refactor: convert script to automtu package with CI workflow

https://chatgpt.com/share/697112b2-0410-800f-93ff-9372b603d43f

.github/workflows/ci.yml

@@ -0,0 +1,46 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  test-and-lint:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+          cache: "pip"
+
+      - name: Install dependencies
+        shell: bash
+        run: |
+          set -euo pipefail
+          python -m pip install --upgrade pip
+          python -m pip install -e .
+          python -m pip install ruff
+
+      - name: Ruff (lint)
+        shell: bash
+        run: |
+          set -euo pipefail
+          ruff check .
+
+      - name: Ruff (format check)
+        shell: bash
+        run: |
+          set -euo pipefail
+          ruff format --check .
+
+      - name: Unit tests
+        shell: bash
+        run: |
+          set -euo pipefail
+          make test

Guide.md

@@ -1,202 +1,30 @@
-# wg-mtu-auto — Practical Guide
+# automtu — Practical Guide
-
-This guide shows **how to *determine* and *set*** correct MTU values:
-
-* **with WireGuard** (`wg0`), and
-* **without WireGuard** (just your egress interface like `eth0`/`wlan0`).
 
 The tool can:
+- auto-detect your egress interface (e.g., eth0)
+- probe Path MTU (PMTU) using `ping -M do`
+- compute a safe WireGuard MTU: `effective_mtu - overhead` (default overhead=80)
+- apply MTU to egress and/or WireGuard (explicit flags)
 
-* auto-detect your **egress interface**
+## Recipes
-* optionally **probe Path MTU (PMTU)** to one or more remote targets
-* compute a safe **WireGuard MTU** (`effective_mtu - 80` by default)
-* **apply** MTU to `wg0` and/or your egress interface
 
----
+1) Only compute/show (safe default):
-
-## TL;DR recipes
-
-### 1) Just compute & set WireGuard MTU (no PMTU probing)
-
-```bash
-sudo automtu
-# Equivalent from repo:
-# sudo python3 main.py
-```
-
-* Detects egress (e.g., `eth0`), reads its MTU (e.g., 1500)
-* Computes `wg0` MTU = `egress_mtu - 80` (min clamp 1280)
-* Applies to `wg0` (if present)
-
-Dry-run:
-
-```bash
     automtu --dry-run
-```
 
----
+2) Probe PMTU and apply to egress:
-
-### 2) Compute & apply MTU on *egress* (non-WireGuard)
-
-Useful if you want the *link itself* (e.g., `eth0`) to use the discovered PMTU.
-
-```bash
     sudo automtu --pmtu-target 1.1.1.1 --apply-egress-mtu
-```
 
-* Probes PMTU to `1.1.1.1`, applies that result to `eth0`
+3) Auto-add WireGuard peer endpoints as PMTU targets and apply WG MTU:
-* Also computes a matching WireGuard MTU (`PMTU - 80`) and sets `wg0` (if present)
+    sudo automtu --auto-pmtu-from-wg --apply-wg-mtu
 
-> If the selected egress is `wg0`, egress application is **skipped** on purpose.
+4) Prefer WireGuard as egress basis if default route uses wg0:
+    sudo automtu --prefer-wg-egress --auto-pmtu-from-wg --apply-wg-mtu
 
----
+5) Force WG MTU:
+    sudo automtu --set-wg-mtu 1372 --apply-wg-mtu
 
-### 3) With WireGuard peers: auto-add endpoints as PMTU targets
+## Notes
 
-```bash
+- Applying MTU requires root (unless `--dry-run`).
-sudo automtu --auto-pmtu-from-wg
+- PMTU probing can fail if ICMP is blocked; the tool then falls back to egress MTU.
-```
+- Runtime MTU changes are not persistent across reboots.
-
-* Reads `wg0` peer endpoints (`wg show ...` / `wg showconf`)
-* Probes PMTU to those endpoints
-* Picks an **effective PMTU** (policy = `min` by default)
-* Applies **`wg0` MTU = effective PMTU − 80**
-
-Add extra targets & choose different policy:
-
-```bash
-sudo automtu --auto-pmtu-from-wg \
-  --pmtu-target 46.4.224.77,1.1.1.1 \
-  --pmtu-policy median
-```
-
----
-
-### 4) Force a specific WireGuard MTU (override)
-
-```bash
-sudo automtu --set-wg-mtu 1372
-```
-
-* Skips the computed value and **forces** 1372 on `wg0` (clamped to ≥1280)
-
----
-
-## When to use which approach?
-
-* **You just use WireGuard** and want a safe default:
-  `sudo automtu` → picks `wg0 = egress_mtu - 80` (e.g., `1500 - 80 = 1420`).
-
-* **You suspect smaller upstream MTU** (PPPoE/ISP/VPN/“somewhere in the path”):
-  Use PMTU probing towards stable targets (your WG peer, DNS resolvers):
-
-  ```bash
-  sudo automtu --pmtu-target 46.4.224.77 --pmtu-target 1.1.1.1
-  ```
-
-  Then optionally apply the PMTU to your egress:
-
-  ```bash
-  sudo automtu --pmtu-target 46.4.224.77 --apply-egress-mtu
-  ```
-
-* **You have WireGuard peers** and want the tool to discover them automatically:
-  `sudo automtu --auto-pmtu-from-wg`
-  (You can still add manual targets and change policy.)
-
----
-
-## How it works (short)
-
-1. **Egress detection**
-   Reads default routes and picks a non-VPN interface (e.g., `eth0`).
-   If you want to prefer `wg0` when the default route already uses it:
-
-   ```bash
-   sudo automtu --prefer-wg-egress --wg-if wg0
-   ```
-
-2. **PMTU probing (optional)**
-   Uses `ping -M do` (DF set) with a quick binary search to find the largest unfragmented payload for each target.
-   From the successful results, selects an **effective PMTU** using a policy:
-
-   * `--pmtu-policy min` (default, safest)
-   * `--pmtu-policy median`
-   * `--pmtu-policy max`
-
-3. **WireGuard MTU calculation**
-   `wg_mtu = max(wg_min, effective_mtu - wg_overhead)`
-   Defaults: `wg_min=1280`, `wg_overhead=80`.
-
-4. **Apply**
-
-   * If `--apply-egress-mtu` is set, apply **effective PMTU** to the egress (unless egress is `wg0`).
-   * Apply **WireGuard MTU** to `wg0` (or the iface passed via `--wg-if`).
-   * If `--set-wg-mtu X` is given, it **overrides** the computed value.
-
----
-
-## Examples (copy & paste)
-
-### A) Quick WireGuard tuning with peer awareness
-
-```bash
-sudo automtu --auto-pmtu-from-wg
-```
-
-### B) Manual targets, conservative (min) policy
-
-```bash
-sudo automtu --pmtu-target 46.4.224.77 --pmtu-target 1.1.1.1
-```
-
-### C) Apply PMTU on egress + set matching wg0
-
-```bash
-sudo automtu --pmtu-target 1.1.1.1 --apply-egress-mtu
-```
-
-### D) Prefer WireGuard as egress (if default route uses WG)
-
-```bash
-sudo automtu --prefer-wg-egress --wg-if wg0 --auto-pmtu-from-wg
-```
-
-### E) Force a specific wg0 MTU
-
-```bash
-sudo automtu --set-wg-mtu 1372
-```
-
-### F) Dry-run any of the above
-
-```bash
-automtu --dry-run --auto-pmtu-from-wg --pmtu-target 1.1.1.1
-```
-
----
-
-## Persisting the value in WireGuard
-
-Runtime changes are **not** permanent. To persist:
-
-* Either let your automation run this tool before/after `wg-quick up wg0`, **or**
-* Add a fixed value in your `wg0` config (`/etc/wireguard/wg0.conf`):
-
-  ```ini
-  [Interface]
-  MTU = 1372
-  ```
-
-  > Static MTU is fine if the path is stable. If your route/ISP changes, prefer running this tool.
-
----
-
-## Notes & Troubleshooting
-
-* If **all PMTU probes fail**, the tool prints a warning and falls back to the egress MTU (e.g., `1500`) and sets `wg0 = egress - 80`.
-  Some networks block ICMP “fragmentation needed”; use multiple targets or rely on egress-only.
-* You can **override defaults** via flags or environment:
-
-  * `WG_IF=wg0 WG_OVERHEAD=80 WG_MIN=1280 automtu ...`
-* The tool **deduplicates targets** and understands IPv4/IPv6 endpoints (e.g., `2a01:...`).

