encode.py

"""multipart/form-data encoding module

This module provides functions that faciliate encoding name/value pairs
as multipart/form-data suitable for a HTTP POST or PUT request.

multipart/form-data is the standard way to upload files over HTTP"""

from past.builtins import cmp
from future import standard_library
standard_library.install_aliases()
from builtins import next
from builtins import str
from builtins import object
import mimetypes
import os
import re
import urllib.request, urllib.parse, urllib.error
from email.header import Header

__all__ = ['gen_boundary', 'encode_and_quote', 'MultipartParam',
           'encode_string', 'encode_file_header', 'get_body_size', 'get_headers',
           'multipart_encode']

try:
    from io import UnsupportedOperation
except ImportError:
    UnsupportedOperation = None

try:
    import uuid


    def gen_boundary():
        """Returns a random string to use as the boundary for a message"""
        return uuid.uuid4().hex
except ImportError:
    import random
    import sha


    def gen_boundary():
        """Returns a random string to use as the boundary for a message"""
        bits = random.getrandbits(160)
        return sha.new(str(bits)).hexdigest()


def encode_and_quote(data):
    """If ``data`` is unicode, return urllib.quote_plus(data.encode("utf-8"))
    otherwise return urllib.quote_plus(data)"""
    if data is None:
        return None

    if isinstance(data, str):
        data = data.encode("utf-8")
    return urllib.parse.quote_plus(data)


def _strify(s):
    """If s is a unicode string, encode it to UTF-8 and return the results,
    otherwise return str(s), or None if s is None"""
    if s is None:
        return None
    if isinstance(s, str):
        return s.encode("utf-8")
    return str(s)


class MultipartParam(object):
    """Represents a single parameter in a multipart/form-data request

    ``name`` is the name of this parameter.

    If ``value`` is set, it must be a string or unicode object to use as the
    data for this parameter.

    If ``filename`` is set, it is what to say that this parameter's filename
    is.  Note that this does not have to be the actual filename any local file.

    If ``filetype`` is set, it is used as the Content-Type for this parameter.
    If unset it defaults to "text/plain; charset=utf8"

    If ``filesize`` is set, it specifies the length of the file ``fileobj``

    If ``fileobj`` is set, it must be a file-like object that supports
    .read().

    Both ``value`` and ``fileobj`` must not be set, doing so will
    raise a ValueError assertion.

    If ``fileobj`` is set, and ``filesize`` is not specified, then
    the file's size will be determined first by stat'ing ``fileobj``'s
    file descriptor, and if that fails, by seeking to the end of the file,
    recording the current position as the size, and then by seeking back to the
    beginning of the file.

    ``cb`` is a callable which will be called from iter_encode with (self,
    current, total), representing the current parameter, current amount
    transferred, and the total size.
    """

    def __init__(self, name, value=None, filename=None, filetype=None,
                 filesize=None, fileobj=None, cb=None):
        self.name = Header(name).encode()
        self.value = _strify(value)
        if filename is None:
            self.filename = None
        else:
            if isinstance(filename, str):
                # Encode with XML entities
                self.filename = filename.encode("ascii", "xmlcharrefreplace")
            else:
                self.filename = str(filename)
            self.filename = self.filename.encode("string_escape"). \
                replace('"', '\\"')
        self.filetype = _strify(filetype)

        self.filesize = filesize
        self.fileobj = fileobj
        self.cb = cb

        if self.value is not None and self.fileobj is not None:
            raise ValueError("Only one of value or fileobj may be specified")

        if fileobj is not None and filesize is None:
            # Try and determine the file size
            try:
                self.filesize = os.fstat(fileobj.fileno()).st_size
            except (OSError, AttributeError, UnsupportedOperation):
                try:
                    fileobj.seek(0, 2)
                    self.filesize = fileobj.tell()
                    fileobj.seek(0)
                except:
                    raise ValueError("Could not determine filesize")

    def __cmp__(self, other):
        attrs = ['name', 'value', 'filename', 'filetype', 'filesize', 'fileobj']
        myattrs = [getattr(self, a) for a in attrs]
        oattrs = [getattr(other, a) for a in attrs]
        return cmp(myattrs, oattrs)

    def reset(self):
        if self.fileobj is not None:
            self.fileobj.seek(0)
        elif self.value is None:
            raise ValueError("Don't know how to reset this parameter")

    @classmethod
    def from_file(cls, paramname, filename):
        """Returns a new MultipartParam object constructed from the local
        file at ``filename``.

