provider.go

/*
Copyright 2017 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package provider

import (
	"context"
	"errors"
	"net"
	"strings"

	"sigs.k8s.io/external-dns/endpoint"
	"sigs.k8s.io/external-dns/plan"
)

// SoftError is an error, that provider will only log as error instead
// of fatal. It is meant for error propagation from providers to tell
// that this is a transient error.
var SoftError error = errors.New("soft error")

// NewSoftError creates a SoftError from the given error
func NewSoftError(err error) error {
	return errors.Join(SoftError, err)
}

// Provider defines the interface DNS providers should implement.
type Provider interface {
	Records(ctx context.Context) ([]*endpoint.Endpoint, error)
	ApplyChanges(ctx context.Context, changes *plan.Changes) error
	// AdjustEndpoints canonicalizes a set of candidate endpoints.
	// It is called with a set of candidate endpoints obtained from the various sources.
	// It returns a set modified as required by the provider. The provider is responsible for
	// adding, removing, and modifying the ProviderSpecific properties to match
	// the endpoints that the provider returns in `Records` so that the change plan will not have
	// unnecessary (potentially failing) changes. It may also modify other fields, add, or remove
	// Endpoints. It is permitted to modify the supplied endpoints.
	AdjustEndpoints(endpoints []*endpoint.Endpoint) ([]*endpoint.Endpoint, error)
	GetDomainFilter() endpoint.DomainFilter
}

type BaseProvider struct{}

func (b BaseProvider) AdjustEndpoints(endpoints []*endpoint.Endpoint) ([]*endpoint.Endpoint, error) {
	return endpoints, nil
}

func (b BaseProvider) GetDomainFilter() endpoint.DomainFilter {
	return endpoint.DomainFilter{}
}

type contextKey struct {
	name string
}

func (k *contextKey) String() string { return "provider context value " + k.name }

// RecordsContextKey is a context key. It can be used during ApplyChanges
// to access previously cached records. The associated value will be of
// type []*endpoint.Endpoint.
var RecordsContextKey = &contextKey{"records"}

// EnsureTrailingDot ensures that the hostname receives a trailing dot if it hasn't already.
func EnsureTrailingDot(hostname string) string {
	if net.ParseIP(hostname) != nil {
		return hostname
	}

	return strings.TrimSuffix(hostname, ".") + "."
}

// Difference tells which entries need to be respectively
// added, removed, or left untouched for "current" to be transformed to "desired"
func Difference(current, desired []string) ([]string, []string, []string) {
	add, remove, leave := []string{}, []string{}, []string{}
	index := make(map[string]struct{}, len(current))
	for _, x := range current {
		index[x] = struct{}{}
	}
	for _, x := range desired {
		if _, found := index[x]; found {
			leave = append(leave, x)
			delete(index, x)
		} else {
			add = append(add, x)
			delete(index, x)
		}
	}
	for x := range index {
		remove = append(remove, x)
	}
	return add, remove, leave
}