ASIHTTPRequest实现断点续传

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);
}