Makefile

@@ -1,4 +1,4 @@
-PY ?= python3
+PYTHON ?= python3
 
 .PHONY: test install help
 
@@ -9,11 +9,4 @@ help:
 	@echo "  make help      - this help"
 
 test:
-	$(PY) -m unittest -v test.py
+	@PYTHONPATH="$(CURDIR)/src" "$(PYTHON)" -m unittest discover -s tests/unit -p "test_*.py" -v
-
-install:
-	@echo "Installation is provided via your package manager:"
-	@echo "  pkgmgr install automtu"
-	@echo ""
-	@echo "Alternatively, run the tool directly:"
-	@echo "  $(PY) main.py [--options]"

README.md

@@ -1,95 +1,29 @@
-# wg-mtu-auto
+# automtu
 [![GitHub Sponsors](https://img.shields.io/badge/Sponsor-GitHub%20Sponsors-blue?logo=github)](https://github.com/sponsors/kevinveenbirkenbach) [![Patreon](https://img.shields.io/badge/Support-Patreon-orange?logo=patreon)](https://www.patreon.com/c/kevinveenbirkenbach) [![Buy Me a Coffee](https://img.shields.io/badge/Buy%20me%20a%20Coffee-Funding-yellow?logo=buymeacoffee)](https://buymeacoffee.com/kevinveenbirkenbach) [![PayPal](https://img.shields.io/badge/Donate-PayPal-blue?logo=paypal)](https://s.veen.world/paypaldonate)
 
+Auto-detect your egress interface, optionally probe Path MTU (PMTU) using DF-ping,
+compute a WireGuard MTU, and apply MTU settings.
 
-Automatically detect the optimal WireGuard MTU by analyzing your local egress interface and optionally probing the Path MTU (PMTU) to one or more remote hosts.  
+## Install (editable)
-The tool ensures stable and efficient VPN connections by preventing fragmentation and latency caused by mismatched MTU settings.
+pip install -e .
 
----
+## Usage
 
-## ✨ Features
+Show only (no changes):
-
-- **Automatic Egress Detection** — Finds your primary internet interface automatically.  
-- **WireGuard MTU Calculation** — Computes `wg0` MTU based on egress MTU minus overhead (default 80 bytes).  
-- **Optional Path MTU Probing** — Uses ICMP “Don’t Fragment” (`ping -M do`) to find the real usable MTU across network paths.  
-- **Multi-Target PMTU Support** — Test multiple remote hosts and choose an effective value via policy (`min`, `median`, `max`).  
-- **Dry-Run Mode** — Simulate changes without applying them.  
-- **Safe for Automation** — Integrates well with WireGuard systemd services or Ansible setups.
-
----
-
-## 🚀 Installation
-
-### Option 1 — Using [pkgmgr](https://github.com/kevinveenbirkenbach/package-manager)
-
-If you use Kevin Veen-Birkenbach’s package manager (`pkgmgr`):
-
-```bash
-pkgmgr install automtu
-````
-
-This will automatically fetch and install `wg-mtu-auto` system-wide.
-
-### Option 2 — Run directly from source
-
-Clone this repository and execute the script manually:
-
-```bash
-git clone https://github.com/kevinveenbirkenbach/wg-mtu-auto.git
-cd wg-mtu-auto
-sudo python3 main.py --help
-```
-
----
-
-## 🧩 Usage Examples
-
-### Basic detection (no PMTU)
-
-```bash
-sudo automtu
-```
-
-### Specify egress interface and force MTU
-
-```bash
-sudo automtu --egress-if eth0 --force-egress-mtu 1452
-```
-
-### Probe multiple PMTU targets (safe policy: `min`)
-
-```bash
-sudo automtu --pmtu-target 46.4.224.77 --pmtu-target 2a01:4f8:2201:4695::2
-```
-
-### Choose median or max policy
-
-```bash
-sudo automtu --pmtu-target 46.4.224.77,1.1.1.1 --pmtu-policy median
-sudo automtu --pmtu-target 46.4.224.77,1.1.1.1 --pmtu-policy max
-```
-
-### Dry-run (no system changes)
-
-```bash
     automtu --dry-run
-```
 
----
+Probe PMTU to targets and apply on egress:
+    sudo automtu --pmtu-target registry-1.docker.io --apply-egress-mtu
 
-## 🧪 Development
+Auto-add WireGuard peer endpoints as targets and apply WG MTU:
+    sudo automtu --auto-pmtu-from-wg --apply-wg-mtu
 
-Run unit tests using:
+Force WG MTU:
+    sudo automtu --set-wg-mtu 1372 --apply-wg-mtu
 
-```bash
+Help:
-make test
+    automtu --help
-```
 
-To see installation guidance (does not install anything):
-
-```bash
-make install
-```
 
