How does Fiddler process Proxy-Connection and Connection headers?

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Franklin Tse

Jul 25, 2013, 2:42:27 AM7/25/13
I am facing a problem about HTTP connection and have some questions about the connection management of Fiddler.
The problem:
Currently, after opening Fiddler, some webpages have extra loading time in IE and Chrome, but not Firefox. There is an upstream proxy (ISA Server I believe) in my environment. I noticed that IE and Chrome use Proxy-Connection while Firefox uses Connection. The upstream proxy returns Proxy-Connection: close or Connection: close for the affected webpages depending on the request header. There is no extra loading time when Fiddler is no used.
The questions:
  1. When Fiddler receives a request with Proxy-Connection: close, does Fiddler close the connection after sending the response the client?
  2. When Fiddler receives a response with Proxy-Connection: close from upstream, does Fiddler close the connection after sending the response the client?
  3. Does Fiddler treat Proxy-Connection the same as Connection? If not, what does Fiddler do when it receives a request with Connection: close and a response with Connection: close?


Jul 25, 2013, 6:19:32 PM7/25/13
It would be helpful to understand more about what "extra loading time" you're referring to.
In terms of your questions:
1> Proxy-Connection: close from the client causes Fiddler to close the client's connection after returning a single response. Connection: close from the client does the same thing.
2> Proxy-Connection: close from upstream server closes the connection to the server after receiving the complete response. Connection: close from the upstream server does the same thing.
If Fiddler receives a Proxy-Connection request header and the request is NOT being sent to a gateway proxy, the Proxy-Connection request header is renamed to just "Connection".
Could you share (or email me) a SAZ file showing the "slower" behavior?
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