ASIHTTPRequest实现断点续传

http://blog.csdn.net/daiyelang/article/category/1377418

ASIHTTPRequest可以实现断点续传。网上有一些介绍类似使用:

 
[request setAllowResumeForFileDownloads:YES];
 
方法的。但是它不是真正意义的断点续传。它只能让应用在下载过程中,暂停和继续。如果退出应用再进入是无效的。
 
不过,通过ASIHTTPRequest的异步请求以及delegate还是可以实现断点续传的。
 
本文还是以Grails编写断点续传服务器端为例。
 
异步请求的代码:
 
 
 
-(void) doSimpleGetBinary{ 
    NSURL *url = [NSURL URLWithString:@"http://localhost:8080/BookProto/book/image"]; 
    ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url]; 
    [request setRequestMethod:@"GET"]; 
    //[request addRequestHeader:@" Range" value:@"bytes=3-"]; 
    [request setDelegate:self]; 
    
    [request startAsynchronous]; 
}
 
这里设置了Delegate, 要在头文件中实现相应的protocol:
 
@interface CFHttpDemoViewController : UIViewController<ASIProgressDelegate> {
 
本例中使用到了delegate的如下方法。
 
requestFinished:
 
- (void)requestFinished:(ASIHTTPRequest *)request{ 
    NSLog(@"response status code: %i",[request responseStatusCode]); 
    NSLog(@"response content length: %@",[[request responseHeaders] objectForKey:@" Content-Length" ]); 
    NSLog(@"request finished."); 
    label.text=@"request finished."; 
}
 
 
 
这个方法在异步请求结束后调用。
 
下面的方法,是当缓冲区接收到部分数据后调用,看起来是每间隔一定的毫秒,就调用一下,并传入缓冲区的NSData对象。
 
-(void)request:(ASIHTTPRequest *)request  didReceiveData:(NSData *)data{ 
    NSLog(@"did receive data, data length: %i",[data length]); 
    
    //复制到字节数组中 
    Byte *byteData=(Byte *)malloc([data length]); 
    memcpy(byteData,[data bytes],[data length]); 
    
    for (int i=0; i<=10; i++) { 
        NSLog(@"%i: %i",i+1,byteData[i]); 
    } 
    
    free(byteData); 
    
    [request cancel]; 
    label.text=@"canceled."; 
}
 
 
 
运行代码,屏蔽:
 
[request addRequestHeader:@"Range" value:@"bytes=3-"];
 
和取消屏蔽,数据分别如下:
 
2011-07-12 14:17:13.497 CFHttpDemo[2647:207] did receive data, data length: 10172 
2011-07-12 14:17:13.514 CFHttpDemo[2647:207] 1: 137 
2011-07-12 14:17:13.515 CFHttpDemo[2647:207] 2: 80 
2011-07-12 14:17:13.516 CFHttpDemo[2647:207] 3: 78 
2011-07-12 14:17:13.516 CFHttpDemo[2647:207] 4: 71 
2011-07-12 14:17:13.517 CFHttpDemo[2647:207] 5: 13 
2011-07-12 14:17:13.518 CFHttpDemo[2647:207] 6: 10 
2011-07-12 14:17:13.518 CFHttpDemo[2647:207] 7: 26 
2011-07-12 14:17:13.519 CFHttpDemo[2647:207] 8: 10 
2011-07-12 14:17:13.520 CFHttpDemo[2647:207] 9: 0 
2011-07-12 14:17:13.520 CFHttpDemo[2647:207] 10: 0 
2011-07-12 14:17:13.521 CFHttpDemo[2647:207] 11: 0 
2011-07-12 14:17:13.522 CFHttpDemo[2647:207] response status code: 200 
2011-07-12 14:17:13.523 CFHttpDemo[2647:207] response content length: 10172 
2011-07-12 14:17:13.523 CFHttpDemo[2647:207] request finished.
 
2011-07-12 14:02:24.551 CFHttpDemo[2578:207] did receive data, data length: 10169 
2011-07-12 14:02:24.553 CFHttpDemo[2578:207] byteData ok. 
2011-07-12 14:02:24.554 CFHttpDemo[2578:207] 1: 71 
2011-07-12 14:02:24.554 CFHttpDemo[2578:207] 2: 13 
2011-07-12 14:02:24.555 CFHttpDemo[2578:207] 3: 10 
2011-07-12 14:02:24.555 CFHttpDemo[2578:207] 4: 26 
2011-07-12 14:02:24.556 CFHttpDemo[2578:207] 5: 10 
2011-07-12 14:02:24.556 CFHttpDemo[2578:207] 6: 0 
2011-07-12 14:02:24.557 CFHttpDemo[2578:207] 7: 0 
2011-07-12 14:02:24.557 CFHttpDemo[2578:207] 8: 0 
2011-07-12 14:02:24.558 CFHttpDemo[2578:207] 9: 13 
2011-07-12 14:02:24.558 CFHttpDemo[2578:207] 10: 73 
2011-07-12 14:02:24.560 CFHttpDemo[2578:207] 11: 72 
2011-07-12 14:02:24.561 CFHttpDemo[2578:207] response status code: 206 
2011-07-12 14:02:24.561 CFHttpDemo[2578:207] response content length: 10169 
2011-07-12 14:02:24.562 CFHttpDemo[2578:207] request finished.
 
2.
 
NSUrlConnection实现断点续传的关键是自定义http request的头部的range域属性。
 
 Range头域
  Range头域可以请求实体的一个或者多个子范围。例如,
  表示头500个字节:bytes=0-499
  表示第二个500字节:bytes=500-999
  表示最后500个字节:bytes=-500
  表示500字节以后的范围:bytes=500-
  第一个和最后一个字节:bytes=0-0,-1
  同时指定几个范围:bytes=500-600,601-999
  但是服务器可以忽略此请求头,如果无条件GET包含Range请求头,响应会以状态码206(PartialContent)返回而不是以200(OK)。
 
在ios中使用NSMutableURLRequest来定义头部域
NSURL *url1=[NSURL URLWithString:@"下载地址";  
NSMutableURLRequest* request1=[NSMutableURLRequest requestWithURL:url1];  
[request1 setValue:@"bytes=20000-" forHTTPHeaderField:@"Range"];   
[request1 setCachePolicy:NSURLRequestReloadIgnoringLocalCacheData];  
NSData *returnData1 = [NSURLConnection sendSynchronousRequest:request1 returningResponse:nil error:nil];   
[self writeToFile:returnData1 fileName:@"SOMEPATH"];  
  
  
  
  
-(void)writeToFile:(NSData *)data fileName:(NSString *) fileName  
{  
    NSString *filePath=[NSString stringWithFormat:@"%@",fileName];  
    if([[NSFileManager defaultManager] fileExistsAtPath:filePath] == NO){  
        NSLog(@"file not exist,create it...");  
        [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];  
    }else {  
    NSLog(@"file exist!!!");  
    }  
  
    FILE *file = fopen([fileName UTF8String], [@"ab+" UTF8String]);  
  
    if(file != NULL){  
        fseek(file, 0, SEEK_END);  
    }  
    int readSize = [data length];  
    fwrite((const void *)[data bytes], readSize, 1, file);  
    fclose(file);  

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