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"""

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    Our WSGI web interface, which can serve the JS UI and any .png tiles via HTTP.

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"""

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from werkzeug import Request, Response, responder

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from werkzeug import exceptions

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import os.path, os

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import pypngtile as pt

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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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### Manipulate request data

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def get_req_path (req) :

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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 it is cached

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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 request

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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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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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    # viewport

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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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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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## 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_req_path(req)

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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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@responder

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def application (env, start_response) :

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    """

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        Main WSGI entry point

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    """

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    req = Request(env, start_response)

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    try :

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        return handle_req(req)

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    except exceptions.HTTPException, e :

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        return e

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