How to handle SSL connection premature closure

I am writing a proxy server that proxies SSL connections, and it is all working perfectly fine for normal traffic. However when there is a large file transfer (Anything over 20KB) like an email attachment, then the connection is reset on the TCP level before the file is finished being written. I am using non-blocking IO, and am spawning a开发者_运维百科 thread for each specific connection.

When a connection comes in I do the following:

• Spawn a thread
• Connect to the client (unencrypted) and read the connect request (all other requests are ignored)
• Create a secure connection (SSL using openssl api) to the server
• Tell the client that we contacted the server (unencrypted)
• Create secure connection to client, and start proxying data between the two using a select loop to determine when reading and writing can occur
• Once the underlying sockets are closed, or there is an error, the connection is closed, and thread is terminated.

Like I said, this works great for normal sized data (regular webpages, and other things) but fails as soon as a file is too large with either an error code (depending on the webapp being used) or a Error: Connection Interrupted.

I have no idea what is causing the connection to close, whether it's something TCP, HTTP, or SSL specific, and I can't find any information on it at all. In some browsers it will start to work if I put a sleep statement immediately after the SSL_write, but this seems to cause other issues in other browsers. The sleep doesn't have to be long, really just a delay. I currently have it set to 4ms per write, and 2ms per read, and this fixes it completely in older firefox, chrome with HTTP uploads, and opera.

Any leads would be appreciated, and let me know if you need any more information. Thanks in advanced!

-Sam

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If the web-app thinks an uploaded file is too large what does it do? If it's entitled to just close the connection, that will cause an ECONN at the sender: 'connection reset'. Whatever it does, as you're writing a proxy, and assuming there are no bugs in your code that are causing this, your mission is to mirror whatever happens to your upstream connection back down the downstream connection. In this case the answer is to just do what you're doing: close the upstream and downstream sockets. If you got an incoming close_notify from the server, do an orderly SSL close to the client; if you got ECONN, just close the client socket directly, bypassing SSL.