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NSStream Class Reference

Overview

NSStream is an abstract class for objects representing streams. Its interface is common to all Cocoa stream classes, including its concrete subclasses NSInputStream and NSOutputStream.

NSStream objects provide an easy way to read and write data to and from a variety of media in a device-independent way. You can create stream objects for data located in memory, in a file, or on a network (using sockets), and you can use stream objects without loading all of the data into memory at once.

By default, NSStream instances that are not file-based are non-seekable, one-way streams (although custom seekable subclasses are possible). Once the data has been provided or consumed, the data cannot be retrieved from the stream.

Subclassing Notes

NSStream is an abstract class, incapable of instantiation and intended to be subclassed. It publishes a programmatic interface that all subclasses must adopt and provide implementations for. The two Apple-provided concrete subclasses of NSStream, NSInputStream and NSOutputStream, are suitable for most purposes. However, there might be situations when you want a peer subclass to NSInputStream and NSOutputStream. For example, you might want a class that implements a full-duplex (two-way) stream, or a class whose instances are capable of seeking through a stream.

Methods to Override

All subclasses must fully implement the following methods, which are presented in functional pairs:

• open and close

  Implement open to open the stream for reading or writing and make the stream available to the client directly or, if the stream object is scheduled on a run loop, to the delegate. Implement close to close the stream and remove the stream object from the run loop, if necessary. A closed stream should still be able to accept new properties and report its current properties. Once a stream is closed, it cannot be reopened.

• delegate and setDelegate:

  Return and set the delegate. By a default, a stream object must be its own delegate; so a setDelegate: message with an argument of nil should restore this delegate. Do not retain the delegate to prevent retain cycles.

  To learn about delegates and delegation, read "Delegates and Data Sources" in Cocoa Fundamentals Guide.

• scheduleInRunLoop:forMode: and removeFromRunLoop:forMode:

  Implement scheduleInRunLoop:forMode: to schedule the stream object on the specified run loop for the specified mode. Implement removeFromRunLoop:forMode: to remove the object from the run loop. See the documentation of the NSRunLoop class for details. Once the stream object for an open stream is scheduled on a run loop, it is the responsibility of the subclass as it processes stream data to send stream:handleEvent: messages to its delegate.

• propertyForKey: and setProperty:forKey:

  Implement these methods to return and set, respectively, the property value for the specified key. You may add custom properties, but be sure to handle all properties defined by NSStream as well.

• streamStatus and streamError

  Implement streamStatus to return the current status of the stream as a NSStreamStatus constant; you may define new NSStreamStatus constants, but be sure to handle the NSStream-defined constants properly. ImplementstreamError to return an NSError object representing the current error. You might decide to return a custom NSError object that can provide complete and localized information about the error.

Tasks

Creating Streams

• + getStreamsToHost:port:inputStream:outputStream:

Configuring Streams

• – propertyForKey:
• – setProperty:forKey:
• – delegate
• – setDelegate:

Using Streams

• – open
• – close
• – stream:handleEvent:  delegate method

Managing Run Loops

• – scheduleInRunLoop:forMode:
• – removeFromRunLoop:forMode:

Getting Stream Information

• – streamStatus
• – streamError

Class Methods

getStreamsToHost:port:inputStream:outputStream:

Creates and returns by reference an NSInputStream object and NSOutputStream object for a socket connection with a given host on a given port.

+ (void)getStreamsToHost:(NSHost *)host port:(NSInteger)port inputStream:(NSInputStream **)inputStream outputStream:(NSOutputStream **)outputStream

Parameters

host

The host to which to connect.

port

The port to connect to on host.

inputStream

Upon return, contains the input stream. If nil is passed, the stream object is not created.

outputStream

Upon return, contains the output stream. If nil is passed, the stream object is not created.

Discussion

If neither port nor host is properly specified, no socket connection is made.

Availability

• Available in Mac OS X v10.3 and later.

Declared In

NSStream.h

Instance Methods

close

Closes the receiver.

