av98.py

#!/usr/bin/env python3
# AV-98 Gemini client
# Dervied from VF-1 (https://github.com/solderpunk/VF-1),
# (C) 2019, 2020 Solderpunk <solderpunk@sdf.org>
# With contributions from:
#  - danceka <hannu.hartikainen@gmail.com>
#  - <jprjr@tilde.club>
#  - <vee@vnsf.xyz>
#  - Klaus Alexander Seistrup <klaus@seistrup.dk>
#  - govynnus <govynnus@sdf.org>

import argparse
import cmd
import cgi
import codecs
import collections
import datetime
import fnmatch
import getpass
import glob
import hashlib
import io
import mimetypes
import os
import os.path
import random
import shlex
import shutil
import socket
import sqlite3
import ssl
from ssl import CertificateError
import subprocess
import sys
import tempfile
import time
import urllib.parse
import uuid
import webbrowser

try:
    import ansiwrap as textwrap
except ModuleNotFoundError:
    import textwrap

try:
    from cryptography import x509
    from cryptography.hazmat.backends import default_backend
    _HAS_CRYPTOGRAPHY = True
    _BACKEND = default_backend()
except ModuleNotFoundError:
    _HAS_CRYPTOGRAPHY = False

_VERSION = "1.0.2dev"

_MAX_REDIRECTS = 5
_MAX_CACHE_SIZE = 10
_MAX_CACHE_AGE_SECS = 180

# Command abbreviations
_ABBREVS = {
    "a":    "add",
    "b":    "back",
    "bb":   "blackbox",
    "bm":   "bookmarks",
    "book": "bookmarks",
    "f":    "fold",
    "fo":   "forward",
    "g":    "go",
    "h":    "history",
    "hist": "history",
    "l":    "less",
    "n":    "next",
    "p":    "previous",
    "prev": "previous",
    "q":    "quit",
    "r":    "reload",
    "s":    "save",
    "se":   "search",
    "/":    "search",
    "t":    "tour",
    "u":    "up",
}

_MIME_HANDLERS = {
    "application/pdf":      "xpdf %s",
    "audio/mpeg":           "mpg123 %s",
    "audio/ogg":            "ogg123 %s",
    "image/*":              "feh %s",
    "text/html":            "lynx -dump -force_html %s",
    "text/*":               "cat %s",
}

# monkey-patch Gemini support in urllib.parse
# see https://github.com/python/cpython/blob/master/Lib/urllib/parse.py
urllib.parse.uses_relative.append("gemini")
urllib.parse.uses_netloc.append("gemini")


def fix_ipv6_url(url):
    if not url.count(":") > 2: # Best way to detect them?
        return url
    # If there's a pair of []s in there, it's probably fine as is.
    if "[" in url and "]" in url:
        return url
    # Easiest case is a raw address, no schema, no path.
    # Just wrap it in square brackets and whack a slash on the end
    if "/" not in url:
        return "[" + url + "]/"
    # Now the trickier cases...
    if "://" in url:
        schema, schemaless = url.split("://")
    else:
        schema, schemaless = None, url
    if "/" in schemaless:
        netloc, rest = schemaless.split("/",1)
        schemaless = "[" + netloc + "]" + "/" + rest
    if schema:
        return schema + "://" + schemaless
    return schemaless

standard_ports = {
        "gemini": 1965,
        "gopher": 70,
}

class GeminiItem():

    def __init__(self, url, name=""):
        if "://" not in url:
            url = "gemini://" + url
        self.url = fix_ipv6_url(url)
        self.name = name
        parsed = urllib.parse.urlparse(self.url)
        self.scheme = parsed.scheme
        self.host = parsed.hostname
        self.port = parsed.port or standard_ports.get(self.scheme, 0)
        self.path = parsed.path

    def root(self):
        return GeminiItem(self._derive_url("/"))

    def up(self):
        pathbits = list(os.path.split(self.path.rstrip('/')))
        # Don't try to go higher than root
        if len(pathbits) == 1:
            return self
        # Get rid of bottom component
        pathbits.pop()
        new_path = os.path.join(*pathbits)
        return GeminiItem(self._derive_url(new_path))

    def query(self, query):
        query = urllib.parse.quote(query)
        return GeminiItem(self._derive_url(query=query))

    def _derive_url(self, path="", query=""):
        """
        A thin wrapper around urlunparse which avoids inserting standard ports
        into URLs just to keep things clean.
        """
        return urllib.parse.urlunparse((self.scheme,
            self.host if self.port == standard_ports[self.scheme] else self.host + ":" + str(self.port),
            path or self.path, "", query, ""))

    def absolutise_url(self, relative_url):
        """
        Convert a relative URL to an absolute URL by using the URL of this
        GeminiItem as a base.
        """
        return urllib.parse.urljoin(self.url, relative_url)

    def to_map_line(self, name=None):
        if name or self.name:
            return "=> {} {}\n".format(self.url, name or self.name)
        else:
            return "=> {}\n".format(self.url)

    @classmethod
    def from_map_line(cls, line, origin_gi):
        assert line.startswith("=>")
        assert line[2:].strip()
        bits = line[2:].strip().split(maxsplit=1)
        bits[0] = origin_gi.absolutise_url(bits[0])
        return cls(*bits)

CRLF = '\r\n'

# Cheap and cheerful URL detector
def looks_like_url(word):
    return "." in word and word.startswith("gemini://")

class UserAbortException(Exception):
    pass

# GeminiClient Decorators
def needs_gi(inner):
    def outer(self, *args, **kwargs):
        if not self.gi:
            print("You need to 'go' somewhere, first")
            return None
        else:
            return inner(self, *args, **kwargs)
    outer.__doc__ = inner.__doc__
    return outer

def restricted(inner):
    def outer(self, *args, **kwargs):
        if self.restricted:
            print("Sorry, this command is not available in restricted mode!")
            return None
        else:
            return inner(self, *args, **kwargs)
    outer.__doc__ = inner.__doc__
    return outer

class GeminiClient(cmd.Cmd):

    def __init__(self, restricted=False):
        cmd.Cmd.__init__(self)

        # Set umask so that nothing we create can be read by anybody else.
        # The certificate cache and TOFU database contain "browser history"
        # type sensitivie information.
        os.umask(0o077)

