onlyoffice: hardcode oonet gateway as callback host, drop docker detection

The cista service account has no docker CLI access, so detecting the
gateway via docker network inspect silently fell back to docker0/legacy
behavior. With the pinned subnet the gateway is always 172.30.0.1;
ONLYOFFICE_CALLBACK_HOST remains as an env override.

mediapreview/office.py

@@ -50,9 +50,11 @@ logger = logging.getLogger(__name__)
 # Isolated docker network for the OnlyOffice container: internal-only (no
 # outbound internet), the container can only reach the host on this bridge.
 # Docker discards published ports on internal networks, so the container is
-# reached at its fixed IP instead of a published localhost port.
+# reached at its fixed IP instead of a published localhost port. The host is
+# always the first address of the pinned subnet (the bridge gateway).
 OO_NETWORK = "oonet"
 OO_SUBNET = "172.30.0.0/24"
+OO_GATEWAY = "172.30.0.1"
 OO_CONTAINER_IP = "172.30.0.2"
 
 # ---------------------------------------------------------------------------
@@ -77,57 +79,16 @@ def _get_jwt_secret() -> str:
     return os.environ.get("ONLYOFFICE_JWT_SECRET", "")
 
 
-def _docker_network_gateway(network: str) -> str | None:
-    """Return the host-side gateway IP of a docker network, or None."""
-    try:
-        result = subprocess.run(
-            [
-                "docker",
-                "network",
-                "inspect",
-                network,
-                "--format",
-                "{{range .IPAM.Config}}{{.Gateway}}{{end}}",
-            ],
-            capture_output=True,
-            text=True,
-            timeout=2,
-            check=False,
-        )
-        gateway = result.stdout.strip()
-        if result.returncode == 0 and gateway:
-            return gateway
-    except Exception:
-        logger.debug("Failed to inspect docker network %s", network)
-    return None
-
-
 @lru_cache(maxsize=1)
 def _get_callback_host() -> str:
-    """Return the host IP that OnlyOffice (in Docker) can use to reach us."""
+    """Return the host IP that OnlyOffice (in Docker) can use to reach us.
+
+    The host is always the gateway of the pinned oonet subnet; no detection
+    is needed (the cista service account may not have docker CLI access).
+    """
     if host := os.environ.get("ONLYOFFICE_CALLBACK_HOST"):
         return host
-    # Prefer the gateway of the isolated network setup_docker() creates —
-    # this is the network the container is actually attached to.
-    if gateway := _docker_network_gateway(OO_NETWORK):
-        return gateway
-    # Fall back to the default docker bridge IP
-    try:
-        result = subprocess.run(
-            ["/sbin/ip", "-4", "addr", "show", "docker0"],
-            capture_output=True,
-            text=True,
-            timeout=2,
-            check=False,
-        )
-        for line in result.stdout.splitlines():
-            if "inet " in line:
-                parts = line.strip().split()
-                addr_part = parts[1]  # e.g. 172.17.0.1/16
-                return addr_part.split("/")[0]
-    except Exception:
-        logger.debug("Failed to auto-detect docker bridge IP")
-    return "127.0.0.1"
+    return OO_GATEWAY
 
 
 # ---------------------------------------------------------------------------
@@ -267,9 +228,7 @@ def setup_docker(name: str = "onlyoffice-mediapreview") -> str:
     # Docker discards published ports on internal networks, so the container
     # is reached at its fixed IP; no localhost port is exposed.
     logger.info("OnlyOffice is running on http://%s", OO_CONTAINER_IP)
-    logger.info(
-        "Callback host for file downloads: %s", _docker_network_gateway(OO_NETWORK)
-    )
+    logger.info("Callback host for file downloads: %s", OO_GATEWAY)
     return secret