How are the libraries of libCURL, OpenSSL, ZLIB, and SSH2 related?
While each of these libraries can be used alone (and are developed by different groups), it turns out they are ACTUALLY VERY TIGHTLY INTEGRATED and I believe should be one distribution and library. For example, libCURL cannot fetch an HTTPS url unless it links with OpenSSL. Here is a layer-cake diagram of the relationships between the libraries libCURL, OpenSSL, ZLIB, and SSH2: As shown in the diagram above, the most stand-alone of any of the libraries is ZLIB which doesn’t know about any of the other libraries, so I drew it in at the very bottom. OpenSSL comes next, it can either be compiled alone, or with a flag to use ZLIB. I have no idea why OpenSSL would use ZLIB, this sounds kind of strange to me, but this is the situation. If you leave SSH2 out of the mix, libCURL is very functional with HTTP and even works with FTP, but cannot transfer files using SFTP (which is the default FTP service enabled on RedHat Linux and thus very very useful).
