[深入浅出Cocoa]iOS网络编程之CFNe…

最新推荐文章于 2016-11-30 16:10:08 发布

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最新推荐文章于 2016-11-30 16:10:08 发布

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分类专栏： IOS基础

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本文详细介绍CFNetwork的基础概念及使用方法，包括如何利用CFReadStream进行网络数据读取，并结合run-loop处理网络事件。

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一，CFNetwork 简介

首先来回顾下。在前文《[深入浅出Cocoa]iOS网络编程之Socket》中，提到iOS网络编程层次模型分为三层：

Cocoa层：NSURL，Bonjour，Game Kit，WebKit
Core Foundation层：基于 C 的 CFNetwork 和 CFNetServices
OS层:基于 C 的 BSD socket

前文讲的是最底层的 socket，本文将介绍位于 Core Foundation 中的 CFNetwork。CFNetwork 只是对 BSD socket 的进行了轻量级的封装，但在 iOS 中使用 CFNetwork 有一个显著的好处，那就是 CFNetwork 与系统级别的设置（如：天线设置）以及 run-loop 结合得很好。每一个线程都有自己的 run-loop，因此我们可以 CFNetwork 当中事件源加入到 run-loop 中，这样就可以在线程的 run-loop 中处理网络事件了。 BTW，大名鼎鼎的 ASIHttpRequest 库就是基于 CFNetwork 封装的。

本文示例代码就是这样做的，源码请查看：

https://github.com/kesalin/iOSSnippet/tree/master/KSNetworkDemo

二，CFNetwork API 简介

CFNetwork 接口是基于 C 的，下面的接口用于创建一对 socket stream，一个用于读取，一个用于写入：

void CFStreamCreatePairWithSocketToHost(CFAllocatorRef alloc, CFStringRef host, UInt32 port, CFReadStreamRef *readStream, CFWriteStreamRef *writeStream);

该函数使用 host 以及 port，CFNetwork 会将该 host 转换为 IP 地址，并转换为网络字节顺序。如果我们只需要一个 socket stream，我们可以将另外一个设置为 NULL。还有另外两个“重载”的创建 socket sream的接口：CFStreamCreatePairWithSocket 和 CFStreamCreatePairWithPeerSocketSignature，在这里就不一一介绍了。

注意：在使用这些 socket stream 之前，必须显式地调用其 open 函数：

Boolean CFReadStreamOpen(CFReadStreamRef stream);

Boolean CFWriteStreamOpen(CFWriteStreamRef stream);

但与 socket 不同的是，这两个接口是异步的，当成功 open 之后，如果调用方设置了获取 kCFStreamEventOpenCompleted 事件的标志的话就会其调用回调函数。

而该回调函数及其参数设置是通过如下接口进行的：

Boolean CFReadStreamSetClient(CFReadStreamRef stream, CFOptionFlags streamEvents, CFReadStreamClientCallBa ck clientCB, CFStreamClientContext *clientContext);

Boolean CFWriteStreamSetClient(CFWriteStreamRef stream, CFOptionFlags streamEvents, CFWriteStreamClientCallB ack clientCB, CFStreamClientContext *clientContext);

该函数用于设置回调函数及相关参数。通过 streamEvents 标志来设置我们对哪些事件感兴趣；clientCB 是一个回调函数，当事件标志对应的事件发生时，该回调函数就会被调用；clientContext 是用于传递参数到回调函数中去。

当设置好回调函数之后，我们可以将 socket stream 当做事件源调度到 run-loop 中去，这样 run-loop 就能分发该 socket stream 的网络事件了。

void CFReadStreamScheduleWithRunLoop(CFReadStreamRef stream, CFRunLoopRef runLoop, CFStringRef runLoopMode);

void CFWriteStreamScheduleWithRunLoop(CFWriteStreamRef stream, CFRunLoopRef runLoop, CFStringRef runLoopMode);

注意，在我们不再关心该 socket stream 的网络事件时，记得要调用如下接口将 socket stream 从 run-loop 的事件源中移除。

void CFReadStreamUnscheduleFromRunLoop(CFReadStreamRef stream, CFRunLoopRef runLoop, CFStringRef runLoopMode);

void CFWriteStreamUnscheduleFromRunLoop(CFWriteStreamRef stream, CFRunLoopRef runLoop, CFStringRef runLoopMode);

当我们将 socket stream 的网络事件调度到 run-loop 之后，我们就能在回调函数中相应各种事件，比如 kCFStreamEventHasBytesAvailable 读取数据：

Boolean CFReadStreamHasBytesAvailable(CFReadStreamRef stream);

CFIndex CFReadStreamRead(CFReadStreamRef stream, UInt8 *buffer, CFIndex bufferLength);

或 kCFStreamEventCanAcceptBytes 写入数据：

Boolean CFWriteStreamCanAcceptBytes(CFWriteStreamRef stream);

CFIndex CFWriteStreamWrite(CFWriteStreamRef stream, const UInt8 *buffer, CFIndex bufferLength);

最后，我们调用 close 方法关闭 socket stream：

void CFReadStreamClose(CFReadStreamRef stream);

void CFWriteStreamClose(CFWriteStreamRef stream);

三，客户端示例代码

与 socket 演示类似，在这里我只演示客户端示例。同样，我们也在一个后台线程中启动网络操作：

[html] view plain copy print ?

