Add ComponentResourceHandler to server

MANIFEST.in

@@ -12,6 +12,8 @@ include panel/models/vtk/*.ts
 include panel/_templates/*.css
 include panel/_templates/*.js
 include panel/_templates/*.html
+include panel/tests/assets/*.css
+include panel/tests/assets/*.js
 include panel/tests/test_data/*.png
 include panel/tests/pane/assets/*.mp3
 include panel/tests/pane/assets/*.mp4

panel/command/serve.py

@@ -221,9 +221,8 @@ def customize_kwargs(self, args, server_kwargs):
         # Handle tranquilized functions in the supplied functions
         kwargs['extra_patterns'] = patterns = kwargs.get('extra_patterns', [])
 
-        if args.static_dirs:
-            static_dirs = parse_vars(args.static_dirs)
-            patterns += get_static_routes(static_dirs)
+        static_dirs = parse_vars(args.static_dirs) if args.static_dirs else {}
+        patterns += get_static_routes(static_dirs)
 
         files = []
         for f in args.files:

panel/io/resources.py

@@ -4,6 +4,7 @@
 """
 import copy
 import glob
+import importlib
 import json
 import os
 
@@ -25,7 +26,7 @@
 from jinja2.environment import Environment
 from jinja2.loaders import FileSystemLoader
 
-from ..util import url_path
+from ..util import isurl, url_path
 from .state import state
 
 
@@ -83,6 +84,19 @@ def set_resource_mode(mode):
         RESOURCE_MODE = old_mode
         _settings.resources.set_value(old_resources)
 
+def resolve_custom_path(obj, path):
+    """
+    Attempts to resolve a path relative to some component.
+    """
+    if not path:
+        return
+    elif path.startswith(os.path.sep):
+        return os.path.isfile(path)
+    try:
+        mod = importlib.import_module(obj.__module__)
+        return (Path(mod.__file__).parent / path).is_file()
+    except Exception:
+        return None
 
 def loading_css():
     from ..config import config
@@ -96,7 +110,6 @@ def loading_css():
     }}
     """
 
-
 def bundled_files(model, file_type='javascript'):
     bdir = os.path.join(PANEL_DIR, 'dist', 'bundled', model.__name__.lower())
     name = model.__name__.lower()
@@ -111,7 +124,6 @@ def bundled_files(model, file_type='javascript'):
             files.append(url)
     return files
 
-
 def bundle_resources(roots, resources):
     from ..config import panel_extension as ext
     global RESOURCE_MODE
@@ -177,6 +189,20 @@ def from_bokeh(cls, bkr):
             root_dir=bkr.root_dir, **kwargs
         )
 
+    def extra_resources(self, resources, resource_type):
+        from ..reactive import ReactiveHTML
+        custom_path = "components"
+        if state.rel_path:
+            custom_path = f"{state.rel_path}/{custom_path}"
+        for model in param.concrete_descendents(ReactiveHTML).values():
+            if not (getattr(model, resource_type, None) and model._loaded()):
+                continue
+            for resource in getattr(model, resource_type, []):
+                if not isurl(resource) and not resource.startswith('static/extensions'):
+                    resource = f'{custom_path}/{model.__module__}/{model.__name__}/{resource_type}/{resource}'
+                if resource not in resources:
+                    resources.append(resource)
+
     @property
     def css_raw(self):
         from ..config import config
@@ -203,15 +229,9 @@ def css_raw(self):
     @property
     def js_files(self):
         from ..config import config
-        from ..reactive import ReactiveHTML
 
         files = super(Resources, self).js_files
-
-        for model in param.concrete_descendents(ReactiveHTML).values():
-            if getattr(model, '__javascript__', None) and model._loaded():
-                for jsfile in model.__javascript__:
-                    if jsfile not in files:
-                        files.append(jsfile)
+        self.extra_resources(files, '__javascript__')
 
         js_files = []
         for js_file in files:
@@ -244,27 +264,16 @@ def js_files(self):
     @property
     def js_modules(self):
         from ..config import config
-        from ..reactive import ReactiveHTML
         modules = list(config.js_modules.values())
-        for model in param.concrete_descendents(ReactiveHTML).values():
-            if hasattr(model, '__javascript_modules__') and model._loaded():
-                for jsmodule in model.__javascript_modules__:
-                    if jsmodule not in modules:
-                        modules.append(jsmodule)
+        self.extra_resources(modules, '__javascript_modules__')
         return modules
 
