app: prevent static file reads from blocking the event loop

Perform reads in a thread so File I/O does not block.

This patch also disables ETags for static files.  Tornado's default behavior of caching file hashes will not work as many of Moonraker's can be updated.  The previous workaround to this was to recalculate the checksum if the modified date changed.  This is inefficient  as its behavior is not much different than using "If-Modified-Since".

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

moonraker/app.py

@@ -9,7 +9,6 @@ import os
 import mimetypes
 import logging
 import json
-import datetime
 from concurrent.futures import ThreadPoolExecutor
 import traceback
 import ssl
@@ -39,6 +38,7 @@ from typing import (
     Union,
     Dict,
     List,
+    AsyncGenerator,
 )
 if TYPE_CHECKING:
     from tornado.httpserver import HTTPServer
@@ -628,6 +628,7 @@ class FileRequestHandler(AuthorizedFileHandler):
         self.modified = self.get_modified_time()
         self.set_headers()
 
+        self.request.headers.pop("If-None-Match", None)
         if self.should_return_304():
             self.set_status(304)
             return
@@ -682,6 +683,7 @@ class FileRequestHandler(AuthorizedFileHandler):
         elif end is not None:
             content_length = end
         elif start is not None:
+            end = size
             content_length = size - start
         else:
             end = size
@@ -689,10 +691,8 @@ class FileRequestHandler(AuthorizedFileHandler):
         self.set_header("Content-Length", content_length)
 
         if include_body:
-            content = self.get_content(self.absolute_path, start, end)
-            if isinstance(content, bytes):
-                content = [content]
-            for chunk in content:
+            content = self.get_content_nonblock(self.absolute_path, start, end)
+            async for chunk in content:
                 try:
                     self.write(chunk)
                     await self.flush()
@@ -707,32 +707,37 @@ class FileRequestHandler(AuthorizedFileHandler):
     def _escape_filename_to_utf8(self, basename: str) -> str:
         return urllib.parse.quote(basename, encoding="utf-8")
 
+    @classmethod
+    async def get_content_nonblock(
+        cls, abspath: str, start: Optional[int] = None,
+        end: Optional[int] = None
+    ) -> AsyncGenerator[bytes, None]:
+        ioloop = IOLoop.current()
+        with open(abspath, "rb") as file:
+            if start is not None:
+                file.seek(start)
+            if end is not None:
+                remaining = end - (start or 0)  # type: Optional[int]
+            else:
+                remaining = None
+            while True:
+                chunk_size = 64 * 1024
+                if remaining is not None and remaining < chunk_size:
+                    chunk_size = remaining
+                with ThreadPoolExecutor(max_workers=1) as tpe:
+                    chunk = await ioloop.run_in_executor(
+                        tpe, file.read, chunk_size)
+                if chunk:
+                    if remaining is not None:
+                        remaining -= len(chunk)
+                    yield chunk
+                else:
+                    if remaining is not None:
+                        assert remaining == 0
+                    return
+
     @classmethod
     def _get_cached_version(cls, abs_path: str) -> Optional[str]:
-        with cls._lock:
-            hashes: Dict[str, Dict[str, Any]] = \
-                cls._static_hashes  # type: ignore
-            try:
-                mtime = datetime.datetime.fromtimestamp(
-                    os.path.getmtime(abs_path), tz=datetime.timezone.utc)
-            except Exception:
-                logging.exception(
-                    f"Unable to get modified time for file: {abs_path}")
-                hashes.pop(abs_path, None)
-                return None
-            if abs_path not in hashes or mtime != hashes[abs_path]['modified']:
-                try:
-                    hashes[abs_path] = {
-                        'modified': mtime,
-                        'hash': cls.get_content_version(abs_path)
-                    }
-                except Exception:
-                    logging.exception(f"Could not open static file {abs_path}")
-                    hashes.pop(abs_path, None)
-                    return None
-            hsh = hashes.get(abs_path, {}).get('hash')
-            if hsh:
-                return hsh
         return None
 
 @tornado.web.stream_request_body