NSURL * url = [NSURL URLWithString:[NSString stringWithFormat:@"%@:%@", serverHost, serverPort]];
NSThread * backgroundThread = [[NSThread alloc] initWithTarget:self
selector:@selector(loadDataFromServerWithURL:)
object:url];
[backgroundThread start];

    NSURL * url = [NSURL URLWithString:[NSString stringWithFormat:@"%@:%@", serverHost, serverPort]];
    NSThread * backgroundThread = [[NSThread alloc] initWithTarget:self
                                                          selector:@selector(loadDataFromServerWithURL:)
                                                            object:url];
        [backgroundThread start];

然后在 loadDataFromServerWithURL 中创建 socket 流，并设置其回调函数，将其加入到 run-loop 的事件源中，然后启动之：

[cpp] view plain copy print ?

- (void)loadDataFromServerWithURL:(NSURL *)url
{
NSString * host = [url host];
NSInteger port = [[url port] integerValue];
// Keep a reference to self to use for controller callbacks
//
CFStreamClientContext ctx = {0, (__bridge void *)(self), NULL, NULL, NULL};
// Get callbacks for stream data, stream end, and any errors
//
CFOptionFlags registeredEvents = (kCFStreamEventHasBytesAvailable | kCFStreamEventEndEncountered | kCFStreamEventErrorOccurred);
// Create a read-only socket
//
CFReadStreamRef readStream;
CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, (__bridge CFStringRef)host, port, &readStream, NULL);
// Schedule the stream on the run loop to enable callbacks
//
if (CFReadStreamSetClient(readStream, registeredEvents, socketCallback, &ctx)) {
CFReadStreamScheduleWithRunLoop(readStream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
}
else {
[self networkFailedWithErrorMessage:@"Failed to assign callback method"];
return;
}
// Open the stream for reading
//
if (CFReadStreamOpen(readStream) == NO) {
[self networkFailedWithErrorMessage:@"Failed to open read stream"];
return;
}
CFErrorRef error = CFReadStreamCopyError(readStream);
if (error != NULL) {
if (CFErrorGetCode(error) != 0) {
NSString * errorInfo = [NSString stringWithFormat:@"Failed to connect stream; error '%@' (code %ld)", (__bridge NSString*)CFErrorGetDomain(error), CFErrorGetCode(error)];
[self networkFailedWithErrorMessage:errorInfo];
}
CFRelease(error);
return;
}
NSLog(@"Successfully connected to %@", url);
// Start processing
//
CFRunLoopRun();
}

- (void)loadDataFromServerWithURL:(NSURL *)url
{
    NSString * host = [url host];
    NSInteger port = [[url port] integerValue];
    
        // Keep a reference to self to use for controller callbacks
    //
        CFStreamClientContext ctx = {0, (__bridge void *)(self), NULL, NULL, NULL};
        
        // Get callbacks for stream data, stream end, and any errors
    //
        CFOptionFlags registeredEvents = (kCFStreamEventHasBytesAvailable | kCFStreamEventEndEncountered | kCFStreamEventErrorOccurred);
        
        // Create a read-only socket
    //
        CFReadStreamRef readStream;
        CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, (__bridge CFStringRef)host, port, &readStream, NULL);
        
        // Schedule the stream on the run loop to enable callbacks
    //
        if (CFReadStreamSetClient(readStream, registeredEvents, socketCallback, &ctx)) {
                CFReadStreamScheduleWithRunLoop(readStream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
                
        }
    else {
        [self networkFailedWithErrorMessage:@"Failed to assign callback method"];
                return;
        }
        
        // Open the stream for reading
    //
        if (CFReadStreamOpen(readStream) == NO) {
        [self networkFailedWithErrorMessage:@"Failed to open read stream"];
                
                return;
        }
        
        CFErrorRef error = CFReadStreamCopyError(readStream);
        if (error != NULL) {
                if (CFErrorGetCode(error) != 0) {
                        NSString * errorInfo = [NSString stringWithFormat:@"Failed to connect stream; error '%@' (code %ld)", (__bridge NSString*)CFErrorGetDomain(error), CFErrorGetCode(error)];
            [self networkFailedWithErrorMessage:errorInfo];
                }
                