        # Find config directory
        ## Look for something pre-existing
        for confdir in ("~/.av98/", "~/.config/av98/"):
            confdir = os.path.expanduser(confdir)
            if os.path.exists(confdir):
                self.config_dir = confdir
                break
        ## Otherwise, make one in .config if it exists
        else:
            if os.path.exists(os.path.expanduser("~/.config/")):
                self.config_dir = os.path.expanduser("~/.config/av98/")
            else:
                self.config_dir = os.path.expanduser("~/.av98/")
            print("Creating config directory {}".format(self.config_dir))
            os.makedirs(self.config_dir)

        self.no_cert_prompt = "\x1b[38;5;76m" + "AV-98" + "\x1b[38;5;255m" + "> " + "\x1b[0m"
        self.cert_prompt = "\x1b[38;5;202m" + "AV-98" + "\x1b[38;5;255m" + "+cert> " + "\x1b[0m"
        self.prompt = self.no_cert_prompt
        self.gi = None
        self.history = []
        self.hist_index = 0
        self.idx_filename = ""
        self.index = []
        self.index_index = -1
        self.lookup = self.index
        self.marks = {}
        self.page_index = 0
        self.permanent_redirects = {}
        self.previous_redirectors = set()
        self.restricted = restricted
        self.tmp_filename = ""
        self.visited_hosts = set()
        self.waypoints = []

        self.client_certs = {
            "active": None
        }
        self.active_cert_domains = []
        self.active_is_transient = False
        self.transient_certs_created = []

        self.options = {
            "debug" : False,
            "ipv6" : True,
            "timeout" : 10,
            "width" : 80,
            "auto_follow_redirects" : True,
            "gopher_proxy" : None,
            "tls_mode" : "tofu",
            "cache" : False
        }

        self.log = {
            "start_time": time.time(),
            "requests": 0,
            "ipv4_requests": 0,
            "ipv6_requests": 0,
            "bytes_recvd": 0,
            "ipv4_bytes_recvd": 0,
            "ipv6_bytes_recvd": 0,
            "dns_failures": 0,
            "refused_connections": 0,
            "reset_connections": 0,
            "timeouts": 0,
            "cache_hits": 0,
        }

        self._connect_to_tofu_db()

        self.cache = {}
        self.cache_timestamps = {}

    def _connect_to_tofu_db(self):

        db_path = os.path.join(self.config_dir, "tofu.db")
        self.db_conn = sqlite3.connect(db_path)
        self.db_cur = self.db_conn.cursor()

        self.db_cur.execute("""CREATE TABLE IF NOT EXISTS cert_cache
            (hostname text, address text, fingerprint text,
            first_seen date, last_seen date, count integer)""")

    def _go_to_gi(self, gi, update_hist=True, check_cache=True, handle=True):
        """This method might be considered "the heart of AV-98".
        Everything involved in fetching a gemini resource happens here:
        sending the request over the network, parsing the response if
        its a menu, storing the response in a temporary file, choosing
        and calling a handler program, and updating the history."""

        # Don't try to speak to servers running other protocols
        if gi.scheme in ("http", "https"):
            webbrowser.open_new_tab(gi.url)
            return
        elif gi.scheme == "gopher" and not self.options.get("gopher_proxy", None):
            print("""AV-98 does not speak Gopher natively.
However, you can use `set gopher_proxy hostname:port` to tell it about a
Gopher-to-Gemini proxy (such as a running Agena instance), in which case
you'll be able to transparently follow links to Gopherspace!""")
            return
        elif gi.scheme not in ("gemini", "gopher"):
            print("Sorry, no support for {} links.".format(gi.scheme))
            return

        # Obey permanent redirects
        if gi.url in self.permanent_redirects:
            new_gi = GeminiItem(self.permanent_redirects[gi.url], name=gi.name)
            self._go_to_gi(new_gi)
            return

        # Use cache, or hit the network if resource is not cached
        if check_cache and self.options["cache"] and self._is_cached(gi.url):
            mime, body, tmpfile = self._get_cached(gi.url)
        else:
            try:
                gi, mime, body, tmpfile = self._fetch_over_network(gi)
            except UserAbortException:
                return
            except Exception as err:
                # Print an error message
                if isinstance(err, socket.gaierror):
                    self.log["dns_failures"] += 1
                    print("ERROR: DNS error!")
                elif isinstance(err, ConnectionRefusedError):
                    self.log["refused_connections"] += 1
                    print("ERROR: Connection refused!")
                elif isinstance(err, ConnectionResetError):
                    self.log["reset_connections"] += 1
                    print("ERROR: Connection reset!")
                elif isinstance(err, (TimeoutError, socket.timeout)):
                    self.log["timeouts"] += 1
                    print("""ERROR: Connection timed out!
    Slow internet connection?  Use 'set timeout' to be more patient.""")
                else:
                    print("ERROR: " + str(err))
                return

        # Pass file to handler, unless we were asked not to
        if handle:
            if mime == "text/gemini":
                self._handle_gemtext(body, gi)
            else:
                cmd_str = self._get_handler_cmd(mime)
                try:
                    subprocess.call(shlex.split(cmd_str % tmpfile))
                except FileNotFoundError:
                    print("Handler program %s not found!" % shlex.split(cmd_str)[0])
                    print("You can use the ! command to specify another handler program or pipeline.")

        # Update state
        self.gi = gi
        self.mime = mime
        if update_hist:
            self._update_history(gi)

    def _fetch_over_network(self, gi):

        # Be careful with client certificates!
        # Are we crossing a domain boundary?
        if self.active_cert_domains and gi.host not in self.active_cert_domains:
            if self.active_is_transient:
                print("Permanently delete currently active transient certificate?")
                resp = input("Y/N? ")
                if resp.strip().lower() in ("y", "yes"):
                    print("Destroying certificate.")
                    self._deactivate_client_cert()
                else:
                    print("Staying here.")
                    raise UserAbortException()
            else:
                print("PRIVACY ALERT: Deactivate client cert before connecting to a new domain?")
                resp = input("Y/N? ")
                if resp.strip().lower() in ("n", "no"):
                    print("Keeping certificate active for {}".format(gi.host))
                else:
                    print("Deactivating certificate.")
                    self._deactivate_client_cert()

        # Suggest reactivating previous certs
        if not self.client_certs["active"] and gi.host in self.client_certs:
            print("PRIVACY ALERT: Reactivate previously used client cert for {}?".format(gi.host))
            resp = input("Y/N? ")
            if resp.strip().lower() in ("y", "yes"):
                self._activate_client_cert(*self.client_certs[gi.host])
            else:
                print("Remaining unidentified.")
                self.client_certs.pop(gi.host)

        # Is this a local file?
        if not gi.host:
            address, f = None, open(gi.path, "rb")
        else:
            address, f = self._send_request(gi)

        # Spec dictates <META> should not exceed 1024 bytes,
        # so maximum valid header length is 1027 bytes.
        header = f.readline(1027)
        header = header.decode("UTF-8")
        if not header or header[-1] != '\n':
            raise RuntimeError("Received invalid header from server!")
        header = header.strip()
        self._debug("Response header: %s." % header)

        # Validate header
        status, meta = header.split(maxsplit=1)
        if len(meta) > 1024 or len(status) != 2 or not status.isnumeric():
            f.close()
            raise RuntimeError("Received invalid header from server!")