- (void)close

Discussion

Closing the stream terminates the flow of bytes and releases system resources that were reserved for the stream when it was opened. If the stream has been scheduled on a run loop, closing the stream implicitly removes the stream from the run loop. A stream that is closed can still be queried for its properties.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – open

Declared In

NSStream.h

delegate

Returns the receiver’s delegate.

- (id)delegate

Return Value

The receiver’s delegate.

Discussion

By default, a stream is its own delegate, and subclasses of NSInputStream and NSOutputStream must maintain this contract.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – setDelegate:

Declared In

NSStream.h

open

Opens the receiving stream.

- (void)open

Discussion

A stream must be created before it can be opened. Once opened, a stream cannot be closed and reopened.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – close

Declared In

NSStream.h

propertyForKey:

Returns the receiver’s property for a given key.

- (id)propertyForKey:(NSString *)key

Parameters

key

The key for one of the receiver's properties. See “Constants” for a description of the available property-key constants and associated values.

Return Value

The receiver’s property for the key key.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – setProperty:forKey:

Declared In

NSStream.h

removeFromRunLoop:forMode:

Removes the receiver from a given run loop running in a given mode.

- (void)removeFromRunLoop:(NSRunLoop *)aRunLoop forMode:(NSString *)mode

Parameters

aRunLoop

The run loop on which the receiver was scheduled.

mode

The mode for the run loop.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – scheduleInRunLoop:forMode:

Declared In

NSStream.h

scheduleInRunLoop:forMode:

Schedules the receiver on a given run loop in a given mode.

- (void)scheduleInRunLoop:(NSRunLoop *)aRunLoop forMode:(NSString *)mode

Parameters

aRunLoop

The run loop on which to schedule the receiver.

mode

The mode for the run loop.

Discussion

Unless the client is polling the stream, it is responsible for ensuring that the stream is scheduled on at least one run loop and that at least one of the run loops on which the stream is scheduled is being run.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – removeFromRunLoop:forMode:

Declared In

NSStream.h

setDelegate:

Sets the receiver’s delegate.

- (void)setDelegate:(id)delegate

Parameters

delegate

The delegate for the receiver.

Discussion

By default, a stream is its own delegate, and subclasses of NSInputStream and NSOutputStream must maintain this contract. If you override this method in a subclass, passing nil must restore the receiver as its own delegate. Delegates are not retained.

To learn about delegates and delegation, read "Delegates and Data Sources" in Cocoa Fundamentals Guide.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – delegate

Declared In

NSStream.h

setProperty:forKey:

Attempts to set the value of a given property of the receiver and returns a Boolean value that indicates whether the value is accepted by the receiver.

- (BOOL)setProperty:(id)property forKey:(NSString *)key

Parameters

property

The value for key.

key

The key for one of the receiver's properties. See “Constants” for a description of the available property-key constants and expected values.

Return Value

YES if the value is accepted by the receiver, otherwise NO.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – propertyForKey:

Declared In

NSStream.h

streamError

Returns an NSError object representing the stream error.

- (NSError *)streamError

Return Value

An NSError object representing the stream error, or nil if no error has been encountered.

Availability

• Available in Mac OS X v10.3 and later.

Declared In

NSStream.h

streamStatus

Returns the receiver’s status.

- (NSStreamStatus)streamStatus

Return Value

The receiver’s status.

Discussion

See “Constants” for a description of the available NSStreamStatus constants.

Availability

• Available in Mac OS X v10.3 and later.

Declared In

NSStream.h

Delegate Methods

stream:handleEvent:

The delegate receives this message when a given event has occurred on a given stream.

- (void)stream:(NSStream *)theStream handleEvent:(NSStreamEvent)streamEvent

Parameters

theStream

The stream on which streamEvent occurred.

streamEvent

The stream event that occurred,

Discussion

The delegate receives this message only if theStream is scheduled on a run loop. The message is sent on the stream object’s thread. The delegate should examine streamEvent to determine the appropriate action it should take.

Availability

• Available in Mac OS X v10.3 and later.

Declared In

NSStream.h

Constants

NSStreamStatus

The type declared for the constants listed in “Stream Status Constants.”

typedef NSUInteger NSStreamStatus;

Availability

• Available in Mac OS X v10.3 and later.

