Initial commit: simtrace2-pysniff v0.1.0

Python-based SIMtrace2 sniffer — drop-in replacement for simtrace2-sniff.
Single dependency (pyusb), auto-reconnect, GSMTAP/PCAP output, library API.

Modules:
  protocol.py — SIMtrace2 USB sniffing protocol parser
  device.py   — USB discovery + SniffSession with exponential backoff reconnect
  gsmtap.py   — GSMTAP UDP sender for Wireshark
  pcap.py     — PCAP file writer (LINKTYPE_GSMTAP)
  dump.py     — hex dump formatters + file output
  __main__.py — CLI entry point

Startup script sniff-start.sh handles udev permission checks and shows
install instructions. udev rule uses TAG+=uaccess (systemd-logind ACL).

sniff-start.sh

@@ -0,0 +1,83 @@
+#!/bin/bash
+# simtrace2-pysniff startup script
+#
+# Usage: ./sniff-start.sh [--gsmtap HOST[:PORT]] [--pcap FILE] [--output FILE] [--inactivity-timeout SECONDS]
+#
+# Options set via environment variables act as defaults; CLI flags override them.
+
+set -euo pipefail
+shopt -s nullglob
+
+PROJECT_DIR="$(cd "$(dirname "$0")" && pwd)"
+
+GSMTAP="${GSMTAP:-}"
+PCAP="${PCAP:-}"
+OUTPUT="${OUTPUT:-}"
+INACTIVITY_TIMEOUT="${INACTIVITY_TIMEOUT:-0}"
+
+while [[ $# -gt 0 ]]; do
+    case "$1" in
+        --gsmtap)              GSMTAP="$2"; shift 2 ;;
+        --pcap)                PCAP="$2"; shift 2 ;;
+        --output|-o)           OUTPUT="$2"; shift 2 ;;
+        --inactivity-timeout)  INACTIVITY_TIMEOUT="$2"; shift 2 ;;
+        --keep-running|--no-reconnect)
+                               EXTRA_ARGS+=("$1"); shift ;;
+        *)                     EXTRA_ARGS+=("$1"); shift ;;
+    esac
+done
+
+check_permissions() {
+    local bad_perms=0
+
+    for devdir in /sys/bus/usb/devices/*/; do
+        [[ -f "${devdir}busnum" ]] || continue
+        [[ -f "${devdir}devnum" ]] || continue
+        [[ -f "${devdir}uevent" ]] || continue
+
+        local vid
+        vid=$(grep -oP 'PRODUCT=\K[a-f0-9]+' "${devdir}uevent" 2>/dev/null || true)
+        [[ "$vid" == "1d50" ]] || continue
+
+        local busnum devnum node
+        busnum=$(<"${devdir}busnum")
+        devnum=$(<"${devdir}devnum")
+        node=$(printf '/dev/bus/usb/%03d/%03d' "$busnum" "$devnum")
+
+        if [[ ! -e "$node" ]]; then
+            continue
+        fi
+
+        if [[ -w "$node" ]]; then
+            return 0
+        fi
+
+        bad_perms=1
+        echo "Permission denied on $node" >&2
+    done
+
+    if [[ $bad_perms -eq 1 ]]; then
+        echo "" >&2
+        echo "Install the udev rule (then reconnect the device):" >&2
+        echo "──────────────────────────────────────────────────" >&2
+        echo "  sudo cp '$PROJECT_DIR/70-simtrace2-pysniff.rules' /etc/udev/rules.d/" >&2
+        echo "  sudo udevadm control --reload-rules" >&2
+        echo "  sudo udevadm trigger" >&2
+        echo "──────────────────────────────────────────────────" >&2
+        return 1
+    fi
+
+    return 0
+}
+
+check_permissions || exit 3
+
+ARGS=()
+[[ -n "$GSMTAP" ]]             && ARGS+=(--gsmtap "$GSMTAP")
+[[ -n "$PCAP" ]]               && ARGS+=(--pcap "$PCAP")
+[[ -n "$OUTPUT" ]]             && ARGS+=(--output "$OUTPUT")
+[[ "$INACTIVITY_TIMEOUT" != "0" ]] && ARGS+=(--inactivity-timeout "$INACTIVITY_TIMEOUT")
+ARGS+=("${EXTRA_ARGS[@]}")
+
+echo "Starting simtrace2-pysniff..." >&2
+exec env PYTHONPATH="$PROJECT_DIR" python3 -m simtrace2_pysniff "${ARGS[@]}"