Fix static _handler pickling error.

Moves the subfunction _handler out to a module-level function, and parameterizes it with functools.partial().
Fixes the case when picking a sanic app which has a registered static route handler. This is usually encountered when attempting to use multiprocessing or auto_reload on OSX or Windows.
Fixes #1774

sanic/static.py

@@ -1,3 +1,4 @@
+from functools import partial, wraps
 from mimetypes import guess_type
 from os import path
 from re import sub
@@ -15,6 +16,91 @@
 from sanic.response import HTTPResponse, file, file_stream
 
 
+async def _static_request_handler(
+        file_or_directory,
+        use_modified_since,
+        use_content_range,
+        stream_large_files,
+        request,
+        content_type=None,
+        file_uri=None
+):
+    # Using this to determine if the URL is trying to break out of the path
+    # served.  os.path.realpath seems to be very slow
+    if file_uri and "../" in file_uri:
+        raise InvalidUsage("Invalid URL")
+    # Merge served directory and requested file if provided
+    # Strip all / that in the beginning of the URL to help prevent python
+    # from herping a derp and treating the uri as an absolute path
+    root_path = file_path = file_or_directory
+    if file_uri:
+        file_path = path.join(
+            file_or_directory, sub("^[/]*", "", file_uri)
+        )
+
+    # URL decode the path sent by the browser otherwise we won't be able to
+    # match filenames which got encoded (filenames with spaces etc)
+    file_path = path.abspath(unquote(file_path))
+    if not file_path.startswith(path.abspath(unquote(root_path))):
+        raise FileNotFound(
+            "File not found", path=file_or_directory, relative_url=file_uri
+        )
+    try:
+        headers = {}
+        # Check if the client has been sent this file before
+        # and it has not been modified since
+        stats = None
+        if use_modified_since:
+            stats = await stat_async(file_path)
+            modified_since = strftime(
+                "%a, %d %b %Y %H:%M:%S GMT", gmtime(stats.st_mtime)
+            )
+            if request.headers.get("If-Modified-Since") == modified_since:
+                return HTTPResponse(status=304)
+            headers["Last-Modified"] = modified_since
+        _range = None
+        if use_content_range:
+            _range = None
+            if not stats:
+                stats = await stat_async(file_path)
+            headers["Accept-Ranges"] = "bytes"
+            headers["Content-Length"] = str(stats.st_size)
+            if request.method != "HEAD":
+                try:
+                    _range = ContentRangeHandler(request, stats)
+                except HeaderNotFound:
+                    pass
+                else:
+                    del headers["Content-Length"]
+                    for key, value in _range.headers.items():
+                        headers[key] = value
+        headers["Content-Type"] = (
+            content_type or guess_type(file_path)[0] or "text/plain"
+        )
+        if request.method == "HEAD":
+            return HTTPResponse(headers=headers)
+        else:
+            if stream_large_files:
+                if type(stream_large_files) == int:
+                    threshold = stream_large_files
+                else:
+                    threshold = 1024 * 1024
+
+                if not stats:
+                    stats = await stat_async(file_path)
+                if stats.st_size >= threshold:
+                    return await file_stream(
+                        file_path, headers=headers, _range=_range
+                    )
+            return await file(file_path, headers=headers, _range=_range)
+    except ContentRangeError:
+        raise
+    except Exception:
+        raise FileNotFound(
+            "File not found", path=file_or_directory, relative_url=file_uri
+        )
+
+
 def register(
     app,
     uri,
@@ -56,86 +142,21 @@ def register(
     if not path.isfile(file_or_directory):
         uri += "<file_uri:" + pattern + ">"
 
-    async def _handler(request, file_uri=None):
-        # Using this to determine if the URL is trying to break out of the path
-        # served.  os.path.realpath seems to be very slow
-        if file_uri and "../" in file_uri:
-            raise InvalidUsage("Invalid URL")
-        # Merge served directory and requested file if provided
-        # Strip all / that in the beginning of the URL to help prevent python
-        # from herping a derp and treating the uri as an absolute path
-        root_path = file_path = file_or_directory
-        if file_uri:
-            file_path = path.join(
-                file_or_directory, sub("^[/]*", "", file_uri)
-            )
-
-        # URL decode the path sent by the browser otherwise we won't be able to
-        # match filenames which got encoded (filenames with spaces etc)
-        file_path = path.abspath(unquote(file_path))
-        if not file_path.startswith(path.abspath(unquote(root_path))):
-            raise FileNotFound(
-                "File not found", path=file_or_directory, relative_url=file_uri
-            )
-        try:
-            headers = {}
-            # Check if the client has been sent this file before
-            # and it has not been modified since
-            stats = None
-            if use_modified_since:
-                stats = await stat_async(file_path)
-                modified_since = strftime(
-                    "%a, %d %b %Y %H:%M:%S GMT", gmtime(stats.st_mtime)
-                )
-                if request.headers.get("If-Modified-Since") == modified_since:
-                    return HTTPResponse(status=304)
-                headers["Last-Modified"] = modified_since
-            _range = None
-            if use_content_range:
-                _range = None
-                if not stats:
-                    stats = await stat_async(file_path)
-                headers["Accept-Ranges"] = "bytes"
-                headers["Content-Length"] = str(stats.st_size)
-                if request.method != "HEAD":
-                    try:
-                        _range = ContentRangeHandler(request, stats)
-                    except HeaderNotFound:
-                        pass
-                    else:
-                        del headers["Content-Length"]
-                        for key, value in _range.headers.items():
-                            headers[key] = value
-            headers["Content-Type"] = (
-                content_type or guess_type(file_path)[0] or "text/plain"
-            )
-            if request.method == "HEAD":
-                return HTTPResponse(headers=headers)
-            else:
-                if stream_large_files:
-                    if type(stream_large_files) == int:
-                        threshold = stream_large_files
-                    else:
-                        threshold = 1024 * 1024
-
-                    if not stats:
-                        stats = await stat_async(file_path)
-                    if stats.st_size >= threshold:
-                        return await file_stream(
-                            file_path, headers=headers, _range=_range
-                        )
-                return await file(file_path, headers=headers, _range=_range)
-        except ContentRangeError:
-            raise
-        except Exception:
-            raise FileNotFound(
-                "File not found", path=file_or_directory, relative_url=file_uri
-            )
-
     # special prefix for static files
     if not name.startswith("_static_"):
         name = f"_static_{name}"
 
+    _handler = wraps(_static_request_handler)(
+        partial(
+            _static_request_handler,
+            file_or_directory,
+            use_modified_since,
+            use_content_range,
+            stream_large_files,
+            content_type=content_type
+        )
+    )
+
     app.route(
         uri,
         methods=["GET", "HEAD"],

tests/test_multiprocessing.py

@@ -87,3 +87,14 @@ def test_pickle_app_with_bp(app, protocol):
     request, response = up_p_app.test_client.get("/")
     assert up_p_app.is_request_stream is False
     assert response.text == "Hello"
+
+@pytest.mark.parametrize("protocol", [3, 4])
+def test_pickle_app_with_static(app, protocol):
+    app.route("/")(handler)
+    app.static('/static', "/tmp/static")
+    p_app = pickle.dumps(app, protocol=protocol)
+    del app
+    up_p_app = pickle.loads(p_app)
+    assert up_p_app
+    request, response = up_p_app.test_client.get("/static/missing.txt")
+    assert response.status == 404