parse dsn fix

[ans-]

#591

Description

I encounter the case ':' in username, ParseDSN can't get the expect result.

my scripts parse "[username[:password]" part reversely, and compatible with old code.

Checklist

• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README / documentation, if necessary
• Added myself / the copyright holder to the AUTHORS file

[julienschmidt]

This would break support for passwords containing colons

[coveralls]

Coverage increased (+0.03%) to 74.918% when pulling 6c44b43 on ans-:parse-dsn-fix into 44fa292 on go-sql-driver:master.

[julienschmidt]

Your test case is user:name:password. In the current implementation we decided that everything left of the first colon is the password. This PR would change the behavior to consider everything of the rightmost colon to be the username, breaking every setup where the password contains a colon (e.g. name:password, like in the test case).

Without additional escaping, it is impossible to support colons in both the username and the password at the same time. Even introducing escaping is likely to break configurations. See the discussion in #591.
That's why we decided to no change the behavior for now.