netchecker

A fast, cross-platform internet reachability checker. It probes your local network infrastructure, DNS resolution, and a set of domestic / global / filtered websites in parallel, and reports each as PASS / FAIL / INFO with timings — in about 1–2 seconds total.

It was built for diagnosing a specific, annoying situation: "my internet is technically up, but which parts actually work — the ISP, DNS, the proxy, the filtered sites?" It's especially useful behind a VPN/proxy where the answer differs per route.

===============================================
   netchecker — Network Standpoint Test
   Running Mode:  DIRECT
   Local IP:      192.168.1.6
   DNS resolvers: 192.168.1.1
   Per-probe timeout: 2 seconds
===============================================
[*] Dispatching parallel probes...

[+] Infrastructure Standpoints:
  [PASS] Local Network Interface        - Active on en0 (192.168.1.6) — Wi-Fi SSID: home
  [PASS] Ping Default Gateway (192.168.1.1) - reachable — 2 ms
  [PASS] Ping Raw Global IP (1.1.1.1)   - Global IP routing up — 4 ms

[+] DNS Resolution:
  [PASS] www.google.com                 - Resolved to 142.251.153.119 — 21 ms
  ...

[*] Domestic Websites (DIRECT Route):
  [PASS] digikala.com                   - HTTP 301 — 119 ms
  ...

Install

cargo install netchecker

Or build from source:

git clone https://github.com/pourmand1376/netchecker
cd netchecker
cargo build --release
./target/release/netchecker

Usage

netchecker            # prompts for mode
netchecker direct     # test the raw ISP connection, bypassing proxies
netchecker proxy      # route global/filtered sites through the system proxy
netchecker -d         # short flags also work (-d / -p)

• Direct mode pins every request to a pre-resolved IP and bypasses all proxies — it tests your raw ISP path.
• Proxy mode sends the global/filtered sites through your system proxy (auto-detected). Domestic sites always go direct.

How it works (and why)

• DNS that can't wedge. On macOS, getaddrinfo() goes through mDNSResponder; when the local resolver is bad or was just changed, that daemon serialises lookups and collapses "parallel" probes into a long stall. netchecker resolves names itself with [hickory-resolver], which talks to the configured nameservers directly over UDP/53 and never touches the OS resolver. A bad lookup fails fast instead of hanging everything.

• IP-pinned probes. On the direct route, each HTTP probe is handed the pre-resolved IP so it never calls the OS resolver — the same anti-wedge guarantee, end to end. Redirects aren't followed on the direct route (a cross-host redirect would trigger a fresh OS lookup); a 3xx still counts as reachable.

• Reachability without root. No ICMP (which needs elevated privileges). netchecker uses TCP connects and races a few common ports — a ConnectionRefused still proves the host answered, so it counts as reachable. Only a host that fails on every port is reported down.

• True egress detection. The active interface is found by asking the kernel which local address it would use to reach the internet (a UDP connect that sends nothing), not by a heuristic. This gets the right answer on split-tunnel VPNs, where the "default route" and the real internet path differ.

Platform support

The core — DNS bypass, HTTP probes, interface/gateway detection, TCP reachability — is native Rust and works the same on all three platforms:

1. Reads scutil --proxy (catches GUI-configured proxies) plus env vars.
2. Reads HTTPS_PROXY / ALL_PROXY / HTTP_PROXY env vars.
3. Best-effort via ipconfig / networksetup; on macOS 14+ the SSID is gated behind Location Services permission and may come back empty.
4. Best-effort via nmcli / iwgetid (NetworkManager).
5. Best-effort via netsh wlan show interfaces.

SSID is the one genuinely fragile piece — there is no dependable cross-platform API for it. When it can't be read, netchecker shows "SSID unavailable or wired" rather than failing.

Customising the site list

The domestic / global / filtered lists live in src/sites.rs. Edit them to match the sites you care about and rebuild.

License

MIT — see LICENSE.