        ``filesize`` is determined by os.path.getsize(``filename``)

        ``filetype`` is determined by mimetypes.guess_type(``filename``)[0]

        ``filename`` is set to os.path.basename(``filename``)
        """

        return cls(paramname, filename=os.path.basename(filename),
                   filetype=mimetypes.guess_type(filename)[0],
                   filesize=os.path.getsize(filename),
                   fileobj=open(filename, "rb"))

    @classmethod
    def from_params(cls, params):
        """Returns a list of MultipartParam objects from a sequence of
        name, value pairs, MultipartParam instances,
        or from a mapping of names to values

        The values may be strings or file objects, or MultipartParam objects.
        MultipartParam object names must match the given names in the
        name,value pairs or mapping, if applicable."""
        if hasattr(params, 'items'):
            params = list(params.items())

        retval = []
        for item in params:
            if isinstance(item, cls):
                retval.append(item)
                continue
            name, value = item
            if isinstance(value, cls):
                assert value.name == name
                retval.append(value)
                continue
            if hasattr(value, 'read'):
                # Looks like a file object
                filename = getattr(value, 'name', None)
                if filename is not None:
                    filetype = mimetypes.guess_type(filename)[0]
                else:
                    filetype = None

                retval.append(cls(name=name, filename=filename,
                                  filetype=filetype, fileobj=value))
            else:
                retval.append(cls(name, value))
        return retval

    def encode_hdr(self, boundary):
        """Returns the header of the encoding of this parameter"""
        boundary = encode_and_quote(boundary)

        headers = ["--%s" % boundary]

        if self.filename:
            disposition = 'form-data; name="%s"; filename="%s"' % (self.name,
                                                                   self.filename)
        else:
            disposition = 'form-data; name="%s"' % self.name

        headers.append("Content-Disposition: %s" % disposition)

        if self.filetype:
            filetype = self.filetype
        else:
            filetype = "text/plain; charset=utf-8"

        headers.append("Content-Type: %s" % filetype)

        headers.append("")
        headers.append("")

        return "\r\n".join(headers)

    def encode(self, boundary):
        """Returns the string encoding of this parameter"""
        if self.value is None:
            value = self.fileobj.read()
        else:
            value = self.value

        if re.search("^--%s$" % re.escape(boundary), value, re.M):
            raise ValueError("boundary found in encoded string")

        return "%s%s\r\n" % (self.encode_hdr(boundary), value)

    def iter_encode(self, boundary, blocksize=4096):
        """Yields the encoding of this parameter
        If self.fileobj is set, then blocks of ``blocksize`` bytes are read and
        yielded."""
        total = self.get_size(boundary)
        current = 0
        if self.value is not None:
            block = self.encode(boundary)
            current += len(block)
            yield block
            if self.cb:
                self.cb(self, current, total)
        else:
            block = self.encode_hdr(boundary)
            current += len(block)
            yield block
            if self.cb:
                self.cb(self, current, total)
            last_block = ""
            encoded_boundary = "--%s" % encode_and_quote(boundary)
            boundary_exp = re.compile("^%s$" % re.escape(encoded_boundary),
                                      re.M)
            while True:
                block = self.fileobj.read(blocksize)
                if not block:
                    current += 2
                    yield "\r\n"
                    if self.cb:
                        self.cb(self, current, total)
                    break
                last_block += block
                if boundary_exp.search(last_block):
                    raise ValueError("boundary found in file data")
                last_block = last_block[-len(encoded_boundary) - 2:]
                current += len(block)
                yield block
                if self.cb:
                    self.cb(self, current, total)

    def get_size(self, boundary):
        """Returns the size in bytes that this param will be when encoded
        with the given boundary."""
        if self.filesize is not None:
            valuesize = self.filesize
        else:
            valuesize = len(self.value)

        return len(self.encode_hdr(boundary)) + 2 + valuesize


def encode_string(boundary, name, value):
    """Returns ``name`` and ``value`` encoded as a multipart/form-data
    variable.  ``boundary`` is the boundary string used throughout
    a single request to separate variables."""

    return MultipartParam(name, value).encode(boundary)


def encode_file_header(boundary, paramname, filesize, filename=None,
                       filetype=None):
    """Returns the leading data for a multipart/form-data field that contains
    file data.

