[深入淺出Cocoa]iOS網(wǎng)絡(luò)編程之NSStream
一占哟，NSStream簡介
首先來回顧下。在前文《
[深入淺出Cocoa]iOS網(wǎng)絡(luò)編程之Socket
》中翩迈，提到iOS網(wǎng)絡(luò)編程層次模型分為三層：
- Cocoa層：NSURL持灰，Bonjour，Game Kit帽馋，WebKit
- Core Foundation層：基于 C 的?CFNetwork 和 CFNetServices
- OS層:基于 C 的 BSD socket
前文《
》?和《
》?講了最底層的 socket 和Core Foundation層的 CFNetwork搅方，本文將介紹位于 Cocoa 中的 NSStream。NSStream 其實(shí)只是用 Objective-C 對(duì) CFNetwork 的簡單封裝绽族，它使用名為?NSStreamDelegate 的協(xié)議來實(shí)現(xiàn) CFNetwork 中的回調(diào)函數(shù)的作用姨涡，同樣，runloop 也與 NSStream 結(jié)合的很好吧慢。NSStream 有兩個(gè)實(shí)體類：NSInputStream 和 NSOutputStream涛漂，分別對(duì)應(yīng) CFNetwork 中的?CFReadStream 和?CFWriteStream。
本文示例代碼請(qǐng)查看：
https://github.com/kesalin/iOSSnippet/tree/master/KSNetworkDemo
二检诗，NSStream 類接口簡介
NSStream?類有如下接口：
- (void)open;
- (void)close;
- (id?<NSStreamDelegate>)delegate;
- (void)setDelegate:(id?<NSStreamDelegate>)delegate;
- (void)scheduleInRunLoop:(NSRunLoop?*)aRunLoop forMode:(NSString?*)mode;
- (void)removeFromRunLoop:(NSRunLoop?*)aRunLoop forMode:(NSString?*)mode;
- (NSStreamStatus)streamStatus;
- (NSError?*)streamError;
NSStream 的一些接口與 CFNetwork 類似匈仗，如打開，關(guān)閉逢慌，獲取狀態(tài)和錯(cuò)誤信息悠轩，以及和 runloop 結(jié)合等在這里就不再重復(fù)了。前面提到 NSStream 是通過 NSStreamDelegate 來實(shí)現(xiàn) CFNetwork 中的回調(diào)函數(shù)攻泼，這個(gè)可選的協(xié)議只有一個(gè)接口：
- (void)stream:(NSStream?*)aStream handleEvent:(NSStreamEvent)eventCode;
NSStreamEvent 是一個(gè)流事件枚舉：
typedef?NS_OPTIONS(NSUInteger, NSStreamEvent) {
? ? NSStreamEventNone =?0,
? ? NSStreamEventOpenCompleted =?1UL <<?0,
? ? NSStreamEventHasBytesAvailable =?1UL <<?1,
? ? NSStreamEventHasSpaceAvailable =?1UL <<?2,
? ? NSStreamEventErrorOccurred =?1UL <<?3,
? ? NSStreamEventEndEncountered =?1UL <<?4
};
這些事件枚舉的含義也和 CFNetwork 中的?CFStreamEventType 類似火架，在此也就不再重復(fù)了。
NSInputStream?類有如下接口：
- (NSInteger)read:(uint8_t?*)buffer maxLength:(NSUInteger)len;
從流中讀取數(shù)據(jù)到 buffer 中忙菠，buffer 的長度不應(yīng)少于 len何鸡，該接口返回實(shí)際讀取的數(shù)據(jù)長度（該長度最大為 len）。
- (BOOL)getBuffer:(uint8_t?**)buffer length:(NSUInteger?*)len;
獲取當(dāng)前流中的數(shù)據(jù)以及大小牛欢，注意 buffer 只在下一個(gè)流操作之前有效骡男。
- (BOOL)hasBytesAvailable;
檢查流中是否還有數(shù)據(jù)。
NSOutputStream?類有如下接口：
- (NSInteger)write:(const?uint8_t?*)buffer maxLength:(NSUInteger)len;
將 buffer 中的數(shù)據(jù)寫入流中傍睹，返回實(shí)際寫入的字節(jié)數(shù)隔盛。
- (BOOL)hasSpaceAvailable;
檢查流中是否還有可供寫入的空間犹菱。
從這些接口可以看出，NSStream 真的就是 CFNetwork 上的一層簡單的 Objective-C 封裝骚亿。但 iOS 中的 NSStream 不支持 NShost已亥，這是一個(gè)缺陷，蘋果也意識(shí)到這問題了（http://developer.apple.com/library/ios/#qa/qa1652/_index.html）来屠，我們可以通過 NSStream 的擴(kuò)展函數(shù)來實(shí)現(xiàn)該功能：
@implementation NSStream(StreamsToHost)
+ (void)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三虑椎，客戶端示例代碼
與前面的示例類似，在這里我只演示客戶端示例俱笛。同樣捆姜，我們也在一個(gè)后臺(tái)線程中啟動(dòng)網(wǎng)絡(luò)操作：
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 中創(chuàng)建 NSInputStream，并設(shè)置其 delegate迎膜，將其加入到 run-loop 的事件源中泥技，然后打開流，運(yùn)行 runloop：
- (void)loadDataFromServerWithURL:(NSURL *)url
{
NSInputStream * readStream;
[NSStream getStreamsToHostNamed:[url host]
port:[[url port] integerValue]
inputStream:&readStream
outputStream:NULL];
[readStream setDelegate:self];
[readStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[readStream open];
[[NSRunLoop currentRunLoop] run];
}因?yàn)槲覀儗?KSNSStreamViewController 當(dāng)作 NSInputStream 的 delegate磕仅，因此要在 KSNSStreamViewController 中實(shí)現(xiàn)該 delgate：
#pragma mark NSStreamDelegate
- (void)stream:(NSStream *)stream handleEvent:(NSStreamEvent)eventCode
{
NSLog(@" >> NSStreamDelegate in Thread %@", [NSThread currentThread]);
switch (eventCode) {
case NSStreamEventHasBytesAvailable: {
if (_receivedData == nil) {
_receivedData = [[NSMutableData alloc] init];
}
uint8_t buf[kBufferSize];
int numBytesRead = [(NSInputStream *)stream read:buf maxLength:kBufferSize];
if (numBytesRead > 0) {
[self didReceiveData:[NSData dataWithBytes:buf length:numBytesRead]];
} else if (numBytesRead == 0) {
NSLog(@" >> End of stream reached");
} else {
NSLog(@" >> Read error occurred");
}
break;
}
case NSStreamEventErrorOccurred: {
NSError * error = [stream streamError];
NSString * errorInfo = [NSString stringWithFormat:@"Failed while reading stream; error '%@' (code %d)", error.localizedDescription, error.code];
[self cleanUpStream:stream];
[self networkFailedWithErrorMessage:errorInfo];
}
case NSStreamEventEndEncountered: {
[self cleanUpStream:stream];
[self didFinishReceivingData];
break;
}
default:
break;
}
}當(dāng)數(shù)據(jù)讀取完畢或者讀取失敗時(shí)珊豹，調(diào)用 cleanUpStream 方法來關(guān)閉流：
- (void)cleanUpStream:(NSStream *)stream
{
[stream removeFromRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[stream close];
stream = nil;
}