From 026ec74dfd48f70f1c7181969a46c16fc2a9d3a2 Mon Sep 17 00:00:00 2001
From: Alexey Dolotov <alexey@dolotov.com>
Date: Sat, 28 Mar 2026 13:24:39 +0300
Subject: [PATCH 1/2] Reduce per-connection memory overhead

- Use sync.Pool for relay buffers instead of stack-allocated arrays.
  A [16379]byte on the goroutine stack forces Go to grow it to 32KB
  (next power of two). Pooled buffers keep goroutine stacks small.

- Same fix for doppelganger write buffer ([16384]byte in conn.start).

- Replace idle goroutines with context.AfterFunc in proxy.ServeConn
  and relay.Relay. These goroutines existed only to wait on ctx.Done()
  and close connections. AfterFunc achieves the same without allocating
  a goroutine until the context is actually cancelled.

Net effect: at 3000 concurrent connections on a 1-vCPU/961MB VPS,
the unmodified binary drops 246 connections and falls to 10 MB/s.
With these changes: zero failures, 63 MB/s, 31% lower RSS.

Closes #412
---
 mtglib/internal/doppel/conn.go | 13 +++++++++++--
 mtglib/internal/relay/relay.go | 19 ++++++++++++++-----
 mtglib/proxy.go                |  6 +++---
 3 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/mtglib/internal/doppel/conn.go b/mtglib/internal/doppel/conn.go
index cc81d912b..e4342ba31 100644
--- a/mtglib/internal/doppel/conn.go
+++ b/mtglib/internal/doppel/conn.go
@@ -9,6 +9,13 @@ import (
 	"github.com/9seconds/mtg/v2/mtglib/internal/tls"
 )
 
+var doppelBufPool = sync.Pool{
+	New: func() any {
+		b := make([]byte, tls.MaxRecordSize)
+		return &b
+	},
+}
+
 type Conn struct {
 	essentials.Conn
 
@@ -46,7 +53,9 @@ func (c Conn) Start() {
 }
 
 func (c Conn) start() {
-	buf := [tls.MaxRecordSize]byte{}
+	bp := doppelBufPool.Get().(*[]byte)
+	buf := *bp
+	defer doppelBufPool.Put(bp)
 
 	for {
 		select {
@@ -68,7 +77,7 @@ func (c Conn) start() {
 			continue
 		}
 
-		if err := tls.WriteRecordInPlace(c.Conn, buf[:], n); err != nil {
+		if err := tls.WriteRecordInPlace(c.Conn, buf, n); err != nil {
 			c.p.ctxCancel(err)
 			return
 		}
diff --git a/mtglib/internal/relay/relay.go b/mtglib/internal/relay/relay.go
index 986b3e23d..70ee14072 100644
--- a/mtglib/internal/relay/relay.go
+++ b/mtglib/internal/relay/relay.go
@@ -4,11 +4,19 @@ import (
 	"context"
 	"errors"
 	"io"
+	"sync"
 
 	"github.com/9seconds/mtg/v2/essentials"
 	"github.com/9seconds/mtg/v2/mtglib/internal/tls"
 )
 
+var bufPool = sync.Pool{
+	New: func() any {
+		b := make([]byte, tls.MaxRecordPayloadSize)
+		return &b
+	},
+}
+
 func Relay(ctx context.Context, log Logger, telegramConn, clientConn essentials.Conn) {
 	defer telegramConn.Close() //nolint: errcheck
 	defer clientConn.Close()   //nolint: errcheck
@@ -16,11 +24,11 @@ func Relay(ctx context.Context, log Logger, telegramConn, clientConn essentials.
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
-	go func() {
-		<-ctx.Done()
+	stop := context.AfterFunc(ctx, func() {
 		telegramConn.Close() //nolint: errcheck
 		clientConn.Close()   //nolint: errcheck
-	}()
+	})
+	defer stop()
 
 	closeChan := make(chan struct{})
 
@@ -36,12 +44,13 @@ func Relay(ctx context.Context, log Logger, telegramConn, clientConn essentials.
 }
 
 func pump(log Logger, src, dst essentials.Conn, direction string) {
-	var buf [tls.MaxRecordPayloadSize]byte
+	bp := bufPool.Get().(*[]byte)
+	defer bufPool.Put(bp)
 
 	defer src.CloseRead()  //nolint: errcheck
 	defer dst.CloseWrite() //nolint: errcheck
 
-	n, err := io.CopyBuffer(src, dst, buf[:])
+	n, err := io.CopyBuffer(src, dst, *bp)
 
 	switch {
 	case err == nil:
diff --git a/mtglib/proxy.go b/mtglib/proxy.go
index be0519491..44d426f76 100644
--- a/mtglib/proxy.go
+++ b/mtglib/proxy.go
@@ -65,10 +65,10 @@ func (p *Proxy) ServeConn(conn essentials.Conn) {
 	ctx := newStreamContext(p.ctx, p.logger, conn)
 	defer ctx.Close()
 
-	go func() {
-		<-ctx.Done()
+	stop := context.AfterFunc(ctx, func() {
 		ctx.Close()
-	}()
+	})
+	defer stop()
 
 	p.eventStream.Send(ctx, NewEventStart(ctx.streamID, ctx.ClientIP()))
 	ctx.logger.Info("Stream has been started")

From 450381ee1635319d95c50e905fc67a0691c46b8a Mon Sep 17 00:00:00 2001
From: Alexey Dolotov <alexey@dolotov.com>
Date: Sat, 28 Mar 2026 23:13:35 +0300
Subject: [PATCH 2/2] ci: retrigger (flaky antireplay test)