 ---
 

main.py

@@ -1,326 +0,0 @@
-#!/usr/bin/env python3
-"""
-wg_mtu_auto.py — Auto-detect egress IF, optionally probe Path MTU to one or more targets,
-compute the correct WireGuard MTU, and apply it.
-
-Examples:
-  sudo ./main.py
-  sudo ./main.py --force-egress-mtu 1452
-  sudo ./main.py --pmtu-target 46.4.224.77 --pmtu-target 2a01:4f8:2201:4695::2
-  sudo ./main.py --pmtu-target 46.4.224.77,2a01:4f8:2201:4695::2 --pmtu-policy min
-  sudo ./main.py --prefer-wg-egress --auto-pmtu-from-wg
-  ./main.py --dry-run
-"""
-import argparse
-import ipaddress
-import os
-import pathlib
-import re
-import statistics
-import subprocess
-import sys
-
-
-# ----------------- helpers -----------------
-
-def run(cmd):  # -> str
-    return subprocess.run(
-        cmd, check=False, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL, text=True
-    ).stdout.strip()
-
-
-def rc(cmd):  # -> int
-    return subprocess.run(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL).returncode
-
-
-def exists_iface(iface):  # -> bool
-    return pathlib.Path(f"/sys/class/net/{iface}").exists()
-
-
-def read_mtu(iface):  # -> int
-    with open(f"/sys/class/net/{iface}/mtu", "r") as f:
-        return int(f.read().strip())
-
-
-def set_mtu(iface, mtu, dry):
-    if dry:
-        print(f"[wg-mtu] DRY-RUN: ip link set mtu {mtu} dev {iface}")
-    else:
-        subprocess.run(["ip", "link", "set", "mtu", str(mtu), "dev", iface], check=True)
-
-
-def require_root(dry):
-    if not dry and os.geteuid() != 0:
-        print("[wg-mtu][ERROR] Please run as root (sudo) or use --dry-run.", file=sys.stderr)
-        sys.exit(1)
-
-
-def is_ipv6(addr):  # -> bool
-    try:
-        return isinstance(ipaddress.ip_address(addr), ipaddress.IPv6Address)
-    except ValueError:
-        # best-effort for hostnames (contains ':')
-        return ":" in addr
-
-
-# ----------------- route & iface selection -----------------
-
-def default_route_lines():
-    lines = []
-    for cmd in (["ip", "-4", "route", "show", "default"], ["ip", "-6", "route", "show", "default"]):
-        out = run(cmd)
-        if out:
-            lines.extend(out.splitlines())
-    return lines
-
-
-def get_default_ifaces(ignore_vpn=True):  # -> list[str]
-    devs = []
-    for line in default_route_lines():
-        m = re.search(r"\bdev\s+(\S+)", line)
-        if m:
-            devs.append(m.group(1))
-    # fallback via route get
-    if not devs:
-        for cmd in (["ip", "route", "get", "1.1.1.1"], ["ip", "-6", "route", "get", "2606:4700:4700::1111"]):
-            out = run(cmd)
-            m = re.search(r"\bdev\s+(\S+)", out)
-            if m:
-                devs.append(m.group(1))
-    uniq = []
-    for d in devs:
-        if not d or d == "lo" or not exists_iface(d):
-            continue
-        if ignore_vpn and re.match(r"^(wg|tun)\d*$", d):
-            continue
-        if d not in uniq:
-            uniq.append(d)
-    return uniq
-
-
-def wg_default_is_active(wg_if: str) -> bool:
-    # check if any default route is via wg_if
-    return any(re.search(rf"\bdev\s+{re.escape(wg_if)}\b", line) for line in default_route_lines())
-
-
-# ----------------- PMTU probing -----------------
-
-def ping_ok(payload, target, timeout_s):  # -> bool
-    base = ["ping", "-M", "do", "-c", "1", "-s", str(payload), "-W", str(max(1, int(round(timeout_s))))]
-    if is_ipv6(target):
-        base.insert(1, "-6")
-    return rc(base + [target]) == 0
-
-
-def probe_pmtu(target, lo_payload=1200, hi_payload=1472, timeout=1.0):  # -> int|None
-    """Binary-search the largest payload that passes with DF. Return Path MTU (payload + hdr) or None.
-       Header: +28 (IPv4), +48 (IPv6)."""
-    hdr = 48 if is_ipv6(target) else 28
-    # ensure lower bound works; if not, try smaller floors
-    if not ping_ok(lo_payload, target, timeout):
-        for p in (1180, 1160, 1140):
-            if ping_ok(p, target, timeout):
-                lo_payload = p
-                break
-        else:
-            return None
-    lo, hi, best = lo_payload, hi_payload, None
-    while lo <= hi:
-        mid = (lo + hi) // 2
-        if ping_ok(mid, target, timeout):
-            best = mid
-            lo = mid + 1
-        else:
-            hi = mid - 1
-    return (best + hdr) if best is not None else None
-
-
-def choose_effective(pmtus, policy="min"):  # -> int
-    if not pmtus:
-        raise ValueError("no PMTUs to choose from")
-    if policy == "min":
-        return min(pmtus)
-    if policy == "max":
-        return max(pmtus)
-    if policy == "median":
-        return int(statistics.median(sorted(pmtus)))
-    raise ValueError(f"unknown policy {policy}")
-
-
-# ----------------- WireGuard helpers (opt-in) -----------------
-
-def wg_is_active(wg_if: str) -> bool:
-    if not exists_iface(wg_if):
-        return False
-    return rc(["wg", "show", wg_if]) == 0
-
-
-def wg_peer_endpoints(wg_if: str) -> list[str]:
-    """Return list of peer endpoints (hostnames/IPs) – port stripped."""
-    targets = []
-
-    # 1) Try: wg show <if> endpoints
-    out = run(["wg", "show", wg_if, "endpoints"])
-    for line in out.splitlines():
-        # format: <peer_public_key>\t<endpoint or (none)>
-        parts = line.strip().split()
-        if len(parts) >= 2 and parts[-1] != "(none)":
-            ep = parts[-1]  # host:port
-            host = ep.rsplit(":", 1)[0]
-            # IPv6 endpoint may be like [2001:db8::1]:51820
-            host = host.strip("[]")
-            targets.append(host)
-
-    # 2) Fallback: wg showconf (root may be required)
-    if not targets:
-        conf = run(["wg", "showconf", wg_if])
-        if conf:
-            for m in re.finditer(r"^Endpoint\s*=\s*(.+)$", conf, flags=re.MULTILINE):
-                ep = m.group(1).strip()
-                host = ep.rsplit(":", 1)[0].strip("[]")
-                targets.append(host)
-
-    # dedupe & sanity
-    cleaned = []
-    for t in targets:
-        if t and t not in cleaned:
-            cleaned.append(t)
-    return cleaned
-
-
-# ----------------- main -----------------
-
-def main():
-    ap = argparse.ArgumentParser(description="Compute/apply WireGuard MTU based on egress MTU and optional multi-target PMTU probing.")
-    ap.add_argument("--egress-if", help="Explicit egress interface (auto-detected if omitted).")
-    ap.add_argument("--prefer-wg-egress", action="store_true",
-                    help="Allow/consider wg* as egress and prefer it if default route uses wg (default: disabled).")
-    ap.add_argument("--auto-pmtu-from-wg", action="store_true",
-                    help="Automatically add WireGuard peer endpoints as PMTU targets (default: disabled).")
-    ap.add_argument("--wg-if", default=os.environ.get("WG_IF", "wg0"), help="WireGuard interface name (default: wg0).")
-    ap.add_argument("--wg-overhead", type=int, default=int(os.environ.get("WG_OVERHEAD", "80")), help="Bytes of WG overhead to subtract (default: 80).")
-    ap.add_argument("--wg-min", type=int, default=int(os.environ.get("WG_MIN", "1280")), help="Minimum allowed WG MTU (default: 1280).")
-    # PMTU (multi-target)
-    ap.add_argument("--pmtu-target", action="append", help="Target hostname/IP to probe PMTU. Can be given multiple times OR comma-separated.")
-    ap.add_argument("--pmtu-timeout", type=float, default=1.0, help="Timeout (seconds) per ping probe (default: 1.0).")
-    ap.add_argument("--pmtu-min-payload", type=int, default=1200, help="Lower bound payload for PMTU search (default: 1200).")
-    ap.add_argument("--pmtu-max-payload", type=int, default=1472, help="Upper bound payload for PMTU search (default: 1472 ~ 1500-28).")
-    ap.add_argument("--pmtu-policy", choices=["min", "median", "max"], default="min",
-                    help="How to choose effective PMTU across multiple targets (default: min).")
-    ap.add_argument("--apply-egress-mtu", action="store_true",
-                    help="Apply the effective Path MTU to the detected egress interface (e.g. eth0).")
-     
-    ap.add_argument("--dry-run", action="store_true", help="Show actions without applying changes.")
-    # NEW: force a specific WireGuard MTU (overrides computed value)
-    ap.add_argument("--set-wg-mtu", type=int, help="Force a specific MTU to apply on the WireGuard interface (overrides computed value).")
-    # (legacy / optional) force egress MTU
-    ap.add_argument("--force-egress-mtu", type=int, help="Force this MTU on the egress interface before computing wg MTU.")
-    args = ap.parse_args()
-
-    require_root(args.dry_run)
-
-    # Egress detection (wg ignored by default)
-    if args.egress_if:
-        egress = args.egress_if
-    else:
-        ignore_vpn = not args.prefer_wg_egress
-        cands = get_default_ifaces(ignore_vpn=ignore_vpn)
-        # If we allow wg and default route is via wg-if, prefer it first
-        if args.prefer_wg_egress and wg_is_active(args.wg_if) and wg_default_is_active(args.wg_if):
-            if args.wg_if in cands:
-                cands.remove(args.wg_if)
-            cands.insert(0, args.wg_if)
-        egress = cands[0] if cands else None
-
-    if not egress:
-        print("[wg-mtu][ERROR] Could not detect egress interface (use --egress-if).", file=sys.stderr)
-        sys.exit(2)
-    if not exists_iface(egress):
-        print(f"[wg-mtu][ERROR] Interface {egress} does not exist.", file=sys.stderr)
-        sys.exit(3)
-    print(f"[wg-mtu] Detected egress interface: {egress}")
-
-    # Egress MTU
-    if args.prefer_wg_egress and egress == args.wg_if:
-        print(f"[wg-mtu] Using WireGuard interface {args.wg_if} as egress basis.")
-    if args.wg_if == egress and not wg_is_active(args.wg_if):
-        print(f"[wg-mtu][WARN] {args.wg_if} selected as egress but WireGuard is not active.", file=sys.stderr)
-
-    if args.force_egress_mtu:
-        print(f"[wg-mtu] Forcing egress MTU {args.force_egress_mtu} on {egress}")
-        set_mtu(egress, args.force_egress_mtu, args.dry_run)
-        base_mtu = args.force_egress_mtu
-    else:
-        base_mtu = read_mtu(egress)
-    print(f"[wg-mtu] Egress base MTU: {base_mtu}")
-
-    # Build PMTU target list
-    pmtu_targets = []
-    if args.pmtu_target:
-        for item in args.pmtu_target:
-            pmtu_targets.extend([x.strip() for x in item.split(",") if x.strip()])
-
-    if args.auto_pmtu_from_wg:
-        if wg_is_active(args.wg_if):
-            wg_targets = wg_peer_endpoints(args.wg_if)
-            if wg_targets:
-                print(f"[wg-mtu] Auto-added WG peer endpoints as PMTU targets: {', '.join(wg_targets)}")
-                pmtu_targets.extend(wg_targets)
-            else:
-                print("[wg-mtu] INFO: No WG peer endpoints discovered (wg show/showconf).")
-        else:
-            print(f"[wg-mtu] INFO: {args.wg_if} is not active; skipping auto PMTU targets from WG.")
-
-    # Deduplicate PMTU targets
-    if pmtu_targets:
-        pmtu_targets = list(dict.fromkeys(pmtu_targets))
-
-    # PMTU probing
-    effective_mtu = base_mtu
-    if pmtu_targets:
-        good = []
-        print(f"[wg-mtu] Probing Path MTU for: {', '.join(pmtu_targets)} (policy={args.pmtu_policy})")
-        for t in pmtu_targets:
-            p = probe_pmtu(t, args.pmtu_min_payload, args.pmtu_max_payload, args.pmtu_timeout)
-            print(f"[wg-mtu]  - {t}: {p if p else 'probe failed'}")
-            if p:
-                good.append(p)
-        if good:
-            chosen = choose_effective(good, args.pmtu_policy)
-            print(f"[wg-mtu] Selected Path MTU (policy={args.pmtu_policy}): {chosen}")
-            effective_mtu = min(base_mtu, chosen)
-        else:
-            print("[wg-mtu] WARNING: All PMTU probes failed. Falling back to egress MTU.")
-
-    # Optionally apply the effective MTU to the egress interface
-    if args.apply_egress_mtu:
-        if egress == args.wg_if:
-            print(f"[wg-mtu] INFO: Skipping egress MTU apply because egress == {args.wg_if}.")
-        else:
-            print(f"[wg-mtu] Applying effective MTU {effective_mtu} to egress {egress}")
-            set_mtu(egress, effective_mtu, args.dry_run)
-
-    # Compute WG MTU
-    wg_mtu = max(args.wg_min, effective_mtu - args.wg_overhead)
-    print(f"[wg-mtu] Computed {args.wg_if} MTU: {wg_mtu}  (overhead={args.wg_overhead}, min={args.wg_min})")
-
-    # --- NEW: override with --set-wg-mtu if provided
-    if args.set_wg_mtu is not None:
-        if args.set_wg_mtu < args.wg_min:
-            print(f"[wg-mtu][WARN] --set-wg-mtu {args.set_wg_mtu} is below wg-min {args.wg_min}; clamping to {args.wg_min}.")
-            args.set_wg_mtu = args.wg_min
-        wg_mtu = args.set_wg_mtu
-        print(f"[wg-mtu] Forcing WireGuard MTU (override): {wg_mtu}")
-
-    # Apply
-    if exists_iface(args.wg_if):
-        set_mtu(args.wg_if, wg_mtu, args.dry_run)
-        print(f"[wg-mtu] Applied: {args.wg_if} MTU {wg_mtu}")
-    else:
-        print(f"[wg-mtu] NOTE: {args.wg_if} not present yet. Start WireGuard first, then re-run this script.")
-
-    print(f"[wg-mtu] Done. Summary: egress={egress} mtu={base_mtu}, effective_mtu={effective_mtu}, {args.wg_if}_mtu={wg_mtu}")
-
-
-if __name__ == "__main__":
-    main()

