the search for services by calling the function CFNetServiceBrowserSearchForServices which is declared like this
Boolean CFNetServiceBrowserSearchForServices (
CFNetServiceBrowserRef browser,
CFStringRef domain,
CFStringRef serviceType,
CFStreamError* error);
The browser argument should be the CFNetServiceBrowserRef returned from the call to CFNetServiceBrowserCreate.
The domain argument should be the absolute name of the domain in which to search, e.g.,
"local."
The serviceType argument should be the domain relative type of the services to search for, e.g.,
"_ipp._tcp."
The documentation for the error argument is a tad confusing.
It states
A pointer to a
CFStreamErrorstructure, that, if an error occurs, will be set to the error and the error’s domain and passed to your callback function.
The
… and passed to your callback
bit does not appear to be true.
If it is not possible to start the search then the function returns false immediately and the domain and error fields of the CFStreamError are set.
5.0 Resolving A Service Asynchronously
Once a service has been found we need to resolve it …
To do this asynchronously we need to
-
make it possible to get the result asynchronously
-
make the
CFNetServiceasynchronous -
start the resolution
5.1 CFNetServiceSetClient
To get the results from CFNetService functions when running asynchronously we must associate a callback function and a context with the CFNetService first.
We do this using the function CFNetServiceSetClient which is declared like this
Boolean CFNetServiceSetClient(
CFNetServiceRef theService,
CFNetServiceClientCallBack clientCB,
CFNetServiceClientContext* clientContext);5.1.1 The clientCB Argument
The clientCB argument is a pointer to a function of type CFNetServiceClientCallBack
This function will be invoked when the service is resolved or an error occurs.
The function type CFNetServiceClientCallBack is declared like this
typedef void (*CFNetServiceClientCallBack) (
CFNetServiceRef theService,
CFStreamError* error,
void* info);…
The info argument is the value of the info field of the CFNetServiceClientContext passed as the clientContext argument in the call to the CFNetServiceSetClient
If an error has occurred, the error and domain fields of error argument will be set.
5.1.2 The clientContext Argument
The clientContext argument is a pointer to a CFNetServiceClientContext which we have already seen used with the function CFNetServiceBrowserCreate.
5.2 CFNetServiceScheduleWithRunLoop
We can add our CFNetService instance to a CFRunLoop using the function CFNetServiceScheduleWithRunLoop which is declared like this.
void CFNetServiceScheduleWithRunLoop(
CFNetServiceRef theService,
CFRunLoopRef runLoop,
CFStringRef runLoopMode);
The easiest way to use this is to add the CFNetService to the main CFRunLoop in the default mode like so
CFNetServiceScheduleWithRunLoop(service, CFRunLoopGetMain(), kCFRunLoopDefaultMode);5.3 CFNetServiceResolveWithTimeout
Once we have made our CFNetService asynchronous we can start the resolution bey calling the function
CFNetServiceResolveWithTimeout which is declared like this
Boolean CFNetServiceResolveWithTimeout(
CFNetServiceRef theService,
CFTimeInterval timeout,
CFStreamError* error);
The timeout argument specifies the amount of time in seconds that the implementation should wait for the resolution to complete If the value is less than or equal to zero the implementation will wait indefinitely.
If it not possible to start the resolution the function returns false immediately and the domain and error fields of the CFStreamError argument are set.
6.0 The FindServices Class
Here is the FindServices class re-written to use the CFNetServices API.
//
// FindServices.m
// XperTakeTwo
//
// Created by Simon Lewis on 12/11/2013.
// Copyright (c) 2013 Simon Lewis. All rights reserved.
