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server_example-URLshortner.py
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server_example-URLshortner.py
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#!/usr/bin/env python3
#
# A *bookmark server* or URI shortener.
import http.server
import requests
from urllib.parse import unquote, parse_qs
memory = {}
form = '''<!DOCTYPE html>
<title>Bookmark Server</title>
<form method="POST">
<label>Long URI:
<input name="longuri">
</label>
<br>
<label>Short name:
<input name="shortname">
</label>
<br>
<button type="submit">Save it!</button>
</form>
<p>URIs I know about:
<pre>
{}
</pre>
'''
def CheckURI(uri, timeout=5):
'''Check whether this URI is reachable, i.e. does it return a 200 OK?
This function returns True if a GET request to uri returns a 200 OK, and
False if that GET request returns any other response, or doesn't return
(i.e. times out).
'''
try:
r = requests.get(uri, timeout=timeout)
# If the GET request returns, was it a 200 OK?
return r.status_code == 200
except requests.RequestException:
# If the GET request raised an exception, it's not OK.
return False
class Shortener(http.server.BaseHTTPRequestHandler):
def do_GET(self):
# A GET request will either be for / (the root path) or for /some-name.
# Strip off the / and we have either empty string or a name.
name = unquote(self.path[1:])
if name:
if name in memory:
# We know that name! Send a redirect to it.
self.send_response(303)
self.send_header('Location', memory[name])
self.end_headers()
else:
# We don't know that name! Send a 404 error.
self.send_response(404)
self.send_header('Content-type', 'text/plain; charset=utf-8')
self.end_headers()
self.wfile.write("I don't know '{}'.".format(name).encode())
else:
# Root path. Send the form.
self.send_response(200)
self.send_header('Content-type', 'text/html')
self.end_headers()
# List the known associations in the form.
known = "\n".join("{} : {}".format(key, memory[key])
for key in sorted(memory.keys()))
self.wfile.write(form.format(known).encode())
def do_POST(self):
# Decode the form data.
length = int(self.headers.get('Content-length', 0))
body = self.rfile.read(length).decode()
params = parse_qs(body)
# Check that the user submitted the form fields.
if "longuri" not in params or "shortname" not in params:
self.send_response(400)
self.send_header('Content-type', 'text/plain; charset=utf-8')
self.end_headers()
self.wfile.write("Missing form fields!".encode())
return
longuri = params["longuri"][0]
shortname = params["shortname"][0]
if CheckURI(longuri):
# This URI is good! Remember it under the specified name.
memory[shortname] = longuri
# Serve a redirect to the form.
self.send_response(303)
self.send_header('Location', '/')
self.end_headers()
else:
# Didn't successfully fetch the long URI.
self.send_response(404)
self.send_header('Content-type', 'text/plain; charset=utf-8')
self.end_headers()
self.wfile.write(
"Couldn't fetch URI '{}'. Sorry!".format(longuri).encode())
if __name__ == '__main__':
server_address = ('', 8000)
httpd = http.server.HTTPServer(server_address, Shortener)
httpd.serve_forever()