        # Update redirect loop/maze escaping state
        if not status.startswith("3"):
            self.previous_redirectors = set()

        # Handle non-SUCCESS headers, which don't have a response body
        # Inputs
        if status.startswith("1"):
            print(meta)
            if status == "11":
                user_input = getpass.getpass("> ")
            else:
                user_input = input("> ")
            return self._fetch_over_network(gi.query(user_input))

        # Redirects
        elif status.startswith("3"):
            new_gi = GeminiItem(gi.absolutise_url(meta))
            if new_gi.url == gi.url:
                raise RuntimeError("URL redirects to itself!")
            elif new_gi.url in self.previous_redirectors:
                raise RuntimeError("Caught in redirect loop!")
            elif len(self.previous_redirectors) == _MAX_REDIRECTS:
                raise RuntimeError("Refusing to follow more than %d consecutive redirects!" % _MAX_REDIRECTS)
            # Never follow cross-domain redirects without asking
            elif new_gi.host != gi.host:
                follow = input("Follow cross-domain redirect to %s? (y/n) " % new_gi.url)
            # Never follow cross-protocol redirects without asking
            elif new_gi.scheme != gi.scheme:
                follow = input("Follow cross-protocol redirect to %s? (y/n) " % new_gi.url)
            # Don't follow *any* redirect without asking if auto-follow is off
            elif not self.options["auto_follow_redirects"]:
                follow = input("Follow redirect to %s? (y/n) " % new_gi.url)
            # Otherwise, follow away
            else:
                follow = "yes"
            if follow.strip().lower() not in ("y", "yes"):
                raise UserAbortException()
            self._debug("Following redirect to %s." % new_gi.url)
            self._debug("This is consecutive redirect number %d." % len(self.previous_redirectors))
            self.previous_redirectors.add(gi.url)
            if status == "31":
                # Permanent redirect
                self.permanent_redirects[gi.url] = new_gi.url
            return self._fetch_over_network(new_gi)

        # Errors
        elif status.startswith("4") or status.startswith("5"):
            raise RuntimeError(meta)

        # Client cert
        elif status.startswith("6"):
            self._handle_cert_request(meta)
            return self._fetch_over_network(gi)

        # Invalid status
        elif not status.startswith("2"):
            raise RuntimeError("Server returned undefined status code %s!" % status)

        # If we're here, this must be a success and there's a response body
        assert status.startswith("2")

        mime = meta
        if mime == "":
            mime = "text/gemini; charset=utf-8"
        mime, mime_options = cgi.parse_header(mime)
        if "charset" in mime_options:
            try:
                codecs.lookup(mime_options["charset"])
            except LookupError:
                raise RuntimeError("Header declared unknown encoding %s" % value)

        # Read the response body over the network
        body = f.read()

        # Save the result in a temporary file
        ## Set file mode
        if mime.startswith("text/"):
            mode = "w"
            encoding = mime_options.get("charset", "UTF-8")
            try:
                body = body.decode(encoding)
            except UnicodeError:
                raise RuntimeError("Could not decode response body using %s encoding declared in header!" % encoding)
        else:
            mode = "wb"
            encoding = None
        ## Write
        tmpf = tempfile.NamedTemporaryFile(mode, encoding=encoding, delete=False)
        size = tmpf.write(body)
        tmpf.close()
        self.tmp_filename = tmpf.name
        self._debug("Wrote %d byte response to %s." % (size, self.tmp_filename))

        # Maintain cache and log
        if self.options["cache"]:
            self._add_to_cache(gi.url, mime, self.tmp_filename)
        self._log_visit(gi, address, size)

        return gi, mime, body, self.tmp_filename

    def _send_request(self, gi):
        """Send a selector to a given host and port.
        Returns the resolved address and binary file with the reply."""
        if gi.scheme == "gemini":
            # For Gemini requests, connect to the host and port specified in the URL
            host, port = gi.host, gi.port
        elif gi.scheme == "gopher":
            # For Gopher requests, use the configured proxy
            host, port = self.options["gopher_proxy"].rsplit(":", 1)
            self._debug("Using gopher proxy: " + self.options["gopher_proxy"])

        # Do DNS resolution
        addresses = self._get_addresses(host, port)

        # Prepare TLS context
        protocol = ssl.PROTOCOL_TLS if sys.version_info.minor >=6 else ssl.PROTOCOL_TLSv1_2
        context = ssl.SSLContext(protocol)
        # Use CAs or TOFU
        if self.options["tls_mode"] == "ca":
            context.verify_mode = ssl.CERT_REQUIRED
            context.check_hostname = True
            context.load_default_certs()
        else:
            context.check_hostname = False
            context.verify_mode = ssl.CERT_NONE
        # Impose minimum TLS version
        ## In 3.7 and above, this is easy...
        if sys.version_info.minor >= 7:
            context.minimum_version = ssl.TLSVersion.TLSv1_2
        ## Otherwise, it seems very hard...
        ## The below is less strict than it ought to be, but trying to disable
        ## TLS v1.1 here using ssl.OP_NO_TLSv1_1 produces unexpected failures
        ## with recent versions of OpenSSL.  What a mess...
        else:
            context.options |= ssl.OP_NO_SSLv3
            context.options |= ssl.OP_NO_SSLv2
        # Try to enforce sensible ciphers
        try:
            context.set_ciphers("AESGCM+ECDHE:AESGCM+DHE:CHACHA20+ECDHE:CHACHA20+DHE:!DSS:!SHA1:!MD5:@STRENGTH")
        except ssl.SSLError:
            # Rely on the server to only support sensible things, I guess...
            pass
        # Load client certificate if needed
        if self.client_certs["active"]:
            certfile, keyfile = self.client_certs["active"]
            context.load_cert_chain(certfile, keyfile)

        # Connect to remote host by any address possible
        err = None
        for address in addresses:
            self._debug("Connecting to: " + str(address[4]))
            s = socket.socket(address[0], address[1])
            s.settimeout(self.options["timeout"])
            s = context.wrap_socket(s, server_hostname = gi.host)
            try:
                s.connect(address[4])
                break
            except OSError as e:
                err = e
        else:
            # If we couldn't connect to *any* of the addresses, just
            # bubble up the exception from the last attempt and deny
            # knowledge of earlier failures.
            raise err

        if sys.version_info.minor >=5:
            self._debug("Established {} connection.".format(s.version()))
        self._debug("Cipher is: {}.".format(s.cipher()))

        # Do TOFU
        if self.options["tls_mode"] != "ca":
            cert = s.getpeercert(binary_form=True)
            self._validate_cert(address[4][0], host, cert)

        # Remember that we showed the current cert to this domain...
        if self.client_certs["active"]:
            self.active_cert_domains.append(gi.host)
            self.client_certs[gi.host] = self.client_certs["active"]

