ASIHttpRequest 学习

下载文件之前获得文件大小

[m_pASIHTTPRequest setDidReceiveResponseHeadersSelector:@selector(didReceiveResponseHeaders:)];
- (void)didReceiveResponseHeaders:(ASIHTTPRequest *)request
{
    NSLog(@"didReceiveResponseHeaders %@",[m_request.responseHeaders valueForKey:@"Content-Length"]);
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