MKNetworkKit的断点续传SIDownloader下载

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https://github.com/MugunthKumar/MKNetworkKit

使用MKNetworkKit

1. 首先把clone下来的MKNetworkKit文件夹拖进你的项目里面
2. 到项目里面增加CFNetwork.Framework SystemConfiguration.framework 和 Security.framework.
3. 把MKNetworkKit.h包含到你的pch文件里面。
4. 如果是 如果是Mac，删除UIAlertView+MKNetworkKitAdditions.h这个文件

这样，再看看介绍里面的例子。应该就能看懂普通用法了。然后畅快的使用MKNetworkKit库了。

改写目标

上次写的ASIHTTPRequest续传其实已经可以用了。但是为什么需要重新写呢。就是重用！！！

一直都很少自己设计接口什么的。其实只是做了写体力的劳动，把一堆逻辑换成代码给堆了起来。觉得没有人会去重用自己的代码。很少去花心思想怎么样才能写好。

这次改写就只有一个目标，为了更好更多人能使用断点续传来 功能

下载应该在下载继续进行。

保持进度条

每次进入 暂停恢复 可以随时暂停下载

这次改写，这些功能都实现了，啊哈哈哈。

实现

MKNetworkKit库修改

最开始使用MKNetworkKit库做

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {

  NSUInteger size = [self.response expectedContentLength] < 0 ? 0 : [self.response expectedContentLength];
  self.response = (NSHTTPURLResponse*) response;

  // dont' save data if the operation was created to download directly to a stream.
  if([self.downloadStreams count] == 0)
    self.mutableData = [NSMutableData dataWithCapacity:size];
  else
    self.mutableData = nil;

  for(NSOutputStream *stream in self.downloadStreams)
    [stream open];

  NSDictionary *httpHeaders = [self.response allHeaderFields];

  // if you attach a stream to the operation, MKNetworkKit will not cache the response.
  // Streams are usually "big data chunks" that doesn't need caching anyways.

  if([self.request.HTTPMethod isEqualToString:@"GET"] && [self.downloadStreams count] == 0) {

    // We have all this complicated cache handling since NSURLRequestReloadRevalidatingCacheData is not implemented
    // do cache processing only if the request is a "GET" method
    NSString *lastModified = [httpHeaders objectForKey:@"Last-Modified"];
    NSString *eTag = [httpHeaders objectForKey:@"ETag"];
    NSString *expiresOn = [httpHeaders objectForKey:@"Expires"];

    NSString *contentType = [httpHeaders objectForKey:@"Content-Type"];
    // if contentType is image,

    NSDate *expiresOnDate = nil;

    if([contentType rangeOfString:@"image"].location != NSNotFound) {

      // For images let's assume a expiry date of 7 days if there is no eTag or Last Modified.
      if(!eTag && !lastModified)
        expiresOnDate = [[NSDate date] dateByAddingTimeInterval:kMKNetworkKitDefaultImageCacheDuration];
      else
        expiresOnDate = [[NSDate date] dateByAddingTimeInterval:kMKNetworkKitDefaultImageHeadRequestDuration];
    }

    NSString *cacheControl = [httpHeaders objectForKey:@"Cache-Control"]; // max-age, must-revalidate, no-cache
    NSArray *cacheControlEntities = [cacheControl componentsSeparatedByString:@","];

    for(NSString *substring in cacheControlEntities) {

      if([substring rangeOfString:@"max-age"].location != NSNotFound) {

        // do some processing to calculate expiresOn
        NSString *maxAge = nil;
        NSArray *array = [substring componentsSeparatedByString:@"="];
        if([array count] > 1)
          maxAge = [array objectAtIndex:1];

        expiresOnDate = [[NSDate date] dateByAddingTimeInterval:[maxAge intValue]];
      }
      if([substring rangeOfString:@"no-cache"].location != NSNotFound) {

        // Don't cache this request
        expiresOnDate = [[NSDate date] dateByAddingTimeInterval:kMKNetworkKitDefaultCacheDuration];
      }
    }

    // if there was a cacheControl entity, we would have a expiresOnDate that is not nil.
    // "Cache-Control" headers take precedence over "Expires" headers

    expiresOn = [expiresOnDate rfc1123String];

    // now remember lastModified, eTag and expires for this request in cache
    if(expiresOn)
      [self.cacheHeaders setObject:expiresOn forKey:@"Expires"];
    if(lastModified)
      [self.cacheHeaders setObject:lastModified forKey:@"Last-Modified"];
    if(eTag)
      [self.cacheHeaders setObject:eTag forKey:@"ETag"];
  }

    if ([self.mutableData length] == 0 || [self.downloadStreams count] > 0) {
        // This is the first batch of data
        // Check for a range header and make changes as neccesary
        NSString *rangeString = [[self request] valueForHTTPHeaderField:@"Range"];
        if ([rangeString hasPrefix:@"bytes="] && [rangeString hasSuffix:@"-"]) {
            NSString *bytesText = [rangeString substringWithRange:NSMakeRange(6, [rangeString length] - 7)];
            self.startPosition = [bytesText integerValue];
            self.downloadedDataSize = self.startPosition;
            DLog(@"Resuming at %d bytes", self.startPosition);
        }
    }
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

  if([self.downloadStreams count] == 0)
    [self.mutableData appendData:data];

  for(NSOutputStream *stream in self.downloadStreams) {

    if ([stream hasSpaceAvailable]) {
      const uint8_t *dataBuffer = [data bytes];
      [stream write:&dataBuffer[0] maxLength:[data length]];
    }
  }

  self.downloadedDataSize += [data length];

  for(MKNKProgressBlock downloadProgressBlock in self.downloadProgressChangedHandlers) {

    if([self.response expectedContentLength] > 0) {

      double progress = (double)(self.downloadedDataSize) / (double)(self.startPosition + [self.response expectedContentLength]);
      downloadProgressBlock(progress);
    }
  }
}

具体改了哪，忘记了。有心思对照源码看看。应该是属于MKNetworkKit的bug。也不知道新版改过来没有。但是你clone我的demo，这个版本是可以的。

断点 其实我一共就写了两个简单的类而已。

基础的是SIBreakpointsDownload。继承于MKNetworkOperation。判断了续传的位置。

一个SIDownloadManager写成单例，继承于MKNetworkEngine。用来管理多任务 使用的时候就只用SIDownloadManager这个类来添加下载。然后想在 demo地址

git@github.com:iiiyu/SIDownloader.git

其实已经很简单了，照着demo改改就能自己用了。

总结

这次改写以后，代码结构变的很清晰。复杂性和耦合性都有所降低。可用性提高。而且，反正我是没有google到可以直接拿来用的断点ios代码库-www.lanrenios.com