#   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

# $Id: byterange.py,v 1.9 2005/02/14 21:55:07 mstenner Exp $

import os

import stat

import urllib

import urllib2

import rfc822

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 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 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 ftplib

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

        # 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 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)