util/git: add domain suffix host matching and fix trailing slash handling

[cuixq]

• Support domain-suffix matching in RegisterHostHandler and getHostHandler when the registered host starts with ., and register a StandardHostHandler for .googlesource.com.
• Strip trailing slashes from res.Path at the start of StandardHostHandler.Canon() before segment counting and .git suffix checks, and re-add the slash at the end only when HasTrailingSlash is true.

[calebbrown]

Hi @cuixq,

Trailing slash support is already in the host handler. Did you consider adding a host handler for chromium.googlesource.com?

[cuixq]

@calebbrown Adding a host handler for chromium.googlesource.com alone doesn't quite fix .git/ URLs, because StandardHostHandler.Canon handles .git before stripping the trailing /.

Also, since RegisterHostHandler only matches exact hostnames, registering chromium.googlesource.com wouldn't cover other *.googlesource.com subdomains.

Do you prefer keeping this in canon.go, or should I instead fix the / and .git ordering in hosts.go/repo.go and add a handler for chromium.googlesource.com?

[calebbrown]

So my prior take on this in https://github.com/ossf/malicious-packages/blob/main/internal/gitname/hosts.go had support for domain suffix mapping. This is definitely worth adding.

I didn't add it here originally since it made the code more complex.

I think the right thing to do is:

1. add the domain-suffix based matching; and
2. fix the .git code in StandardHostHandler so that it strips any trailing slashes before adding the .git suffix is checked. This probably should be done independently of HasTrailingSlash. So example.com/path/to/repo/ becomes example.com/path/to/repo.git (or example.com/path/to/repo.git/ if HasTrailingSlash is true)