Go port of @patterniha's SNI-Spoofing / DPI-bypass TCP forwarder — his idea, all credit to him. This is just a faithful reimplementation of the original Windows (WinDivert + Python) tool.

Linux and macOS. Linux uses AF_PACKET raw sockets (CAP_NET_RAW / root). macOS uses BPF via /dev/bpf* (needs root, or r/w access to a bpf device).

A local TCP forwarder that tricks stateful DPI into whitelisting the flow before the real TLS ClientHello is sent:

1. Accept a client, dial the upstream, let the kernel do the TCP 3-way handshake normally.
2. An AF_PACKET sniffer watches the handshake. It records the outbound SYN's ISN, and the instant it sees the outbound 3rd-handshake ACK it injects a crafted TLS ClientHello frame carrying an innocuous FAKE_SNI (e.g. security.vercel.com).
3. The fake packet uses seq = ISN + 1 - len(fake) — i.e. a sequence number before the server's receive window. DPI parses it and whitelists the connection; the server drops it as out-of-window.
4. The sniffer waits for the server's reply ACK with ack == ISN + 1, which proves the server ignored the fake and is still expecting the real byte stream. Only then does the forwarder start relaying real client↔server data. The real ClientHello is now invisible to DPI.
5. If that confirmation doesn't arrive within 2s, the connection is aborted.

go build -o sni-spoof .
sudo ./sni-spoof config.json

Works on Linux and macOS (amd64 / arm64). On macOS you may need to allow the binary to open /dev/bpf* — running under sudo is the simplest option.

config.json:

{
  "LISTEN_HOST": "0.0.0.0",
  "LISTEN_PORT": 40443,
  "CONNECT_IP": "104.18.4.130",
  "CONNECT_PORT": 443,
  "FAKE_SNI": "security.vercel.com"
}

Point your client (xray, etc.) at LISTEN_HOST:LISTEN_PORT instead of the real upstream.