cocoa - 为什么我收到 1 个 302 响应时会得到两个重定向响应？

Question

我使用以下代码:

- (NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)request redirectResponse:(NSHTTPURLResponse *)response {
NSLog(@"Received redirect Response: %@ %@", [response allHeaderFields], [NSHTTPURLResponse localizedStringForStatusCode:[response statusCode]]);
return request;
}

当我收到包含以下 header 数据的 302 时:

< HTTP/1.1 302 Found  
< Date: Wed, 03 Mar 2010 07:47:17 GMT  
< Server: lighttpd/1.4.19  
< Content-length: 0  
< Content-type: text/html;charset=utf-8  
< Location: `<new Location>`  
< Vary: Accept-Encoding  

这是 gdb 控制台中的输出:

2010-03-03 08:42:03.265 MyProg[68106:207] Received redirect Response: (null) server error 2010-03-03 08:42:14.414 MyProg[68106:207] Received redirect Response: {
Connection = "Keep-Alive";
"Content-Encoding" = gzip;
"Content-Length" = 20;
"Content-Type" = "text/html;charset=utf-8";
Date = "Wed, 03 Mar 2010 07:42:10 GMT";
"Keep-Alive" = "timeout=15, max=100";
Location = "<new Location>";
Server = "lighttpd/1.4.19";
Vary = "Accept-Encoding"; } found

当使用 Curl 时，我只得到一个响应，并且 Tracedump 也给出相同的信息，因此我确信服务器只发送一个重定向。
为什么这个选择器被调用两次？

Answer 1

connection:willSendRequest:redirectResponse: 在每个请求之前被调用，因此它在原始请求上调用一次，这不是重定向，因此响应为零；然后在加载重定向目标时调用它，其中响应是对初始请求的 302 响应。