    ``boundary`` is the boundary string used throughout a single request to
    separate variables.

    ``paramname`` is the name of the variable in this request.

    ``filesize`` is the size of the file data.

    ``filename`` if specified is the filename to give to this field.  This
    field is only useful to the server for determining the original filename.

    ``filetype`` if specified is the MIME type of this file.

    The actual file data should be sent after this header has been sent.
    """

    return MultipartParam(paramname, filesize=filesize, filename=filename,
                          filetype=filetype).encode_hdr(boundary)


def get_body_size(params, boundary):
    """Returns the number of bytes that the multipart/form-data encoding
    of ``params`` will be."""
    size = sum(p.get_size(boundary) for p in MultipartParam.from_params(params))
    return size + len(boundary) + 6


def get_headers(params, boundary):
    """Returns a dictionary with Content-Type and Content-Length headers
    for the multipart/form-data encoding of ``params``."""
    headers = {}
    boundary = urllib.parse.quote_plus(boundary)
    headers['Content-Type'] = "multipart/form-data; boundary=%s" % boundary
    headers['Content-Length'] = str(get_body_size(params, boundary))
    return headers


class MultipartYielder(object):
    def __init__(self, params, boundary, cb):
        self.params = params
        self.boundary = boundary
        self.cb = cb

        self.i = 0
        self.p = None
        self.param_iter = None
        self.current = 0
        self.total = get_body_size(params, boundary)

    def __iter__(self):
        return self

    def __next__(self):
        """generator function to yield multipart/form-data representation
        of parameters"""
        if self.param_iter is not None:
            try:
                block = next(self.param_iter)
                self.current += len(block)
                if self.cb:
                    self.cb(self.p, self.current, self.total)
                return block
            except StopIteration:
                self.p = None
                self.param_iter = None

        if self.i is None:
            raise StopIteration
        elif self.i >= len(self.params):
            self.param_iter = None
            self.p = None
            self.i = None
            block = "--%s--\r\n" % self.boundary
            self.current += len(block)
            if self.cb:
                self.cb(self.p, self.current, self.total)
            return block

        self.p = self.params[self.i]
        self.param_iter = self.p.iter_encode(self.boundary)
        self.i += 1
        return next(self)

    def reset(self):
        self.i = 0
        self.current = 0
        for param in self.params:
            param.reset()


def multipart_encode(params, boundary=None, cb=None):
    """Encode ``params`` as multipart/form-data.

    ``params`` should be a sequence of (name, value) pairs or MultipartParam
    objects, or a mapping of names to values.
    Values are either strings parameter values, or file-like objects to use as
    the parameter value.  The file-like objects must support .read() and either
    .fileno() or both .seek() and .tell().

    If ``boundary`` is set, then it as used as the MIME boundary.  Otherwise
    a randomly generated boundary will be used.  In either case, if the
    boundary string appears in the parameter values a ValueError will be
    raised.

    If ``cb`` is set, it should be a callback which will get called as blocks
    of data are encoded.  It will be called with (param, current, total),
    indicating the current parameter being encoded, the current amount encoded,
    and the total amount to encode.

    Returns a tuple of `datagen`, `headers`, where `datagen` is a
    generator that will yield blocks of data that make up the encoded
    parameters, and `headers` is a dictionary with the assoicated
    Content-Type and Content-Length headers.

    Examples:

    >>> datagen, headers = multipart_encode( [("key", "value1"), ("key", "value2")] )
    >>> s = "".join(datagen)
    >>> assert "value2" in s and "value1" in s

    >>> p = MultipartParam("key", "value2")
    >>> datagen, headers = multipart_encode( [("key", "value1"), p] )
    >>> s = "".join(datagen)
    >>> assert "value2" in s and "value1" in s

    >>> datagen, headers = multipart_encode( {"key": "value1"} )
    >>> s = "".join(datagen)
    >>> assert "value2" not in s and "value1" in s

    """
    if boundary is None:
        boundary = gen_boundary()
    else:
        boundary = urllib.parse.quote_plus(boundary)

    headers = get_headers(params, boundary)
    params = MultipartParam.from_params(params)

    return MultipartYielder(params, boundary, cb), headers