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

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 [email protected]"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、NSURLConnection

提供了初始化、开始、和取消一个连接。

4、NSURLResponse

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];
                }
            }
    }];
}

Asynchronous Requests：

#import <Foundation/Foundation.h>

#define kDownloadComplete   @"downloadComplete"

@class DownloadProgressView;

@interface AsyncDownloader : NSObject <NSURLConnectionDelegate> {
    // The number of bytes that need to be downloaded
    long long   downloadSize;
    // the total amount downloaded thus far
    long long   totalDownloaded;
}
// A reference to the progress view to show the user how things are progressing
@property (assign) DownloadProgressView *progressView;
// The target MP4 file
@property (strong) NSString *targetFile;
// The original URL to download.  Due to redirects the actual content may come from another URL
@property (strong) NSString *srcURL;
// The open file to which the content is written
@property (strong) NSFileHandle *outputHandle;
// The name of the temp file to which the content is streamed. This file is moved to the target file when
// the download is complete
@property (strong) NSString *tempFile;
@property (strong) NSURLConnection *conn;

// instructs the class to start the download.
- (void) start;
@end

//
//  AsyncDownloader.m
//  VideoDownloader
//
//  Created by Jack Cox on 4/7/12.
//
//

#import "AsyncDownloader.h"
#import "DownloadProgressView.h"

@implementation AsyncDownloader

@synthesize targetFile;
@synthesize srcURL;
@synthesize outputHandle;
@synthesize tempFile;
@synthesize progressView;
@synthesize conn;

- (void) start {
    NSLog(@"Starting to download %@", srcURL);

    // create the URL
    NSURL *url = [NSURL URLWithString:srcURL];

    // Create the request
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    // create the connection with the target request and this class as the delegate
    self.conn =
         [NSURLConnection connectionWithRequest:request
                                       delegate:self];

    // start the connection
    [self.conn start];
}

/**
 * Creates a UUID to use as the temporary file name during the download
 */
- (NSString *)createUUID
{
    CFUUIDRef uuidRef = CFUUIDCreate(NULL);
    CFStringRef uuidStringRef = CFUUIDCreateString(NULL, uuidRef);
    CFRelease(uuidRef);
    NSString *uuid = [NSString stringWithString:(__bridge NSString *)
                      uuidStringRef];
    CFRelease(uuidStringRef);
    return uuid;
}
#pragma mark NSURLConnectionDelegate methods
/**
 * This delegate method is called when the NSURLConnection gets a 300 series response that indicates
 * that the request needs to be redirected.  It is implemented here to display any redirects that might
 * occur. This method is optional.  If omitted the client will follow all redirects.
 **/
- (NSURLRequest *)connection:(NSURLConnection *)connection
             willSendRequest:(NSURLRequest *)request
            redirectResponse:(NSURLResponse *)redirectResponse {

    // Dump debugging information
    NSLog(@"Redirect request for %@ redirecting to %@", srcURL, request.URL);
    NSLog(@"All headers = %@",
          [(NSHTTPURLResponse*) redirectResponse allHeaderFields]);

    // Follow the redirect
    return request;
}

/**
 * This delegate method is called when the NSURLConnection connects to the server.  It contains the
 * NSURLResponse object with the headers returned by the server.  This method may be called multiple times.
 * Therefore, it is important to reset the data on each call.  Do not assume that it is the first call
 * of this method.
 **/
- (void) connection:(NSURLConnection *)connection
 didReceiveResponse:(NSURLResponse *)response {
    NSLog(@"Received response from request to url %@", srcURL);

    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
    NSLog(@"All headers = %@", [httpResponse allHeaderFields]);

    if (httpResponse.statusCode != 200) {// something went wrong, abort the whole thing
        // reset the download counts
        if (downloadSize != 0L) {
            [progressView addAmountToDownload:-downloadSize];
            [progressView addAmountDownloaded:-totalDownloaded];
        }
        [connection cancel];
        return;
    }

    NSFileManager *fm = [NSFileManager defaultManager];

    // If we have a temp file already, close it and delete it
    if (self.tempFile != nil) {
        [self.outputHandle closeFile];

        NSError *error;
        [fm removeItemAtPath:self.tempFile error:&error];
    }

    // remove any pre-existing target file
    NSError *error;
    [fm removeItemAtPath:targetFile error:&error];

    // get the temporary directory name and make a temp file name
    NSString *tempDir = NSTemporaryDirectory();
    self.tempFile = [tempDir stringByAppendingPathComponent:[self createUUID]];
    NSLog(@"Writing content to %@", self.tempFile);

    // create and open the temporary file
    [fm createFileAtPath:self.tempFile contents:nil attributes:nil];
    self.outputHandle = [NSFileHandle fileHandleForWritingAtPath:self.tempFile];

    // prime the download progress view
    NSString *contentLengthString = [[httpResponse allHeaderFields] objectForKey:@"Content-length"];
    // reset the download counts
    if (downloadSize != 0L) {
        [progressView addAmountToDownload:-downloadSize];
        [progressView addAmountDownloaded:-totalDownloaded];
    }
    downloadSize = [contentLengthString longLongValue];
    totalDownloaded = 0L;

    [progressView addAmountToDownload:downloadSize];
}
/**
 * This delegate method is called for each chunk of data received from the server.  The chunk size
 * is dependent on the network type and the server configuration.
 */
- (void)connection:(NSURLConnection *)connection
    didReceiveData:(NSData *)data {
    // figure out how many bytes in this chunk
    totalDownloaded+=[data length];

    // Uncomment if you want a packet by packet log of the bytes received.
    NSLog(@"Received %lld of %lld (%f%%) bytes of data for URL %@",
          totalDownloaded,
          downloadSize,
          ((double)totalDownloaded/(double)downloadSize)*100.0,
          srcURL);

    // inform the progress view that data is downloaded
    [progressView addAmountDownloaded:[data length]];

    // save the bytes received
    [self.outputHandle writeData:data];
}

/**
 * This delegate methodis called if the connection cannot be established to the server.
 * The error object will have a description of the error
 **/
- (void)connection:(NSURLConnection *)connection
  didFailWithError:(NSError *)error {
    NSLog(@"Load failed with error %@",
          [error localizedDescription]);

    NSFileManager *fm = [NSFileManager defaultManager];

    // If we have a temp file already, close it and delete it
    if (self.tempFile != nil) {
        [self.outputHandle closeFile];

        NSError *error;
        [fm removeItemAtPath:self.tempFile error:&error];
    }

    // reset the progress view
    if (downloadSize != 0L) {
        [progressView addAmountToDownload:-downloadSize];
        [progressView addAmountDownloaded:-totalDownloaded];
    }
}

/**
 * This delegate method is called when the data load is complete.  The delegate will be released
 * following this call
 **/
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    // close the file
    [self.outputHandle closeFile];

    // Move the file to the target location
    NSFileManager *fm = [NSFileManager defaultManager];
    NSError *error;
    [fm moveItemAtPath:self.tempFile
                toPath:self.targetFile
                 error:&error];

    // Notify any concerned classes that the download is complete
    [[NSNotificationCenter defaultCenter]
     postNotificationName:kDownloadComplete
     object:nil
     userInfo:nil];
}
@end