feat: conform to XDG Base Directory Specification on Linux (#988)

This is an extension of #964 with some cleanup.

---------

Co-authored-by: majiayu000 <1835304752@qq.com>

src/exo/shared/constants.py

@@ -1,35 +1,46 @@
 import os
+import sys
 from pathlib import Path
 
-EXO_HOME_RELATIVE_PATH = os.environ.get("EXO_HOME", ".exo")
-EXO_HOME = Path.home() / EXO_HOME_RELATIVE_PATH
+_EXO_HOME_ENV = os.environ.get("EXO_HOME", None)
 
-EXO_MODELS_DIR_ENV = os.environ.get("EXO_MODELS_DIR")
-EXO_MODELS_DIR = Path(EXO_MODELS_DIR_ENV) if EXO_MODELS_DIR_ENV else EXO_HOME / "models"
 
-EXO_GLOBAL_EVENT_DB = EXO_HOME / "global_events.db"
-EXO_WORKER_EVENT_DB = EXO_HOME / "worker_events.db"
-EXO_MASTER_STATE = EXO_HOME / "master_state.json"
-EXO_WORKER_STATE = EXO_HOME / "worker_state.json"
-EXO_MASTER_LOG = EXO_HOME / "master.log"
-EXO_WORKER_LOG = EXO_HOME / "worker.log"
-EXO_LOG = EXO_HOME / "exo.log"
-EXO_TEST_LOG = EXO_HOME / "exo_test.log"
+def _get_xdg_dir(env_var: str, fallback: str) -> Path:
+    """Get XDG directory, prioritising EXO_HOME environment variable if its set. On non-Linux platforms, default to ~/.exo."""
 
-EXO_NODE_ID_KEYPAIR = EXO_HOME / "node_id.keypair"
+    if _EXO_HOME_ENV is not None:
+        return Path.home() / _EXO_HOME_ENV
 
-EXO_WORKER_KEYRING_FILE = EXO_HOME / "worker_keyring"
-EXO_MASTER_KEYRING_FILE = EXO_HOME / "master_keyring"
+    if sys.platform != "linux":
+        return Path.home() / ".exo"
 
-EXO_IPC_DIR = EXO_HOME / "ipc"
+    xdg_value = os.environ.get(env_var, None)
+    if xdg_value is not None:
+        return Path(xdg_value) / "exo"
+    return Path.home() / fallback / "exo"
+
+
+EXO_CONFIG_HOME = _get_xdg_dir("XDG_CONFIG_HOME", ".config")
+EXO_DATA_HOME = _get_xdg_dir("XDG_DATA_HOME", ".local/share")
+EXO_CACHE_HOME = _get_xdg_dir("XDG_CACHE_HOME", ".cache")
+
+# Models directory (data)
+_EXO_MODELS_DIR_ENV = os.environ.get("EXO_MODELS_DIR", None)
+EXO_MODELS_DIR = (
+    EXO_DATA_HOME / "models"
+    if _EXO_MODELS_DIR_ENV is None
+    else Path.home() / _EXO_MODELS_DIR_ENV
+)
+
+# Log files (data/logs or cache)
+EXO_LOG = EXO_CACHE_HOME / "exo.log"
+EXO_TEST_LOG = EXO_CACHE_HOME / "exo_test.log"
+
+# Identity (config)
+EXO_NODE_ID_KEYPAIR = EXO_CONFIG_HOME / "node_id.keypair"
 
 # libp2p topics for event forwarding
 LIBP2P_LOCAL_EVENTS_TOPIC = "worker_events"
 LIBP2P_GLOBAL_EVENTS_TOPIC = "global_events"
 LIBP2P_ELECTION_MESSAGES_TOPIC = "election_message"
 LIBP2P_COMMANDS_TOPIC = "commands"
-
-# lower bounds define timeouts for flops and memory bandwidth - these are the values for the M1 chip.
-LB_TFLOPS = 2.3
-LB_MEMBW_GBPS = 68
-LB_DISK_GBPS = 1.5