        # Send request and wrap response in a file descriptor
        self._debug("Sending %s<CRLF>" % gi.url)
        s.sendall((gi.url + CRLF).encode("UTF-8"))
        return address, s.makefile(mode = "rb")

    def _get_addresses(self, host, port):
        # DNS lookup - will get IPv4 and IPv6 records if IPv6 is enabled
        if ":" in host:
            # This is likely a literal IPv6 address, so we can *only* ask for
            # IPv6 addresses or getaddrinfo will complain
            family_mask = socket.AF_INET6
        elif socket.has_ipv6 and self.options["ipv6"]:
            # Accept either IPv4 or IPv6 addresses
            family_mask = 0
        else:
            # IPv4 only
            family_mask = socket.AF_INET
        addresses = socket.getaddrinfo(host, port, family=family_mask,
                type=socket.SOCK_STREAM)
        # Sort addresses so IPv6 ones come first
        addresses.sort(key=lambda add: add[0] == socket.AF_INET6, reverse=True)

        return addresses

    def _is_cached(self, url):
        if url not in self.cache:
            return False
        now = time.time()
        cached = self.cache_timestamps[url]
        if now - cached > _MAX_CACHE_AGE_SECS:
            self._debug("Expiring old cached copy of resource.")
            self._remove_from_cache(url)
            return False
        self._debug("Found cached copy of resource.")
        return True

    def _remove_from_cache(self, url):
        self.cache_timestamps.pop(url)
        mime, filename = self.cache.pop(url)
        os.unlink(filename)
        self._validate_cache()

    def _add_to_cache(self, url, mime, filename):

        self.cache_timestamps[url] = time.time()
        self.cache[url] = (mime, filename)
        if len(self.cache) > _MAX_CACHE_SIZE:
            self._trim_cache()
        self._validate_cache()

    def _trim_cache(self):
        # Order cache entries by age
        lru = [(t, u) for (u, t) in self.cache_timestamps.items()]
        lru.sort()
        # Drop the oldest entry no matter what
        _, url = lru[0]
        self._debug("Dropping cached copy of {} from full cache.".format(url))
        self._remove_from_cache(url)
        # Drop other entries if they are older than the limit
        now = time.time()
        for cached, url in lru[1:]:
            if now - cached > _MAX_CACHE_AGE_SECS:
                self._debug("Dropping cached copy of {} from full cache.".format(url))
                self._remove_from_cache(url)
            else:
                break
        self._validate_cache()

    def _get_cached(self, url):
        mime, filename = self.cache[url]
        self.log["cache_hits"] += 1
        if mime.startswith("text/gemini"):
            with open(filename, "r") as fp:
                body = fp.read()
                return mime, body, filename
        else:
            return mime, None, filename

    def _empty_cache(self):
        for mime, filename in self.cache.values():
            if os.path.exists(filename):
                os.unlink(filename)

    def _validate_cache(self):
        assert self.cache.keys() == self.cache_timestamps.keys()
        for _, filename in self.cache.values():
            assert os.path.isfile(filename)

    def _handle_cert_request(self, meta):

        # Don't do client cert stuff in restricted mode, as in principle
        # it could be used to fill up the disk by creating a whole lot of
        # certificates
        if self.restricted:
            print("The server is requesting a client certificate.")
            print("These are not supported in restricted mode, sorry.")
            raise UserAbortException()

        print("SERVER SAYS: ", meta)
        # Present different messages for different 6x statuses, but
        # handle them the same.
        if status in ("64", "65"):
            print("The server rejected your certificate because it is either expired or not yet valid.")
        elif status == "63":
            print("The server did not accept your certificate.")
            print("You may need to e.g. coordinate with the admin to get your certificate fingerprint whitelisted.")
        else:
            print("The site {} is requesting a client certificate.".format(gi.host))
            print("This will allow the site to recognise you across requests.")

        # Give the user choices
        print("What do you want to do?")
        print("1. Give up.")
        print("2. Generate a new transient certificate.")
        print("3. Generate a new persistent certificate.")
        print("4. Load a previously generated persistent.")
        print("5. Load certificate from an external file.")
        choice = input("> ").strip()
        if choice == "2":
            self._generate_transient_cert_cert()
        elif choice == "3":
            self._generate_persistent_client_cert()
        elif choice == "4":
            self._choose_client_cert()
        elif choice == "5":
            self._load_client_cert()
        else:
            print("Giving up.")
            raise UserAbortException()

    def _validate_cert(self, address, host, cert):
        """
        Validate a TLS certificate in TOFU mode.

        If the cryptography module is installed:
         - Check the certificate Common Name or SAN matches `host`
         - Check the certificate's not valid before date is in the past
         - Check the certificate's not valid after date is in the future

        Whether the cryptography module is installed or not, check the
        certificate's fingerprint against the TOFU database to see if we've
        previously encountered a different certificate for this IP address and
        hostname.
        """
        now = datetime.datetime.utcnow()
        if _HAS_CRYPTOGRAPHY:
            # Using the cryptography module we can get detailed access
            # to the properties of even self-signed certs, unlike in
            # the standard ssl library...
            c = x509.load_der_x509_certificate(cert, _BACKEND)

            # Check certificate validity dates
            if c.not_valid_before >= now:
                raise CertificateError("Certificate not valid until: {}!".format(c.not_valid_before))
            elif c.not_valid_after <= now:
                raise CertificateError("Certificate expired as of: {})!".format(c.not_valid_after))

            # Check certificate hostnames
            names = []
            common_name = c.subject.get_attributes_for_oid(x509.oid.NameOID.COMMON_NAME)
            if common_name:
                names.append(common_name[0].value)
            try:
                names.extend([alt.value for alt in c.extensions.get_extension_for_oid(x509.oid.ExtensionOID.SUBJECT_ALTERNATIVE_NAME).value])
            except x509.ExtensionNotFound:
                pass
            names = set(names)
            for name in names:
                try:
                    ssl._dnsname_match(name, host)
                    break
                except CertificateError:
                    continue
            else:
                # If we didn't break out, none of the names were valid
                raise CertificateError("Hostname does not match certificate common name or any alternative names.")

        sha = hashlib.sha256()
        sha.update(cert)
        fingerprint = sha.hexdigest()

        # Have we been here before?
        self.db_cur.execute("""SELECT fingerprint, first_seen, last_seen, count
            FROM cert_cache
            WHERE hostname=? AND address=?""", (host, address))
        cached_certs = self.db_cur.fetchall()

        # If so, check for a match
        if cached_certs:
            max_count = 0
            most_frequent_cert = None
            for cached_fingerprint, first, last, count in cached_certs:
                if count > max_count:
                    max_count = count
                    most_frequent_cert = cached_fingerprint
                if fingerprint == cached_fingerprint:
                    # Matched!
                    self._debug("TOFU: Accepting previously seen ({} times) certificate {}".format(count, fingerprint))
                    self.db_cur.execute("""UPDATE cert_cache
                        SET last_seen=?, count=?
                        WHERE hostname=? AND address=? AND fingerprint=?""",
                        (now, count+1, host, address, fingerprint))
                    self.db_conn.commit()
                    break
            else:
                if _HAS_CRYPTOGRAPHY:
                    # Load the most frequently seen certificate to see if it has
                    # expired
                    certdir = os.path.join(self.config_dir, "cert_cache")
                    with open(os.path.join(certdir, most_frequent_cert+".crt"), "rb") as fp:
                        previous_cert = fp.read()
                    previous_cert = x509.load_der_x509_certificate(previous_cert, _BACKEND)
                    previous_ttl = previous_cert.not_valid_after - now
                    print(previous_ttl)

