SCNetworkReachability Reference

Overview

The SCNetworkReachability programming interface allows an application to determine the status of a system's current network configuration and the reachability of a target host. A remote host is considered reachable when a data packet, sent by an application into the network stack, can leave the local device. Reachability does not guarantee that the data packet will actually be received by the host.

The SCNetworkReachability programming interface supports a synchronous and an asynchronous model. In the synchronous model, you get the reachability status by calling the SCNetworkReachabilityGetFlags function. In the asynchronous model, you can schedule the SCNetworkReachability object on the run loop of a client object’s thread. The client implements a callback function to receive notifications when the reachability status of a given remote host changes. Note that these functions follow Core Foundation naming conventions. A function that has "Create" or "Copy" in its name returns a reference you must release with the CFRelease function.

For information about detecting and interpreting errors generated by calling these functions, see System Configuration Reference.

Functions by Task

Creating a Reachability Reference

• SCNetworkReachabilityCreateWithAddress
• SCNetworkReachabilityCreateWithAddressPair
• SCNetworkReachabilityCreateWithName

Determining Reachability Status

• SCNetworkReachabilityGetFlags

Preparing to Determine Reachability

• SCNetworkReachabilityGetTypeID
• SCNetworkReachabilitySetCallback
• SCNetworkReachabilityScheduleWithRunLoop
• SCNetworkReachabilityUnscheduleFromRunLoop
• SCNetworkReachabilitySetDispatchQueue

Functions

SCNetworkReachabilityCreateWithAddress

Creates a reachability reference to the specified network address.

SCNetworkReachabilityRef SCNetworkReachabilityCreateWithAddress (
   CFAllocatorRef allocator,
   const struct sockaddr *address
);

SCNetworkReachabilityCreateWithAddressPair

Creates a reachability reference to the specified network address.

SCNetworkReachabilityRef SCNetworkReachabilityCreateWithAddressPair (
   CFAllocatorRef allocator,
   const struct sockaddr *localAddress,
   const struct sockaddr *remoteAddress
);

SCNetworkReachabilityCreateWithName

Creates a reachability reference to the specified network host or node name.

SCNetworkReachabilityRef SCNetworkReachabilityCreateWithName (
   CFAllocatorRef allocator,
   const char *nodename
);

SCNetworkReachabilityGetFlags

Determines if the specified network target is reachable using the current network configuration.

Boolean SCNetworkReachabilityGetFlags (
   SCNetworkReachabilityRef target,
   SCNetworkReachabilityFlags *flags
);

SCNetworkReachabilityGetTypeID

Returns the type identifier of all SCNetworkReachability instances.

CFTypeID SCNetworkReachabilityGetTypeID (
   void
);

SCNetworkReachabilityScheduleWithRunLoop

Schedules the specified network target with the specified run loop and mode.

Boolean SCNetworkReachabilityScheduleWithRunLoop (
   SCNetworkReachabilityRef target,
   CFRunLoopRef runLoop,
   CFStringRef runLoopMode
);

SCNetworkReachabilitySetCallback

Assigns a client to the specified target, which receives callbacks when the reachability of the target changes.

Boolean SCNetworkReachabilitySetCallback (
   SCNetworkReachabilityRef target,
   SCNetworkReachabilityCallBack callout,
   SCNetworkReachabilityContext *context
);

SCNetworkReachabilitySetDispatchQueue

Schedules callbacks for the specified target on the specified dispatch queue.

Boolean SCNetworkReachabilitySetDispatchQueue (
   SCNetworkReachabilityRef target,
   dispatch_queue_t queue
);

SCNetworkReachabilityUnscheduleFromRunLoop

Unschedules the specified target from the specified run loop and mode.

Boolean SCNetworkReachabilityUnscheduleFromRunLoop (
   SCNetworkReachabilityRef target,
   CFRunLoopRef runLoop,
   CFStringRef runLoopMode
);

Callbacks

SCNetworkReachabilityCallBack

Type of callback function used when the reachability of a network address or name changes.

typedef void (*SCNetworkReachabilityCallBack)    (
   SCNetworkReachabilityRef target,
   SCNetworkReachabilityFlags flags,
   void *info
);

If you name your function MyNetworkReachabilityCallBack, you would declare it like this:

void MyNetworkReachabilityCallBack(
   SCNetworkReachabilityRef target,
   SCNetworkReachabilityFlags flags,
   void *info
);

Data Types

SCNetworkReachabilityRef

The handle to a network address or name.

typedef const struct __SCNetworkReachability * SCNetworkReachabilityRef;

SCNetworkReachabilityContext

Structure containing user-specified data and callbacks used with SCNetworkReachabilitySetCallback.

typedef struct {
      CFIndex version;
      void * info;
      const void *(*retain)(const void *info);
      void (*release)(const void *info);
      CFStringRef (*copyDescription)(const void *info);
} SCNetworkReachabilityContext;

Fields

version

The version number of the structure type being passed in as a parameter to an SCDynamicStore creation function. This structure is version 0.

info

A C pointer to a user-specified block of data.

retain

The callback used to add a retain for the info field. If this parameter is not a pointer to a function of the correct prototype, the behavior is undefined. The value can be NULL.

release

The callback used to remove a retain previously added for the info field. If this parameter is not a pointer to a function of the correct prototype, the behavior is undefined. The value can be NULL.

copyDescription

The callback used to provide a description of the info field.

