Fix container failing to start with UDS (#169)

As far as I can tell there is an issue with binding a socket and
`chmod`-ing it on macOS. I have repro'd the issue here:

```
>>> server_socket = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
>>>
>>> server_socket.bind(socket_path)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'socket_path' is not defined
>>> server_socket.bind("/tmp/run/test.sock")
>>> import os
>>> os.chmod("/tmp/run/test.sock", 0o722)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 22] Invalid argument: '/tmp/run/test.sock'
```

I think it has something to due with volumes and sockets not playing
nicely together on docker for mac.

Anyway, this crashes the test agent on start-up and it's not the end of
the world if the permissions don't get set. So fail softly in this case.

ddapm_test_agent/agent.py

@@ -1267,7 +1267,10 @@ def main(args: Optional[List[str]] = None) -> None:
             os.unlink(parsed_args.trace_uds_socket)
         apm_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
         apm_sock.bind(parsed_args.trace_uds_socket)
-        os.chmod(parsed_args.trace_uds_socket, 0o722)
+        try:
+            os.chmod(parsed_args.trace_uds_socket, 0o722)
+        except OSError as e:
+            log.warning("could not set permissions on UDS socket %r due to %r", parsed_args.trace_uds_socket, str(e))
         atexit.register(lambda: os.unlink(parsed_args.trace_uds_socket))
 
     if parsed_args.trace_request_delay is not None:

releasenotes/notes/uds-container-8138f8b1438b1a0a.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Workaround an issue where `chmod`ing the UDS socket in containers causes
+    the testagent to crash. Instead, a warning is emitted.

tests/test_container.py

@@ -0,0 +1,101 @@
+import contextlib
+import os
+import platform
+import subprocess
+import time
+from typing import Dict
+from typing import Generator
+from typing import List
+from typing import Tuple
+
+import pytest
+
+
+pytestmark = pytest.mark.skipif(os.getenv("SKIP_CONTAINER") is not None, reason="SKIP_CONTAINER set")
+
+
+class DockerContainer:
+    def __init__(self, cid: str):
+        self.id = cid
+
+    def logs(self):
+        p = subprocess.run(["docker", "logs", self.id], capture_output=True, check=True)
+        return p.stdout.decode(), p.stderr.decode()
+
+
+@contextlib.contextmanager
+def docker_run(
+    image: str,
+    env: Dict[str, str],
+    volumes: List[str],
+    cmd: List[str] = [],
+    ports: List[Tuple[str, str]] = [],
+) -> Generator[DockerContainer, None, None]:
+    _cmd: List[str] = [
+        "docker",
+        "run",
+        "-i",
+        "--rm",
+        "--detach",
+    ]
+    for k, v in env.items():
+        _cmd.extend(["-e", "%s=%s" % (k, v)])
+    for v in volumes:
+        _cmd.extend(["-v", v])
+    for k, v in ports:
+        _cmd.extend(["-p", "%s:%s" % (k, v)])
+    _cmd += [image]
+    _cmd.extend(cmd)
+
+    # Run the docker container
+    p = subprocess.run(_cmd, capture_output=True)
+    assert p.returncode == 0, p.stderr
+    cid = p.stdout.decode().strip()
+    assert cid
+    yield DockerContainer(cid)
+    # Kill the container
+    subprocess.run(["docker", "kill", cid], capture_output=True, check=True)
+
+
+@pytest.fixture(scope="session")
+def build_image():
+    subprocess.run(
+        [
+            "docker",
+            "build",
+            "-t",
+            "ddapm-test-agent:test",
+            "-f",
+            "Dockerfile",
+            ".",
+        ],
+        check=True,
+    )
+    yield
+    subprocess.run(
+        [
+            "docker",
+            "rmi",
+            "-f",
+            "ddapm-test-agent:test",
+        ],
+        check=True,
+    )
+
+
+@pytest.mark.skipif(platform.system() == "Linux", reason="No socket mounting issues on Linux")
+def test_container_uds(build_image, tmp_path_factory):
+    uds_dir = tmp_path_factory.mktemp("uds")
+
+    with docker_run(
+        image="ddapm-test-agent:test",
+        volumes=[f"{str(uds_dir)}:/opt/datadog-agent/run"],
+        env={"DD_APM_RECEIVER_SOCKET": "/opt/datadog-agent/run/apm.socket"},
+    ) as c:
+        for i in range(50):
+            stdout, stderr = c.logs()
+            if "could not set permissions" in stderr:
+                break
+            time.sleep(0.1)
+        else:
+            raise Exception("Test agent did not start in time: %s" % stderr)