WebHost: Better host room (#3496)

* add Range= to log, making responses a lot smaller for massive rooms
* switch xhr to fetch
* post the form using fetch if possible
  * also refresh log faster while waiting for command echo / response
  * do not follow redirect, saving a request
  * do not post empty body
* smooth-scroll the log view
* paste the log into the div when loading the HTML (up to 1MB, rest will be `fetch`ed)
* fix duplicate charset in display_log response

WebHostLib/misc.py

@@ -1,6 +1,6 @@
 import datetime
 import os
-from typing import List, Dict, Union
+from typing import Dict, Iterator, List, Tuple, Union
 
 import jinja2.exceptions
 from flask import request, redirect, url_for, render_template, Response, session, abort, send_from_directory
@@ -97,25 +97,36 @@ def new_room(seed: UUID):
     return redirect(url_for("host_room", room=room.id))
 
 
-def _read_log(path: str):
-    if os.path.exists(path):
-        with open(path, encoding="utf-8-sig") as log:
-            yield from log
-    else:
-        yield f"Logfile {path} does not exist. " \
-              f"Likely a crash during spinup of multiworld instance or it is still spinning up."
+def _read_log(path: str, offset: int = 0) -> Iterator[bytes]:
+    with open(path, "rb") as log:
+        marker = log.read(3)  # skip optional BOM
+        if marker != b'\xEF\xBB\xBF':
+            log.seek(0, os.SEEK_SET)
+        log.seek(offset, os.SEEK_CUR)
+        yield from log
 
 
 @app.route('/log/<suuid:room>')
-def display_log(room: UUID):
+def display_log(room: UUID) -> Union[str, Response, Tuple[str, int]]:
     room = Room.get(id=room)
     if room is None:
         return abort(404)
     if room.owner == session["_id"]:
         file_path = os.path.join("logs", str(room.id) + ".txt")
-        if os.path.exists(file_path):
-            return Response(_read_log(file_path), mimetype="text/plain;charset=UTF-8")
-        return "Log File does not exist."
+        try:
+            range_header = request.headers.get("Range")
+            if range_header:
+                range_type, range_values = range_header.split('=')
+                start, end = map(str.strip, range_values.split('-', 1))
+                if range_type != "bytes" or end != "":
+                    return "Unsupported range", 500
+                # NOTE: we skip Content-Range in the response here, which isn't great but works for our JS
+                return Response(_read_log(file_path, int(start)), mimetype="text/plain", status=206)
+            return Response(_read_log(file_path), mimetype="text/plain")
+        except FileNotFoundError:
+            return Response(f"Logfile {file_path} does not exist. "
+                            f"Likely a crash during spinup of multiworld instance or it is still spinning up.",
+                            mimetype="text/plain")
 
     return "Access Denied", 403
 
@@ -139,7 +150,21 @@ def host_room(room: UUID):
     with db_session:
         room.last_activity = now  # will trigger a spinup, if it's not already running
 
-    return render_template("hostRoom.html", room=room, should_refresh=should_refresh)
+    def get_log(max_size: int = 1024000) -> str:
+        try:
+            raw_size = 0
+            fragments: List[str] = []
+            for block in _read_log(os.path.join("logs", str(room.id) + ".txt")):
+                if raw_size + len(block) > max_size:
+                    fragments.append("…")
+                    break
+                raw_size += len(block)
+                fragments.append(block.decode("utf-8"))
+            return "".join(fragments)
+        except FileNotFoundError:
+            return ""
+
+    return render_template("hostRoom.html", room=room, should_refresh=should_refresh, get_log=get_log)
 
 
 @app.route('/favicon.ico')