A comprehensive RFC7208 implementation

The SPF Library implements Sender Policy Framework described in RFC 7208. It aims to cover all rough edge cases from RFC 7208. Hence, the library does not operate on strings only, rather "understands" SPF records and reacts properly to valid and invalid input. Wherever I found it useful, I added comments with RFC sections and quotes directly in the source code, so the readers can follow implemented logic.

The library is still under development. API may change, including function/methods names and signatures. I will consider it correct and stable once it passess all tests described in the most popular SPF implementation - pyspf.

Testing is an important part of this implementation. There are unit tests that will run locally in your environment, however there are also configuration files for named DNS server that would be able to respond implemented testcases. (In fact, for the long time I used a real DNS server with such configuration as a testing infrastructure for my code). There is a plan to implement simple DNS server that would be able to read .yaml files with comprehensive testsuite defined in pyspf package. Code coverage is also important part of the development and the aim is to keep it as high as 9x %

SPF library depends on another DNS library. Sadly, Go's builtin DNS library is not elastic enough and does not allow for controlling underlying DNS queries/responses.

If you have any comments about code structure feel free to reach out or simply make a Pull Request