Update MTProxy checker documentation and logic to clarify probing modes and improve error handling. Modify README and Docker documentation to reflect changes in the -probe flag behavior, including detailed descriptions of exit codes and timeout handling. Refactor connection handling to enhance robustness and align with Telethon's approach.

internal/checker/checker.go

@@ -18,9 +18,6 @@ import (
 // ErrProxyClosed indicates the peer closed the TCP connection during the check (Telethon #1134 style).
 var ErrProxyClosed = errors.New("mtproxy closed connection after initial payload")
 
-// ErrNoDataAfterHeader is returned in ProbeFast when the proxy sends nothing after the init payload within the wait window.
-var ErrNoDataAfterHeader = errors.New("no data from proxy after mtproxy header (timeout)")
-
 // Check runs Fake-TLS/dd handshake and MTProxy init; further steps depend on opts.Probe (see Options). opts nil => ProbeFast.
 func Check(ctx context.Context, host string, port int, parsed *secret.Parsed, dcID int16, opts *Options) error {
 	conn, err := dialTCP(ctx, host, port)
@@ -54,6 +51,7 @@ func checkEE(ctx context.Context, conn net.Conn, p *secret.Parsed, dcID int16, o
 	if _, err := conn.Write(ch.Record); err != nil {
 		return fmt.Errorf("write client hello: %w", err)
 	}
+	// ServerHello читаем с сырого conn (ровно длина записи), как в tdesktop Read — без readahead.
 	resp, err := faketls.ReadServerHello(conn)
 	if err != nil {
 		return fmt.Errorf("read server hello: %w", err)
@@ -69,11 +67,12 @@ func checkEE(ctx context.Context, conn net.Conn, p *secret.Parsed, dcID int16, o
 	if err := faketls.WriteTLSApplicationData(conn, hdr); err != nil {
 		return fmt.Errorf("write mtproxy header: %w", err)
 	}
-	if o.Probe == ProbeFast {
-		return waitPostPayload(conn)
-	}
+	// После init один bufio на чтение TLS 0x17 (Telethon/telemt: не смешивать conn.Read и буфер).
 	br := bufio.NewReader(conn)
-	if err := tgquick.DrainPostInitEE(ctx, br, conn, dec, 2*time.Second); err != nil {
+	if o.Probe == ProbeFast {
+		return waitPostPayload(br, conn)
+	}
+	if err := tgquick.DrainPostInitEE(ctx, br, conn, dec, 5*time.Second); err != nil {
 		return err
 	}
 	if err := tgquick.VerifyResPQ(ctx, conn, enc, dec, br); err != nil {
@@ -94,7 +93,7 @@ func checkDD(ctx context.Context, conn net.Conn, p *secret.Parsed, dcID int16, o
 		return fmt.Errorf("write mtproxy header: %w", err)
 	}
 	if o.Probe == ProbeFast {
-		return waitPostPayload(conn)
+		return waitPostPayload(conn, conn)
 	}
 	if err := tgquick.VerifyResPQ(ctx, conn, enc, dec, nil); err != nil {
 		if errors.Is(err, tgquick.ErrPeerClosed) {
@@ -105,29 +104,32 @@ func checkDD(ctx context.Context, conn net.Conn, p *secret.Parsed, dcID int16, o
 	return nil
 }
 
-func waitPostPayload(conn net.Conn) error {
+// waitPostPayload после init повторяет логику Telethon TcpMTProxy._connect (#1134):
+// ждём появления данных или таймаут, затем считаем успехом только если соединение не закрыто сразу после payload.
+// Наличие входящих байтов не обязательно — часть прокси молчит до первого MTProto от клиента.
+func waitPostPayload(r io.Reader, c net.Conn) error {
 	deadline := time.Now().Add(2 * time.Second)
 	buf := make([]byte, 4096)
 	for time.Now().Before(deadline) {
-		_ = conn.SetReadDeadline(time.Now().Add(200 * time.Millisecond))
-		n, err := conn.Read(buf)
+		_ = c.SetReadDeadline(time.Now().Add(200 * time.Millisecond))
+		n, err := r.Read(buf)
 		if n > 0 {
-			_ = conn.SetReadDeadline(time.Time{})
+			_ = c.SetReadDeadline(time.Time{})
 			return nil
 		}
 		if err != nil {
 			if errors.Is(err, io.EOF) {
-				_ = conn.SetReadDeadline(time.Time{})
+				_ = c.SetReadDeadline(time.Time{})
 				return ErrProxyClosed
 			}
 			var ne net.Error
 			if errors.As(err, &ne) && ne.Timeout() {
 				continue
 			}
-			_ = conn.SetReadDeadline(time.Time{})
+			_ = c.SetReadDeadline(time.Time{})
 			return err
 		}
 	}
-	_ = conn.SetReadDeadline(time.Time{})
-	return ErrNoDataAfterHeader
+	_ = c.SetReadDeadline(time.Time{})
+	return nil
 }

internal/checker/options.go

@@ -6,7 +6,7 @@ import "strings"
 type ProbeMode int
 
 const (
-	// ProbeFast: handshake + init, then any inbound data within a short window (legacy behavior; fast).
+	// ProbeFast: handshake + init, then short wait like Telethon TcpMTProxy (#1134): OK if proxy does not close immediately.
 	ProbeFast ProbeMode = iota
 	// ProbeDeep: MTProto req_pq and expect resPQ from Telegram DC through the tunnel (stricter; slower).
 	ProbeDeep