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import os, os.path

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import pypngtile as pt

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from werkzeug import Response, exceptions

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from pngtile import render

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# path to images

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DATA_ROOT = os.environ.get("PNGTILE_DATA_PATH") or os.path.abspath('data/')

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# only open each image once

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IMAGE_CACHE = {}

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### Parse request data

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def get_path (req_path) :

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    """

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        Returns the name and path requested

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    """

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    # check DATA_ROOT exists..

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    if not os.path.isdir(DATA_ROOT) :

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        raise exceptions.InternalServerError("Missing DATA_ROOT")

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    # path to image

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    image_name = req_path.lstrip('/')

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    # build absolute path

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    image_path = os.path.abspath(os.path.join(DATA_ROOT, image_name))

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    # ensure the path points inside the data root

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    if not image_path.startswith(DATA_ROOT) :

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        raise exceptions.NotFound(image_name)

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    return image_name, image_path

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def get_image (name, path) :

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    """

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        Gets an Image object from the cache, ensuring that the cached is available

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    """

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    # get Image object

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    if path in IMAGE_CACHE :

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        # get from cache

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        image = IMAGE_CACHE[path]

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    else :

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        # open

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        image = pt.Image(path)

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        # check

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        if image.status() not in (pt.CACHE_FRESH, pt.CACHE_STALE) :

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            raise exceptions.InternalServerError("Image cache not available: %s" % name)

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        # load

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        image.open()

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        # cache

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        IMAGE_CACHE[path] = image

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    return image

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### Handle werkzeug.Request objects -> werkzeug.Response

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def handle_dir (req, name, path) :

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    """

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        Handle request for a directory

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    """

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    prefix = os.path.dirname(req.script_root).rstrip('/')

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    return Response(render.dir_html(prefix, name, path), content_type="text/html")

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def handle_img_viewport (req, image, name) :

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    """

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        Handle request for image viewport

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    """

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    prefix = os.path.dirname(req.script_root).rstrip('/')

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    # viewport

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    return Response(render.img_html(prefix, name, image), content_type="text/html")

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def handle_img_region (req, image) :

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    """

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        Handle request for an image region

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    """

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    # specific image

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    width = int(req.args['w'])

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    height = int(req.args['h'])

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    cx = int(req.args['cx'])

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    cy = int(req.args['cy'])

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    zoom = int(req.args.get('zl', "0"))

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    try :

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        # yay full render

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        return Response(render.img_png_region(image, cx, cy, zoom, width, height), content_type="image/png")

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    except ValueError, ex :

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        # too large

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        raise exceptions.Forbidden(str(ex))

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def handle_img_tile (req, image) :

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    """

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        Handle request for image tile

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    """

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    # tile

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    x = int(req.args['x'])

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    y = int(req.args['y'])

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    zoom = int(req.args.get('zl', "0"))

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    # yay render

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    return Response(render.img_png_tile(image, x, y, zoom), content_type="image/png")

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## Dispatch req to handle_img_*

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def handle_img (req, name, path) :

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    """

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        Handle request for an image

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    """

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    # get image object

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    image = get_image(name, path)

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    # what view?

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    if not req.args :

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        return handle_img_viewport(req, image, name)

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    elif 'w' in req.args and 'h' in req.args and 'cx' in req.args and 'cy' in req.args :

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        return handle_img_region(req, image)

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    elif 'x' in req.args and 'y' in req.args :

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        return handle_img_tile(req, image)

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    else :

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        raise exceptions.BadRequest("Unknown args")

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## Dispatch request to handle_*

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def handle_req (req) :

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    """

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        Main request handler

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    """

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    # decode req

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    name, path = get_path(req.path)

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    # determine dir/image

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    if os.path.isdir(path) :

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        # directory

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        return handle_dir(req, name, path)

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    elif not os.path.exists(path) :

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        # no such file

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        raise exceptions.NotFound(name)

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    elif not name or not name.endswith('.png') :

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        # invalid file

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        raise exceptions.BadRequest("Not a PNG file")

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    else :

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        # image

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        return handle_img(req, name, path)

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