//
#import "Service.h"
#import "FindServices.h"
@interface FindServices ()
@property NSString* type;
@property NSString* domain;
@property NSMutableDictionary* services;
- (void)serviceFound:(CFNetServiceRef)theService;
- (void)serviceLost:(CFNetServiceRef)theService;
- (void)resolved:(CFNetServiceRef)theService;
- (void)resolveFailed:(CFNetServiceRef)theService withError:(CFStreamError*)theError;
- (void)stopBrowser;
- (void)stopService:(CFNetServiceRef)theService;
- (void)log:(NSString*)theMessage service:(CFNetServiceRef)theService;
@end
@implementation FindServices
{
CFNetServiceBrowserRef browser;
}
- (FindServices*)initWithType:(NSString*)theType andDomain:(NSString*)theDomain
{
self = [super init];
if (self != nil)
{
self.type = theType;
self.domain = theDomain;
self.services = [NSMutableDictionary dictionaryWithCapacity:8];
}
return self;
}
static void browserCallBack(
CFNetServiceBrowserRef theBrowser,
CFOptionFlags theFlags,
CFTypeRef theDomainOrService,
CFStreamError* theError,
void* theInfo)
{
NSLog(@"browserCallBack");
if ((theError->error) != 0)
{
NSLog(@"error: %d\n", (int)theError->error);
}
else
if ((theFlags & kCFNetServiceFlagIsDomain) != 0)
{
NSLog(@"domain !\n");
}
else // service
if ((theFlags & kCFNetServiceFlagRemove) == 0)
{
[(__bridge FindServices*)theInfo serviceFound:(CFNetServiceRef)theDomainOrService];
}
else
{
[(__bridge FindServices*)theInfo serviceLost:(CFNetServiceRef)theDomainOrService];
}
}
- (void)start
{
CFNetServiceClientContext context;
memset(&context, 0, sizeof(context));
context.info = (__bridge void *)(self);
browser = CFNetServiceBrowserCreate(kCFAllocatorDefault, browserCallBack, &context);
CFNetServiceBrowserScheduleWithRunLoop(browser, CFRunLoopGetMain(), kCFRunLoopDefaultMode);
Boolean status;
CFStreamError error;
status = CFNetServiceBrowserSearchForServices(
browser,
(__bridge CFStringRef)self.domain,
(__bridge CFStringRef)self.type,
&error);
if (status == 0)
{
NSLog(@"error.error == %d\n", (int)error.error);
[self stopBrowser];
}
}
static void resolveCallBack(
CFNetServiceRef theService,
CFStreamError* theError,
void* theInfo)
{
NSLog(@"resolveCallback");
if (theError->error == 0)
{
[(__bridge FindServices*)theInfo resolved:theService];
}
else
{
[(__bridge FindServices*)theInfo resolveFailed:theService withError:theError];
}
}
- (void)serviceFound:(CFNetServiceRef)theService
{
[self log:@"service found: %@.%@%@" service:theService];
CFNetServiceClientContext context;
memset(&context, 0, sizeof(context));
context.info = (__bridge void *)(self);
CFNetServiceSetClient(theService, resolveCallBack, &context);
CFNetServiceScheduleWithRunLoop(theService, CFRunLoopGetMain(), kCFRunLoopDefaultMode);
Boolean status;
CFStreamError error;
status = CFNetServiceResolveWithTimeout(theService, 0.0, &error);
if (status == 0)
{
NSLog(@"error.error == %d\n", (int)error.error);
[self stopService:theService];
}
}
- (void)serviceLost:(CFNetServiceRef)theService
{
[self log: @"service lost: %@.%@%@" service:theService];
NSString* name = [NSString stringWithFormat:
@"%@.%@%@",
CFNetServiceGetName(
theService),
CFNetServiceGetType(
theService),
CFNetServiceGetDomain(
theService)];
Service* service = [self.services objectForKey:name];
if (service != nil)
{
[service lost];
[self.services removeObjectForKey:name];
[self.delegate findServices:self didLoseService:service];
}
else
{
[self log: @"service lost but was not found: %@.%@%@" service:theService];
}
}
- (void)resolved:(CFNetServiceRef)theService
{
[self log:@"service resolved: %@.%@%@" service:theService];
CFArrayRef addresses = CFNetServiceGetAddressing(theService);