pyproject.toml

@@ -0,0 +1,23 @@
+[build-system]
+requires = ["setuptools>=69"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "automtu"
+version = "0.1.0"
+description = "Auto-detect egress interface, probe Path MTU, and apply MTU (WireGuard/egress)."
+readme = "README.md"
+requires-python = ">=3.10"
+license = { text = "MIT" }
+authors = [{ name = "Kevin Veen-Birkenbach" }]
+keywords = ["mtu", "wireguard", "pmtu", "networking"]
+dependencies = []
+
+[project.scripts]
+automtu = "automtu.__main__:main"
+
+[tool.setuptools]
+package-dir = { "" = "src" }
+
+[tool.setuptools.packages.find]
+where = ["src"]

src/automtu/__init__.py

@@ -0,0 +1,2 @@
+__all__ = ["__version__"]
+__version__ = "0.1.0"

src/automtu/__main__.py

@@ -0,0 +1,13 @@
+from __future__ import annotations
+
+from .cli import build_parser
+from .core import run_automtu
+
+
+def main() -> int:
+    args = build_parser().parse_args()
+    return run_automtu(args)
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

src/automtu/cli.py

@@ -0,0 +1,93 @@
+from __future__ import annotations
+
+import argparse
+import os
+
+
+def build_parser() -> argparse.ArgumentParser:
+    ap = argparse.ArgumentParser(
+        prog="automtu",
+        description="Probe Path MTU and compute/apply MTU for egress and/or WireGuard.",
+    )
+
+    ap.add_argument(
+        "--egress-if", help="Explicit egress interface (auto-detected if omitted)."
+    )
+    ap.add_argument(
+        "--prefer-wg-egress",
+        action="store_true",
+        help="Allow wg* as egress and prefer it if default route uses wg (default: off).",
+    )
+
+    ap.add_argument(
+        "--pmtu-target",
+        action="append",
+        help="Target hostname/IP to probe PMTU. Repeatable or comma-separated.",
+    )
+    ap.add_argument(
+        "--pmtu-timeout",
+        type=float,
+        default=1.0,
+        help="Ping timeout seconds (default: 1.0).",
+    )
+    ap.add_argument(
+        "--pmtu-min-payload",
+        type=int,
+        default=1200,
+        help="PMTU lower payload bound (default: 1200).",
+    )
+    ap.add_argument(
+        "--pmtu-max-payload",
+        type=int,
+        default=1472,
+        help="PMTU upper payload bound (default: 1472).",
+    )
+    ap.add_argument(
+        "--pmtu-policy",
+        choices=["min", "median", "max"],
+        default="min",
+        help="Aggregate PMTU across targets (default: min).",
+    )
+
+    ap.add_argument(
+        "--apply-egress-mtu",
+        action="store_true",
+        help="Apply effective MTU to egress interface.",
+    )
+    ap.add_argument(
+        "--apply-wg-mtu", action="store_true", help="Apply MTU to WireGuard interface."
+    )
+
+    ap.add_argument(
+        "--wg-if",
+        default=os.environ.get("WG_IF", "wg0"),
+        help="WireGuard interface (default: wg0).",
+    )
+    ap.add_argument(
+        "--wg-overhead",
+        type=int,
+        default=int(os.environ.get("WG_OVERHEAD", "80")),
+        help="WG overhead.",
+    )
+    ap.add_argument(
+        "--wg-min",
+        type=int,
+        default=int(os.environ.get("WG_MIN", "1280")),
+        help="Minimum WG MTU.",
+    )
+    ap.add_argument(
+        "--auto-pmtu-from-wg",
+        action="store_true",
+        help="Add WG peer endpoints as PMTU targets.",
+    )
+    ap.add_argument("--set-wg-mtu", type=int, help="Force MTU for WireGuard interface.")
+
+    ap.add_argument(
+        "--force-egress-mtu",
+        type=int,
+        help="Force MTU on the egress interface before computing.",
+    )
+    ap.add_argument(
+        "--dry-run", action="store_true", help="Show actions without applying changes."
+    )
+    return ap

src/automtu/core.py

@@ -0,0 +1,161 @@
+from __future__ import annotations
+
+import statistics
+import sys
+from dataclasses import dataclass
+from typing import Iterable, Optional
+
+from .net import (
+    default_route_uses_iface,
+    detect_egress_iface,
+    iface_exists,
+    read_iface_mtu,
+    require_root,
+    set_iface_mtu,
+)
+from .pmtu import probe_pmtu
+from .wg import wg_is_active, wg_peer_endpoints
+
+
+@dataclass(frozen=True)
+class Result:
+    egress: str
+    base_mtu: int
+    effective_mtu: int
+    wg_if: str
+    wg_mtu: int
+
+
+def _split_targets(items: Optional[list[str]]) -> list[str]:
+    raw: list[str] = []
+    for item in items or []:
+        raw.extend([x.strip() for x in item.split(",") if x.strip()])
+    return list(dict.fromkeys(raw))
+
+
+def _choose(values: Iterable[int], policy: str) -> int:
+    vals = sorted(values)
+    if policy == "min":
+        return vals[0]
+    if policy == "max":
+        return vals[-1]
+    if policy == "median":
+        return int(statistics.median(vals))
+    raise ValueError(f"unknown policy: {policy}")
+
+
+def run_automtu(args) -> int:
+    require_root(args.dry_run)
+
+    egress = args.egress_if or detect_egress_iface(ignore_vpn=not args.prefer_wg_egress)
+    if not egress:
+        print(
+            "[automtu][ERROR] Could not detect egress interface (use --egress-if).",
+            file=sys.stderr,
+        )
+        return 2
+    if not iface_exists(egress):
+        print(f"[automtu][ERROR] Interface {egress} does not exist.", file=sys.stderr)
+        return 3
+
+    if (
+        args.egress_if is None
+        and args.prefer_wg_egress
+        and iface_exists(args.wg_if)
+        and wg_is_active(args.wg_if)
+        and default_route_uses_iface(args.wg_if)
+    ):
+        egress = args.wg_if
+        print(f"[automtu] Using WireGuard interface {args.wg_if} as egress basis.")
+
+    print(f"[automtu] Detected egress interface: {egress}")
+
+    if args.force_egress_mtu:
+        print(f"[automtu] Forcing egress MTU {args.force_egress_mtu} on {egress}")
+        set_iface_mtu(egress, args.force_egress_mtu, args.dry_run)
+        base_mtu = args.force_egress_mtu
+    else:
+        base_mtu = read_iface_mtu(egress)
+    print(f"[automtu] Egress base MTU: {base_mtu}")
+
+    targets = _split_targets(args.pmtu_target)
+    if args.auto_pmtu_from_wg:
+        if wg_is_active(args.wg_if):
+            peers = wg_peer_endpoints(args.wg_if)
+            if peers:
+                print(
+                    f"[automtu] Auto-added WG peer endpoints as PMTU targets: {', '.join(peers)}"
+                )
+                targets = list(dict.fromkeys([*targets, *peers]))
+        else:
+            print(
+                f"[automtu] INFO: {args.wg_if} not active; skipping auto PMTU targets."
+            )
+
+    effective_mtu = base_mtu
+    if targets:
+        print(
+            f"[automtu] Probing Path MTU for: {', '.join(targets)} (policy={args.pmtu_policy})"
+        )
+        good: list[int] = []
+        for t in targets:
+            p = probe_pmtu(
+                t, args.pmtu_min_payload, args.pmtu_max_payload, args.pmtu_timeout
+            )
+            print(f"[automtu]  - {t}: {p if p else 'probe failed'}")
+            if p:
+                good.append(p)
+
+        if good:
+            chosen = _choose(good, args.pmtu_policy)
+            print(f"[automtu] Selected Path MTU (policy={args.pmtu_policy}): {chosen}")
+            effective_mtu = min(base_mtu, chosen)
+        else:
+            print(
+                "[automtu] WARNING: All PMTU probes failed. Falling back to egress MTU."
+            )
+
+    if args.apply_egress_mtu:
+        if egress == args.wg_if:
+            print(
+                f"[automtu] INFO: Skipping egress MTU apply because egress == {args.wg_if}."
+            )
+        else:
+            print(
+                f"[automtu] Applying effective MTU {effective_mtu} to egress {egress}"
+            )
+            set_iface_mtu(egress, effective_mtu, args.dry_run)
+
+    wg_mtu = max(int(args.wg_min), int(effective_mtu) - int(args.wg_overhead))
+    print(
+        f"[automtu] Computed {args.wg_if} MTU: {wg_mtu} (overhead={args.wg_overhead}, min={args.wg_min})"
+    )
+
+    if args.set_wg_mtu is not None:
+        forced = max(int(args.wg_min), int(args.set_wg_mtu))
+        if forced != int(args.set_wg_mtu):
+            print(
+                f"[automtu][WARN] --set-wg-mtu clamped to {forced} (wg-min={args.wg_min})."
+            )
+        wg_mtu = forced
+        print(f"[automtu] Forcing WireGuard MTU (override): {wg_mtu}")
+
+    if args.apply_wg_mtu:
+        if iface_exists(args.wg_if):
+            set_iface_mtu(args.wg_if, wg_mtu, args.dry_run)
+            print(f"[automtu] Applied: {args.wg_if} MTU {wg_mtu}")
+        else:
+            print(
+                f"[automtu] NOTE: {args.wg_if} not present yet. Start WireGuard first, then re-run."
+            )
+    else:
+        print("[automtu] INFO: Not applying WireGuard MTU (use --apply-wg-mtu).")
+
+    _ = Result(
+        egress=egress,
+        base_mtu=base_mtu,
+        effective_mtu=effective_mtu,
+        wg_if=args.wg_if,
+        wg_mtu=wg_mtu,
+    )
+    return 0

