IOS网络编程：HTTP

HTTP定义了一种在服务器和客户端之间传递数据的途径。

URL定义了一种唯一标示资源在网络中位置的途径。



REQUESTS 和 RESPONSES：





客户端先建立一个TCP连接，然后发送一个请求。服务器受到请求处理后发送一个响应向客户端传递数据。然后客户端可以继续发送请求或者关闭这个TCP连接。

HTTPS：

在TCP连接建立后，发送请求之前，需要建立一个一个SSL会话。

request方法和它们的用途







注意：想server发送大量数据需要用POST，因为GET仅支持发送少量数据（8KB）。



iOS的NSURLRequest和它的子类NSMutableURLRequest提供了建立HTTP请求的方法。

NSURLResponse 和 它的子类NSHTTPURLResponse 处理返回的数据。

URL：









Protocol包括HTTP、FTP和file。

URL编码：

NSString *urlString = @"http://myhost.com?query=This is a question"; 
NSString *encoded = [urlString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSURL用来管理URL。



IOS HTTP APIS：



涉及到下面一些类：

NSURL, NSURLRequest, NSURLConnection, 和 NSURLResponse.

1、NSURL

NSURL可以定义本地文件和网络文件

NSURL *url = [NSURL urlWithString:@"http://www.google.com"];

NSData *data = [NSData dataWithContentsOfURL:url];

NSURL定义了很多访问器：

if (url.port == nil) { 
　　NSLog(@"Port is nil");
} else {
　　NSLog(@"Port is not nil");
}

2、NSURLRequest

创建了NSURL后，就可以用NSURLRequest建立请求了：

NSURL *url = [NSURL URLWithString: @"https://gdata.youtube.com/feeds/api/standardfeeds/top_rated"];
if (url == nil) {
     NSLog(@"Invalid URL"); 

　　 return;
}
NSURLRequest *request = [NSURLRequest requestWithURL:url]; 

if (request == nil) {
　　NSLog(@"Invalid Request");
    return; 
}

NSMutableURLRequest是NSURLRequest 的子类，提供了改变请求的属性的方法：

NSURL *url = [NSURL urlWithString@"http://server.com/postme"]; 
NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url]; 
[req setHTTPMethod:@"POST"];
[req setHTTPBody:[@"Post body" dataUsingEncoding:NSUTF8StringEncoding]];

如果你要发送一个图片或者视频，那么用需要用NSInputStream，它没有把数据全部加在到内存。

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
NSInputStream *inStream = [NSInputStream inputStreamWithFileAtPath:srcFilePath];
[request setHTTPBodyStream:inStream];
[request setHTTPMethod:@"POST"];

3、NSURLResponse





4、NSURLConnection

提供了初始化、开始、和取消一个连接。

发送同步请求：

- (NSArray *) doSyncRequest:(NSString *)urlString {
    // make the NSURL object from the string
    NSURL *url = [NSURL URLWithString:urlString];
    
    // Create the request object with a 30 second timeout and a cache policy to always retrieve the
    // feed regardless of cachability.
    NSURLRequest *request = 
       [NSURLRequest requestWithURL:url 
                        cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData 
                    timeoutInterval:30.0];
    
    // Send the request and wait for a response
    NSHTTPURLResponse   *response;
    NSError             *error;
    NSData *data = [NSURLConnection sendSynchronousRequest:request 
                                         returningResponse:&response 
                                                     error:&error];
    // check for an error
    if (error != nil) {
        NSLog(@"Error on load = %@", [error localizedDescription]);
        return nil;
    }
    
    // check the HTTP status
    if ([response isKindOfClass:[NSHTTPURLResponse class]]) {
        NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
        if (httpResponse.statusCode != 200) {
            return nil;
        }
        NSLog(@"Headers: %@", [httpResponse allHeaderFields]);
    }
    
    // Parse the data returned into an NSDictionary
    NSDictionary *dictionary = 
        [XMLReader dictionaryForXMLData:data 
                                  error:&error];
    // Dump the dictionary to the log file
    NSLog(@"feed = %@", dictionary);
    
    NSArray *entries =[self getEntriesArray:dictionary];
    
