Dispatcher.py

import cherrypy

# This class is a slightly modified version of the default CherryPy
# Dispatcher.  The default dispatcher requires all paramaters to occur at
# the end of the URI.  This dispatcher permits nested parameters with dynamic
# Controller initialization.
#
# Example: /vdsm-api/storagedomains/<sd-UUID>/images/<img-UUID>/volumes/
# This URI will instantiate a controller for the storage domain with the given
# UUID.  This Controller has an 'images' handler which provides a list of
# images associated with the given storage domain.  Next, an Image Controller is
# loaded for 'imgUUID'.  This controller exposes volumes to provide a list of
# volumes belonging to the given image.
#
# All changes are identified in find_handler().

class vdsm_cpDispatcher(cherrypy.dispatch.Dispatcher):
    """CherryPy Dispatcher which walks a tree of objects to find a handler.
    
    The tree is rooted at cherrypy.request.app.root, and each hierarchical
    component in the path_info argument is matched to a corresponding nested
    attribute of the root object. Matching handlers must have an 'exposed'
    attribute which evaluates to True. The special method name "index"
    matches a URI which ends in a slash ("/"). The special method name
    "default" may match a portion of the path_info (but only when no longer
    substring of the path_info matches some other object).
    
    This is the default, built-in dispatcher for CherryPy.
    """
    
    def __call__(self, path_info):
        """Set handler and config for the current request."""
        request = cherrypy.request
        func, vpath = self.find_handler(path_info)
        
        if func:
            # Decode any leftover %2F in the virtual_path atoms.
            vpath = [x.replace("%2F", "/") for x in vpath]
            request.handler = cherrypy.dispatch.LateParamPageHandler(func, *vpath)
        else:
            request.handler = cherrypy.NotFound()
    
    def find_handler(self, path):
        """Return the appropriate page handler, plus any virtual path.
        
        This will return two objects. The first will be a callable,
        which can be used to generate page output. Any parameters from
        the query string or request body will be sent to that callable
        as keyword arguments.
        
        The callable is found by traversing the application's tree,
        starting from cherrypy.request.app.root, and matching path
        components to successive objects in the tree. For example, the
        URL "/path/to/handler" might return root.path.to.handler.
        
        The second object returned will be a list of names which are
        'virtual path' components: parts of the URL which are dynamic,
        and were not used when looking up the handler.
        These virtual path components are passed to the handler as
        positional arguments.
        """
        request = cherrypy.request
        app = request.app
        root = app.root
        
        # Get config for the root object/path.
        curpath = ""
        nodeconf = {}
        if hasattr(root, "_cp_config"):
            nodeconf.update(root._cp_config)
        if "/" in app.config:
            nodeconf.update(app.config["/"])
        object_trail = [['root', root, nodeconf, curpath]]
        
        node = root
        names = [x for x in path.strip('/').split('/') if x] + ['index']
        for name in names:
            # map to legal Python identifiers (replace '.' with '_')
            objname = name.replace('.', '_')
            
            nodeconf = {}
            
            # CHANGE: Check if the current node has a _dispatch_lookup function
            # If so, try to instantiate the next node from the next path
            # component.  If _dispatch_lookup returns None, the lookup was not
            # successful: continue searching using the regular algorithm.
            new_node = None
            if objname != 'index' and hasattr(node, '_dispatch_lookup'):
                new_node = node._dispatch_lookup(objname)
            if new_node is None:
                new_node = getattr(node, objname, None)
            node = new_node
            if node is not None:
                # Get _cp_config attached to this node.
                if hasattr(node, "_cp_config"):
                    nodeconf.update(node._cp_config)
            
            # Mix in values from app.config for this path.
            curpath = "/".join((curpath, name))
            if curpath in app.config:
                nodeconf.update(app.config[curpath])
            
            object_trail.append([name, node, nodeconf, curpath])
        
        def set_conf():
            """Collapse all object_trail config into cherrypy.request.config."""
            base = cherrypy.config.copy()
            # Note that we merge the config from each node
            # even if that node was None.
            for name, obj, conf, curpath in object_trail:
                base.update(conf)
                if 'tools.staticdir.dir' in conf:
                    base['tools.staticdir.section'] = curpath
            return base
        
        # Try successive objects (reverse order)
        num_candidates = len(object_trail) - 1
        for i in xrange(num_candidates, -1, -1):
            
            name, candidate, nodeconf, curpath = object_trail[i]
            if candidate is None:
                continue
            
            # Try a "default" method on the current leaf.
            
            # CHANGE: The _dispatch_lookup() function overrides the behavior of
            # the 'default' method for this node.  In this case, don't try 'default'
            if hasattr(candidate, "default") and not hasattr(node, '_dispatch_lookup'):
                defhandler = candidate.default
                if getattr(defhandler, 'exposed', False):
                    # Insert any extra _cp_config from the default handler.
                    conf = getattr(defhandler, "_cp_config", {})
                    object_trail.insert(i+1, ["default", defhandler, conf, curpath])
                    request.config = set_conf()
                    # See http://www.cherrypy.org/ticket/613
                    request.is_index = path.endswith("/")
                    return defhandler, names[i:-1]
            
            # Uncomment the next line to restrict positional params to "default".
            # if i < num_candidates - 2: continue
            
            # Try the current leaf.
            if getattr(candidate, 'exposed', False):
                request.config = set_conf()
                if i == num_candidates:
                    # We found the extra ".index". Mark request so tools
                    # can redirect if path_info has no trailing slash.
                    request.is_index = True
                else:
                    # We're not at an 'index' handler. Mark request so tools
                    # can redirect if path_info has NO trailing slash.
                    # Note that this also includes handlers which take
                    # positional parameters (virtual paths).
                    request.is_index = False
                return candidate, names[i:-1]
        
        # We didn't find anything
        request.config = set_conf()
        return None, []