Full Unicode support + MariaDB compatibility

[collinhundley]

This PR fixes the Unicode issue discussed in #25, and adds the ability to connect to MariaDB instead of MySQL.

In order to support MariaDB without breaking the existing MySQL support, a new compiler flag was added: -DMARIADB. If this flag is passed to the compiler, it will link against the MariaDB C module CMariaDBLinux. If omitted, it will continue to link against the MySQL module as usual.

See PR #3 in vapor/cmysql, which is also required for these changes to take effect.

[loganwright]

can we get this comment updated too

[collinhundley]

Sure, I can fix that. But I'm also curious why it was written in the first place, because I want to make sure I'm not overlooking something. Maybe @tannernelson will know.

[loganwright]

I'm trying to figure that out as well to make sure we're not setting something off.

[collinhundley]

Agreed. After further inspection and testing, I think we should be safe. Char is only used while populating the buffer, and MySQL has no concept of "signed" vs "unsigned" - it's just raw bytes in a buffer. So in reality UInt8 accounts for everything Int8 was handling, but it also accounts for the characters that were causing overflow.

[loganwright]

@collinhundley sounds perfect, I know we generally prefer [UInt8] type. @tannernelson can you give final merge word on this one! You have much more MySQL context.

👍 from me.

[collinhundley]

It would be great to get this merged. I need to make some changes to my fork but they'll affect this merge if I push them right now...

[loganwright]

Hey @collinhundley, awesome contribution here!

I have a couple questions about MariaDB, and particular the compiler flag / imports you're using. Can you tell me where the CMariaDBLinux etc. live and how they're being integrated?

[collinhundley]

@loganwright Check out this PR for the C module here: vapor-community/cmysql#3

Once that PR has been accepted, a new module named CMariaDBLinux will become available for this package. At that point, the user may set a compiler flag like this:

-Xswiftc -DMARIADB

which will cause this package to import that module instead of CMySQLLinux. If the flag is not included, then the MariaDB imports will be ignored and MySQL will be used as usual.

[tanner0101]

@collinhundley Does MariaDB not work with macOS?

[collinhundley]

@tannernelson It does work on macOS.

For reasons I don't understand, the C library is inconsistent between macOS and Linux. On both platforms it is a drop-in replacement for MySQL (with identical headers, etc) but for some reason the files/directories are named differently on Linux. On macOS the library/headers are found in the same location as MySQL, which is why there is no need for a separate CMariaDBMac module.

It's possible that this could change depending on the user's operating system and/or MariaDB version, but I've tested it to work on Ubuntu 15.10/16.04 and macOS 10.11/10.12.

[tanner0101]

Cool, sounds good. :)

Thanks for the contribution!