From 251659145364f628a0dd915a522ad322f5ef10b2 Mon Sep 17 00:00:00 2001
From: Mike Kolganov <mkolganov@zetaglobal.com>
Date: Thu, 2 Apr 2026 02:11:39 +0600
Subject: [PATCH] feat: add --interface flag to bind connections to a specific
 network interface

Adds -interface flag that uses SO_BINDTODEVICE to bind all outgoing HTTP
connections to a specified network interface (e.g. tun0, eth1). Linux only;
on other platforms the flag is accepted but has no effect.
---
 .gitignore                 |  1 +
 README.md                  |  1 +
 go.mod                     |  2 +-
 main.go                    |  2 ++
 pkg/yandex/client.go       | 12 ++++++++----
 pkg/yandex/client_linux.go | 35 +++++++++++++++++++++++++++++++++++
 pkg/yandex/client_other.go |  9 +++++++++
 7 files changed, 57 insertions(+), 5 deletions(-)
 create mode 100644 .gitignore
 create mode 100644 pkg/yandex/client_linux.go
 create mode 100644 pkg/yandex/client_other.go

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..08cb523
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+go.sum
diff --git a/README.md b/README.md
index e0b1b8d..bf55648 100644
--- a/README.md
+++ b/README.md
@@ -39,3 +39,4 @@ go build -o internetometer main.go
 - `--save log.jsonl`: Сохранить результат в лог-файл.
 - `--prometheus`: Вывод в формате метрик Prometheus.
 - `--concurrency 4`: Количество параллельных потоков.
+- `--interface tun0`: Привязать исходящие соединения к указанному сетевому интерфейсу (использует `SO_BINDTODEVICE`, только Linux).
diff --git a/go.mod b/go.mod
index b1f38dd..b8b744f 100644
--- a/go.mod
+++ b/go.mod
@@ -6,6 +6,7 @@ require (
 	github.com/charmbracelet/bubbles v1.0.0
 	github.com/charmbracelet/bubbletea v1.3.10
 	github.com/charmbracelet/lipgloss v1.1.0
+	golang.org/x/sys v0.38.0
 )
 
 require (
@@ -28,6 +29,5 @@ require (
 	github.com/muesli/termenv v0.16.0 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
-	golang.org/x/sys v0.38.0 // indirect
 	golang.org/x/text v0.3.8 // indirect
 )
diff --git a/main.go b/main.go
index df30843..0e3e231 100644
--- a/main.go
+++ b/main.go
@@ -23,6 +23,7 @@ func main() {
 	prometheus := flag.Bool("prometheus", false, "Output results in Prometheus metrics format")
 	useTUI := flag.Bool("tui", false, "Use interactive TUI for progress")
 	timeout := flag.Duration("timeout", 60*time.Second, "Timeout for the entire operation")
+	iface := flag.String("interface", "", "Bind outgoing connections to this network interface, e.g. tun0 (uses SO_BINDTODEVICE)")
 
 	flag.Parse()
 
@@ -34,6 +35,7 @@ func main() {
 		Timeout:     *timeout,
 		Language:    *lang,
 		Concurrency: *concurrency,
+		Interface:   *iface,
 	})
 
 	if *useTUI {
diff --git a/pkg/yandex/client.go b/pkg/yandex/client.go
index 4b1a4a9..5fb7aeb 100644
--- a/pkg/yandex/client.go
+++ b/pkg/yandex/client.go
@@ -14,6 +14,7 @@ type Config struct {
 	Timeout     time.Duration
 	Language    string // "ru" or "en"
 	Concurrency int
+	Interface   string // bind outgoing connections to this network interface (SO_BINDTODEVICE, Linux only)
 }
 
 type Client struct {
@@ -37,11 +38,14 @@ func NewClient(cfg *Config) *Client {
 		cfg.Concurrency = 4
 	}
 
+	httpClient := &http.Client{Timeout: cfg.Timeout}
+	if t := interfaceTransport(cfg.Interface); t != nil {
+		httpClient.Transport = t
+	}
+
 	return &Client{
-		httpClient: &http.Client{
-			Timeout: cfg.Timeout,
-		},
-		config: cfg,
+		httpClient: httpClient,
+		config:     cfg,
 	}
 }
 
diff --git a/pkg/yandex/client_linux.go b/pkg/yandex/client_linux.go
new file mode 100644
index 0000000..7d489e3
--- /dev/null
+++ b/pkg/yandex/client_linux.go
@@ -0,0 +1,35 @@
+//go:build linux
+
+package yandex
+
+import (
+	"net"
+	"net/http"
+	"syscall"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+func interfaceTransport(iface string) http.RoundTripper {
+	if iface == "" {
+		return nil
+	}
+	dialer := &net.Dialer{
+		Timeout:   30 * time.Second,
+		KeepAlive: 30 * time.Second,
+		Control: func(network, address string, c syscall.RawConn) error {
+			var sockErr error
+			err := c.Control(func(fd uintptr) {
+				sockErr = unix.SetsockoptString(int(fd), unix.SOL_SOCKET, unix.SO_BINDTODEVICE, iface)
+			})
+			if err != nil {
+				return err
+			}
+			return sockErr
+		},
+	}
+	return &http.Transport{
+		DialContext: dialer.DialContext,
+	}
+}
diff --git a/pkg/yandex/client_other.go b/pkg/yandex/client_other.go
new file mode 100644
index 0000000..187a1db
--- /dev/null
+++ b/pkg/yandex/client_other.go
@@ -0,0 +1,9 @@
+//go:build !linux
+
+package yandex
+
+import "net/http"
+
+func interfaceTransport(_ string) http.RoundTripper {
+	return nil
+}