Make multiplexer constants configurable via env vars

README.md

@@ -62,3 +62,14 @@ Message Flags/Types:
 - `0x08`: Ping | The extra data is a `ping` or `pong` response to a ping.
 - `0x16`: Pause the remote reader
 - `0x32`: Resume the remote reader
+
+## Configuration via environment variables
+
+The following environment variables, which, to be effective, must be set before importing this package, are available to override internal defaults:
+
+- `MULTIPLEXER_INCOMING_QUEUE_MAX_BYTES_CHANNEL` - The maximum number of bytes allowed in the incoming queue for each multiplexer channel.
+- `MULTIPLEXER_INCOMING_QUEUE_LOW_WATERMARK` - The low watermark threshold, in bytes, for the incoming queue for each multiplexer channel.
+- `MULTIPLEXER_INCOMING_QUEUE_HIGH_WATERMARK` - The high watermark threshold, in bytes, for the incoming queue for each multiplexer channel.
+- `MULTIPLEXER_OUTGOING_QUEUE_MAX_BYTES_CHANNEL` - The maximum number of bytes allowed in the outgoing queue for the multiplexer channel.
+- `MULTIPLEXER_OUTGOING_QUEUE_LOW_WATERMARK` - The low watermark threshold, in bytes, for the outgoing queue for each multiplexer channel.
+- `MULTIPLEXER_OUTGOING_QUEUE_HIGH_WATERMARK` - The high watermark threshold, in bytes, for the outgoing queue for each multiplexer channel.

snitun/multiplexer/const.py

@@ -1,15 +1,55 @@
 """This file contains the constants used by the multiplexer."""
 
+import os
+
 # When downloading a file, the message size will be
 # ~4199990 bytes which is the protocol maximum. Make
 # sure we have enough space to store 16 messages
 # in the incoming queue before we drop the connection.
-INCOMING_QUEUE_MAX_BYTES_CHANNEL = 1024 * 1024 * 65
-INCOMING_QUEUE_LOW_WATERMARK = 1024 * 512
-INCOMING_QUEUE_HIGH_WATERMARK = 1024 * 1024 * 2
+DEFAULT_INCOMING_QUEUE_MAX_BYTES_CHANNEL = 1024 * 1024 * 65
+DEFAULT_INCOMING_QUEUE_LOW_WATERMARK = 1024 * 512
+DEFAULT_INCOMING_QUEUE_HIGH_WATERMARK = 1024 * 1024 * 2
+
+DEFAULT_OUTGOING_QUEUE_MAX_BYTES_CHANNEL = 1024 * 1024 * 12
+DEFAULT_OUTGOING_QUEUE_LOW_WATERMARK = 1024 * 512
+DEFAULT_OUTGOING_QUEUE_HIGH_WATERMARK = 1024 * 1024 * 1
+
+INCOMING_QUEUE_MAX_BYTES_CHANNEL = int(
+    os.getenv(
+        "MULTIPLEXER_INCOMING_QUEUE_MAX_BYTES_CHANNEL",
+        DEFAULT_INCOMING_QUEUE_MAX_BYTES_CHANNEL,
+    ),
+)
+INCOMING_QUEUE_LOW_WATERMARK = int(
+    os.getenv(
+        "MULTIPLEXER_INCOMING_QUEUE_LOW_WATERMARK",
+        DEFAULT_INCOMING_QUEUE_LOW_WATERMARK,
+    ),
+)
+INCOMING_QUEUE_HIGH_WATERMARK = int(
+    os.getenv(
+        "MULTIPLEXER_INCOMING_QUEUE_HIGH_WATERMARK",
+        DEFAULT_INCOMING_QUEUE_HIGH_WATERMARK,
+    ),
+)
 
-OUTGOING_QUEUE_MAX_BYTES_CHANNEL = 1024 * 1024 * 12
-OUTGOING_QUEUE_LOW_WATERMARK = 1024 * 512
-OUTGOING_QUEUE_HIGH_WATERMARK = 1024 * 1024 * 1
+OUTGOING_QUEUE_MAX_BYTES_CHANNEL = int(
+    os.getenv(
+        "MULTIPLEXER_OUTGOING_QUEUE_MAX_BYTES_CHANNEL",
+        DEFAULT_OUTGOING_QUEUE_MAX_BYTES_CHANNEL,
+    ),
+)
+OUTGOING_QUEUE_LOW_WATERMARK = int(
+    os.getenv(
+        "MULTIPLEXER_OUTGOING_QUEUE_LOW_WATERMARK",
+        DEFAULT_OUTGOING_QUEUE_LOW_WATERMARK,
+    ),
+)
+OUTGOING_QUEUE_HIGH_WATERMARK = int(
+    os.getenv(
+        "MULTIPLEXER_OUTGOING_QUEUE_HIGH_WATERMARK",
+        DEFAULT_OUTGOING_QUEUE_HIGH_WATERMARK,
+    ),
+)
 