                CFRelease(error);
                
                return;
        }
        
        NSLog(@"Successfully connected to %@", url);
        
        // Start processing
    //
        CFRunLoopRun();
}

参考前面的接口说明，相信你不难理解上面的代码。前面唯一没有提到的接口就是 CFReadStreamCopyError，该接口用于获取当前的错误信息，如果没有错误则返回 NULL。

CFErrorRef CFReadStreamCopyError(CFReadStreamRef stream);

CFErrorRef CFWriteStreamCopyError(CFWriteStreamRef stream);

此外，我们还可以调用如下接口获取 socket stream 的当前状态：

CFStreamStatus CFReadStreamGetStatus(CFReadStreamRef stream);

CFStreamStatus CFWriteStreamGetStatus(CFWriteStreamRef stream);

在上面的代码中，我们设置了当有数据可以读取，流到达结尾处时以及错误发生时调用回调函数 socketCallback：

[html] view plain copy print ?

void socketCallback(CFReadStreamRef stream, CFStreamEventType event, void * myPtr)
{
KSCFNetworkViewController * controller = (__bridge KSCFNetworkViewController *)myPtr;
switch(event) {
case kCFStreamEventHasBytesAvailable: {
// Read bytes until there are no more
//
while (<STRONG>CFReadStreamHasBytesAvailable</STRONG>(stream)) {
UInt8 buffer[kBufferSize];
int numBytesRead = <STRONG>CFReadStreamRead</STRONG>(stream, buffer, kBufferSize);
[controller didReceiveData:[NSData dataWithBytes:buffer length:numBytesRead]];
}
break;
}
case kCFStreamEventErrorOccurred: {
CFErrorRef error = <STRONG>CFReadStreamCopyError</STRONG>(stream);
if (error != NULL) {
if (CFErrorGetCode(error) != 0) {
NSString * errorInfo = [NSString stringWithFormat:@"Failed while reading stream; error '%@' (code %ld)", (__bridge NSString*)CFErrorGetDomain(error), CFErrorGetCode(error)];
[controller networkFailedWithErrorMessage:errorInfo];
}
CFRelease(error);
}
break;
}
case kCFStreamEventEndEncountered:
// Finnish receiveing data
//
[controller didFinishReceivingData];
// Clean up
//
<STRONG>CFReadStreamClose</STRONG>(stream);
<STRONG>CFReadStreamUnscheduleFromRunLoop</STRONG>(stream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
<STRONG>CFRunLoopStop</STRONG>(CFRunLoopGetCurrent());
break;
default:
break;
}
}

void socketCallback(CFReadStreamRef stream, CFStreamEventType event, void * myPtr)
{
    KSCFNetworkViewController * controller = (__bridge KSCFNetworkViewController *)myPtr;
        
        switch(event) {
        case kCFStreamEventHasBytesAvailable: {
                        // Read bytes until there are no more
            //
            while (CFReadStreamHasBytesAvailable(stream)) {
                                UInt8 buffer[kBufferSize];
                                int numBytesRead = CFReadStreamRead(stream, buffer, kBufferSize);
                                
                                [controller didReceiveData:[NSData dataWithBytes:buffer length:numBytesRead]];
                        }
                        
            break;
        }
            
        case kCFStreamEventErrorOccurred: {
                        CFErrorRef error = CFReadStreamCopyError(stream);
                        if (error != NULL) {
                                if (CFErrorGetCode(error) != 0) {
                                        NSString * errorInfo = [NSString stringWithFormat:@"Failed while reading stream; error '%@' (code %ld)", (__bridge NSString*)CFErrorGetDomain(error), CFErrorGetCode(error)];
                    
                    [controller networkFailedWithErrorMessage:errorInfo];
                                }
                                
                                CFRelease(error);
                        }
                        
                        
            break;
                }
                        
        case kCFStreamEventEndEncountered:
            // Finnish receiveing data
            //
                        [controller didFinishReceivingData];
                        
                        // Clean up
            //
                        CFReadStreamClose(stream);
                        CFReadStreamUnscheduleFromRunLoop(stream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
                        CFRunLoopStop(CFRunLoopGetCurrent());
            
            break;
                        
        default:
            break;
    }
}

上面的代码也很好理解，当有数据可以读取时，读取之，然后更新 UI；当流到达结尾处时，关闭流，执行清理工作；当错误发送时，报告错误信息。

四，扩展

虽然上面的代码只演示了如何使用 CFNetwork 的 CFReadStream 来读取数据，写入数据使用 CFWriteStream，其工作流程也是一样的。在这里就不再介绍了。更多《深入浅出Cocoa》系列文章，敬请访问优快云专栏：http://blog.youkuaiyun.com/column/details/cocoa.html