Technical Q&A QA1652

Using NSStreams For A TCP Connection Without NSHost

Q:  Given that +getStreamsToHost:port:inputStream:outputStream: is not supported on iOS, how can I create NSStreams for a TCP connection to a named host?

A: You can do this by exploiting the toll-free bridge between NSStream and CFStream. Use CFStreamCreatePairWithSocketToHost to create CFStreams to the host, and then cast the resulting CFStreams to NSStreams.

Listing 1 shows an example of this. It adds a category to NSStream that implements a replacement for +getStreamsToHost:port:inputStream:outputStream:.

Listing 1  A category to create TCP streams to a named host

@interface NSStream (QNetworkAdditions)
 
+ (void)qNetworkAdditions_getStreamsToHostNamed:(NSString *)hostName
    port:(NSInteger)port
    inputStream:(out NSInputStream **)inputStreamPtr
    outputStream:(out NSOutputStream **)outputStreamPtr;
 
@end
 
@implementation NSStream (QNetworkAdditions)
 
+ (void)qNetworkAdditions_getStreamsToHostNamed:(NSString *)hostName
    port:(NSInteger)port
    inputStream:(out NSInputStream **)inputStreamPtr
    outputStream:(out NSOutputStream **)outputStreamPtr
{
    CFReadStreamRef     readStream;
    CFWriteStreamRef    writeStream;
 
    assert(hostName != nil);
    assert( (port > 0) && (port < 65536) );
    assert( (inputStreamPtr != NULL) || (outputStreamPtr != NULL) );
 
    readStream = NULL;
    writeStream = NULL;
 
    CFStreamCreatePairWithSocketToHost(
        NULL,
        (__bridge CFStringRef) hostName,
        port,
        ((inputStreamPtr  != NULL) ? &readStream : NULL),
        ((outputStreamPtr != NULL) ? &writeStream : NULL)
    );
 
    if (inputStreamPtr != NULL) {
        *inputStreamPtr  = CFBridgingRelease(readStream);
    }
    if (outputStreamPtr != NULL) {
        *outputStreamPtr = CFBridgingRelease(writeStream);
    }
}
 
@end

Document Revision History


DateNotes
2012-03-27

Fixed a typo (r. 11064426).

2011-10-19

Updated the code to support automatic reference counting (ARC).

2009-06-23

New document that describes how to create TCP NSStreams without NSHost (which is not supported on iOS).




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