src/automtu/net.py

@@ -0,0 +1,82 @@
+from __future__ import annotations
+
+import os
+import pathlib
+import re
+import subprocess
+import sys
+from typing import Optional
+
+
+def _run(cmd: list[str]) -> str:
+    return subprocess.run(
+        cmd, check=False, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL, text=True
+    ).stdout.strip()
+
+
+def iface_exists(iface: str) -> bool:
+    return pathlib.Path(f"/sys/class/net/{iface}").exists()
+
+
+def read_iface_mtu(iface: str) -> int:
+    return int(pathlib.Path(f"/sys/class/net/{iface}/mtu").read_text().strip())
+
+
+def set_iface_mtu(iface: str, mtu: int, dry: bool) -> None:
+    if dry:
+        print(f"[automtu] DRY-RUN: ip link set mtu {mtu} dev {iface}")
+        return
+    subprocess.run(["ip", "link", "set", "mtu", str(mtu), "dev", iface], check=True)
+
+
+def require_root(dry: bool) -> None:
+    if not dry and os.geteuid() != 0:
+        print(
+            "[automtu][ERROR] Please run as root (sudo) or use --dry-run.",
+            file=sys.stderr,
+        )
+        raise SystemExit(1)
+
+
+def detect_egress_iface(ignore_vpn: bool = True) -> Optional[str]:
+    devs: list[str] = []
+    for cmd in (
+        ["ip", "-4", "route", "show", "default"],
+        ["ip", "-6", "route", "show", "default"],
+    ):
+        for line in _run(cmd).splitlines():
+            m = re.search(r"\bdev\s+(\S+)", line)
+            if m:
+                devs.append(m.group(1))
+
+    if not devs:
+        for cmd in (
+            ["ip", "route", "get", "1.1.1.1"],
+            ["ip", "-6", "route", "get", "2606:4700:4700::1111"],
+        ):
+            m = re.search(r"\bdev\s+(\S+)", _run(cmd))
+            if m:
+                devs.append(m.group(1))
+
+    seen: set[str] = set()
+    for d in devs:
+        if not d or d == "lo" or not iface_exists(d):
+            continue
+        if ignore_vpn and re.match(r"^(wg|tun)\d*$", d):
+            continue
+        if d in seen:
+            continue
+        seen.add(d)
+        return d
+    return None
+
+
+def default_route_uses_iface(iface: str) -> bool:
+    pat = rf"\bdev\s+{re.escape(iface)}\b"
+    for cmd in (
+        ["ip", "-4", "route", "show", "default"],
+        ["ip", "-6", "route", "show", "default"],
+    ):
+        if re.search(pat, _run(cmd)):
+            return True
+    return False

src/automtu/pmtu.py

@@ -0,0 +1,60 @@
+from __future__ import annotations
+
+import ipaddress
+import subprocess
+from typing import Optional
+
+
+def _is_ipv6(target: str) -> bool:
+    try:
+        return isinstance(ipaddress.ip_address(target), ipaddress.IPv6Address)
+    except ValueError:
+        return ":" in target  # best-effort for hostnames
+
+
+def _rc(cmd: list[str]) -> int:
+    return subprocess.run(
+        cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL
+    ).returncode
+
+
+def _ping_ok(payload: int, target: str, timeout_s: float) -> bool:
+    cmd = [
+        "ping",
+        "-M",
+        "do",
+        "-c",
+        "1",
+        "-s",
+        str(payload),
+        "-W",
+        str(max(1, int(round(timeout_s)))),
+    ]
+    if _is_ipv6(target):
+        cmd.insert(1, "-6")
+    return _rc(cmd + [target]) == 0
+
+
+def probe_pmtu(
+    target: str, lo_payload: int = 1200, hi_payload: int = 1472, timeout: float = 1.0
+) -> Optional[int]:
+    hdr = 48 if _is_ipv6(target) else 28
+
+    if not _ping_ok(lo_payload, target, timeout):
+        for p in (1180, 1160, 1140):
+            if _ping_ok(p, target, timeout):
+                lo_payload = p
+                break
+        else:
+            return None
+
+    lo, hi, best = lo_payload, hi_payload, None
+    while lo <= hi:
+        mid = (lo + hi) // 2
+        if _ping_ok(mid, target, timeout):
+            best = mid
+            lo = mid + 1
+        else:
+            hi = mid - 1
+
+    return (best + hdr) if best is not None else None

src/automtu/wg.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+
+import re
+import subprocess
+from typing import List
+
+from .net import iface_exists
+
+
+def _run(cmd: list[str]) -> str:
+    return subprocess.run(
+        cmd, check=False, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL, text=True
+    ).stdout.strip()
+
+
+def _rc(cmd: list[str]) -> int:
+    return subprocess.run(
+        cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL
+    ).returncode
+
+
+def wg_is_active(wg_if: str) -> bool:
+    return iface_exists(wg_if) and _rc(["wg", "show", wg_if]) == 0
+
+
+def wg_peer_endpoints(wg_if: str) -> List[str]:
+    targets: list[str] = []
+
+    out = _run(["wg", "show", wg_if, "endpoints"])
+    for line in out.splitlines():
+        parts = line.strip().split()
+        if len(parts) >= 2 and parts[-1] != "(none)":
+            ep = parts[-1]
+            host = ep.rsplit(":", 1)[0].strip("[]")
+            targets.append(host)
+
+    if not targets:
+        conf = _run(["wg", "showconf", wg_if])
+        for m in re.finditer(r"^Endpoint\s*=\s*(.+)$", conf, flags=re.MULTILINE):
+            ep = m.group(1).strip()
+            host = ep.rsplit(":", 1)[0].strip("[]")
+            targets.append(host)
+
+    dedup: list[str] = []
+    for t in targets:
+        if t and t not in dedup:
+            dedup.append(t)
+    return dedup