if (CFArrayGetCount(addresses) != 0)
{
Service* service = [[Service alloc] init:theService];
[self.services setObject:service forKey:service.name];
[self.delegate findServices:self didFindService:service];
}
else
{
NSLog(@"service has 0 addresses: lost ?");
}
}
- (void)resolveFailed:(CFNetServiceRef)theService withError:(CFStreamError *)theError
{
[self log:@"service resolvedFailed: %@.%@%@" service:theService];
[self stopService:theService];
}
- (void)stopBrowser
{
CFNetServiceBrowserUnscheduleFromRunLoop(browser, CFRunLoopGetMain(), kCFRunLoopDefaultMode);
CFNetServiceBrowserInvalidate(browser);
CFNetServiceBrowserStopSearch(browser, NULL);
}
- (void)stopService:(CFNetServiceRef)theService
{
CFNetServiceClientContext context;
memset(&context, 0, sizeof(context));
CFNetServiceUnscheduleFromRunLoop(theService, CFRunLoopGetMain(), kCFRunLoopDefaultMode);
CFNetServiceSetClient(theService, NULL, &context);
CFNetServiceCancel(theService);
}
- (void)log:(NSString*)theMessage service:(CFNetServiceRef)theService
{
NSLog(
theMessage,
CFNetServiceGetName(
theService),
CFNetServiceGetType(
theService),
CFNetServiceGetDomain(
theService));
}
@end7.0 Examples
In each case FindServices is looking for services of type
"_ipp._tcp."in the domain
"local."
In each case the log output is from FindServices and its delegate running on an iPad running iOS 7.0.
7.1 A Single IPPServer
A single instance of the CUPS test server IPPServer with the name ipp_server_1 running on a Mac and then being stopped.
...
2013-11-14 14:07:07.561 XperTakeTwo[665:60b] browserCallBack
2013-11-14 14:07:07.564 XperTakeTwo[665:60b] service found: ipp_server_1._ipp._tcp.local.
2013-11-14 14:07:07.593 XperTakeTwo[665:60b] resolveCallback
2013-11-14 14:07:07.595 XperTakeTwo[665:60b] service resolved: ipp_server_1._ipp._tcp.local.
2013-11-14 14:07:07.597 XperTakeTwo[665:60b] findServices:didFindService:<Service: 0x14e86990>
2013-11-14 14:07:13.931 XperTakeTwo[665:60b] browserCallBack
2013-11-14 14:07:13.933 XperTakeTwo[665:60b] service lost: ipp_server_1._ipp._tcp.local.
2013-11-14 14:07:13.935 XperTakeTwo[665:60b] findServices:didLoseService::<Service: 0x14e86990>
...7.2 A Single Printer
A printer being turned on and then turned a couple of minutes later.
Note the lines shown in bold for emphasis.
When the printer is turned off the resolveCallback function is being called for a second time but this time the CFNetService has no addresses.
This is the same thing that happened in this case when using the NSNetServiceBrowser/NSNetService API. (see here)
...
2013-11-14 14:07:55.177 XperTakeTwo[671:60b] browserCallBack
2013-11-14 14:07:55.180 XperTakeTwo[671:60b] service found: Canon MG6200 series._ipp._tcp.local.
2013-11-14 14:07:55.250 XperTakeTwo[671:60b] resolveCallback
2013-11-14 14:07:55.252 XperTakeTwo[671:60b] service resolved: Canon MG6200 series._ipp._tcp.local.
2013-11-14 14:07:55.255 XperTakeTwo[671:60b] findServices:didFindService:<Service: 0x1452e060>
2013-11-14 14:09:05.838 XperTakeTwo[671:60b] resolveCallback
2013-11-14 14:09:05.840 XperTakeTwo[671:60b] service resolved: Canon MG6200 series._ipp._tcp.local.
2013-11-14 14:09:05.843 XperTakeTwo[671:60b] service has 0 addresses: lost ?
2013-11-14 14:09:06.910 XperTakeTwo[671:60b] browserCallBack
2013-11-14 14:09:06.912 XperTakeTwo[671:60b] service lost: Canon MG6200 series._ipp._tcp.local.
2013-11-14 14:09:06.915 XperTakeTwo[671:60b] findServices:didLoseService::<Service: 0x1452e060>
...Copyright (c) 2013 By Simon Lewis. All Rights Reserved.
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