#!/usr/bin/env bash

# This project is licensed under the Blue Oak Model License 1.0.0.
# See: https://blueoakcouncil.org/license/1.0.0

# A Bash-based Finger client (RFC 1288) using /dev/tcp for socket connections.
# Full support for 8-bit characters, long files and ASCII art.

# install  : chmod +x bfinger && sudo install bfinger /usr/local/bin
# uninstall: sudo rm /usr/local/bin/bfinger

# bfinger -h --help (for help)

# Version 2.0 (May 30, 2025)
# Added DoS protection:
#   - Hard memory limit (~1MB default, configurable via BFINGER_MAX_BYTES)
#   - Per-byte timeouts (-t 5)
#   - Clean stream truncation with visual cue

# Version 1.0 (May 01, 2025)
# A complete Finger client
#   - Uses Bash's /dev/tcp for socket connections
#   - Full 8-bit character support (bfinger codepage437@happynetbox.com)
#   - No artificial stream limits (v2.0 adds 1MB default, configurable)
#   - Per-byte timeout protection (-t 5) without buffering delays

# ------------------------------ Start Script -------------------------------

set -eo pipefail  # Removed -u to avoid unbound variable errors
[ -n "${DEBUG:-}" ] && set -xu  # Only enable -u in debug mode

VERSION="2.0 (May 30, 2025)"

# enforce consistent locale for byte handling
export LC_ALL=C

# Cleanup on interrupt
cleanup() {
  exec 3<&- 3>&- 2>/dev/null || true
  exit 130
}
trap cleanup INT

# Memory safety - arbitrary stream limit (~1MB) - adjust as needed.
# Protects against endless data streams (malicious/poorly behaving servers)
MAX_BYTES=${BFINGER_MAX_BYTES:-1000000}

# Show usage if no args or help flag
if [ $# -eq 0 ] || [[ "$1" =~ ^(/|\-){1,2}(\?|h|help)$ ]]; then
  echo ""
  echo "bfinger $VERSION - A Bash-based Finger Client (RFC 1288)"
  echo ""
  echo "Uses Bash's /dev/tcp for socket connections to query remote Finger"
  echo "servers. Full support for 8-bit characters, long files and ASCII art."
  echo ""
  echo "Usage:"
  echo "  bfinger @domain.com         # Queries host"
  echo "  bfinger user@domain.com     # Specific user"
  echo "  bfinger user domain.com     # Alternative"
  echo "  bfinger @localhost          # fingerd must be installed locally"
  echo ""
  echo "Options:"
  echo "  -v, --version               Show version info"
  echo "  -h, --help, -?, /?          Show this help message"
  echo ""
  echo "Examples:"
  echo "  bfinger fingerverse@happynetbox.com | less"
  echo "  bfinger @plan.cat | head -n 20"
  echo ""
  echo "install:   chmod +x bfinger && sudo install bfinger /usr/local/bin"
  echo "uninstall: sudo rm /usr/local/bin/bfinger"
  echo ""
  exit 0
fi

# Show version
if [[ "${1:-}" == "--version" || "${1:-}" == "-v" ]]; then
  echo "bfinger $VERSION - A Bash-based finger client"
  exit 0
fi

# Parse input
if [[ "$1" == @* ]]; then
  USER=""
  HOST="${1#@}"
elif [[ "$1" =~ @ ]]; then
  USER="${1%%@*}"
  HOST="${1##*@}"
else
  USER="${1:-}"
  HOST="${2:-}"
fi

PORT=79

# validate host. Good enough...
if [ -z "$HOST" ]; then
  echo "Error: No host specified" >&2
  exit 1
fi

# basic hostname validation. Also good enough:-)
if [[ ! "$HOST" =~ ^[a-zA-Z0-9._-]+$ ]]; then
  echo "Error: Hostname contains invalid characters" >&2
  exit 1
fi

# check DNS resolution
if ! getent hosts "$HOST" >/dev/null; then
  echo "Error: Host '$HOST' could not be resolved" >&2
  exit 1
fi

# Connect and stream response
if ! timeout 5 bash -c "exec 3<>/dev/tcp/$HOST/$PORT"; then
  echo "Error: Connection to $HOST:$PORT timed out or failed" >&2
  echo "Tip: Try 'telnet $HOST $PORT' to debug" >&2
  exit 1
fi
exec 3<>/dev/tcp/"$HOST"/"$PORT"

# Send request
printf "%s\r\n" "$USER" >&3

# Read response with 8-bit and whitespace preservation
bytes_read=0
while IFS= read -r -t 5 -N 1 char <&3 && (( bytes_read++ < MAX_BYTES )); do
  printf "%s" "$char"
done
(( bytes_read >= MAX_BYTES )) && echo >&2  # Adds a line break when truncated (visual cue)

# Cleanup
exec 3<&- 3>&-

# .-----------------------------.  .-------------.  .-------------------------.
# | https://640kb.neocities.org |--| 30 May 2025 |--| bfinger@happynetbox.com |
# '-----------------------------'  '-------------'  '-------------------------'