                self._debug("TOFU: Unrecognised certificate {}!  Raising the alarm...".format(fingerprint))
                print("****************************************")
                print("[SECURITY WARNING] Unrecognised certificate!")
                print("The certificate presented for {} ({}) has never been seen before.".format(host, address))
                print("This MIGHT be a Man-in-the-Middle attack.")
                print("A different certificate has previously been seen {} times.".format(max_count))
                if _HAS_CRYPTOGRAPHY:
                    if previous_ttl < datetime.timedelta():
                        print("That certificate has expired, which reduces suspicion somewhat.")
                    else:
                        print("That certificate is still valid for: {}".format(previous_ttl))
                print("****************************************")
                print("Attempt to verify the new certificate fingerprint out-of-band:")
                print(fingerprint)
                choice = input("Accept this new certificate? Y/N ").strip().lower()
                if choice in ("y", "yes"):
                    self.db_cur.execute("""INSERT INTO cert_cache
                        VALUES (?, ?, ?, ?, ?, ?)""",
                        (host, address, fingerprint, now, now, 1))
                    self.db_conn.commit()
                    with open(os.path.join(certdir, fingerprint+".crt"), "wb") as fp:
                        fp.write(cert)
                else:
                    raise Exception("TOFU Failure!")

        # If not, cache this cert
        else:
            self._debug("TOFU: Blindly trusting first ever certificate for this host!")
            self.db_cur.execute("""INSERT INTO cert_cache
                VALUES (?, ?, ?, ?, ?, ?)""",
                (host, address, fingerprint, now, now, 1))
            self.db_conn.commit()
            certdir = os.path.join(self.config_dir, "cert_cache")
            if not os.path.exists(certdir):
                os.makedirs(certdir)
            with open(os.path.join(certdir, fingerprint+".crt"), "wb") as fp:
                fp.write(cert)

    def _get_handler_cmd(self, mimetype):
        # Now look for a handler for this mimetype
        # Consider exact matches before wildcard matches
        exact_matches = []
        wildcard_matches = []
        for handled_mime, cmd_str in _MIME_HANDLERS.items():
            if "*" in handled_mime:
                wildcard_matches.append((handled_mime, cmd_str))
            else:
                exact_matches.append((handled_mime, cmd_str))
        for handled_mime, cmd_str in exact_matches + wildcard_matches:
            if fnmatch.fnmatch(mimetype, handled_mime):
                break
        else:
            # Use "xdg-open" as a last resort.
            cmd_str = "xdg-open %s"
        self._debug("Using handler: %s" % cmd_str)
        return cmd_str

    def _handle_gemtext(self, body, menu_gi, display=True):
        self.index = []
        preformatted = False
        if self.idx_filename:
            os.unlink(self.idx_filename)
        tmpf = tempfile.NamedTemporaryFile("w", encoding="UTF-8", delete=False)
        self.idx_filename = tmpf.name
        for line in body.splitlines():
            if line.startswith("```"):
                preformatted = not preformatted
            elif preformatted:
                tmpf.write(line + "\n")
            elif line.startswith("=>"):
                try:
                    gi = GeminiItem.from_map_line(line, menu_gi)
                    self.index.append(gi)
                    tmpf.write(self._format_geminiitem(len(self.index), gi) + "\n")
                except:
                    self._debug("Skipping possible link: %s" % line)
            elif line.startswith("* "):
                line = line[1:].lstrip("\t ")
                tmpf.write(textwrap.fill(line, self.options["width"],
                    initial_indent = "• ", subsequent_indent="  ") + "\n")
            elif line.startswith(">"):
                line = line[1:].lstrip("\t ")
                tmpf.write(textwrap.fill(line, self.options["width"],
                    initial_indent = "> ", subsequent_indent="> ") + "\n")
            elif line.startswith("###"):
                line = line[3:].lstrip("\t ")
                tmpf.write("\x1b[4m" + line + "\x1b[0m""\n")
            elif line.startswith("##"):
                line = line[2:].lstrip("\t ")
                tmpf.write("\x1b[1m" + line + "\x1b[0m""\n")
            elif line.startswith("#"):
                line = line[1:].lstrip("\t ")
                tmpf.write("\x1b[1m\x1b[4m" + line + "\x1b[0m""\n")
            else:
                tmpf.write(textwrap.fill(line, self.options["width"]) + "\n")
        tmpf.close()

        self.lookup = self.index
        self.page_index = 0
        self.index_index = -1

        if display:
            cmd_str = self._get_handler_cmd("text/gemini")
            subprocess.call(shlex.split(cmd_str % self.idx_filename))

    def _format_geminiitem(self, index, gi, url=False):
        protocol = "" if gi.scheme == "gemini" else " %s" % gi.scheme
        line = "[%d%s] %s" % (index, protocol, gi.name or gi.url)
        if gi.name and url:
            line += " (%s)" % gi.url
        return line

    def _show_lookup(self, offset=0, end=None, url=False):
        for n, gi in enumerate(self.lookup[offset:end]):
            print(self._format_geminiitem(n+offset+1, gi, url))

    def _update_history(self, gi):
        # Don't duplicate
        if self.history and self.history[self.hist_index] == gi:
            return
        self.history = self.history[0:self.hist_index+1]
        self.history.append(gi)
        self.hist_index = len(self.history) - 1

    def _log_visit(self, gi, address, size):
        if not address:
            return
        self.log["requests"] += 1
        self.log["bytes_recvd"] += size
        self.visited_hosts.add(address)
        if address[0] == socket.AF_INET:
            self.log["ipv4_requests"] += 1
            self.log["ipv4_bytes_recvd"] += size
        elif address[0] == socket.AF_INET6:
            self.log["ipv6_requests"] += 1
            self.log["ipv6_bytes_recvd"] += size

    def _get_active_tmpfile(self):
        if self.mime == "text/gemini":
            return self.idx_filename
        else:
            return self.tmp_filename

    def _debug(self, debug_text):
        if not self.options["debug"]:
            return
        debug_text = "\x1b[0;32m[DEBUG] " + debug_text + "\x1b[0m"
        print(debug_text)

    def _load_client_cert(self):
        """
        Interactively load a TLS client certificate from the filesystem in PEM
        format.
        """
        print("Loading client certificate file, in PEM format (blank line to cancel)")
        certfile = input("Certfile path: ").strip()
        if not certfile:
            print("Aborting.")
            return
        certfile = os.path.expanduser(certfile)
        if not os.path.isfile(certfile):
            print("Certificate file {} does not exist.".format(certfile))
            return
        print("Loading private key file, in PEM format (blank line to cancel)")
        keyfile = input("Keyfile path: ").strip()
        if not keyfile:
            print("Aborting.")
            return
        keyfile = os.path.expanduser(keyfile)
        if not os.path.isfile(keyfile):
            print("Private key file {} does not exist.".format(keyfile))
            return
        self._activate_client_cert(certfile, keyfile)

    def _generate_transient_cert_cert(self):
        """
        Use `openssl` command to generate a new transient client certificate
        with 24 hours of validity.
        """
        certdir = os.path.join(self.config_dir, "transient_certs")
        name = str(uuid.uuid4())
        self._generate_client_cert(certdir, name, transient=True)
        self.active_is_transient = True
        self.transient_certs_created.append(name)

