Towards a standard access mechanism for URLs.

Lib/urlopen.py

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+# Open an arbitrary URL
+#
+# See the following document for a tentative description of URLs:
+#     Uniform Resource Locators              Tim Berners-Lee
+#     INTERNET DRAFT                                    CERN
+#     IETF URL Working Group                    14 July 1993
+#     draft-ietf-uri-url-01.txt
+#
+# The object returned by urlopen() will differ per protocol.
+# All you know is that is has methods read(), fileno(), close() and info().
+# The read(), fileno() and close() methods work like those of open files.
+# The info() method returns an rfc822.Message object which can be
+# used to query various info about the object, if available.
+# (rfc822.Message objects are queried with the getheader() method.)
+
+import socket
+import regex
+import regsub
+import string
+import rfc822
+import ftplib
+
+
+# External interface -- use urlopen(file) as if it were open(file, 'r')
+def urlopen(url):
+	url = string.strip(url)
+	if url[:1] == '<' and url[-1:] == '>': url = string.strip(url[1:-1])
+	if url[:4] == 'URL:': url = string.strip(url[4:])
+	type, url = splittype(url)
+	if not type: type = 'file'
+	type = regsub.gsub('-', '_', type)
+	try:
+		func = eval('open_' + type)
+	except NameError:
+		raise IOError, ('url error', 'unknown url type', type)
+	try:
+		return func(url)
+	except socket.error, msg:
+		raise IOError, ('socket error', msg)
+
+
+# Each routine of the form open_<type> knows how to open that type of URL
+
+# Use HTTP protocol
+def open_http(url):
+	import httplib
+	host, selector = splithost(url)
+	h = httplib.HTTP(host)
+	h.putrequest('GET', selector)
+	errcode, errmsg, headers = h.getreply()
+	if errcode == 200: return makefile(h.getfile(), headers)
+	else: raise IOError, ('http error', errcode, errmsg, headers)
+
+# Empty rfc822.Message object
+noheaders = rfc822.Message(open('/dev/null', 'r'))
+noheaders.fp.close()			# Recycle file descriptor
+
+# Use Gopher protocol
+def open_gopher(url):
+	import gopherlib
+	host, selector = splithost(url)
+	type, selector = splitgophertype(selector)
+	selector, query = splitquery(selector)
+	if query: fp = gopherlib.send_query(selector, query, host)
+	else: fp = gopherlib.send_selector(selector, host)
+	return makefile(fp, noheaders)
+
+# Use local file or FTP depending on form of URL
+localhost = socket.gethostbyname('localhost')
+thishost = socket.gethostbyname(socket.gethostname())
+def open_file(url):
+	host, file = splithost(url)
+	if not host: return makefile(open(file, 'r'), noheaders)
+	host, port = splitport(host)
+	if not port and socket.gethostbyname(host) in (localhost, thishost):
+		try: fp = open(file, 'r')
+		except IOError: fp = None
+		if fp: return makefile(fp, noheaders)
+	return open_ftp(url)
+
+# Use FTP protocol
+ftpcache = {}
+ftperrors = (ftplib.error_reply,
+	     ftplib.error_temp,
+	     ftplib.error_perm,
+	     ftplib.error_proto)
+def open_ftp(url):
+	host, file = splithost(url)
+	host, port = splitport(host)
+	host = socket.gethostbyname(host)
+	if not port: port = ftplib.FTP_PORT
+	key = (host, port)
+	try:
+		if not ftpcache.has_key(key):
+			ftpcache[key] = ftpwrapper(host, port)
+		return makefile(ftpcache[key].retrfile(file), noheaders)
+	except ftperrors, msg:
