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About this Document

 This document will attempt to describe the general principle and some basic

 This document attempts to describe the general principles and some basic

 approaches to consider when programming with libcurl. The text will focus

 mainly on the C interface but might apply fairly well on other interfaces as

 well as they usually follow the C one pretty closely.

 libcurl can either connect to the server a second time or tell the server to

 connect back to it. The first option is the default and it is also what works

 best for all the people behind firewals, NATs or ip-masquarading setups.

 best for all the people behind firewalls, NATs or IP-masquarading setups.

 libcurl then tells the server to open up a new port and wait for a second

 connection. This is by default attempted with EPSV first, and if that doesn't

 work it tries PASV instead. (EPSV is an extension to the original FTP spec

 You can prevent libcurl from first trying the EPSV command by setting

 CURLOPT_FTP_USE_EPSV to FALSE.

 In some cases, you will perfer to have the server connect back to you for the

 In some cases, you will prefer to have the server connect back to you for the

 second connection. This might be when the server is perhaps behind a firewall

 or something and only allows connections on a single port. libcurl then

 informs the remote server which IP address and port number to connect to.