    def _generate_persistent_client_cert(self):
        """
        Interactively use `openssl` command to generate a new persistent client
        certificate with one year of validity.
        """
        certdir = os.path.join(self.config_dir, "client_certs")
        print("What do you want to name this new certificate?")
        print("Answering `mycert` will create `{0}/mycert.crt` and `{0}/mycert.key`".format(certdir))
        name = input("> ")
        if not name.strip():
            print("Aborting.")
            return
        self._generate_client_cert(certdir, name)

    def _generate_client_cert(self, certdir, basename, transient=False):
        """
        Use `openssl` binary to generate a client certificate (which may be
        transient or persistent) and save the certificate and private key to the
        specified directory with the specified basename.
        """
        if not os.path.exists(certdir):
            os.makedirs(certdir)
        certfile = os.path.join(certdir, basename+".crt")
        keyfile = os.path.join(certdir, basename+".key")
        cmd = "openssl req -x509 -newkey rsa:2048 -days {} -nodes -keyout {} -out {}".format(1 if transient else 365, keyfile, certfile)
        if transient:
            cmd += " -subj '/CN={}'".format(basename)
        os.system(cmd)
        self._activate_client_cert(certfile, keyfile)

    def _choose_client_cert(self):
        """
        Interactively select a previously generated client certificate and
        activate it.
        """
        certdir = os.path.join(self.config_dir, "client_certs")
        certs = glob.glob(os.path.join(certdir, "*.crt"))
        if len(certs) == 0:
            print("There are no previously generated certificates.")
            return
        certdir = {}
        for n, cert in enumerate(certs):
            certdir[str(n+1)] = (cert, os.path.splitext(cert)[0] + ".key")
            print("{}. {}".format(n+1, os.path.splitext(os.path.basename(cert))[0]))
        choice = input("> ").strip()
        if choice in certdir:
            certfile, keyfile = certdir[choice]
            self._activate_client_cert(certfile, keyfile)
        else:
            print("What?")

    def _activate_client_cert(self, certfile, keyfile):
        self.client_certs["active"] = (certfile, keyfile)
        self.active_cert_domains = []
        self.prompt = self.cert_prompt
        self._debug("Using ID {} / {}.".format(*self.client_certs["active"]))

    def _deactivate_client_cert(self):
        if self.active_is_transient:
            for filename in self.client_certs["active"]:
                os.remove(filename)
            for domain in self.active_cert_domains:
                self.client_certs.pop(domain)
        self.client_certs["active"] = None
        self.active_cert_domains = []
        self.prompt = self.no_cert_prompt
        self.active_is_transient = False

    # Cmd implementation follows

    def default(self, line):
        if line.strip() == "EOF":
            return self.onecmd("quit")
        elif line.strip() == "..":
            return self.do_up()
        elif line.startswith("/"):
            return self.do_search(line[1:])

        # Expand abbreviated commands
        first_word = line.split()[0].strip()
        if first_word in _ABBREVS:
            full_cmd = _ABBREVS[first_word]
            expanded = line.replace(first_word, full_cmd, 1)
            return self.onecmd(expanded)

        # Try to parse numerical index for lookup table
        try:
            n = int(line.strip())
        except ValueError:
            print("What?")
            return

        try:
            gi = self.lookup[n-1]
        except IndexError:
            print ("Index too high!")
            return

        self.index_index = n
        self._go_to_gi(gi)

    ### Settings
    @restricted
    def do_set(self, line):
        """View or set various options."""
        if not line.strip():
            # Show all current settings
            for option in sorted(self.options.keys()):
                print("%s   %s" % (option, self.options[option]))
        elif len(line.split()) == 1:
            # Show current value of one specific setting
            option = line.strip()
            if option in self.options:
                print("%s   %s" % (option, self.options[option]))
            else:
                print("Unrecognised option %s" % option)
        else:
            # Set value of one specific setting
            option, value = line.split(" ", 1)
            if option not in self.options:
                print("Unrecognised option %s" % option)
                return
            # Validate / convert values
            if option == "gopher_proxy":
                if ":" not in value:
                    value += ":1965"
                else:
                    host, port = value.rsplit(":",1)
                    if not port.isnumeric():
                        print("Invalid proxy port %s" % port)
                        return
            elif option == "tls_mode":
                if value.lower() not in ("ca", "tofu"):
                    print("TLS mode must be `ca` or `tofu`!")
                    return
            elif value.isnumeric():
                value = int(value)
            elif value.lower() == "false":
                value = False
            elif value.lower() == "true":
                value = True
            else:
                try:
                    value = float(value)
                except ValueError:
                    pass
            self.options[option] = value

    @restricted
    def do_cert(self, line):
        """Manage client certificates"""
        print("Managing client certificates")
        if self.client_certs["active"]:
            print("Active certificate: {}".format(self.client_certs["active"][0]))
        print("1. Deactivate client certificate.")
        print("2. Generate new certificate.")
        print("3. Load previously generated certificate.")
        print("4. Load externally created client certificate from file.")
        print("Enter blank line to exit certificate manager.")
        choice = input("> ").strip()
        if choice == "1":
            print("Deactivating client certificate.")
            self._deactivate_client_cert()
        elif choice == "2":
            self._generate_persistent_client_cert()
        elif choice == "3":
            self._choose_client_cert()
        elif choice == "4":
            self._load_client_cert()
        else:
            print("Aborting.")

    @restricted
    def do_handler(self, line):
        """View or set handler commands for different MIME types."""
        if not line.strip():
            # Show all current handlers
            for mime in sorted(_MIME_HANDLERS.keys()):
                print("%s   %s" % (mime, _MIME_HANDLERS[mime]))
        elif len(line.split()) == 1:
            mime = line.strip()
            if mime in _MIME_HANDLERS:
                print("%s   %s" % (mime, _MIME_HANDLERS[mime]))
            else:
                print("No handler set for MIME type %s" % mime)
        else:
            mime, handler = line.split(" ", 1)
            _MIME_HANDLERS[mime] = handler
            if "%s" not in handler:
                print("Are you sure you don't want to pass the filename to the handler?")

    def do_abbrevs(self, *args):
        """Print all AV-98 command abbreviations."""
        header = "Command Abbreviations:"
        self.stdout.write("\n{}\n".format(str(header)))
        if self.ruler:
            self.stdout.write("{}\n".format(str(self.ruler * len(header))))
        for k, v in _ABBREVS.items():
            self.stdout.write("{:<7}  {}\n".format(k, v))
        self.stdout.write("\n")

    ### Stuff for getting around
    def do_go(self, line):
        """Go to a gemini URL or marked item."""
        line = line.strip()
        if not line:
            print("Go where?")
        # First, check for possible marks
        elif line in self.marks:
            gi = self.marks[line]
            self._go_to_gi(gi)
        # or a local file
        elif os.path.exists(os.path.expanduser(line)):
            gi = GeminiItem(None, None, os.path.expanduser(line),
                            "1", line, False)
            self._go_to_gi(gi)
        # If this isn't a mark, treat it as a URL
        else:
            self._go_to_gi(GeminiItem(line))