     @property
     def css_files(self):
         from ..config import config
-        from ..reactive import ReactiveHTML
 
         files = super(Resources, self).css_files
-
-        for model in param.concrete_descendents(ReactiveHTML).values():
-            if getattr(model, '__css__', None) and model._loaded():
-                for css_file in model.__css__:
-                    if css_file not in files:
-                        files.append(css_file)
+        self.extra_resources(files, '__css__')
 
         for cssf in config.css_files:
             if os.path.isfile(cssf) or cssf in files:
@@ -277,6 +286,7 @@ def css_files(self):
                 dist_dir = LOCAL_DIST
         else:
             dist_dir = CDN_DIST
+
         for cssf in glob.glob(str(DIST_DIR / 'css' / '*.css')):
             if self.mode == 'inline':
                 break

panel/io/server.py

@@ -4,6 +4,7 @@
 import datetime as dt
 import gc
 import html
+import importlib
 import logging
 import os
 import pathlib
@@ -41,7 +42,7 @@
 
 # Tornado imports
 from tornado.ioloop import IOLoop
-from tornado.web import RequestHandler, StaticFileHandler, authenticated
+from tornado.web import HTTPError, RequestHandler, StaticFileHandler, authenticated
 from tornado.wsgi import WSGIContainer
 
 # Internal imports
@@ -292,6 +293,88 @@ async def get(self, *args, **kwargs):
 
 per_app_patterns[3] = (r'/autoload.js', AutoloadJsHandler)
 
+
+class ComponentResourceHandler(StaticFileHandler):
+    """
+    A handler that serves local resources relative to a Python module.
+    The handler resolves a specific Panel component by module reference
+    and name, then resolves an attribute on that component to check
+    if it contains the requested resource path.
+
+    /<endpoint>/<module>/<class>/<attribute>/<path>
+    """
+
+    _resource_attrs = [
+        '__css__', '__javascript__', '__js_module__',  '_resources',
+        '_css', '_js', 'base_css', 'css'
+    ]
+
+    def initialize(self, path=None, default_filename=None):
+        self.root = path
+        self.default_filename = default_filename
+
+    def parse_url_path(self, path):
+        """
+        Resolves the resource the URL pattern refers to.
+        """
+        parts = path.split('/')
+        if len(parts) < 4:
+            raise HTTPError(400, 'Malformed URL')
+        module, cls, rtype, *subpath = parts
+        try:
+            module = importlib.import_module(module)
+        except ModuleNotFoundError:
+            raise HTTPError(404, 'Module not found')
+        try:
+            component = getattr(module, cls)
+        except AttributeError:
+            raise HTTPError(404, 'Component not found')
+
+        # May only access resources listed in specific attributes
+        if rtype not in self._resource_attrs:
+            raise HTTPError(403, 'Requested resource type not valid.')
+
+        try:
+            resources = getattr(component, rtype)
+        except AttributeError:
+            raise HTTPError(404, 'Resource type not found')
+
+        # Handle template resources
+        if rtype == '_resources':
+            rtype = subpath[0]
+            subpath = subpath[1:]
+            if rtype in resources:
+                resources = resources[rtype]
+            else:
+                raise HTTPError(404, 'Resource type not found')
+
+        if isinstance(resources, dict):
+            resources = list(resources.values())
+
+        if subpath[0] == '':
+            subpath = tuple('/')+subpath[1:]
+        path = '/'.join(subpath)
+
+        # Important: May only access resources explicitly listed on the component
+        # Otherwise this potentially exposes all files to the web
+        if path not in resources and f'./{path}' not in resources:
+            raise HTTPError(403, 'Requested resource was not listed.')
+
+        if not path.startswith('/'):
+            path = pathlib.Path(module.__file__).parent / path
+        return path
+
+    def get_absolute_path(self, root, path):
+        return path
+
+    def validate_absolute_path(self, root, absolute_path):
+        if not os.path.exists(absolute_path):
+            raise HTTPError(404)
+        if not os.path.isfile(absolute_path):
+            raise HTTPError(403, "%s is not a file", self.path)
+        return absolute_path
+
+
 def modify_document(self, doc):
     from bokeh.io.doc import set_curdoc as bk_set_curdoc
     from ..config import config
@@ -505,6 +588,9 @@ def get_static_routes(static_dirs):
         patterns.append(
             (r"%s/(.*)" % slug, StaticFileHandler, {"path": path})
         )
+    patterns.append((
+        '/components/(.*)', ComponentResourceHandler, {}
+    ))
     return patterns