test.py

@@ -1,287 +0,0 @@
-import io
-import sys
-import unittest
-from unittest.mock import patch
-from contextlib import redirect_stdout
-
-# Import the script as a module
-import main as automtu
-
-
-class TestWgMtuAutoExtended(unittest.TestCase):
-    # ---------- Baseline behavior (unchanged) ----------
-
-    @patch("main.set_mtu")
-    @patch("main.read_mtu", return_value=1500)
-    @patch("main.exists_iface", return_value=True)
-    @patch("main.get_default_ifaces", return_value=["eth0"])
-    @patch("main.require_root", return_value=None)
-    def test_no_pmtu_uses_egress_minus_overhead(
-        self, _req_root, mock_get_def, _exists, _read_mtu, mock_set_mtu
-    ):
-        argv = ["main.py", "--dry-run"]
-        with patch.object(sys, "argv", argv):
-            buf = io.StringIO()
-            with redirect_stdout(buf):
-                automtu.main()
-
-        out = buf.getvalue()
-        self.assertIn("Detected egress interface: eth0", out)
-        self.assertIn("Egress base MTU: 1500", out)
-        self.assertIn("Computed wg0 MTU: 1420", out)
-        mock_set_mtu.assert_any_call("wg0", 1420, True)
-        # get_default_ifaces should be called with ignore_vpn=True by default
-        mock_get_def.assert_called_with(ignore_vpn=True)
-
-    # ---------- prefer-wg-egress selection ----------
-
-    @patch("main.wg_default_is_active", return_value=True)
-    @patch("main.wg_is_active", return_value=True)
-    @patch("main.set_mtu")
-    @patch("main.read_mtu", return_value=1420)
-    @patch("main.exists_iface", return_value=True)
-    @patch("main.get_default_ifaces", return_value=["eth0", "wg0"])
-    @patch("main.require_root", return_value=None)
-    def test_prefer_wg_egress_picks_wg0_when_default_route_via_wg(
-        self, _req_root, mock_get_def, _exists, _read_mtu, _set_mtu, _wg_is_active, _wg_def_active
-    ):
-        argv = ["main.py", "--dry-run", "--prefer-wg-egress", "--wg-if", "wg0"]
-        with patch.object(sys, "argv", argv):
-            buf = io.StringIO()
-            with redirect_stdout(buf):
-                automtu.main()
-
-        out = buf.getvalue()
-        # When prefer-wg is set AND wg default route is active, wg0 should be chosen as egress
-        self.assertIn("Detected egress interface: wg0", out)
-        self.assertIn("Using WireGuard interface wg0 as egress basis.", out)
-        # Computed MTU: base 1420 - 80 = 1340 (clamped by min=1280)
-        self.assertIn("Computed wg0 MTU: 1340", out)
-        # get_default_ifaces should be called with ignore_vpn=False (because prefer-wg)
-        mock_get_def.assert_called_with(ignore_vpn=False)
-
-    # ---------- auto-pmtu-from-wg adds peer endpoints ----------
-
-    @patch("main.wg_peer_endpoints", return_value=["46.4.224.77", "2a01:db8::1"])
-    @patch("main.wg_is_active", return_value=True)
-    @patch("main.probe_pmtu", side_effect=[1452, 1420])  # results for two peers
-    @patch("main.set_mtu")
-    @patch("main.read_mtu", return_value=1500)
-    @patch("main.exists_iface", return_value=True)
-    @patch("main.get_default_ifaces", return_value=["eth0"])
-    @patch("main.require_root", return_value=None)
-    def test_auto_pmtu_from_wg_adds_targets_and_uses_min_policy(
-        self, _req_root, _get_def, _exists, _read_mtu, _set_mtu, _probe_pmtu, _wg_active, _wg_peers
-    ):
-        argv = ["main.py", "--dry-run", "--auto-pmtu-from-wg", "--wg-if", "wg0"]
-        with patch.object(sys, "argv", argv):
-            buf = io.StringIO()
-            with redirect_stdout(buf):
-                automtu.main()
-
-        out = buf.getvalue()
-        # Confirm WG peers were added
-        self.assertIn("Auto-added WG peer endpoints as PMTU targets: 46.4.224.77, 2a01:db8::1", out)
-        # The policy default is 'min', so chosen PMTU should be 1420
-        self.assertIn("Selected Path MTU (policy=min): 1420", out)
-        # Computed wg0 MTU: 1420 - 80 = 1340
-        self.assertIn("Computed wg0 MTU: 1340", out)
-        # Ensure probe was called twice (for both peers)
-        self.assertEqual(_probe_pmtu.call_count, 2)
-
-    # ---------- manual PMTU still works with prefer-wg-egress ----------
-
-    @patch("main.wg_default_is_active", return_value=True)
-    @patch("main.wg_is_active", return_value=True)
-    @patch("main.probe_pmtu", side_effect=[1472, 1452, 1500])
-    @patch("main.set_mtu")
-    @patch("main.read_mtu", return_value=1500)
-    @patch("main.exists_iface", return_value=True)
-    @patch("main.get_default_ifaces", return_value=["eth0"])
-    @patch("main.require_root", return_value=None)
-    def test_prefer_wg_egress_with_manual_targets_and_median_policy(
-        self, _req_root, _get_def, _exists, _read_mtu, _set_mtu, _probe_pmtu, _wg_is_active, _wg_def_active
-    ):
-        argv = [
-            "main.py", "--dry-run",
-            "--prefer-wg-egress", "--wg-if", "wg0",
-            "--pmtu-target", "a", "--pmtu-target", "b", "--pmtu-target", "c",
-            "--pmtu-policy", "median"
-        ]
-        with patch.object(sys, "argv", argv):
-            buf = io.StringIO()
-            with redirect_stdout(buf):
-                automtu.main()
-
-        out = buf.getvalue()
-        # As default route via wg is active, wg0 should be used
-        self.assertIn("Detected egress interface: wg0", out)
-        # PMTU values: 1472, 1452, 1500 -> median = 1472
-        self.assertIn("Selected Path MTU (policy=median): 1472", out)
-        # Computed WG MTU: 1472 - 80 = 1392
-        self.assertIn("Computed wg0 MTU: 1392", out)
-        self.assertEqual(_probe_pmtu.call_count, 3)
-
-    # ---------- PMTU all fail fallback ----------
-
-    @patch("main.set_mtu")
-    @patch("main.read_mtu", return_value=1500)
-    @patch("main.exists_iface", return_value=True)
-    @patch("main.get_default_ifaces", return_value=["eth0"])
-    @patch("main.require_root", return_value=None)
-    def test_pmtu_all_fail_falls_back_to_base(
-        self, _req_root, _get_def, _exists, _read_mtu, mock_set_mtu
-    ):
-        with patch("main.probe_pmtu", side_effect=[None, None]):
-            argv = ["main.py", "--dry-run", "--pmtu-target", "bad1", "--pmtu-target", "bad2"]
-            with patch.object(sys, "argv", argv):
-                buf = io.StringIO()
-                with redirect_stdout(buf):
-                    automtu.main()
-
-        out = buf.getvalue()
-        self.assertIn("WARNING: All PMTU probes failed. Falling back to egress MTU.", out)
-        self.assertIn("Computed wg0 MTU: 1420", out)  # 1500 - 80
-        mock_set_mtu.assert_any_call("wg0", 1420, True)
-
-    # ---------- NEW: --set-wg-mtu overrides computed ----------
-
-    @patch("main.set_mtu")
-    @patch("main.read_mtu", return_value=1500)
-    @patch("main.exists_iface", return_value=True)
-    @patch("main.get_default_ifaces", return_value=["eth0"])
-    @patch("main.require_root", return_value=None)
-    def test_force_set_wg_mtu_overrides_computed(
-        self, _req_root, _get_def, _exists, _read_mtu, mock_set_mtu
-    ):
-        """
-        --set-wg-mtu must override the computed value.
-        Base=1500 -> computed 1420 (1500-80), but we force 1300.
-        """
-        argv = ["main.py", "--dry-run", "--set-wg-mtu", "1300"]
-        with patch.object(sys, "argv", argv):
-            buf = io.StringIO()
-            with redirect_stdout(buf):
-                automtu.main()
-
-        out = buf.getvalue()
-        # Computation is printed first
-        self.assertIn("Computed wg0 MTU: 1420", out)
-        # Then override message appears and applied value is 1300
-        self.assertIn("Forcing WireGuard MTU (override): 1300", out)
-        mock_set_mtu.assert_any_call("wg0", 1300, True)
-
-        # also test clamping below wg-min
-        argv2 = ["main.py", "--dry-run", "--set-wg-mtu", "1200"]  # below default wg_min=1280
-        with patch.object(sys, "argv", argv2):
-            out2 = io.StringIO()
-            with redirect_stdout(out2):
-                automtu.main()
-        s = out2.getvalue()
-        self.assertIn("[wg-mtu][WARN] --set-wg-mtu 1200 is below wg-min 1280; clamping to 1280.", s)
-        self.assertIn("Forcing WireGuard MTU (override): 1280", s)
-        mock_set_mtu.assert_any_call("wg0", 1280, True)
-        
-    # ---------- --apply-egress-mtu: setzt egress vor wg ----------
-
-    @patch("main.set_mtu")
-    @patch("main.probe_pmtu", return_value=1452)
-    @patch("main.read_mtu", return_value=1500)
-    @patch("main.exists_iface", return_value=True)
-    @patch("main.get_default_ifaces", return_value=["eth0"])
-    @patch("main.require_root", return_value=None)
-    def test_apply_egress_mtu_sets_egress_then_wg(
-        self, _req_root, _get_def, _exists, _read_mtu, _probe_pmtu, mock_set_mtu
-    ):
-        """
-        --apply-egress-mtu setzt egress=eth0 auf effective MTU (1452) und danach wg0 auf 1452-80=1372.
-        Reihenfolge der set_mtu-Aufrufe: erst eth0, dann wg0.
-        """
-        argv = ["main.py", "--dry-run", "--apply-egress-mtu", "--pmtu-target", "46.4.224.77"]
-        with patch.object(sys, "argv", argv):
-            buf = io.StringIO()
-            with redirect_stdout(buf):
-                automtu.main()
-
-        out = buf.getvalue()
-        self.assertIn("Applying effective MTU 1452 to egress eth0", out)
-        self.assertIn("Computed wg0 MTU: 1372", out)
-
-        # Call order prüfen
-        calls = [
-            unittest.mock.call("eth0", 1452, True),  # egress zuerst
-            unittest.mock.call("wg0", 1372, True),   # dann wg0
-        ]
-        mock_set_mtu.assert_has_calls(calls, any_order=False)
-        self.assertEqual(mock_set_mtu.call_count, 2)
-
-    # ---------- --apply-egress-mtu: egress == wg_if -> skip apply auf egress ----------
-
-    @patch("main.wg_default_is_active", return_value=True)
-    @patch("main.wg_is_active", return_value=True)
-    @patch("main.set_mtu")
-    @patch("main.probe_pmtu", return_value=1500)
-    @patch("main.read_mtu", return_value=1500)
-    @patch("main.exists_iface", return_value=True)
-    @patch("main.get_default_ifaces", return_value=["wg0"])  # wg0 wird als egress gewählt
-    @patch("main.require_root", return_value=None)
-    def test_apply_egress_mtu_skips_when_egress_is_wg(
-        self, _req_root, _get_def, _exists, _read_mtu, _probe, mock_set_mtu, _wg_active, _wg_def_active
-    ):
-        """
-        Wenn egress == wg0, soll das Skript den egress-Apply überspringen, aber wg0 ganz normal setzen.
-        """
-        argv = ["main.py", "--dry-run", "--apply-egress-mtu", "--prefer-wg-egress", "--wg-if", "wg0"]
-        with patch.object(sys, "argv", argv):
-            out = io.StringIO()
-            with redirect_stdout(out):
-                automtu.main()
-        s = out.getvalue()
-
-        self.assertIn("Detected egress interface: wg0", s)
-        self.assertIn("Skipping egress MTU apply because egress == wg0", s)
-        # wg0 wird trotzdem gesetzt (1500-80=1420)
-        mock_set_mtu.assert_any_call("wg0", 1420, True)
-        # Es darf nur ein set_mtu-Aufruf erfolgen (kein separater egress-Apply)
-        self.assertEqual(mock_set_mtu.call_count, 1)
-
-    # ---------- --apply-egress-mtu plus --set-wg-mtu override ----------
-
-    @patch("main.set_mtu")
-    @patch("main.probe_pmtu", return_value=1452)
-    @patch("main.read_mtu", return_value=1500)
-    @patch("main.exists_iface", return_value=True)
-    @patch("main.get_default_ifaces", return_value=["eth0"])
-    @patch("main.require_root", return_value=None)
-    def test_apply_egress_mtu_with_forced_wg_override(
-        self, _req_root, _get_def, _exists, _read_mtu, _probe_pmtu, mock_set_mtu
-    ):
-        """
-        Egress wird auf 1452 gesetzt, aber wg0 wird mit --set-wg-mtu (z. B. 1300) überschrieben,
-        unabhängig vom berechneten Wert (1372).
-        """
-        argv = [
-            "main.py", "--dry-run",
-            "--apply-egress-mtu",
-            "--pmtu-target", "1.1.1.1",
-            "--set-wg-mtu", "1300",
-        ]
-        with patch.object(sys, "argv", argv):
-            buf = io.StringIO()
-            with redirect_stdout(buf):
-                automtu.main()
-
-        out = buf.getvalue()
-        self.assertIn("Applying effective MTU 1452 to egress eth0", out)
-        self.assertIn("Computed wg0 MTU: 1372", out)  # erst berechnet
-        self.assertIn("Forcing WireGuard MTU (override): 1300", out)  # dann überschrieben
-
-        calls = [
-            unittest.mock.call("eth0", 1452, True),
-            unittest.mock.call("wg0", 1300, True),
-        ]
-        mock_set_mtu.assert_has_calls(calls, any_order=False)
-        self.assertEqual(mock_set_mtu.call_count, 2)
-
-if __name__ == "__main__":
-    unittest.main(verbosity=2)