 PEER_TCP_TIMEOUT = 90

tests/multiplexer/test_const.py

@@ -0,0 +1,79 @@
+import importlib
+import os
+
+from snitun.multiplexer import const
+
+
+def test_override_constants_from_env():
+    """Test overriding constants from environment variables."""
+    os.environ.pop("MULTIPLEXER_INCOMING_QUEUE_MAX_BYTES_CHANNEL", None)
+    os.environ.pop("MULTIPLEXER_INCOMING_QUEUE_LOW_WATERMARK", None)
+    os.environ.pop("MULTIPLEXER_INCOMING_QUEUE_HIGH_WATERMARK", None)
+    os.environ.pop("MULTIPLEXER_OUTGOING_QUEUE_MAX_BYTES_CHANNEL", None)
+    os.environ.pop("MULTIPLEXER_OUTGOING_QUEUE_LOW_WATERMARK", None)
+    os.environ.pop("MULTIPLEXER_OUTGOING_QUEUE_HIGH_WATERMARK", None)
+    importlib.reload(const)
+    assert (
+        const.INCOMING_QUEUE_MAX_BYTES_CHANNEL
+        == const.DEFAULT_INCOMING_QUEUE_MAX_BYTES_CHANNEL
+    )
+    assert (
+        const.INCOMING_QUEUE_LOW_WATERMARK == const.DEFAULT_INCOMING_QUEUE_LOW_WATERMARK
+    )
+    assert (
+        const.INCOMING_QUEUE_HIGH_WATERMARK
+        == const.DEFAULT_INCOMING_QUEUE_HIGH_WATERMARK
+    )
+    assert (
+        const.OUTGOING_QUEUE_MAX_BYTES_CHANNEL
+        == const.DEFAULT_OUTGOING_QUEUE_MAX_BYTES_CHANNEL
+    )
+    assert (
+        const.OUTGOING_QUEUE_LOW_WATERMARK == const.DEFAULT_OUTGOING_QUEUE_LOW_WATERMARK
+    )
+    assert (
+        const.OUTGOING_QUEUE_HIGH_WATERMARK
+        == const.DEFAULT_OUTGOING_QUEUE_HIGH_WATERMARK
+    )
+    os.environ["MULTIPLEXER_INCOMING_QUEUE_MAX_BYTES_CHANNEL"] = "1"
+    os.environ["MULTIPLEXER_INCOMING_QUEUE_LOW_WATERMARK"] = "2"
+    os.environ["MULTIPLEXER_INCOMING_QUEUE_HIGH_WATERMARK"] = "3"
+    os.environ["MULTIPLEXER_OUTGOING_QUEUE_MAX_BYTES_CHANNEL"] = "4"
+    os.environ["MULTIPLEXER_OUTGOING_QUEUE_LOW_WATERMARK"] = "5"
+    os.environ["MULTIPLEXER_OUTGOING_QUEUE_HIGH_WATERMARK"] = "6"
+    importlib.reload(const)
+    assert const.INCOMING_QUEUE_MAX_BYTES_CHANNEL == 1
+    assert const.INCOMING_QUEUE_LOW_WATERMARK == 2
+    assert const.INCOMING_QUEUE_HIGH_WATERMARK == 3
+    assert const.OUTGOING_QUEUE_MAX_BYTES_CHANNEL == 4
+    assert const.OUTGOING_QUEUE_LOW_WATERMARK == 5
+    assert const.OUTGOING_QUEUE_HIGH_WATERMARK == 6
+    del os.environ["MULTIPLEXER_INCOMING_QUEUE_MAX_BYTES_CHANNEL"]
+    del os.environ["MULTIPLEXER_INCOMING_QUEUE_LOW_WATERMARK"]
+    del os.environ["MULTIPLEXER_INCOMING_QUEUE_HIGH_WATERMARK"]
+    del os.environ["MULTIPLEXER_OUTGOING_QUEUE_MAX_BYTES_CHANNEL"]
+    del os.environ["MULTIPLEXER_OUTGOING_QUEUE_LOW_WATERMARK"]
+    del os.environ["MULTIPLEXER_OUTGOING_QUEUE_HIGH_WATERMARK"]
+    importlib.reload(const)
+    assert (
+        const.INCOMING_QUEUE_MAX_BYTES_CHANNEL
+        == const.DEFAULT_INCOMING_QUEUE_MAX_BYTES_CHANNEL
+    )
+    assert (
+        const.INCOMING_QUEUE_LOW_WATERMARK == const.DEFAULT_INCOMING_QUEUE_LOW_WATERMARK
+    )
+    assert (
+        const.INCOMING_QUEUE_HIGH_WATERMARK
+        == const.DEFAULT_INCOMING_QUEUE_HIGH_WATERMARK
+    )
+    assert (
+        const.OUTGOING_QUEUE_MAX_BYTES_CHANNEL
+        == const.DEFAULT_OUTGOING_QUEUE_MAX_BYTES_CHANNEL
+    )
+    assert (
+        const.OUTGOING_QUEUE_LOW_WATERMARK == const.DEFAULT_OUTGOING_QUEUE_LOW_WATERMARK
+    )
+    assert (
+        const.OUTGOING_QUEUE_HIGH_WATERMARK
+        == const.DEFAULT_OUTGOING_QUEUE_HIGH_WATERMARK
+    )