    @needs_gi
    def do_reload(self, *args):
        """Reload the current URL."""
        self._go_to_gi(self.gi, check_cache=False)

    @needs_gi
    def do_up(self, *args):
        """Go up one directory in the path."""
        self._go_to_gi(self.gi.up())

    def do_back(self, *args):
        """Go back to the previous gemini item."""
        if not self.history or self.hist_index == 0:
            return
        self.hist_index -= 1
        gi = self.history[self.hist_index]
        self._go_to_gi(gi, update_hist=False)

    def do_forward(self, *args):
        """Go forward to the next gemini item."""
        if not self.history or self.hist_index == len(self.history) - 1:
            return
        self.hist_index += 1
        gi = self.history[self.hist_index]
        self._go_to_gi(gi, update_hist=False)

    def do_next(self, *args):
        """Go to next item after current in index."""
        return self.onecmd(str(self.index_index+1))

    def do_previous(self, *args):
        """Go to previous item before current in index."""
        self.lookup = self.index
        return self.onecmd(str(self.index_index-1))

    @needs_gi
    def do_root(self, *args):
        """Go to root selector of the server hosting current item."""
        self._go_to_gi(self.gi.root())

    def do_tour(self, line):
        """Add index items as waypoints on a tour, which is basically a FIFO
queue of gemini items.

Items can be added with `tour 1 2 3 4` or ranges like `tour 1-4`.
All items in current menu can be added with `tour *`.
Current tour can be listed with `tour ls` and scrubbed with `tour clear`."""
        line = line.strip()
        if not line:
            # Fly to next waypoint on tour
            if not self.waypoints:
                print("End of tour.")
            else:
                gi = self.waypoints.pop(0)
                self._go_to_gi(gi)
        elif line == "ls":
            old_lookup = self.lookup
            self.lookup = self.waypoints
            self._show_lookup()
            self.lookup = old_lookup
        elif line == "clear":
            self.waypoints = []
        elif line == "*":
            self.waypoints.extend(self.lookup)
        elif looks_like_url(line):
            self.waypoints.append(GeminiItem(line))
        else:
            for index in line.split():
                try:
                    pair = index.split('-')
                    if len(pair) == 1:
                        # Just a single index
                        n = int(index)
                        gi = self.lookup[n-1]
                        self.waypoints.append(gi)
                    elif len(pair) == 2:
                        # Two endpoints for a range of indices
                        for n in range(int(pair[0]), int(pair[1]) + 1):
                            gi = self.lookup[n-1]
                            self.waypoints.append(gi)
                    else:
                        # Syntax error
                        print("Invalid use of range syntax %s, skipping" % index)
                except ValueError:
                    print("Non-numeric index %s, skipping." % index)
                except IndexError:
                    print("Invalid index %d, skipping." % n)

    @needs_gi
    def do_mark(self, line):
        """Mark the current item with a single letter.  This letter can then
be passed to the 'go' command to return to the current item later.
Think of it like marks in vi: 'mark a'='ma' and 'go a'=''a'."""
        line = line.strip()
        if not line:
            for mark, gi in self.marks.items():
                print("[%s] %s (%s)" % (mark, gi.name, gi.url))
        elif line.isalpha() and len(line) == 1:
            self.marks[line] = self.gi
        else:
            print("Invalid mark, must be one letter")

    def do_version(self, line):
        """Display version information."""
        print("AV-98 " + _VERSION)

    ### Stuff that modifies the lookup table
    def do_ls(self, line):
        """List contents of current index.
Use 'ls -l' to see URLs."""
        self.lookup = self.index
        self._show_lookup(url = "-l" in line)
        self.page_index = 0

    def do_gus(self, line):
        """Submit a search query to the GUS search engine."""
        gus = GeminiItem("gemini://gus.guru/search")
        self._go_to_gi(gus.query(line))

    def do_history(self, *args):
        """Display history."""
        self.lookup = self.history
        self._show_lookup(url=True)
        self.page_index = 0

    def do_search(self, searchterm):
        """Search index (case insensitive)."""
        results = [
            gi for gi in self.lookup if searchterm.lower() in gi.name.lower()]
        if results:
            self.lookup = results
            self._show_lookup()
            self.page_index = 0
        else:
            print("No results found.")

    def emptyline(self):
        """Page through index ten lines at a time."""
        i = self.page_index
        if i > len(self.lookup):
            return
        self._show_lookup(offset=i, end=i+10)
        self.page_index += 10

    ### Stuff that does something to most recently viewed item
    @needs_gi
    def do_cat(self, *args):
        """Run most recently visited item through "cat" command."""
        subprocess.call(shlex.split("cat %s" % self._get_active_tmpfile()))

    @needs_gi
    def do_less(self, *args):
        """Run most recently visited item through "less" command."""
        cmd_str = self._get_handler_cmd(self.mime)
        cmd_str = cmd_str % self._get_active_tmpfile()
        subprocess.call("%s | less -R" % cmd_str, shell=True)

    @needs_gi
    def do_fold(self, *args):
        """Run most recently visited item through "fold" command."""
        cmd_str = self._get_handler_cmd(self.mime)
        cmd_str = cmd_str % self._get_active_tmpfile()
        subprocess.call("%s | fold -w 70 -s" % cmd_str, shell=True)

    @restricted
    @needs_gi
    def do_shell(self, line):
        """'cat' most recently visited item through a shell pipeline."""
        subprocess.call(("cat %s |" % self._get_active_tmpfile()) + line, shell=True)

    @restricted
    @needs_gi
    def do_save(self, line):
        """Save an item to the filesystem.
'save n filename' saves menu item n to the specified filename.
'save filename' saves the last viewed item to the specified filename.
'save n' saves menu item n to an automagic filename."""
        args = line.strip().split()

        # First things first, figure out what our arguments are
        if len(args) == 0:
            # No arguments given at all
            # Save current item, if there is one, to a file whose name is
            # inferred from the gemini path
            if not self.tmp_filename:
                print("You need to visit an item first!")
                return
            else:
                index = None
                filename = None
        elif len(args) == 1:
            # One argument given
            # If it's numeric, treat it as an index, and infer the filename
            try:
                index = int(args[0])
                filename = None
            # If it's not numeric, treat it as a filename and
            # save the current item
            except ValueError:
                index = None
                filename = os.path.expanduser(args[0])
        elif len(args) == 2:
            # Two arguments given
            # Treat first as an index and second as filename
            index, filename = args
            try:
                index = int(index)
            except ValueError:
                print("First argument is not a valid item index!")
                return
            filename = os.path.expanduser(filename)
        else:
            print("You must provide an index, a filename, or both.")
            return

        # Next, fetch the item to save, if it's not the current one.
        if index:
            last_gi = self.gi
            try:
                gi = self.lookup[index-1]
                self._go_to_gi(gi, update_hist = False, handle = False)
            except IndexError:
                print ("Index too high!")
                self.gi = last_gi
                return
        else:
            gi = self.gi