Declared In

NSStream.h

Stream Status Constants

These constants indicate the current status of a stream. They are returned by streamStatus.

typedef enum {
   NSStreamStatusNotOpen = 0,
   NSStreamStatusOpening = 1,
   NSStreamStatusOpen = 2,
   NSStreamStatusReading = 3,
   NSStreamStatusWriting = 4,
   NSStreamStatusAtEnd = 5,
   NSStreamStatusClosed = 6,
   NSStreamStatusError = 7
};

Constants

NSStreamStatusNotOpen

The stream is not open for reading or writing. This status is returned before the underlying call to open a stream but after it’s been created.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamStatusOpening

The stream is in the process of being opened for reading or for writing. For network streams, this status might include the time after the stream was opened, but while network DNS resolution is happening.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamStatusOpen

The stream is open, but no reading or writing is occurring.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamStatusReading

Data is being read from the stream. This status would be returned if code on another thread were to call streamStatus on the stream while a read:maxLength: call (NSInputStream) was in progress.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamStatusWriting

Data is being written to the stream. This status would be returned if code on another thread were to call streamStatus on the stream while a write:maxLength: call (NSOutputStream) was in progress.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamStatusAtEnd

There is no more data to read, or no more data can be written to the stream. When this status is returned, the stream is in a “non-blocking” mode and no data are available.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamStatusClosed

The stream is closed (close has been called on it).

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamStatusError

The remote end of the connection can’t be contacted, or the connection has been severed for some other reason.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

Declared In

NSStream.h

NSStreamEvent

The type declared for the constants listed in “Stream Event Constants.”

typedef NSUInteger NSStreamEvent;

Availability

• Available in Mac OS X v10.3 and later.

Declared In

NSStream.h

Stream Event Constants

One or more of these constants may be sent to the delegate as a bit field in the second parameter of stream:handleEvent:.

typedef enum {
   NSStreamEventNone = 0,
   NSStreamEventOpenCompleted = 1 << 0,
   NSStreamEventHasBytesAvailable = 1 << 1,
   NSStreamEventHasSpaceAvailable = 1 << 2,
   NSStreamEventErrorOccurred = 1 << 3,
   NSStreamEventEndEncountered = 1 << 4
};

Constants

NSStreamEventNone

No event has occurred.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamEventOpenCompleted

The open has completed successfully.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamEventHasBytesAvailable

The stream has bytes to be read.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamEventHasSpaceAvailable

The stream can accept bytes for writing.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamEventErrorOccurred

An error has occurred on the stream.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamEventEndEncountered

The end of the stream has been reached.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

Declared In

NSStream.h

NSStream Property Keys

NSStream defines these string constants as keys for accessing stream properties using propertyForKey: and setting properties with setProperty:forKey::

extern NSString * const NSStreamSocketSecurityLevelKey  ;
extern NSString * const NSStreamSocketSecurityLevelNone ;
extern NSString * const NSStreamSocketSecurityLevelSSLv2 ;
extern NSString * const NSStreamSocketSecurityLevelSSLv3 ;
extern NSString * const NSStreamSocketSecurityLevelTLSv1 ;
extern NSString * const NSStreamSocketSecurityLevelNegotiatedSSL;
extern NSString * const NSStreamSOCKSProxyConfigurationKey  ;
extern NSString * const NSStreamSOCKSProxyHostKey  ;
extern NSString * const NSStreamSOCKSProxyPortKey  ;
extern NSString * const NSStreamSOCKSProxyVersionKey  ;
extern NSString * const NSStreamSOCKSProxyUserKey  ;
extern NSString * const NSStreamSOCKSProxyPasswordKey ;
extern NSString * const NSStreamSOCKSProxyVersion4  ;
extern NSString * const NSStreamSOCKSProxyVersion5  ;
extern NSString * const NSStreamDataWrittenToMemoryStreamKey ;
extern NSString * const NSStreamFileCurrentOffsetKey  ;

Constants

NSStreamSocketSecurityLevelKey

The security level of the target stream. May be one of the following values: NSStreamSocketSecurityLevelNone, NSStreamSocketSecurityLevelSSLv2, NSStreamSocketSecurityLevelSSLv3, NSStreamSocketSecurityLevelTLSv1, or NSStreamSocketSecurityLevelNegotiatedSSL.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSOCKSProxyConfigurationKey

Value is an NSDictionary object containing SOCKS proxy configuration information.

