syncer.go

package usersync

import (
	"errors"
	"fmt"
	"net/url"
	"regexp"
	"strings"
	"text/template"

	validator "github.com/asaskevich/govalidator"
	"github.com/prebid/prebid-server/config"
	"github.com/prebid/prebid-server/macros"
	"github.com/prebid/prebid-server/privacy"
)

var (
	errNoSyncTypesProvided        = errors.New("no sync types provided")
	errNoSyncTypesSupported       = errors.New("no sync types supported")
	errDefaultTypeMissingIFrame   = errors.New("default is set to iframe but no iframe endpoint is configured")
	errDefaultTypeMissingRedirect = errors.New("default is set to redirect but no redirect endpoint is configured")
)

// Syncer represents the user sync configuration for a bidder or a shared set of bidders.
type Syncer interface {
	// Key is the name of the syncer as stored in the user's cookie. This is often, but not
	// necessarily, a one-to-one mapping with a bidder.
	Key() string

	// DefaultSyncType is the default SyncType for this syncer.
	DefaultSyncType() SyncType

	// SupportsType returns true if the syncer supports at least one of the specified sync types.
	SupportsType(syncTypes []SyncType) bool

	// GetSync returns a user sync for the user's device to perform, or an error if the none of the
	// sync types are supported or if macro substitution fails.
	GetSync(syncTypes []SyncType, privacyPolicies privacy.Policies) (Sync, error)
}

// Sync represents a user sync to be performed by the user's device.
type Sync struct {
	URL         string
	Type        SyncType
	SupportCORS bool
}

type standardSyncer struct {
	key             string
	defaultSyncType SyncType
	iframe          *template.Template
	redirect        *template.Template
	supportCORS     bool
}

const (
	setuidSyncTypeIFrame   = "b" // b = blank HTML response
	setuidSyncTypeRedirect = "i" // i = image response
)

var ErrSyncerEndpointRequired = errors.New("at least one endpoint (iframe and/or redirect) is required")
var ErrSyncerKeyRequired = errors.New("key is required")

// NewSyncer creates a new Syncer from the provided configuration, or return an error if macro substition
// fails or an endpoint url is invalid.
func NewSyncer(hostConfig config.UserSync, syncerConfig config.Syncer) (Syncer, error) {
	if syncerConfig.Key == "" {
		return nil, ErrSyncerKeyRequired
	}

	if syncerConfig.IFrame == nil && syncerConfig.Redirect == nil {
		return nil, ErrSyncerEndpointRequired
	}

	syncer := standardSyncer{
		key:             syncerConfig.Key,
		defaultSyncType: resolveDefaultSyncType(syncerConfig),
		supportCORS:     syncerConfig.SupportCORS != nil && *syncerConfig.SupportCORS,
	}

	if syncerConfig.IFrame != nil {
		var err error
		syncer.iframe, err = buildTemplate(syncerConfig.Key, setuidSyncTypeIFrame, hostConfig, syncerConfig.ExternalURL, *syncerConfig.IFrame)
		if err != nil {
			return nil, fmt.Errorf("iframe %v", err)
		}
		if err := validateTemplate(syncer.iframe); err != nil {
			return nil, fmt.Errorf("iframe %v", err)
		}
	}

	if syncerConfig.Redirect != nil {
		var err error
		syncer.redirect, err = buildTemplate(syncerConfig.Key, setuidSyncTypeRedirect, hostConfig, syncerConfig.ExternalURL, *syncerConfig.Redirect)
		if err != nil {
			return nil, fmt.Errorf("redirect %v", err)
		}
		if err := validateTemplate(syncer.redirect); err != nil {
			return nil, fmt.Errorf("redirect %v", err)
		}
	}

	return syncer, nil
}

func resolveDefaultSyncType(syncerConfig config.Syncer) SyncType {
	if syncerConfig.IFrame != nil {
		return SyncTypeIFrame
	}
	return SyncTypeRedirect
}

// macro substitution regex
var (
	macroRegexExternalHost = regexp.MustCompile(`{{\s*\.ExternalURL\s*}}`)
	macroRegexSyncerKey    = regexp.MustCompile(`{{\s*\.SyncerKey\s*}}`)
	macroRegexSyncType     = regexp.MustCompile(`{{\s*\.SyncType\s*}}`)
	macroRegexUserMacro    = regexp.MustCompile(`{{\s*\.UserMacro\s*}}`)
	macroRegexRedirect     = regexp.MustCompile(`{{\s*\.RedirectURL\s*}}`)
	macroRegex             = regexp.MustCompile(`{{\s*\..*?\s*}}`)
)

func buildTemplate(key, syncTypeValue string, hostConfig config.UserSync, syncerExternalURL string, syncerEndpoint config.SyncerEndpoint) (*template.Template, error) {
	redirectTemplate := syncerEndpoint.RedirectURL
	if redirectTemplate == "" {
		redirectTemplate = hostConfig.RedirectURL
	}