src/exo/shared/tests/test_xdg_paths.py

@@ -0,0 +1,118 @@
+"""Tests for XDG Base Directory Specification compliance."""
+
+import os
+import sys
+from pathlib import Path
+from unittest import mock
+
+
+def test_xdg_paths_on_linux():
+    """Test that XDG paths are used on Linux when XDG env vars are set."""
+    with (
+        mock.patch.dict(
+            os.environ,
+            {
+                "XDG_CONFIG_HOME": "/tmp/test-config",
+                "XDG_DATA_HOME": "/tmp/test-data",
+                "XDG_CACHE_HOME": "/tmp/test-cache",
+            },
+            clear=False,
+        ),
+        mock.patch.object(sys, "platform", "linux"),
+    ):
+        # Re-import to pick up mocked values
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        assert Path("/tmp/test-config/exo") == constants.EXO_CONFIG_HOME
+        assert Path("/tmp/test-data/exo") == constants.EXO_DATA_HOME
+        assert Path("/tmp/test-cache/exo") == constants.EXO_CACHE_HOME
+
+
+def test_xdg_default_paths_on_linux():
+    """Test that XDG default paths are used on Linux when env vars are not set."""
+    # Remove XDG env vars and EXO_HOME
+    env = {
+        k: v
+        for k, v in os.environ.items()
+        if not k.startswith("XDG_") and k != "EXO_HOME"
+    }
+    with (
+        mock.patch.dict(os.environ, env, clear=True),
+        mock.patch.object(sys, "platform", "linux"),
+    ):
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        home = Path.home()
+        assert home / ".config" / "exo" == constants.EXO_CONFIG_HOME
+        assert home / ".local/share" / "exo" == constants.EXO_DATA_HOME
+        assert home / ".cache" / "exo" == constants.EXO_CACHE_HOME
+
+
+def test_legacy_exo_home_takes_precedence():
+    """Test that EXO_HOME environment variable takes precedence for backward compatibility."""
+    with mock.patch.dict(
+        os.environ,
+        {
+            "EXO_HOME": ".custom-exo",
+            "XDG_CONFIG_HOME": "/tmp/test-config",
+        },
+        clear=False,
+    ):
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        home = Path.home()
+        assert home / ".custom-exo" == constants.EXO_CONFIG_HOME
+        assert home / ".custom-exo" == constants.EXO_DATA_HOME
+
+
+def test_macos_uses_traditional_paths():
+    """Test that macOS uses traditional ~/.exo directory."""
+    # Remove EXO_HOME to ensure we test the default behavior
+    env = {k: v for k, v in os.environ.items() if k != "EXO_HOME"}
+    with (
+        mock.patch.dict(os.environ, env, clear=True),
+        mock.patch.object(sys, "platform", "darwin"),
+    ):
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        home = Path.home()
+        assert home / ".exo" == constants.EXO_CONFIG_HOME
+        assert home / ".exo" == constants.EXO_DATA_HOME
+        assert home / ".exo" == constants.EXO_CACHE_HOME
+
+
+def test_node_id_in_config_dir():
+    """Test that node ID keypair is in the config directory."""
+    import exo.shared.constants as constants
+
+    assert constants.EXO_NODE_ID_KEYPAIR.parent == constants.EXO_CONFIG_HOME
+
+
+def test_models_in_data_dir():
+    """Test that models directory is in the data directory."""
+    # Clear EXO_MODELS_DIR to test default behavior
+    env = {k: v for k, v in os.environ.items() if k != "EXO_MODELS_DIR"}
+    with mock.patch.dict(os.environ, env, clear=True):
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        assert constants.EXO_MODELS_DIR.parent == constants.EXO_DATA_HOME

src/exo/worker/download/download_utils.py

@@ -24,7 +24,7 @@ from pydantic import (
     TypeAdapter,
 )
 
-from exo.shared.constants import EXO_HOME, EXO_MODELS_DIR
+from exo.shared.constants import EXO_MODELS_DIR
 from exo.shared.types.memory import Memory
 from exo.shared.types.worker.downloads import DownloadProgressData
 from exo.shared.types.worker.shards import ShardMetadata
@@ -132,25 +132,6 @@ async def resolve_model_path_for_repo(repo_id: str) -> Path:
     return (await ensure_models_dir()) / repo_id.replace("/", "--")
 
 
-async def ensure_exo_home() -> Path:
-    await aios.makedirs(EXO_HOME, exist_ok=True)
-    return EXO_HOME
-
-
-async def has_exo_home_read_access() -> bool:
-    try:
-        return await aios.access(EXO_HOME, os.R_OK)
-    except OSError:
-        return False
-
-
-async def has_exo_home_write_access() -> bool:
-    try:
-        return await aios.access(EXO_HOME, os.W_OK)
-    except OSError:
-        return False
-
-
 async def ensure_models_dir() -> Path:
     await aios.makedirs(EXO_MODELS_DIR, exist_ok=True)
     return EXO_MODELS_DIR