Read Me About CFHostSample |
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2.0 |
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CFHostSample shows how to use the CFHost API to do asynchronous DNS name-to-address and address-to-name translation. |
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CFHostSample requires Mac OS X 10.7 or later. Additionally, the core code works unmodified on iOS 5.0 or later. |
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Note: The core concepts should work on any version of iOS and Mac OS X 10.3 or later (where CFHost was introduced), but supporting older platforms will require some tweaks (for example, switching from "weak" references to "unsafe_unretained" references, adding explicit ivars to support the old runtime, and so on). |
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Before You Start |
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CFHost is only necessary if you have specialist DNS needs, for example, if you want to map all of the addresses in a log file to their host names. If you just want to connect to a DNS name, it's both easier and better to use a connect-by-name API, that is, an API that takes a DNS name and does the resolution on your behalf. For example: |
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o +[NSHost +getStreamsToHost:port:inputStream:outputStream:] on Mac OS X |
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o CFStreamCreatePairWithSocketToHost on iOS, as shown in QA1652 "Using NSStreams For A TCP Connection Without NSHost" |
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</RU/iOS/#qa/qa1652/_index.html> |
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Packing List |
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The sample contains the following items: |
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o Read Me About CFHostSample.txt -- This document. |
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o CFHostSample.xcodeproj -- An Xcode project to build the code. |
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o CFHostSample -- A directory containing the code. |
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o build -- A directory containing a pre-built binary. |
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Within the "CFHostSample" directory you'll find: |
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o main.m -- A command line tool that exercises the core code. |
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o QCFHostResolver.[hm] -- The core code. |
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Using the Sample |
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The sample supports two functions. To test name-to-address mapping, run the tool with the "-h" option: |
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$ build/Debug/CFHostSample -h apple.com |
apple.com -> 17.172.224.47, 17.149.160.49 |
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To test address-to-name mapping, run the tool with the "-a" option: |
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$ build/Debug/CFHostSample -a 17.172.224.47 |
17.172.224.47 -> apple.com |
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Building the Sample |
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The sample was built using Xcode 4.3.1 on Mac OS X 10.7.3 with the Mac OS X 10.7 SDK. You should be able to just open the project and choose Build from the Product menu. |
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How It Works |
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The main program is a simple command line tool that accepts parameters, creates QCFHostResolver objects, runs them, and prints the results. |
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QCFHostResolver is an Objective-C wrapper around CFHost; read the comments in "QCFHostResolver.h" for more information on how to use it, and the comments in "QCFHostResolver.m" for more information on how it works. |
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QCFHostResolver builds and works on iOS 5.0 and later. |
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Caveats |
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The previous version of the sample let you do reachability tests using kCFHostReachability. This is a rarely used feature of CFHost, and something generally better done with the SCNetworkReachability API, and so it's been removed from the sample. |
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The bug referenced by the previous version of this sample, <rdar://problem/3612320>, which caused CFHost to fail if you did a reachability query using an address rather than a name, was fixed in Mac OS X 10.4. |
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Credits and Version History |
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If you find any problems with this sample, please file a bug against it. |
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<http://developer.apple.com/bugreporter/> |
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1.0 (Apr 2004) was the first shipping version. |
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2.0 (Mar 2012) was a major rewrite to use the latest tools and techniques. |
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Share and Enjoy |
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Apple Developer Technical Support |
Core OS/Hardware |
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23 Mar 2012 |
