Edit File: byterange.py
# This library is free software; you can redistribute it and/or # modify it under the terms of the GNU Lesser General Public # License as published by the Free Software Foundation; either # version 2.1 of the License, or (at your option) any later version. # # This library is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU # Lesser General Public License for more details. # # You should have received a copy of the GNU Lesser General Public # License along with this library; if not, write to the # Free Software Foundation, Inc., # 59 Temple Place, Suite 330, # Boston, MA 02111-1307 USA # This file is part of urlgrabber, a high-level cross-protocol url-grabber # Copyright 2002-2004 Michael D. Stenner, Ryan Tomayko import os import stat import urllib import urllib2 import rfc822 DEBUG = None try: from cStringIO import StringIO except ImportError, msg: from StringIO import StringIO class RangeError(IOError): """Error raised when an unsatisfiable range is requested.""" pass class HTTPRangeHandler(urllib2.BaseHandler): """Handler that enables HTTP Range headers. This was extremely simple. The Range header is a HTTP feature to begin with so all this class does is tell urllib2 that the "206 Partial Content" reponse from the HTTP server is what we expected. Example: import urllib2 import byterange range_handler = range.HTTPRangeHandler() opener = urllib2.build_opener(range_handler) # install it urllib2.install_opener(opener) # create Request and set Range header req = urllib2.Request('http://www.python.org/') req.header['Range'] = 'bytes=30-50' f = urllib2.urlopen(req) """ def http_error_206(self, req, fp, code, msg, hdrs): # 206 Partial Content Response r = urllib.addinfourl(fp, hdrs, req.get_full_url()) r.code = code r.msg = msg return r def http_error_416(self, req, fp, code, msg, hdrs): # HTTP's Range Not Satisfiable error raise RangeError('Requested Range Not Satisfiable') class HTTPSRangeHandler(HTTPRangeHandler): """ Range Header support for HTTPS. """ def https_error_206(self, req, fp, code, msg, hdrs): return self.http_error_206(req, fp, code, msg, hdrs) def https_error_416(self, req, fp, code, msg, hdrs): self.https_error_416(req, fp, code, msg, hdrs) class RangeableFileObject: """File object wrapper to enable raw range handling. This was implemented primarilary for handling range specifications for file:// urls. This object effectively makes a file object look like it consists only of a range of bytes in the stream. Examples: # expose 10 bytes, starting at byte position 20, from # /etc/aliases. >>> fo = RangeableFileObject(file('/etc/passwd', 'r'), (20,30)) # seek seeks within the range (to position 23 in this case) >>> fo.seek(3) # tell tells where your at _within the range_ (position 3 in # this case) >>> fo.tell() # read EOFs if an attempt is made to read past the last # byte in the range. the following will return only 7 bytes. >>> fo.read(30) """ def __init__(self, fo, rangetup): """Create a RangeableFileObject. fo -- a file like object. only the read() method need be supported but supporting an optimized seek() is preferable. rangetup -- a (firstbyte,lastbyte) tuple specifying the range to work over. The file object provided is assumed to be at byte offset 0. """ self.fo = fo (self.firstbyte, self.lastbyte) = range_tuple_normalize(rangetup) self.realpos = 0 self._do_seek(self.firstbyte) def __getattr__(self, name): """This effectively allows us to wrap at the instance level. Any attribute not found in _this_ object will be searched for in self.fo. This includes methods.""" if hasattr(self.fo, name): return getattr(self.fo, name) raise AttributeError, name def tell(self): """Return the position within the range. This is different from fo.seek in that position 0 is the first byte position of the range tuple. For example, if this object was created with a range tuple of (500,899), tell() will return 0 when at byte position 500 of the file. """ return (self.realpos - self.firstbyte) def seek(self,offset,whence=0): """Seek within the byte range. Positioning is identical to that described under tell(). """ assert whence in (0, 1, 2) if whence == 0: # absolute seek realoffset = self.firstbyte + offset elif whence == 1: # relative seek realoffset = self.realpos + offset elif whence == 2: # absolute from end of file # XXX: are we raising the right Error here? raise IOError('seek from end of file not supported.') # do not allow seek past lastbyte in range if self.lastbyte and (realoffset >= self.lastbyte): realoffset = self.lastbyte self._do_seek(realoffset - self.realpos) def read(self, size=-1): """Read within the range. This method will limit the size read based on the range. """ size = self._calc_read_size(size) rslt = self.fo.read(size) self.realpos += len(rslt) return rslt def readline(self, size=-1): """Read lines within the range. This method will limit the size read based on the range. """ size = self._calc_read_size(size) rslt = self.fo.readline(size) self.realpos += len(rslt) return rslt def _calc_read_size(self, size): """Handles calculating the amount of data to read based on the range. """ if self.lastbyte: if size > -1: if ((self.realpos + size) >= self.lastbyte): size = (self.lastbyte - self.realpos) else: size = (self.lastbyte - self.realpos) return size def _do_seek(self,offset): """Seek based on whether wrapped object supports seek(). offset is relative to the current position (self.realpos). """ assert offset >= 0 if not hasattr(self.fo, 'seek'): self._poor_mans_seek(offset) else: self.fo.seek(self.realpos + offset) self.realpos+= offset def _poor_mans_seek(self,offset): """Seek by calling the wrapped file objects read() method. This is used for file like objects that do not have native seek support. The wrapped objects read() method is called to manually seek to the desired position. offset -- read this number of bytes from the wrapped file object. raise RangeError if we encounter EOF before reaching the specified offset. """ pos = 0 bufsize = 1024 while pos < offset: if (pos + bufsize) > offset: bufsize = offset - pos buf = self.fo.read(bufsize) if len(buf) != bufsize: raise RangeError('Requested Range Not Satisfiable') pos+= bufsize class FileRangeHandler(urllib2.FileHandler): """FileHandler subclass that adds Range support. This class handles Range headers exactly like an HTTP server would. """ def open_local_file(self, req): import mimetypes import mimetools host = req.get_host() file = req.get_selector() localfile = urllib.url2pathname(file) stats = os.stat(localfile) size = stats[stat.ST_SIZE] modified = rfc822.formatdate(stats[stat.ST_MTIME]) mtype = mimetypes.guess_type(file)[0] if host: host, port = urllib.splitport(host) if port or socket.gethostbyname(host) not in self.get_names(): raise urllib2.URLError('file not on local host') fo = open(localfile,'rb') brange = req.headers.get('Range',None) brange = range_header_to_tuple(brange) assert brange != () if brange: (fb,lb) = brange if lb == '': lb = size if fb < 0 or fb > size or lb > size: raise RangeError('Requested Range Not Satisfiable') size = (lb - fb) fo = RangeableFileObject(fo, (fb,lb)) headers = mimetools.Message(StringIO( 'Content-Type: %s\nContent-Length: %d\nLast-modified: %s\n' % (mtype or 'text/plain', size, modified))) return urllib.addinfourl(fo, headers, 'file:'+file) # FTP Range Support # Unfortunately, a large amount of base FTP code had to be copied # from urllib and urllib2 in order to insert the FTP REST command. # Code modifications for range support have been commented as # follows: # -- range support modifications start/end here from urllib import splitport, splituser, splitpasswd, splitattr, \ unquote, addclosehook, addinfourl import ftplib import socket import sys import mimetypes import mimetools class FTPRangeHandler(urllib2.FTPHandler): def ftp_open(self, req): host = req.get_host() if not host: raise IOError, ('ftp error', 'no host given') host, port = splitport(host) if port is None: port = ftplib.FTP_PORT else: port = int(port) # username/password handling user, host = splituser(host) if user: user, passwd = splitpasswd(user) else: passwd = None host = unquote(host) user = unquote(user or '') passwd = unquote(passwd or '') try: host = socket.gethostbyname(host) except socket.error, msg: raise urllib2.URLError(msg) path, attrs = splitattr(req.get_selector()) dirs = path.split('/') dirs = map(unquote, dirs) dirs, file = dirs[:-1], dirs[-1] if dirs and not dirs[0]: dirs = dirs[1:] try: fw = self.connect_ftp(user, passwd, host, port, dirs) type = file and 'I' or 'D' for attr in attrs: attr, value = splitattr(attr) if attr.lower() == 'type' and \ value in ('a', 'A', 'i', 'I', 'd', 'D'): type = value.upper() # -- range support modifications start here rest = None range_tup = range_header_to_tuple(req.headers.get('Range',None)) assert range_tup != () if range_tup: (fb,lb) = range_tup if fb > 0: rest = fb # -- range support modifications end here fp, retrlen = fw.retrfile(file, type, rest) # -- range