Use context managers for aio connectors

Not sure why we didn't do this initially, but this ensures that we
always close all connectors properly, and also gives much clearer scope
regarding their life-cycles.

tests/conftest.py

@@ -63,8 +63,5 @@ async def aio_session(event_loop):
 
 @pytest.fixture
 async def aio_connector(event_loop):
-    conn = aiohttp.TCPConnector(limit_per_host=16)
-    try:
+    async with aiohttp.TCPConnector(limit_per_host=16) as conn:
         yield conn
-    finally:
-        await conn.close()

vdirsyncer/cli/__init__.py

@@ -127,27 +127,25 @@ def sync(ctx, collections, force_delete):
     from .tasks import sync_collection
 
     async def main(collections):
-        conn = aiohttp.TCPConnector(limit_per_host=16)
-
-        tasks = []
-        for pair_name, collections in collections:
-            async for collection, config in prepare_pair(
-                pair_name=pair_name,
-                collections=collections,
-                config=ctx.config,
-                connector=conn,
-            ):
-                tasks.append(
-                    sync_collection(
-                        collection=collection,
-                        general=config,
-                        force_delete=force_delete,
-                        connector=conn,
+        async with aiohttp.TCPConnector(limit_per_host=16) as conn:
+            tasks = []
+            for pair_name, collections in collections:
+                async for collection, config in prepare_pair(
+                    pair_name=pair_name,
+                    collections=collections,
+                    config=ctx.config,
+                    connector=conn,
+                ):
+                    tasks.append(
+                        sync_collection(
+                            collection=collection,
+                            general=config,
+                            force_delete=force_delete,
+                            connector=conn,
+                        )
                     )
-                )
 
-        await asyncio.gather(*tasks)
-        await conn.close()
+            await asyncio.gather(*tasks)
 
     asyncio.run(main(collections))
 
@@ -166,28 +164,26 @@ def metasync(ctx, collections):
     from .tasks import prepare_pair
 
     async def main(collections):
-        conn = aiohttp.TCPConnector(limit_per_host=16)
-
-        for pair_name, collections in collections:
-            collections = prepare_pair(
-                pair_name=pair_name,
-                collections=collections,
-                config=ctx.config,
-                connector=conn,
-            )
-
-            await asyncio.gather(
-                *[
-                    metasync_collection(
-                        collection=collection,
-                        general=config,
-                        connector=conn,
-                    )
-                    async for collection, config in collections
-                ]
-            )
+        async with aiohttp.TCPConnector(limit_per_host=16) as conn:
+
+            for pair_name, collections in collections:
+                collections = prepare_pair(
+                    pair_name=pair_name,
+                    collections=collections,
+                    config=ctx.config,
+                    connector=conn,
+                )
 
-        await conn.close()
+                await asyncio.gather(
+                    *[
+                        metasync_collection(
+                            collection=collection,
+                            general=config,
+                            connector=conn,
+                        )
+                        async for collection, config in collections
+                    ]
+                )
 
     asyncio.run(main(collections))
 
@@ -213,18 +209,15 @@ def discover(ctx, pairs, list):
     config = ctx.config
 
     async def main():
-        conn = aiohttp.TCPConnector(limit_per_host=16)
-
-        for pair_name in pairs or config.pairs:
-            await discover_collections(
-                status_path=config.general["status_path"],
-                pair=config.get_pair(pair_name),
-                from_cache=False,
-                list_collections=list,
-                connector=conn,
-            )
-
-        await conn.close()
+        async with aiohttp.TCPConnector(limit_per_host=16) as conn:
+            for pair_name in pairs or config.pairs:
+                await discover_collections(
+                    status_path=config.general["status_path"],
+                    pair=config.get_pair(pair_name),
+                    from_cache=False,
+                    list_collections=list,
+                    connector=conn,
+                )
 
     asyncio.run(main())
 
@@ -267,14 +260,13 @@ def repair(ctx, collection, repair_unsafe_uid):
     click.confirm("Do you want to continue?", abort=True)
 
     async def main():
-        conn = aiohttp.TCPConnector(limit_per_host=16)
-        await repair_collection(
-            ctx.config,
-            collection,
-            repair_unsafe_uid=repair_unsafe_uid,
-            connector=conn,
-        )
-        await conn.close()
+        async with aiohttp.TCPConnector(limit_per_host=16) as conn:
+            await repair_collection(
+                ctx.config,
+                collection,
+                repair_unsafe_uid=repair_unsafe_uid,
+                connector=conn,
+            )
 
     asyncio.run(main())