        # Derive filename from current GI's path, if one hasn't been set
        if not filename:
            filename = os.path.basename(gi.path)

        # Check for filename collisions and actually do the save if safe
        if os.path.exists(filename):
            print("File %s already exists!" % filename)
        else:
            # Don't use _get_active_tmpfile() here, because we want to save the
            # "source code" of menus, not the rendered view - this way AV-98
            # can navigate to it later.
            shutil.copyfile(self.tmp_filename, filename)
            print("Saved to %s" % filename)

        # Restore gi if necessary
        if index != None:
            self._go_to_gi(last_gi, handle=False)

    @needs_gi
    def do_url(self, *args):
        """Print URL of most recently visited item."""
        print(self.gi.url)

    ### Bookmarking stuff
    @restricted
    @needs_gi
    def do_add(self, line):
        """Add the current URL to the bookmarks menu.
Optionally, specify the new name for the bookmark."""
        with open(os.path.join(self.config_dir, "bookmarks.gmi"), "a") as fp:
            fp.write(self.gi.to_map_line(line))

    def do_bookmarks(self, line):
        """Show or access the bookmarks menu.
'bookmarks' shows all bookmarks.
'bookmarks n' navigates immediately to item n in the bookmark menu.
Bookmarks are stored using the 'add' command."""
        bm_file = os.path.join(self.config_dir, "bookmarks.gmi")
        if not os.path.exists(bm_file):
            print("You need to 'add' some bookmarks, first!")
            return
        args = line.strip()
        if len(args.split()) > 1 or (args and not args.isnumeric()):
            print("bookmarks command takes a single integer argument!")
            return
        with open(bm_file, "r") as fp:
            body = fp.read()
            gi = GeminiItem("localhost/" + bm_file)
            self._handle_gemtext(body, gi, display = not args)
            if args:
                # Use argument as a numeric index
                self.default(line)

    ### Help
    def do_help(self, arg):
        """ALARM! Recursion detected! ALARM! Prepare to eject!"""
        if arg == "!":
            print("! is an alias for 'shell'")
        elif arg == "?":
            print("? is an alias for 'help'")
        else:
            cmd.Cmd.do_help(self, arg)

    ### Flight recorder
    def do_blackbox(self, *args):
        """Display contents of flight recorder, showing statistics for the
current gemini browsing session."""
        lines = []
        # Compute flight time
        now = time.time()
        delta = now - self.log["start_time"]
        hours, remainder = divmod(delta, 3600)
        minutes, seconds = divmod(remainder, 60)
        # Count hosts
        ipv4_hosts = len([host for host in self.visited_hosts if host[0] == socket.AF_INET])
        ipv6_hosts = len([host for host in self.visited_hosts if host[0] == socket.AF_INET6])
        # Assemble lines
        lines.append(("Patrol duration", "%02d:%02d:%02d" % (hours, minutes, seconds)))
        lines.append(("Requests sent:", self.log["requests"]))
        lines.append(("   IPv4 requests:", self.log["ipv4_requests"]))
        lines.append(("   IPv6 requests:", self.log["ipv6_requests"]))
        lines.append(("Bytes received:", self.log["bytes_recvd"]))
        lines.append(("   IPv4 bytes:", self.log["ipv4_bytes_recvd"]))
        lines.append(("   IPv6 bytes:", self.log["ipv6_bytes_recvd"]))
        lines.append(("Unique hosts visited:", len(self.visited_hosts)))
        lines.append(("   IPv4 hosts:", ipv4_hosts))
        lines.append(("   IPv6 hosts:", ipv6_hosts))
        lines.append(("DNS failures:", self.log["dns_failures"]))
        lines.append(("Timeouts:", self.log["timeouts"]))
        lines.append(("Refused connections:", self.log["refused_connections"]))
        lines.append(("Reset connections:", self.log["reset_connections"]))
        lines.append(("Cache hits:", self.log["cache_hits"]))
        # Print
        for key, value in lines:
            print(key.ljust(24) + str(value).rjust(8))

    ### The end!
    def do_quit(self, *args):
        """Exit AV-98."""
        # Close TOFU DB
        self.db_conn.commit()
        self.db_conn.close()
        # Clean up after ourself
        self._empty_cache()
        if self.tmp_filename and os.path.exists(self.tmp_filename):
            os.unlink(self.tmp_filename)
        if self.idx_filename and os.path.exists(self.idx_filename):
            os.unlink(self.idx_filename)

        for cert in self.transient_certs_created:
            for ext in (".crt", ".key"):
                certfile = os.path.join(self.config_dir, "transient_certs", cert+ext)
                if os.path.exists(certfile):
                    os.remove(certfile)
        print()
        print("Thank you for flying AV-98!")
        sys.exit()

    do_exit = do_quit

# Main function
def main():

    # Parse args
    parser = argparse.ArgumentParser(description='A command line gemini client.')
    parser.add_argument('--bookmarks', action='store_true',
                        help='start with your list of bookmarks')
    parser.add_argument('--tls-cert', metavar='FILE', help='TLS client certificate file')
    parser.add_argument('--tls-key', metavar='FILE', help='TLS client certificate private key file')
    parser.add_argument('--restricted', action="store_true", help='Disallow shell, add, and save commands')
    parser.add_argument('--version', action='store_true',
                        help='display version information and quit')
    parser.add_argument('url', metavar='URL', nargs='*',
                        help='start with this URL')
    args = parser.parse_args()

    # Handle --version
    if args.version:
        print("AV-98 " + _VERSION)
        sys.exit()

    # Instantiate client
    gc = GeminiClient(args.restricted)

    # Process config file
    rcfile = os.path.join(gc.config_dir, "av98rc")
    if os.path.exists(rcfile):
        print("Using config %s" % rcfile)
        with open(rcfile, "r") as fp:
            for line in fp:
                line = line.strip()
                if ((args.bookmarks or args.url) and
                    any((line.startswith(x) for x in ("go", "g", "tour", "t")))
                   ):
                    if args.bookmarks:
                        print("Skipping rc command \"%s\" due to --bookmarks option." % line)
                    else:
                        print("Skipping rc command \"%s\" due to provided URLs." % line)
                    continue
                gc.cmdqueue.append(line)

    # Say hi
    print("Welcome to AV-98!")
    if args.restricted:
        print("Restricted mode engaged!")
    print("Enjoy your patrol through Geminispace...")

    # Act on args
    if args.tls_cert:
        # If tls_key is None, python will attempt to load the key from tls_cert.
        gc._activate_client_cert(args.tls_cert, args.tls_key)
    if args.bookmarks:
        gc.cmdqueue.append("bookmarks")
    elif args.url:
        if len(args.url) == 1:
            gc.cmdqueue.append("go %s" % args.url[0])
        else:
            for url in args.url:
                if not url.startswith("gemini://"):
                    url = "gemini://" + url
                gc.cmdqueue.append("tour %s" % url)
            gc.cmdqueue.append("tour")

    # Endless interpret loop
    while True:
        try:
            gc.cmdloop()
        except KeyboardInterrupt:
            print("")

if __name__ == '__main__':
    main()