The dictionary returned from the System Configuration framework for SOCKS proxies usually suffices.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamDataWrittenToMemoryStreamKey

Value is an NSData instance containing the data written to a memory stream.

Use this property when you have an output-stream object instantiated to collect written data in memory. The value of this property is read-only.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamFileCurrentOffsetKey

Value is an NSNumber object containing the current absolute offset of the stream.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

Declared In

NSStream.h

NSStream Error Domains

NSStream defines these string constants to represent error domains that can be returned by streamError:

extern NSString * const NSStreamSocketSSLErrorDomain  ;
extern NSString * const NSStreamSOCKSErrorDomain  ;

Constants

NSStreamSocketSSLErrorDomain

The error domain used by NSError when reporting SSL errors.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSOCKSErrorDomain

The error domain used by NSError when reporting SOCKS errors.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

Declared In

NSStream.h

Secure-Socket Layer (SSL) Security Level

NSStream defines these string constants for specifying the secure-socket layer (SSL) security level.

NSString * const NSStreamSocketSecurityLevelNone;
NSString * const NSStreamSocketSecurityLevelSSLv2;
NSString * const NSStreamSocketSecurityLevelSSLv3;
NSString * const NSStreamSocketSecurityLevelTLSv1;
NSString * const NSStreamSocketSecurityLevelNegotiatedSSL

Constants

NSStreamSocketSecurityLevelNone

Specifies that no security level be set for a socket stream.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSocketSecurityLevelSSLv2

Specifies that SSL version 2 be set as the security protocol for a socket stream.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSocketSecurityLevelSSLv3

Specifies that SSL version 3 be set as the security protocol for a socket stream.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSocketSecurityLevelTLSv1

Specifies that TLS version 1 be set as the security protocol for a socket stream.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSocketSecurityLevelNegotiatedSSL

Specifies that the highest level security protocol that can be negotiated be set as the security protocol for a socket stream.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

Discussion

You access and set these values using the NSStreamSocketSecurityLevelKey property key.

Declared In

NSStream.h

SOCKS Proxy Configuration Values

NSStream defines these string constants for use as keys to specify SOCKS proxy configuration values in an NSDictionary object.

NSString * const NSStreamSOCKSProxyHostKey;
NSString * const NSStreamSOCKSProxyPortKey;
NSString * const NSStreamSOCKSProxyVersionKey;
NSString * const NSStreamSOCKSProxyUserKey;
NSString * const NSStreamSOCKSProxyPasswordKey;
NSString * const NSStreamSOCKSProxyVersion4;
NSString * const NSStreamSOCKSProxyVersion5

Constants

NSStreamSOCKSProxyHostKey

Value is an NSString object that represents the SOCKS proxy host.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSOCKSProxyPortKey

Value is an NSNumber object containing an integer that represents the port on which the proxy listens.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSOCKSProxyVersionKey

Value is either NSStreamSOCKSProxyVersion4 or NSStreamSOCKSProxyVersion5.

If this key is not present, NSStreamSOCKSProxyVersion5 is used by default.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSOCKSProxyUserKey

Value is an NSString object containing the user’s name.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSOCKSProxyPasswordKey

Value is an NSString object containing the user’s password.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSOCKSProxyVersion4

Possible value for NSStreamSOCKSProxyVersionKey.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

NSStreamSOCKSProxyVersion5

Possible value for NSStreamSOCKSProxyVersionKey.

Available in Mac OS X v10.3 and later.

Declared in NSStream.h.

Discussion

You set the dictionary object as the current SOCKS proxy configuration using the NSStreamSOCKSProxyConfigurationKey key

Declared In

NSStream.h

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