tests/unit/test___init__.py

@@ -0,0 +1,14 @@
+import unittest
+
+import automtu
+
+
+class TestInit(unittest.TestCase):
+    def test_version_is_exposed(self) -> None:
+        self.assertTrue(hasattr(automtu, "__version__"))
+        self.assertIsInstance(automtu.__version__, str)
+        self.assertRegex(automtu.__version__, r"^\d+\.\d+\.\d+$")
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)

tests/unit/test___main__.py

@@ -0,0 +1,26 @@
+import unittest
+from unittest.mock import Mock, patch
+
+import automtu.__main__ as entry
+
+
+class TestMain(unittest.TestCase):
+    def test_main_calls_parser_and_core(self) -> None:
+        fake_args = object()
+        fake_parser = Mock()
+        fake_parser.parse_args.return_value = fake_args
+
+        with (
+            patch("automtu.__main__.build_parser", return_value=fake_parser) as p_build,
+            patch("automtu.__main__.run_automtu", return_value=0) as p_run,
+        ):
+            rc = entry.main()
+
+        self.assertEqual(rc, 0)
+        p_build.assert_called_once_with()
+        fake_parser.parse_args.assert_called_once_with()
+        p_run.assert_called_once_with(fake_args)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)

tests/unit/test_cli.py

@@ -0,0 +1,62 @@
+import unittest
+
+from automtu.cli import build_parser
+
+
+class TestCli(unittest.TestCase):
+    def test_build_parser_accepts_known_args(self) -> None:
+        p = build_parser()
+
+        # Parse only; no side effects.
+        args = p.parse_args(
+            [
+                "--egress-if",
+                "eth0",
+                "--prefer-wg-egress",
+                "--pmtu-target",
+                "1.1.1.1,8.8.8.8",
+                "--pmtu-timeout",
+                "2.0",
+                "--pmtu-min-payload",
+                "1200",
+                "--pmtu-max-payload",
+                "1472",
+                "--pmtu-policy",
+                "median",
+                "--apply-egress-mtu",
+                "--apply-wg-mtu",
+                "--wg-if",
+                "wg0",
+                "--wg-overhead",
+                "80",
+                "--wg-min",
+                "1280",
+                "--auto-pmtu-from-wg",
+                "--set-wg-mtu",
+                "1372",
+                "--force-egress-mtu",
+                "1452",
+                "--dry-run",
+            ]
+        )
+
+        self.assertEqual(args.egress_if, "eth0")
+        self.assertTrue(args.prefer_wg_egress)
+        self.assertEqual(args.pmtu_target, ["1.1.1.1,8.8.8.8"])
+        self.assertEqual(args.pmtu_timeout, 2.0)
+        self.assertEqual(args.pmtu_min_payload, 1200)
+        self.assertEqual(args.pmtu_max_payload, 1472)
+        self.assertEqual(args.pmtu_policy, "median")
+        self.assertTrue(args.apply_egress_mtu)
+        self.assertTrue(args.apply_wg_mtu)
+        self.assertEqual(args.wg_if, "wg0")
+        self.assertEqual(args.wg_overhead, 80)
+        self.assertEqual(args.wg_min, 1280)
+        self.assertTrue(args.auto_pmtu_from_wg)
+        self.assertEqual(args.set_wg_mtu, 1372)
+        self.assertEqual(args.force_egress_mtu, 1452)
+        self.assertTrue(args.dry_run)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)

