fix(dashboard): serve per-request metadata to trusted-gateway peers

CHANGELOG.md

@@ -9,6 +9,19 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 
 ### Fixed
+- The dashboard's per-request metadata (the `recent_requests` / `request_logs`
+  tail and the `config` block with upstream URLs) is gated to loopback callers
+  via `_request_is_loopback`. When Headroom runs in a bridge-network container
+  (Docker/podman, or Apple Containerization / mocker), a browser on the host
+  reaches the proxy through the container gateway, so `request.client.host` is
+  the gateway IP rather than `127.0.0.1` — the sensitive block was stripped and
+  the "Recent Requests" table rendered empty even though the operator is local.
+  A peer inside an operator-configured trusted-gateway CIDR
+  (`HEADROOM_PROXY_TRUSTED_GATEWAY_CIDRS`, already used to sanitize
+  `X-Forwarded-*`) is now treated as loopback-equivalent, while the loopback
+  `Host`-header gate is retained as the DNS-rebinding defence. Opt-in and empty
+  by default, so there is no behavior change unless the gateway CIDR is
+  allow-listed.
 - Non-finite values (`NaN`, `Infinity`) in `proxy_savings.json` or in upstream
   cost/token metadata no longer crash the proxy or corrupt the savings
   dashboard. `SavingsTracker`'s numeric coercion caught only `TypeError` and

headroom/proxy/server.py

@@ -1934,7 +1934,29 @@ def _request_is_loopback(request: Request) -> bool:
         host_header = request.headers.get("host")
     except AttributeError:
         host_header = None
-    return is_loopback_host(client_host) and is_loopback_host_header(host_header)
+
+    # The Host-header gate is the DNS-rebinding defence and always applies.
+    if not is_loopback_host_header(host_header):
+        return False
+
+    # Genuine loopback peer (native run, or curl inside the container).
+    if is_loopback_host(client_host):
+        return True
+
+    # Containerized dashboards: when Headroom runs in a bridge-network
+    # container, a browser on the host reaches it via the container's
+    # gateway, so ``request.client.host`` is the gateway IP, not 127.0.0.1
+    # — and the per-request logs / upstream URLs get stripped even though
+    # the operator is local. Treat a peer inside an operator-configured
+    # trusted-gateway CIDR as loopback-equivalent. Opt-in and empty by
+    # default (HEADROOM_PROXY_TRUSTED_GATEWAY_CIDRS), so this is a no-op
+    # unless the operator explicitly allow-lists their container gateway.
+    from headroom.proxy.forwarded_headers import (
+        load_trusted_gateway_cidrs,
+        peer_is_trusted_gateway,
+    )
+
+    return peer_is_trusted_gateway(client_host, load_trusted_gateway_cidrs())
 
 
 def _is_known_websocket_callback_failure(context: dict[str, Any]) -> bool:

tests/test_proxy_loopback_gating.py

@@ -150,3 +150,38 @@ def test_stats_per_request_metadata_is_loopback_only() -> None:
     local = _client(loopback=True).get("/stats").json()
     assert "recent_requests" in local
     assert "config" in local
+
+
+def test_stats_metadata_served_to_trusted_gateway_peer(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Containerized dashboards: a browser on the host reaches a bridge-network
+    container via the gateway IP, so the peer isn't 127.0.0.1 and per-request
+    metadata gets stripped. When the operator allow-lists the gateway CIDR via
+    HEADROOM_PROXY_TRUSTED_GATEWAY_CIDRS, the peer is treated as
+    loopback-equivalent and the metadata is served again."""
+    gateway_ip = "172.18.0.1"  # typical docker/mocker bridge gateway
+    app = _make_app()
+
+    def _gateway_client() -> TestClient:
+        # Loopback Host header (the operator browses http://127.0.0.1:8787) but
+        # the peer IP is the container gateway, not loopback.
+        return TestClient(app, base_url="http://127.0.0.1", client=(gateway_ip, 54321))
+
+    # Without the allow-list, the gateway peer is untrusted → metadata stripped.
+    monkeypatch.delenv("HEADROOM_PROXY_TRUSTED_GATEWAY_CIDRS", raising=False)
+    stripped = _gateway_client().get("/stats").json()
+    assert "recent_requests" not in stripped
+    assert "config" not in stripped
+
+    # Allow-list the gateway CIDR → peer trusted → metadata served.
+    monkeypatch.setenv("HEADROOM_PROXY_TRUSTED_GATEWAY_CIDRS", "172.18.0.0/16")
+    served = _gateway_client().get("/stats").json()
+    assert "recent_requests" in served
+    assert "config" in served
+
+    # DNS-rebinding defence still applies even for a trusted gateway peer: a
+    # non-loopback Host header must be rejected.
+    rebind = TestClient(app, base_url="http://attacker.example", client=(gateway_ip, 54321))
+    payload = rebind.get("/stats").json()
+    assert "recent_requests" not in payload