refactor: decouple IPInfo from the service handlers (#200)

* Add structure logging with `slog`.

* Structure forgotten log.

* Another forgotten log.

* Remove IPInfo logic from TCP and UDP handling into the metrics collector.

* Refactor metrics into separate collectors.

* Rename some types to remove `Collector` suffix.

* Use an LRU cache to manage the ipInfos for Prometheus metrics.

* Use `nil` instead of `context.TODO()`.

* Use `LogAttrs` for `debug...()` log functions.

* Update logging in `metrics.go`.

* Fix another race condition.

* Revert renaming.

* Replace LRU cache with a simpler map that expires unused items.

* Move `SetBuildInfo()` call up.

* refactor: change `outlineMetrics` to implement the `prometheus.Collector` interface

* Address review comments.

* Refactor collectors so the connections/associations keep track of the connection metrics.

* Address review comments.

* Make metrics interfaces for bytes consistently use `int64`.

* Rename `Collector` to `Metrics`.

cmd/outline-ss-server/main.go

@@ -16,6 +16,7 @@ package main
 
 import (
 	"container/list"
+	"context"
 	"flag"
 	"fmt"
 	"log/slog"
@@ -28,6 +29,7 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/Jigsaw-Code/outline-sdk/transport"
 	"github.com/Jigsaw-Code/outline-sdk/transport/shadowsocks"
 	"github.com/Jigsaw-Code/outline-ss-server/ipinfo"
 	"github.com/Jigsaw-Code/outline-ss-server/service"
@@ -61,7 +63,7 @@ type SSServer struct {
 	stopConfig  func() error
 	lnManager   service.ListenerManager
 	natTimeout  time.Duration
-	m           *outlineMetricsCollector
+	m           *outlineMetrics
 	replayCache service.ReplayCache
 }
 
@@ -85,13 +87,13 @@ func (s *SSServer) loadConfig(filename string) error {
 }
 
 func (s *SSServer) NewShadowsocksStreamHandler(ciphers service.CipherList) service.StreamHandler {
-	authFunc := service.NewShadowsocksStreamAuthenticator(ciphers, &s.replayCache, s.m)
+	authFunc := service.NewShadowsocksStreamAuthenticator(ciphers, &s.replayCache, s.m.tcpServiceMetrics)
 	// TODO: Register initial data metrics at zero.
-	return service.NewStreamHandler(authFunc, s.m, tcpReadTimeout)
+	return service.NewStreamHandler(authFunc, tcpReadTimeout)
 }
 
 func (s *SSServer) NewShadowsocksPacketHandler(ciphers service.CipherList) service.PacketHandler {
-	return service.NewPacketHandler(s.natTimeout, ciphers, s.m)
+	return service.NewPacketHandler(s.natTimeout, ciphers, s.m, s.m.udpServiceMetrics)
 }
 
 type listenerSet struct {
@@ -196,7 +198,10 @@ func (s *SSServer) runConfig(config Config) (func() error, error) {
 					return err
 				}
 				slog.Info("Shadowsocks TCP service started.", "address", ln.Addr().String())
-				go service.StreamServe(ln.AcceptStream, sh.Handle)
+				go service.StreamServe(ln.AcceptStream, func(ctx context.Context, conn transport.StreamConn) {
+					connMetrics := s.m.AddOpenTCPConnection(conn)
+					sh.Handle(ctx, conn, connMetrics)
+				})
 
 				pc, err := lnSet.ListenPacket(addr)
 				if err != nil {
@@ -243,7 +248,7 @@ func (s *SSServer) Stop() error {
 }
 
 // RunSSServer starts a shadowsocks server running, and returns the server or an error.
-func RunSSServer(filename string, natTimeout time.Duration, sm *outlineMetricsCollector, replayHistory int) (*SSServer, error) {
+func RunSSServer(filename string, natTimeout time.Duration, sm *outlineMetrics, replayHistory int) (*SSServer, error) {
 	server := &SSServer{
 		lnManager:   service.NewListenerManager(),
 		natTimeout:  natTimeout,
@@ -348,7 +353,10 @@ func main() {
 	}
 	defer ip2info.Close()
 
-	metrics := newPrometheusOutlineMetrics(ip2info)
+	metrics, err := newPrometheusOutlineMetrics(ip2info)
+	if err != nil {
+		slog.Error("Failed to create Outline Prometheus metrics. Aborting.", "err", err)
+	}
 	metrics.SetBuildInfo(version)
 	r := prometheus.WrapRegistererWithPrefix("shadowsocks_", prometheus.DefaultRegisterer)
 	r.MustRegister(metrics)