	externalURL := chooseExternalURL(syncerEndpoint.ExternalURL, syncerExternalURL, hostConfig.ExternalURL)

	redirectURL := macroRegexSyncerKey.ReplaceAllLiteralString(redirectTemplate, key)
	redirectURL = macroRegexSyncType.ReplaceAllLiteralString(redirectURL, syncTypeValue)
	redirectURL = macroRegexUserMacro.ReplaceAllLiteralString(redirectURL, syncerEndpoint.UserMacro)
	redirectURL = macroRegexExternalHost.ReplaceAllLiteralString(redirectURL, externalURL)
	redirectURL = escapeTemplate(redirectURL)

	url := macroRegexRedirect.ReplaceAllString(syncerEndpoint.URL, redirectURL)

	templateName := strings.ToLower(key) + "_usersync_url"
	return template.New(templateName).Parse(url)
}

// chooseExternalURL selects the external url to use for the template, where the most specific config wins.
func chooseExternalURL(syncerEndpointURL, syncerURL, hostConfigURL string) string {
	if syncerEndpointURL != "" {
		return syncerEndpointURL
	}

	if syncerURL != "" {
		return syncerURL
	}

	return hostConfigURL
}

// escapeTemplate url encodes a string template leaving the macro tags unaffected.
func escapeTemplate(x string) string {
	escaped := strings.Builder{}

	i := 0
	for _, m := range macroRegex.FindAllStringIndex(x, -1) {
		escaped.WriteString(url.QueryEscape(x[i:m[0]]))
		escaped.WriteString(x[m[0]:m[1]])
		i = m[1]
	}
	escaped.WriteString(url.QueryEscape(x[i:]))

	return escaped.String()
}

var templateTestValues = macros.UserSyncTemplateParams{
	GDPR:        "anyGDPR",
	GDPRConsent: "anyGDPRConsent",
	USPrivacy:   "anyCCPAConsent",
}

func validateTemplate(template *template.Template) error {
	url, err := macros.ResolveMacros(template, templateTestValues)
	if err != nil {
		return err
	}

	if !validator.IsURL(url) || !validator.IsRequestURL(url) {
		return fmt.Errorf(`composed url: "%s" is invalid`, url)
	}

	return nil
}

func (s standardSyncer) Key() string {
	return s.key
}

func (s standardSyncer) DefaultSyncType() SyncType {
	return s.defaultSyncType
}

func (s standardSyncer) SupportsType(syncTypes []SyncType) bool {
	supported := s.filterSupportedSyncTypes(syncTypes)
	return len(supported) > 0
}

func (s standardSyncer) filterSupportedSyncTypes(syncTypes []SyncType) []SyncType {
	supported := make([]SyncType, 0, len(syncTypes))
	for _, syncType := range syncTypes {
		switch syncType {
		case SyncTypeIFrame:
			if s.iframe != nil {
				supported = append(supported, SyncTypeIFrame)
			}
		case SyncTypeRedirect:
			if s.redirect != nil {
				supported = append(supported, SyncTypeRedirect)
			}
		}
	}
	return supported
}

func (s standardSyncer) GetSync(syncTypes []SyncType, privacyPolicies privacy.Policies) (Sync, error) {
	syncType, err := s.chooseSyncType(syncTypes)
	if err != nil {
		return Sync{}, err
	}

	syncTemplate := s.chooseTemplate(syncType)

	url, err := macros.ResolveMacros(syncTemplate, macros.UserSyncTemplateParams{
		GDPR:        privacyPolicies.GDPR.Signal,
		GDPRConsent: privacyPolicies.GDPR.Consent,
		USPrivacy:   privacyPolicies.CCPA.Consent,
	})
	if err != nil {
		return Sync{}, err
	}

	sync := Sync{
		URL:         url,
		Type:        syncType,
		SupportCORS: s.supportCORS,
	}
	return sync, nil
}

func (s standardSyncer) chooseSyncType(syncTypes []SyncType) (SyncType, error) {
	if len(syncTypes) == 0 {
		return SyncTypeUnknown, errNoSyncTypesProvided
	}

	supported := s.filterSupportedSyncTypes(syncTypes)
	if len(supported) == 0 {
		return SyncTypeUnknown, errNoSyncTypesSupported
	}

	// prefer default type
	for _, syncType := range supported {
		if syncType == s.defaultSyncType {
			return syncType, nil
		}
	}

	return syncTypes[0], nil
}

func (s standardSyncer) chooseTemplate(syncType SyncType) *template.Template {
	switch syncType {
	case SyncTypeIFrame:
		return s.iframe
	case SyncTypeRedirect:
		return s.redirect
	default:
		return nil
	}
}