BizHawkClient: Add support for multiple concurrent instances (#2475)

This allows multiple client/connector pairs to run at the same time. It also includes a few other miscellaneous small changes that accumulated as I went. They can be split if desired

- Whatever the `client_socket:send` line (~440) was doing with that missing operator, it's no longer doing. Don't ask me how it was working before. Lua is witchcraft.
- Removed the `settimeout(2)` which causes the infamous emulator freeze (and replaced it with a `settimeout(0)` when the server socket is created). It appears to be unnecessary to set a timeout for discovering a client. Maybe at some point in time it was useful to keep the success rate for connecting high, but it seems to not be a problem if the timeout is 0 instead.
  - Also updated the Emerald setup to remove mention of the freezing.
- Connector script now picks the first port that's not in use in a range of 5 ports.
  - To summarize why I was previously under the impression that multiple running scripts would not detect when a port was in use:
    1. Calling `socket.bind` in the existing script will first create an ipv6 socket.
    2. A second concurrent script trying to bind to the same port would I think fail to create an ipv6 socket but then succeed in creating an ipv4 socket on the same port.
    3. That second socket could never communicate with a client; extra clients would just bounce off the first script.
    4. The third concurrent script will then fail on both and actually give an `address already in use` error.  
  - I'm not _really_ sure what's going on there. But forcing one or the other by calling `socket.tcp4()` or `socket.tcp6()` means that only one script will believe it has the port while any others will give `address already in use` as you'd expect.
  - As a side note, our `socket.lua` is much wonkier than I had previously thought. I understand some parts were added for LADX and when BizHawk 2.9 came out, but as far back as the file's history in this repo, it has provided a strange, modified interface as compared to the file it was originally derived from, to no benefit as far as I can tell.
- The connector script closes `server` once it finds a client and opens a new one if the connection drops. I'm not sure this ultimately has an effect, but it seems more proper.
- If the connector script's main function returns because of some error or refusal to proceed, the script no longer tries to resume the coroutine it was part of, which would flood the log with irrelevant errors.
- Creating `SyncError`s in `guarded_read` and `guarded_write` would raise its own error because the wrong variable was being used in its message.
- A call to `_bizhawk.connect` can take a while as the client tries the possible ports. There's a modification that will wait on either the `connect` or the exit event. And if the exit event fires while still looking for a connector script, this cancels the `connect` so the window can close.
  - Related: It takes 2-3 seconds for a call to `asyncio.open_connection` to come back with any sort of response on my machine, which can be significant now that we're trying multiple ports in sequence. I guess it could fire off 5 tasks at once. Might cause some weirdness if there exist multiple scripts and multiple clients looking for each other at the same time.
  - Also related: The first time a client attempts to connect to a script, they accept each other and start communicating as expected. The second client to try that port seems to believe it connects and will then time out on the first message. And then all subsequent attempts to connect to that port by any client will be refused (as expected) until the script shuts down or restarts. I haven't been able to explain this behavior. It adds more time to a client's search for a script, but doesn't ultimately cause problems.

worlds/_bizhawk/__init__.py

@@ -12,7 +12,8 @@ import json
 import typing
 
 
-BIZHAWK_SOCKET_PORT = 43055
+BIZHAWK_SOCKET_PORT_RANGE_START = 43055
+BIZHAWK_SOCKET_PORT_RANGE_SIZE = 5
 
 
 class ConnectionStatus(enum.IntEnum):
@@ -45,11 +46,13 @@ class BizHawkContext:
     streams: typing.Optional[typing.Tuple[asyncio.StreamReader, asyncio.StreamWriter]]
     connection_status: ConnectionStatus
     _lock: asyncio.Lock
+    _port: typing.Optional[int]
 
     def __init__(self) -> None:
         self.streams = None
         self.connection_status = ConnectionStatus.NOT_CONNECTED
         self._lock = asyncio.Lock()
+        self._port = None
 
     async def _send_message(self, message: str):
         async with self._lock:
@@ -86,15 +89,24 @@ class BizHawkContext:
 
 
 async def connect(ctx: BizHawkContext) -> bool:
-    """Attempts to establish a connection with the connector script. Returns True if successful."""
-    try:
-        ctx.streams = await asyncio.open_connection("localhost", BIZHAWK_SOCKET_PORT)
-        ctx.connection_status = ConnectionStatus.TENTATIVE
-        return True
-    except (TimeoutError, ConnectionRefusedError):
-        ctx.streams = None
-        ctx.connection_status = ConnectionStatus.NOT_CONNECTED
-        return False
+    """Attempts to establish a connection with a connector script. Returns True if successful."""
+    rotation_steps = 0 if ctx._port is None else ctx._port - BIZHAWK_SOCKET_PORT_RANGE_START
+    ports = [*range(BIZHAWK_SOCKET_PORT_RANGE_START, BIZHAWK_SOCKET_PORT_RANGE_START + BIZHAWK_SOCKET_PORT_RANGE_SIZE)]
+    ports = ports[rotation_steps:] + ports[:rotation_steps]
+
+    for port in ports:
+        try:
+            ctx.streams = await asyncio.open_connection("localhost", port)
+            ctx.connection_status = ConnectionStatus.TENTATIVE
+            ctx._port = port
+            return True
+        except (TimeoutError, ConnectionRefusedError):
+            continue
+    
+    # No ports worked
+    ctx.streams = None
+    ctx.connection_status = ConnectionStatus.NOT_CONNECTED
+    return False
 
 
 def disconnect(ctx: BizHawkContext) -> None:
@@ -233,7 +245,7 @@ async def guarded_read(ctx: BizHawkContext, read_list: typing.List[typing.Tuple[
                 return None
         else:
             if item["type"] != "READ_RESPONSE":
-                raise SyncError(f"Expected response of type READ_RESPONSE or GUARD_RESPONSE but got {res['type']}")
+                raise SyncError(f"Expected response of type READ_RESPONSE or GUARD_RESPONSE but got {item['type']}")
 
             ret.append(base64.b64decode(item["value"]))
 
@@ -285,7 +297,7 @@ async def guarded_write(ctx: BizHawkContext, write_list: typing.List[typing.Tupl
                 return False
         else:
             if item["type"] != "WRITE_RESPONSE":
-                raise SyncError(f"Expected response of type WRITE_RESPONSE or GUARD_RESPONSE but got {res['type']}")
+                raise SyncError(f"Expected response of type WRITE_RESPONSE or GUARD_RESPONSE but got {item['type']}")
 
     return True
 

worlds/_bizhawk/context.py

@@ -130,7 +130,18 @@ async def _game_watcher(ctx: BizHawkClientContext):
                     logger.info("Waiting to connect to BizHawk...")
                     showed_connecting_message = True
 
-                if not await connect(ctx.bizhawk_ctx):
+                # Since a call to `connect` can take a while to return, this will cancel connecting
+                # if the user has decided to close the client.
+                connect_task = asyncio.create_task(connect(ctx.bizhawk_ctx), name="BizHawkConnect")
+                exit_task = asyncio.create_task(ctx.exit_event.wait(), name="ExitWait")
+                await asyncio.wait([connect_task, exit_task], return_when=asyncio.FIRST_COMPLETED)
+
+                if exit_task.done():
+                    connect_task.cancel()
+                    return
+
+                if not connect_task.result():
+                    # Failed to connect
                     continue
 
                 showed_no_handler_message = False