    // return the list if items from the feed.
    return entries;

}

Queued Asynchronous Requests：

- (void) doQueuedRequest:(NSString *)urlString  delegate:(id)delegate {
    // make the NSURL object
    NSURL *url = [NSURL URLWithString:urlString];
    
    // create the request object with a no cache policy and a 30 second timeout.
    NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:30.0];
    
    // If the queue doesn't exist, create one.
    if (queue == nil) {
        queue = [[NSOperationQueue alloc] init];
    }
    
    // send the request and specify the code to execute when the request completes or fails.
    [NSURLConnection sendAsynchronousRequest:request 
                                       queue:queue 
                           completionHandler:^(NSURLResponse *response, 
                                               NSData *data, 
                                               NSError *error) {
                               
            if (error != nil) {
               NSLog(@"Error on load = %@", [error localizedDescription]);
            } else {
                
                // check the HTTP status
                if ([response isKindOfClass:[NSHTTPURLResponse class]]) {
                    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
                    if (httpResponse.statusCode != 200) {
                        return;
                    }
                    NSLog(@"Headers: %@", [httpResponse allHeaderFields]);
                }
                               
                // parse the results and make a dictionary
                NSDictionary *dictionary = 
                   [XMLReader dictionaryForXMLData:data 
                                             error:&error];
                NSLog(@"feed = %@", dictionary);

                // get the dictionary entries.
                NSArray *entries =[self getEntriesArray:dictionary];

                // call the delegate
                if ([delegate respondsToSelector:@selector(setVideos:)]) {
                    [delegate performSelectorOnMainThread:@selector(setVideos:) 
                                               withObject:entries 
                                            waitUntilDone:YES];
                }
            }
    }];
}

NSURLConnection start方法和Delegate：



GET：

　NSURL  *url=[[ NSURL   alloc ] initWithString :urlString];

     NSMutableURLRequest  *request=[[NSMutableURLRequest  alloc ] init ];

     NSURLConnection  *connection = [[ NSURLConnection   alloc ]  initWithRequest :request delegate : self ];
     if (connection)
     {
             [connection start];
         }
     else
     {
             NSLog ( @"sorry" );
     }

/*
* NSURLConnectionDataDelegate
*/
- (void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse *)response
{
　　[activityIndicator startAnimating]; //UIActivityIndicatorView
    NSLog(@"Did Receive Response %@", response);
    responseData = [[NSMutableData alloc]init];
}
- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data
{
    //NSLog(@"Did Receive Data %@", data);
    [responseData appendData:data]; //NSMutableData
}
- (void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error
{
    NSLog(@"Did Fail");
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{

[activityIndicator stopAnimating];

NSLog(@"Did Finish");
    // Do something with responseData
}

POST：

//initialize new mutable data
    NSMutableData *data = [[NSMutableData alloc] init];
    self.receivedData = data;
    
    //initialize url that is going to be fetched.
    NSURL *url = [NSURL URLWithString:@"http://www.snee.com/xml/crud/posttest.cgi"];
    
    //initialize a request from url
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[url standardizedURL]];
    
    //set http method
    [request setHTTPMethod:@"POST"];
    //initialize a post data
    NSString *postData = [[NSString alloc] initWithString:@"fname=example&lname=example"];
    //set request content type we MUST set this value.
    
    [request setValue:@"application/x-www-form-urlencoded; charset=utf-8" forHTTPHeaderField:@"Content-Type"];
    
    //set post data of request
    [request setHTTPBody:[postData dataUsingEncoding:NSUTF8StringEncoding]];
    
    //initialize a connection from request
    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
    self.connection = connection;
    //start the connection
    [connection start];

异步请求：

异步请求需要一个run loop来操作代理对象，GCD和NSOperationQueue默认并没有run loop，所以如果你想在后台发起一个HTTP请求，必须确保有run loop。

NSURLConnection connection = [[NSURLConnection alloc] initWithRequest:request
delegate:self startImmediately:NO];
[connection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
[connection start];

上面的代码是在主线程运行，如果想在其他线程运行，可以在其他线程新建一个run loop，并绑定到connection。