support modifications start here if range_tup: (fb,lb) = range_tup if lb == '': if retrlen is None or retrlen == 0: raise RangeError('Requested Range Not Satisfiable due to unobtainable file length.') lb = retrlen retrlen = lb - fb if retrlen < 0: # beginning of range is larger than file raise RangeError('Requested Range Not Satisfiable') else: retrlen = lb - fb fp = RangeableFileObject(fp, (0,retrlen)) # -- range support modifications end here headers = "" mtype = mimetypes.guess_type(req.get_full_url())[0] if mtype: headers += "Content-Type: %s\n" % mtype if retrlen is not None and retrlen >= 0: headers += "Content-Length: %d\n" % retrlen sf = StringIO(headers) headers = mimetools.Message(sf) return addinfourl(fp, headers, req.get_full_url()) except ftplib.all_errors, msg: raise IOError, ('ftp error', msg), sys.exc_info()[2] def connect_ftp(self, user, passwd, host, port, dirs): fw = ftpwrapper(user, passwd, host, port, dirs) return fw class ftpwrapper(urllib.ftpwrapper): # range support note: # this ftpwrapper code is copied directly from # urllib. The only enhancement is to add the rest # argument and pass it on to ftp.ntransfercmd def retrfile(self, file, type, rest=None): self.endtransfer() if type in ('d', 'D'): cmd = 'TYPE A'; isdir = 1 else: cmd = 'TYPE ' + type; isdir = 0 try: self.ftp.voidcmd(cmd) except ftplib.all_errors: self.init() self.ftp.voidcmd(cmd) conn = None if file and not isdir: # Use nlst to see if the file exists at all try: self.ftp.nlst(file) except ftplib.error_perm, reason: raise IOError, ('ftp error', reason), sys.exc_info()[2] # Restore the transfer mode! self.ftp.voidcmd(cmd) # Try to retrieve as a file try: cmd = 'RETR ' + file conn = self.ftp.ntransfercmd(cmd, rest) except ftplib.error_perm, reason: if str(reason)[:3] == '501': # workaround for REST not supported error fp, retrlen = self.retrfile(file, type) fp = RangeableFileObject(fp, (rest,'')) return (fp, retrlen) elif str(reason)[:3] != '550': raise IOError, ('ftp error', reason), sys.exc_info()[2] if not conn: # Set transfer mode to ASCII! self.ftp.voidcmd('TYPE A') # Try a directory listing if file: cmd = 'LIST ' + file else: cmd = 'LIST' conn = self.ftp.ntransfercmd(cmd) self.busy = 1 # Pass back both a suitably decorated object and a retrieval length return (addclosehook(conn[0].makefile('rb'), self.endtransfer), conn[1]) #################################################################### # Range Tuple Functions # XXX: These range tuple functions might go better in a class. _rangere = None def range_header_to_tuple(range_header): """Get a (firstbyte,lastbyte) tuple from a Range header value. Range headers have the form "bytes=<firstbyte>-<lastbyte>". This function pulls the firstbyte and lastbyte values and returns a (firstbyte,lastbyte) tuple. If lastbyte is not specified in the header value, it is returned as an empty string in the tuple. Return None if range_header is None Return () if range_header does not conform to the range spec pattern. """ global _rangere if range_header is None: return None if _rangere is None: import re _rangere = re.compile(r'^bytes=(\d{1,})-(\d*)') match = _rangere.match(range_header) if match: tup = range_tuple_normalize(match.group(1,2)) if tup and tup[1]: tup = (tup[0],tup[1]+1) return tup return () def range_tuple_to_header(range_tup): """Convert a range tuple to a Range header value. Return a string of the form "bytes=<firstbyte>-<lastbyte>" or None if no range is needed. """ if range_tup is None: return None range_tup = range_tuple_normalize(range_tup) if range_tup: if range_tup[1]: range_tup = (range_tup[0],range_tup[1] - 1) return 'bytes=%s-%s' % range_tup def range_tuple_normalize(range_tup): """Normalize a (first_byte,last_byte) range tuple. Return a tuple whose first element is guaranteed to be an int and whose second element will be '' (meaning: the last byte) or an int. Finally, return None if the normalized tuple == (0,'') as that is equivelant to retrieving the entire file. """ if range_tup is None: return None # handle first byte fb = range_tup[0] if fb in (None,''): fb = 0 else: fb = int(fb) # handle last byte try: lb = range_tup[1] except IndexError: lb = '' else: if lb is None: lb = '' elif lb != '': lb = int(lb) # check if range is over the entire file if (fb,lb) == (0,''): return None # check that the range is valid if lb < fb: raise RangeError('Invalid byte range: %s-%s' % (fb,lb)) return (fb,lb)
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