Switch to go-ldap/ldap for filter (de-)compilation

[rhafer]

The filter parsing code that was originally imported from
https://github.com/nmcclain/ldap/ had some issues with decompiling Filters
from BER to their string representation. This removes the filter
parsing from idm and uses the code from go-ldap/ldap now, which is
basically a drop-in replacement.

Fixes: #67

[longsleep]

@rhafer i dont remember exactly why I added a local variant of the filter functionality in the first place. Is the go-ldap stuff newer?

There are some changes in the filter implementation https://github.com/libregraph/idm/commits/ba794e219d769b14407879d54008d6e13cf8f593/internal/ldapserver/filter.go?browsing_rename_history=true&new_path=pkg/ldapserver/filter.go&original_branch=master - please verify that those are indeed no longer needed / useful.

[longsleep]

@rhafer can we keep this change API compatible / not remove or change any publich API in the ldapserver package. Should be doable by importing them from go-ldap in the filter.go file and exporting public identifiers or wrapper functions for the stuff. This would avoid the need for a new major release and makes the fix available for anyone using the ldapserver package from here.

[rhafer]

i dont remember exactly why I added a local variant of the filter functionality in the first place. Is the go-ldap stuff newer?

Yes. E.q. it has the required Escape fixes https://github.com/go-ldap/ldap/blob/master/v3/filter.go#L148

[rhafer]

There are some changes in the filter implementation https://github.com/libregraph/idm/commits/ba794e219d769b14407879d54008d6e13cf8f593/internal/ldapserver/filter.go?browsing_rename_history=true&new_path=pkg/ldapserver/filter.go&original_branch=master - please verify that those are indeed no longer needed / useful.

As far as I can see the only relevant change in idm that we would loose in idm is this hunk from c2b9f72

 func CompileFilter(filter string) (*ber.Packet, error) {
-	if len(filter) == 0 || filter[0] != '(' {
+	if filter == "" || filter[0] != '(' {
		return nil, ldap.NewError(ldap.ErrorFilterCompile, errors.New("ldap: filter does not start with an '('"))
	}
	packet, pos, err := compileFilter(filter, 1)

I seriously doubt that that change has any relevant impact. 😄

[longsleep]

I seriously doubt that that change has any relevant impact.

This one probably not. But others were made after benchmarking / profiling. Especially the stuff with the case insensitive comparison.

[rhafer]

This one probably not. But others were made after benchmarking / profiling. Especially the stuff with the case insensitive comparison.

Sure. But that was in ServerApplyFilter. Which I haven't touched.

[longsleep]

LGTM 👍