Add GeoIP and GeoSite support for expr (#38)

* feat: copy something from hysteria/extras/outbounds/acl

* feat: add geoip and geosite support for expr

* refactor: geo matcher

* fix: typo

* refactor: geo matcher

* feat: expose config options to specify local geoip/geosite db files

* refactor: engine.Config should not contains geo

* feat: make geosite and geoip lazy downloaded

* chore: minor code improvement

* docs: add geoip/geosite usage

---------

Co-authored-by: Toby <tobyxdd@gmail.com>

ruleset/builtins/geo/geo_matcher.go

@@ -0,0 +1,115 @@
+package geo
+
+import (
+	"net"
+	"strings"
+	"sync"
+)
+
+type GeoMatcher struct {
+	geoLoader       GeoLoader
+	geoSiteMatcher  map[string]hostMatcher
+	siteMatcherLock sync.Mutex
+	geoIpMatcher    map[string]hostMatcher
+	ipMatcherLock   sync.Mutex
+}
+
+func NewGeoMatcher(geoSiteFilename, geoIpFilename string) (*GeoMatcher, error) {
+	geoLoader := NewDefaultGeoLoader(geoSiteFilename, geoIpFilename)
+
+	return &GeoMatcher{
+		geoLoader:      geoLoader,
+		geoSiteMatcher: make(map[string]hostMatcher),
+		geoIpMatcher:   make(map[string]hostMatcher),
+	}, nil
+}
+
+func (g *GeoMatcher) MatchGeoIp(ip, condition string) bool {
+	g.ipMatcherLock.Lock()
+	defer g.ipMatcherLock.Unlock()
+
+	matcher, ok := g.geoIpMatcher[condition]
+	if !ok {
+		// GeoIP matcher
+		condition = strings.ToLower(condition)
+		country := condition
+		if len(country) == 0 {
+			return false
+		}
+		gMap, err := g.geoLoader.LoadGeoIP()
+		if err != nil {
+			return false
+		}
+		list, ok := gMap[country]
+		if !ok || list == nil {
+			return false
+		}
+		matcher, err = newGeoIPMatcher(list)
+		if err != nil {
+			return false
+		}
+		g.geoIpMatcher[condition] = matcher
+	}
+	parseIp := net.ParseIP(ip)
+	if parseIp == nil {
+		return false
+	}
+	ipv4 := parseIp.To4()
+	if ipv4 != nil {
+		return matcher.Match(HostInfo{IPv4: ipv4})
+	}
+	ipv6 := parseIp.To16()
+	if ipv6 != nil {
+		return matcher.Match(HostInfo{IPv6: ipv6})
+	}
+	return false
+}
+
+func (g *GeoMatcher) MatchGeoSite(site, condition string) bool {
+	g.siteMatcherLock.Lock()
+	defer g.siteMatcherLock.Unlock()
+
+	matcher, ok := g.geoSiteMatcher[condition]
+	if !ok {
+		// MatchGeoSite matcher
+		condition = strings.ToLower(condition)
+		name, attrs := parseGeoSiteName(condition)
+		if len(name) == 0 {
+			return false
+		}
+		gMap, err := g.geoLoader.LoadGeoSite()
+		if err != nil {
+			return false
+		}
+		list, ok := gMap[name]
+		if !ok || list == nil {
+			return false
+		}
+		matcher, err = newGeositeMatcher(list, attrs)
+		if err != nil {
+			return false
+		}
+		g.geoSiteMatcher[condition] = matcher
+	}
+	return matcher.Match(HostInfo{Name: site})
+}
+
+func (g *GeoMatcher) LoadGeoSite() error {
+	_, err := g.geoLoader.LoadGeoSite()
+	return err
+}
+
+func (g *GeoMatcher) LoadGeoIP() error {
+	_, err := g.geoLoader.LoadGeoIP()
+	return err
+}
+
+func parseGeoSiteName(s string) (string, []string) {
+	parts := strings.Split(s, "@")
+	base := strings.TrimSpace(parts[0])
+	attrs := parts[1:]
+	for i := range attrs {
+		attrs[i] = strings.TrimSpace(attrs[i])
+	}
+	return base, attrs
+}