tests/unit/test_core.py

@@ -0,0 +1,94 @@
+import io
+import unittest
+from contextlib import redirect_stdout
+from types import SimpleNamespace
+from unittest.mock import patch
+
+from automtu.core import run_automtu
+
+
+class TestCore(unittest.TestCase):
+    def test_run_automtu_happy_path_all_mocked(self) -> None:
+        args = SimpleNamespace(
+            dry_run=True,
+            egress_if=None,
+            prefer_wg_egress=False,
+            force_egress_mtu=None,
+            pmtu_target=["1.1.1.1,8.8.8.8"],
+            auto_pmtu_from_wg=False,
+            pmtu_min_payload=1200,
+            pmtu_max_payload=1472,
+            pmtu_timeout=1.0,
+            pmtu_policy="min",
+            apply_egress_mtu=True,
+            apply_wg_mtu=True,
+            wg_if="wg0",
+            wg_overhead=80,
+            wg_min=1280,
+            set_wg_mtu=None,
+        )
+
+        # PMTU probes: 1452 and 1500 -> min policy => 1452, effective=min(base(1500),1452)=1452
+        # wg_mtu = 1452-80 = 1372
+        with (
+            patch("automtu.core.require_root", return_value=None),
+            patch("automtu.core.detect_egress_iface", return_value="eth0"),
+            patch("automtu.core.iface_exists", return_value=True),
+            patch("automtu.core.read_iface_mtu", return_value=1500),
+            patch("automtu.core.probe_pmtu", side_effect=[1452, 1500]),
+            patch("automtu.core.set_iface_mtu") as mock_set,
+            patch("automtu.core.wg_is_active", return_value=False),
+            patch("automtu.core.wg_peer_endpoints", return_value=[]),
+            patch("automtu.core.default_route_uses_iface", return_value=False),
+        ):
+            buf = io.StringIO()
+            with redirect_stdout(buf):
+                rc = run_automtu(args)
+
+        self.assertEqual(rc, 0)
+        s = buf.getvalue()
+        self.assertIn("Detected egress interface: eth0", s)
+        self.assertIn("Egress base MTU: 1500", s)
+        self.assertIn("Selected Path MTU (policy=min): 1452", s)
+        self.assertIn("Computed wg0 MTU: 1372", s)
+
+        # apply egress and wg are both true -> two calls in order
+        mock_set.assert_any_call("eth0", 1452, True)
+        mock_set.assert_any_call("wg0", 1372, True)
+
+    def test_run_automtu_does_not_apply_wg_without_flag(self) -> None:
+        args = SimpleNamespace(
+            dry_run=True,
+            egress_if="eth0",
+            prefer_wg_egress=False,
+            force_egress_mtu=None,
+            pmtu_target=None,
+            auto_pmtu_from_wg=False,
+            pmtu_min_payload=1200,
+            pmtu_max_payload=1472,
+            pmtu_timeout=1.0,
+            pmtu_policy="min",
+            apply_egress_mtu=False,
+            apply_wg_mtu=False,
+            wg_if="wg0",
+            wg_overhead=80,
+            wg_min=1280,
+            set_wg_mtu=None,
+        )
+
+        with (
+            patch("automtu.core.require_root", return_value=None),
+            patch("automtu.core.iface_exists", return_value=True),
+            patch("automtu.core.read_iface_mtu", return_value=1500),
+            patch("automtu.core.set_iface_mtu") as mock_set,
+        ):
+            buf = io.StringIO()
+            with redirect_stdout(buf):
+                rc = run_automtu(args)
+
+        self.assertEqual(rc, 0)
+        mock_set.assert_not_called()
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)

tests/unit/test_net.py

@@ -0,0 +1,49 @@
+import unittest
+from unittest.mock import patch
+
+import automtu.net as net
+
+
+class TestNet(unittest.TestCase):
+    def test_detect_egress_iface_parses_default_route_and_ignores_vpn(self) -> None:
+        # Simulate: ip route show default -> dev wg0 first, then eth0
+        ip4_default = (
+            "default via 10.0.0.1 dev wg0 proto dhcp src 10.0.0.2 metric 100\n"
+        )
+        ip6_default = "default via fe80::1 dev eth0 proto ra metric 100\n"
+
+        def fake_run(cmd: list[str]) -> str:
+            if cmd[:4] == ["ip", "-4", "route", "show"]:
+                return ip4_default.strip()
+            if cmd[:4] == ["ip", "-6", "route", "show"]:
+                return ip6_default.strip()
+            return ""
+
+        with (
+            patch("automtu.net._run", side_effect=fake_run),
+            patch("automtu.net.iface_exists", return_value=True),
+        ):
+            # ignore_vpn=True -> should skip wg0 and pick eth0
+            self.assertEqual(net.detect_egress_iface(ignore_vpn=True), "eth0")
+
+            # ignore_vpn=False -> first seen is wg0
+            self.assertEqual(net.detect_egress_iface(ignore_vpn=False), "wg0")
+
+    def test_default_route_uses_iface_true_false(self) -> None:
+        ip4_default = "default via 10.0.0.1 dev eth0\n"
+        ip6_default = ""
+
+        def fake_run(cmd: list[str]) -> str:
+            if cmd[:4] == ["ip", "-4", "route", "show"]:
+                return ip4_default.strip()
+            if cmd[:4] == ["ip", "-6", "route", "show"]:
+                return ip6_default.strip()
+            return ""
+
+        with patch("automtu.net._run", side_effect=fake_run):
+            self.assertTrue(net.default_route_uses_iface("eth0"))
+            self.assertFalse(net.default_route_uses_iface("wg0"))
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)

tests/unit/test_pmtu.py

@@ -0,0 +1,36 @@
+import unittest
+from unittest.mock import patch
+
+import automtu.pmtu as pmtu
+
+
+class TestPmtu(unittest.TestCase):
+    def test_probe_pmtu_binary_search_and_hdr_addition(self) -> None:
+        # Mock _is_ipv6 -> IPv4, so hdr = 28.
+        # Mock _ping_ok so that payload <= 1400 works, >1400 fails.
+        def fake_ping_ok(payload: int, target: str, timeout_s: float) -> bool:
+            return payload <= 1400
+
+        with (
+            patch("automtu.pmtu._is_ipv6", return_value=False),
+            patch("automtu.pmtu._ping_ok", side_effect=fake_ping_ok),
+        ):
+            # lo=1200 works, hi=1472 partially works -> best = 1400 -> mtu = 1400+28 = 1428
+            mtu = pmtu.probe_pmtu(
+                "1.1.1.1", lo_payload=1200, hi_payload=1472, timeout=1.0
+            )
+            self.assertEqual(mtu, 1428)
+
+    def test_probe_pmtu_returns_none_if_even_floor_fails(self) -> None:
+        with (
+            patch("automtu.pmtu._is_ipv6", return_value=False),
+            patch("automtu.pmtu._ping_ok", return_value=False),
+        ):
+            mtu = pmtu.probe_pmtu(
+                "1.1.1.1", lo_payload=1200, hi_payload=1472, timeout=1.0
+            )
+            self.assertIsNone(mtu)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)

tests/unit/test_wg.py

@@ -0,0 +1,58 @@
+import unittest
+from unittest.mock import patch
+
+import automtu.wg as wg
+
+
+class TestWg(unittest.TestCase):
+    def test_wg_peer_endpoints_from_wg_show(self) -> None:
+        # wg show wg0 endpoints output
+        out = "abcde12345\t46.4.224.77:51820\nfffff00000\t[2a01:db8::1]:51820\n"
+
+        with (
+            patch(
+                "automtu.wg._run",
+                side_effect=lambda cmd: out if cmd[:3] == ["wg", "show", "wg0"] else "",
+            ),
+            patch("automtu.wg.iface_exists", return_value=True),
+            patch("automtu.wg._rc", return_value=0),
+        ):
+            eps = wg.wg_peer_endpoints("wg0")
+
+        self.assertEqual(eps, ["46.4.224.77", "2a01:db8::1"])
+
+    def test_wg_peer_endpoints_fallback_showconf(self) -> None:
+        show_endpoints_empty = ""
+        showconf = (
+            "[Interface]\n"
+            "PrivateKey = x\n"
+            "[Peer]\n"
+            "Endpoint = 46.4.224.77:51820\n"
+            "[Peer]\n"
+            "Endpoint = [2a01:db8::1]:51820\n"
+        )
+
+        def fake_run(cmd: list[str]) -> str:
+            if cmd == ["wg", "show", "wg0", "endpoints"]:
+                return show_endpoints_empty
+            if cmd == ["wg", "showconf", "wg0"]:
+                return showconf
+            return ""
+
+        with patch("automtu.wg._run", side_effect=fake_run):
+            eps = wg.wg_peer_endpoints("wg0")
+
+        self.assertEqual(eps, ["46.4.224.77", "2a01:db8::1"])
+
+    def test_wg_is_active_uses_iface_exists_and_wg_show_rc(self) -> None:
+        with (
+            patch("automtu.wg.iface_exists", return_value=True),
+            patch("automtu.wg._rc", return_value=0),
+        ):
+            self.assertTrue(wg.wg_is_active("wg0"))
+        with patch("automtu.wg.iface_exists", return_value=False):
+            self.assertFalse(wg.wg_is_active("wg0"))
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)