WeasyPrint/weasyprint/images.py

# coding: utf8

#  WeasyPrint converts web documents (HTML, CSS, ...) to PDF.
#  Copyright (C) 2011  Simon Sapin
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU Affero General Public License as
#  published by the Free Software Foundation, either version 3 of the
#  License, or (at your option) any later version.
#
#  This program 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 Affero General Public License for more details.
#
#  You should have received a copy of the GNU Affero General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
Handle various image formats.
"""

from __future__ import division, unicode_literals

from io import BytesIO
import contextlib

import cairo

from .utils import urlopen
from .css.computed_values import LENGTHS_TO_PIXELS
from .logger import LOGGER


# Map MIME types to functions that take a byte stream and return
# ``(pattern, width, height)`` a cairo Pattern and its dimension in pixels.
FORMAT_HANDLERS = {}

# TODO: currently CairoSVG only support images with an explicit
# width and height. When it supports images with only an intrinsic ratio
# this API will need to change.


def register_format(mime_type):
    """Register a handler for a give image MIME type."""
    def _decorator(function):
        FORMAT_HANDLERS[mime_type] = function
        return function
    return _decorator


@register_format('image/png')
def png_handler(file_like, _uri):
    """Return a cairo Surface from a PNG byte stream."""
    surface = cairo.ImageSurface.create_from_png(file_like)
    pattern = cairo.SurfacePattern(surface)
    return pattern, surface.get_width(), surface.get_height()


@register_format('image/svg+xml')
def cairosvg_handler(file_like, uri):
    """Return a cairo Surface from a SVG byte stream.

    This handler uses CairoSVG: http://cairosvg.org/
    """
    try:
        import cairosvg as _
    except ImportError as exception:
        return exception
    from cairosvg.surface import SVGSurface
    from cairosvg.parser import Tree, ParseError

    class ScaledSVGSurface(SVGSurface):
        """
        Have the cairo Surface object have intrinsic dimension
        in pixels instead of points.
        """
        @property
        def device_units_per_user_units(self):
            scale = super(ScaledSVGSurface, self).device_units_per_user_units
            return scale * LENGTHS_TO_PIXELS['pt']

    if uri.startswith('data:'):
        # Don’t pass data URIs to CairoSVG.
        # They are useless for relative URIs anyway.
        uri = None
    try:
        # Draw to a cairo surface but do not write to a file
        tree = Tree(file_obj=file_like, url=uri)
        surface = ScaledSVGSurface(tree, output=None, dpi=96)
    except (ParseError, NotImplementedError) as exception:
        return exception
    pattern = cairo.SurfacePattern(surface.cairo)
    return pattern, surface.width, surface.height


def fallback_handler(file_like, uri):
    """
    Parse a byte stream with PIL and return a cairo Surface.

    PIL supports many raster image formats and does not take a `format`
    parameter, it guesses the format from the content.
    """
    try:
        import pystacia as _
    except ImportError as exception:
        return exception
    from pystacia import read_blob
    from pystacia.util import TinyException
    try:
        with contextlib.closing(read_blob(file_like.read())) as image:
            png_bytes = image.get_blob('png')
    except TinyException as exception:
        return exception
    else:
        return png_handler(BytesIO(png_bytes), uri)


def get_image_from_uri(uri, type_=None):
    """Get a :class:`cairo.Surface`` from an image URI."""
    try:
        file_like, mime_type, _charset = urlopen(uri)
    except (IOError, ValueError) as exc:
        LOGGER.warn('Error while fetching an image from %s : %r', uri, exc)
        return None

    if not type_:
        type_ = mime_type  # Use eg. the HTTP header
    #else: the type was forced by eg. a 'type' attribute on <embed>
    handler = FORMAT_HANDLERS.get(type_, fallback_handler)
    exception = None
    try:
        image = handler(file_like, uri)
    except (IOError, MemoryError) as e:
        exception = e # Network or parsing error
    else:
        if isinstance(image, Exception):
            exception = image
    finally:
        try:
            file_like.close()
        except Exception:
            # Do not hide a more relevant exception.
            pass

    if exception is None:
        return image
    else:
        LOGGER.warn('Error while parsing an image at %s : %r', uri, exception)
        return None