gemini-certificate-validation-demo-1/gemini-demo.py

#!/usr/bin/env python3

import cgi
import mailcap
import os
import socket
import ssl
import tempfile
import textwrap
import urllib.parse
import socks

timeout = 5

tor_validation = True
accepted_certs = {}

caps = mailcap.getcaps()
menu = []
hist = []

def absolutise_url(base, relative):
    # Absolutise relative links
    if "://" not in relative:
        # Python's URL tools somehow only work with known schemes?
        base = base.replace("gemini://","http://")
        relative = urllib.parse.urljoin(base, relative)
        relative = relative.replace("http://", "gemini://")
    return relative

while True:
    # Get input
    cmd = input("> ").strip()
    # Handle things other than requests
    if cmd.lower() == "q":
        print("Bye!")
        break
    # Get URL, from menu, history or direct entry
    if cmd.isnumeric():
        url = menu[int(cmd)-1]
    elif cmd.lower() == "b":
        # Yes, twice
        url = hist.pop()
        url = hist.pop()
    else:
        url = cmd
        if not "://" in url:
            url = "gemini://" + url
    parsed_url = urllib.parse.urlparse(url)
    if parsed_url.scheme != "gemini":
        print("Sorry, Gemini links only.")
        continue
    # Do the Gemini transaction
    try:
        while True:
            context = ssl.SSLContext()
            context.check_hostname = False
            context.verify_mode = ssl.CERT_NONE

            host = parsed_url.hostname
            port = parsed_url.port or 1965

            s = socket.create_connection((host, port), timeout)
            s = context.wrap_socket(s, server_hostname = host)
            cert = s.getpeercert(True)

            if tor_validation \
                    and (host not in accepted_certs \
                        or accepted_certs[host] != cert):

                # Verify TLS certificate from the vantage point
                # of a random Tor exit node.
                print("Validating certificate...")

                # Get certificate via Tor (SOCKS5 @ localhost:9050).
                # DNS lookup is done over Tor.
                tor_socket = socks.socksocket()
                tor_socket.set_proxy(socks.SOCKS5, "127.0.0.1", 9050, rdns=True)
                tor_socket.settimeout(timeout)
                tor_connection_successful = True
                validation_problem_encountered = False
                try:
                    tor_socket.connect((host, port))
                except socks.ProxyConnectionError:
                    validation_problem_encountered = True
                    tor_connection_successful = False
                    print("Tor proxy not available on localhost:9050.")
                    print("Certificate validation can't be performed.")
                    print("Continue browsing with validation disabled? [y/N]")
                    if input(">> ").strip().lower() == "y":
                        tor_validation = False
                    else:
                        raise Exception("Connection cancelled.")
                except socks.GeneralProxyError:
                    validation_problem_encountered = True
                    tor_connection_successful = False
                    print("Tor connection timed out.")
                    print("Certificate validation can't be performed.")
                    print("Continue connection? [y/N]")
                    if input(">> ").strip().lower() != "y":
                        raise Exception("Connection cancelled.")
                if tor_connection_successful:
                    tor_socket = context.wrap_socket(tor_socket, server_hostname = host)
                    cert_via_tor = tor_socket.getpeercert(True)
                    tor_socket.shutdown(socket.SHUT_RDWR)
                    tor_socket.close()
                    # Compare certs.
                    if cert != cert_via_tor:
                        validation_problem_encountered = True
                        print("[SECURITY WARNING] Certificate validation failed!")
                        print("This MIGHT be a Man-in-the-Middle attack.")
                        print("Continue connection? [y/N]")
                        if input(">> ").strip().lower() != "y":
                            raise Exception("Connection cancelled.")

                accepted_certs[host] = cert

                if not validation_problem_encountered:
                    print("OK")
                    print()

            s.sendall((url + '\r\n').encode("UTF-8"))
            # Get header and check for redirects
            fp = s.makefile("rb")
            header = fp.readline()
            header = header.decode("UTF-8").strip()
            status, mime = header.split(maxsplit=1)
            # Handle input requests
            if status.startswith("1"):
                # Prompt
                query = input("INPUT " + mime + "> ")
                url += "?" + urllib.parse.quote(query) # Bit lazy...
            # Follow redirects
            elif status.startswith("3"):
                url = absolutise_url(url, mime)
                parsed_url = urllib.parse.urlparse(url)
            # Otherwise, we're done.
            else:
                break
    except Exception as err:
        print(err)
        continue
    # Fail if transaction was not successful
    if not status.startswith("2"):
        print("Error %s: %s" % (status, mime))
        continue
    # Handle text
    if mime.startswith("text/"):
        # Decode according to declared charset
        mime, mime_opts = cgi.parse_header(mime)
        body = fp.read()
        body = body.decode(mime_opts.get("charset","UTF-8"))
        # Handle a Gemini map
        if mime == "text/gemini":
            menu = []
            preformatted = False
            for line in body.splitlines():
                if line.startswith("```"):
                    preformatted = not preformatted
                elif preformatted:
                    print(line)
                elif line.startswith("=>") and line[2:].strip():
                    bits = line[2:].strip().split(maxsplit=1)
                    link_url = bits[0]
                    link_url = absolutise_url(url, link_url)
                    menu.append(link_url)
                    text = bits[1] if len(bits) == 2 else link_url
                    print("[%d] %s" % (len(menu), text))
                else:
                    print(textwrap.fill(line, 80))
        # Handle any other plain text
        else:
            print(body)
    # Handle non-text
    else:
        tmpfp = tempfile.NamedTemporaryFile("wb", delete=False)
        tmpfp.write(fp.read())
        tmpfp.close()
        cmd_str, _ = mailcap.findmatch(caps, mime, filename=tmpfp.name)
        os.system(cmd_str)
        os.unlink(tmpfp.name)
    # Update history
    hist.append(url)