Constants

Network Reachability Flags

Flags that indicate the reachability of a network node name or address, including whether a connection is required, and whether some user intervention might be required when establishing a connection.

enum {
   kSCNetworkReachabilityFlagsTransientConnection = 1<<0,
   kSCNetworkReachabilityFlagsReachable = 1<<1,
   kSCNetworkReachabilityFlagsConnectionRequired = 1<<2,
   kSCNetworkReachabilityFlagsConnectionOnTraffic = 1<<3,
   kSCNetworkReachabilityFlagsInterventionRequired = 1<<4,
   kSCNetworkReachabilityFlagsConnectionOnDemand = 1<<5,
   kSCNetworkReachabilityFlagsIsLocalAddress = 1<<16,
   kSCNetworkReachabilityFlagsIsDirect = 1<<17,
   kSCNetworkReachabilityFlagsIsWWAN = 1<<18,
   kSCNetworkReachabilityFlagsConnectionAutomatic    = kSCNetworkReachabilityFlagsConnectionOnTraffic
};
typedef    uint32_t    SCNetworkReachabilityFlags;

Constants

kSCNetworkReachabilityFlagsTransientConnection

The specified node name or address can be reached via a transient connection, such as PPP.

Available in iOS 2.0 and later.

Declared in SCNetworkReachability.h.

kSCNetworkReachabilityFlagsReachable

The specified node name or address can be reached using the current network configuration.

Available in iOS 2.0 and later.

Declared in SCNetworkReachability.h.

kSCNetworkReachabilityFlagsConnectionRequired

The specified node name or address can be reached using the current network configuration, but a connection must first be established. If this flag is set, the kSCNetworkReachabilityFlagsConnectionOnTraffic flag, kSCNetworkReachabilityFlagsConnectionOnDemand flag, or kSCNetworkReachabilityFlagsIsWWAN flag is also typically set to indicate the type of connection required. If the user must manually make the connection, the kSCNetworkReachabilityFlagsInterventionRequired flag is also set.

Available in iOS 2.0 and later.

Declared in SCNetworkReachability.h.

kSCNetworkReachabilityFlagsConnectionOnTraffic

The specified node name or address can be reached using the current network configuration, but a connection must first be established. Any traffic directed to the specified name or address will initiate the connection.

This flag was previously named kSCNetworkReachabilityFlagsConnectionAutomatic.

Available in iOS 3.0 and later.

Declared in SCNetworkReachability.h.

kSCNetworkReachabilityFlagsInterventionRequired

The specified node name or address can be reached using the current network configuration, but a connection must first be established.

In addition, some form of user intervention will be required to establish this connection, such as providing a password, an authentication token, etc.

Currently, this flag is returned only when there is a dial-on-traffic configuration (kSCNetworkReachabilityFlagsConnectionOnTraffic), an attempt to connect has already been made, and when some error (such as no dial tone, no answer, bad password, etc.) occurred during the automatic connection attempt. In this case the PPP controller stops attempting to establish a connection until the user has intervened.

Available in iOS 2.0 and later.

Declared in SCNetworkReachability.h.

kSCNetworkReachabilityFlagsConnectionOnDemand

The specified node name or address can be reached using the current network configuration, but a connection must first be established. The connection will be established "On Demand" by the CFSocketStream programming interface (see CFStream Socket Additions for information on this). Other functions will not establish the connection.

Available in iOS 3.0 and later.

Declared in SCNetworkReachability.h.

kSCNetworkReachabilityFlagsIsLocalAddress

The specified node name or address is one that is associated with a network interface on the current system.

Available in iOS 2.0 and later.

Declared in SCNetworkReachability.h.

kSCNetworkReachabilityFlagsIsDirect

Network traffic to the specified node name or address will not go through a gateway, but is routed directly to one of the interfaces in the system.

Available in iOS 2.0 and later.

Declared in SCNetworkReachability.h.

kSCNetworkReachabilityFlagsIsWWAN

The specified node name or address can be reached via a cellular connection, such as EDGE or GPRS.

Important: This absence of this flag does not necessarily mean that a connection will never pass over a cellular network. If you need to robustly prevent cellular networking, read “Networking Tips and Pitfalls” in Networking Overview.

Available in iOS 2.0 and later.

Declared in SCNetworkReachability.h.

kSCNetworkReachabilityFlagsConnectionAutomatic

The specified node name or address can be reached using the current network configuration, but a connection must first be established. Any traffic directed to the specified name or address will initiate the connection. This flag is a synonym for kSCNetworkReachabilityFlagsConnectionOnTraffic.

Available in iOS 2.0 and later.

Declared in SCNetworkReachability.h.