+		raise IOError, ('ftp error', msg)
+
+
+# Utility classes
+
+# Class used to add an info() method to a file object
+class makefile:
+	def __init__(self, fp, headers):
+		self.fp = fp
+		self.headers = headers
+		self.read = self.fp.read
+		self.fileno = self.fp.fileno
+		self.close = self.fp.close
+	def info(self):
+		return self.headers
+
+# Class used by open_ftp() for cache of open FTP connections
+class ftpwrapper:
+	def __init__(self, host, port):
+		self.host = host
+		self.port = port
+		self.init()
+	def init(self):
+		self.ftp = ftplib.FTP()
+		self.ftp.connect(self.host, self.port)
+		self.ftp.login()
+	def retrfile(self, file):
+		try:
+			self.ftp.voidcmd('TYPE I')
+		except ftplib.all_errors:
+			self.init()
+			self.ftp.voidcmd('TYPE I')
+		conn = None
+		if file:
+			try:
+				cmd = 'RETR ' + file
+				conn = self.ftp.transfercmd(cmd)
+			except ftplib.error_perm, reason:
+				if reason[:3] != '550':
+					raise IOError, ('ftp error', reason)
+		if not conn:
+			# Try a directory listing
+			if file: cmd = 'NLST ' + file
+			else: cmd = 'NLST'
+			conn = self.ftp.transfercmd(cmd)
+		return fakefile(self.ftp, conn)
+
+# Class used by ftpwrapper to handle response when transfer is complete
+class fakefile:
+	def __init__(self, ftp, conn):
+		self.ftp = ftp
+		self.conn = conn
+		self.fp = self.conn.makefile('r')
+		self.read = self.fp.read
+		self.fileno = self.fp.fileno
+	def __del__(self):
+		self.close()
+	def close(self):
+		self.conn = None
+		self.fp = None
+		self.read = None
+		if self.ftp: self.ftp.voidresp()
+		self.ftp = None
+
+
+# Utilities to split url parts into components:
+# splittype('type:opaquestring') --> 'type', 'opaquestring'
+# splithost('//host[:port]/path') --> 'host[:port]', '/path'
+# splitport('host:port') --> 'host', 'port'
+# splitquery('/path?query') --> '/path', 'query'
+# splittag('/path#tag') --> '/path', 'tag'
+# splitgophertype('/Xselector') --> 'X', 'selector'
+
+typeprog = regex.compile('^\([^/:]+\):\(.*\)$')
+def splittype(url):
+	if typeprog.match(url) >= 0: return typeprog.group(1, 2)
+	return None, url
+
+hostprog = regex.compile('^//\([^/]+\)\(.*\)$')
+def splithost(url):
+	if hostprog.match(url) >= 0: return hostprog.group(1, 2)
+	return None, url
+
+portprog = regex.compile('^\(.*\):\([0-9]+\)$')
+def splitport(host):
+	if portprog.match(host) >= 0: return portprog.group(1, 2)
+	return host, None
+
+queryprog = regex.compile('^\(.*\)\?\([^?]*\)$')
+def splitquery(url):
+	if queryprog.match(url) >= 0: return queryprog.group(1, 2)
+	return url, None
+
+tagprog = regex.compile('^\(.*\)#\([^#]*\)$')
+def splittag(url):
+	if tagprog.match(url) >= 0: return tagprog.group(1, 2)
+	return url, None
+
+def splitgophertype(selector):
+	if selector[:1] == '/' and selector[1:2]:
+		return selector[1], selector[2:]
+	return None, selector
+
+
+# Test program
+def test():
+	import sys
+	args = sys.argv[1:]
+	if not args:
+		args = [
+			'/etc/passwd',
+			'file:/etc/passwd',
+			'file://localhost/etc/passwd',
+			'ftp://ftp.cwi.nl/etc/passwd',
+			'gopher://gopher.cwi.nl/11/',
+			'http://www.cwi.nl/index.html',
+			]
+	for arg in args:
+		print '-'*10, arg, '-'*10
+		print regsub.gsub('\r', '', urlopen(arg).read())
+	print '-'*40
+
+# Run test program when run as a script
+if __name__ == '__main__':
+	test()