Hermes-agent

2026-06-14 14:30:48 -04:00
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+"""Helpers for X-Forwarded-Prefix support.
+
+Mission-control style deploys reverse-proxy the dashboard at a path
+prefix (e.g. ``mission-control.tilos.com/hermes/*`` -> dashboard on
+:9119), injecting ``X-Forwarded-Prefix: /hermes`` so the backend can
+reconstruct prefixed URLs (Location: headers, OAuth redirect_uri,
+cookie Path attributes, SPA asset URLs).
+
+This module is also the home of the ``HERMES_DASHBOARD_PUBLIC_URL`` /
+``dashboard.public_url`` resolution — when the operator declares a
+complete public URL (scheme + host + optional path prefix), we use
+that directly for the OAuth ``redirect_uri`` and skip the
+X-Forwarded-Prefix reconstruction. Relief valve for deploys where the
+proxy header chain isn't reliable.
+
+The single source of truth for both helpers lives here so the gate
+middleware, the OAuth routes, the cookie helpers, and the SPA mount
+all agree on validation rules.
+"""
+from __future__ import annotations
+
+import logging
+import os
+import urllib.parse
+from typing import Optional
+
+_log = logging.getLogger(__name__)
+
+# Characters that, if present in a public_url or prefix value, indicate
+# either a typo or a header-injection attempt. Reject the whole value
+# rather than try to sanitise — the operator can fix their config.
+_REJECT_CHARS = frozenset(('"', "'", "<", ">", " ", "\n", "\r", "\t"))
+
+# Remember which (source, value) pairs we've already warned about.
+# ``resolve_public_url`` runs on every authenticated request, so an
+# un-deduplicated warning would flood the logs once per request for a
+# misconfigured deploy. Keyed on the raw value too, so changing the
+# config and reloading surfaces a fresh warning.
+_warned_malformed_public_urls: set = set()
+
+
+def _warn_if_malformed(source: str, raw: str) -> None:
+    """Warn (once per distinct value) when a non-empty public-url value
+    was rejected by :func:`_normalise_public_url`.
+
+    A non-empty value that normalises to ``""`` is almost always a
+    missing scheme (``hermes.example.com`` instead of
+    ``https://hermes.example.com``) — the single most common cause of
+    "I set HERMES_DASHBOARD_PUBLIC_URL but the OAuth callback is still
+    http://". Without this warning the value is silently discarded and
+    the dashboard falls back to reconstructing the redirect URI from
+    request headers, which behind a reverse proxy can yield the wrong
+    scheme. Surfacing it turns a silent footgun into a self-diagnosing
+    one.
+    """
+    cleaned = raw.strip() if raw else ""
+    if not cleaned:
+        return  # empty/unset is a legitimate "no override" — not malformed
+    key = (source, cleaned)
+    if key in _warned_malformed_public_urls:
+        return
+    _warned_malformed_public_urls.add(key)
+    _log.warning(
+        "%s is set to %r but was ignored because it is not a valid "
+        "absolute URL — it must include an http:// or https:// scheme "
+        "(e.g. https://%s). Falling back to reconstructing the OAuth "
+        "redirect URI from request headers, which may produce the wrong "
+        "scheme behind a reverse proxy.",
+        source,
+        cleaned,
+        cleaned.split("://")[-1] or "hermes.example.com",
+    )
+
+
+def normalise_prefix(raw: Optional[str]) -> str:
+    """Normalise an X-Forwarded-Prefix header value.
+
+    Returns a string like ``"/hermes"`` (no trailing slash) or ``""``
+    when no prefix is set / the header is malformed. We deliberately
+    reject anything containing ``..`` or non-printable bytes so a
+    hostile proxy can't inject HTML or path-traversal sequences via the
+    prefix.
+    """
+    if not raw:
+        return ""
+    p = raw.strip()
+    if not p:
+        return ""
+    if not p.startswith("/"):
+        p = "/" + p
+    p = p.rstrip("/")
+    if (
+        "//" in p
+        or ".." in p
+        or any(c in p for c in _REJECT_CHARS)
+    ):
+        return ""
+    if len(p) > 64:
+        return ""
+    return p
+
+
+def prefix_from_request(request) -> str:
+    """Convenience wrapper that reads the header off a Starlette/FastAPI
+    Request and normalises it. Returns ``""`` when no prefix.
+    """
+    return normalise_prefix(request.headers.get("x-forwarded-prefix"))
+
+
+# ---------------------------------------------------------------------------
+# HERMES_DASHBOARD_PUBLIC_URL / dashboard.public_url
+# ---------------------------------------------------------------------------
+
+
+def _normalise_public_url(raw: Optional[str]) -> str:
+    """Normalise a ``dashboard.public_url`` value.
+
+    Returns the cleaned URL (scheme://netloc[/path], trailing slash
+    removed) on success, or ``""`` when the value is empty, malformed,
+    or contains characters that suggest header injection. The caller
+    must treat ``""`` as "fall back to request reconstruction" — never
+    as "the user explicitly chose no public URL", because the two are
+    indistinguishable from an empty env var.
+    """
+    if not raw:
+        return ""
+    url = raw.strip()
+    if not url:
+        return ""
+    # Reject control / quote / whitespace characters before trying to
+    # parse — urlparse is permissive enough to accept some hostile
+    # values (e.g. embedded newlines) and we want a hard "no" rather
+    # than a soft "maybe".
+    if any(c in url for c in _REJECT_CHARS):
+        return ""
+    try:
+        parsed = urllib.parse.urlparse(url)
+    except ValueError:
+        return ""
+    if parsed.scheme not in {"http", "https"}:
+        return ""
+    if not parsed.netloc:
+        return ""
+    # Strip a single trailing slash so callers can append paths without
+    # producing ``//`` double-slashes.
+    return url.rstrip("/")
+
+
+def _load_dashboard_section() -> dict:
+    """Return the ``dashboard`` block from ``config.yaml`` if it exists
+    and is a dict; otherwise an empty dict.
+
+    Robust to (a) load_config() raising (malformed YAML, IO error,
+    config.yaml absent), and (b) ``dashboard`` being absent or non-dict.
+    Both shapes fall through to ``{}`` so the caller can rely on
+    ``.get(...)`` access.
+    """
+    try:
+        from hermes_cli.config import load_config
+    except Exception:
+        return {}
+    try:
+        cfg = load_config()
+    except Exception as exc:  # noqa: BLE001 — broad catch is intentional
+        _log.debug(
+            "dashboard-auth.prefix: load_config() raised %s; "
+            "falling back to env-only configuration",
+            exc,
+        )
+        return {}
+    section = cfg.get("dashboard") if isinstance(cfg, dict) else None
+    return section if isinstance(section, dict) else {}
+
+
+def resolve_public_url() -> str:
+    """Resolve the operator-declared dashboard public URL.
+
+    Precedence (mirrors ``dashboard.oauth.client_id``):
+
+      1. ``HERMES_DASHBOARD_PUBLIC_URL`` env var (when non-empty after
+         strip — empty values are treated as unset so a provisioned-but-
+         not-populated Fly secret can't shadow a valid config.yaml entry).
+      2. ``dashboard.public_url`` in ``config.yaml``.
+      3. Empty string — signals "no override, reconstruct from request"
+         to the caller.
+
+    Each candidate value is run through :func:`_normalise_public_url`.
+    A malformed env var falls through to the config.yaml entry; a
+    malformed config entry falls through to ``""``. This means a typo
+    in one surface doesn't prevent the other from working.
+    """
+    env_raw = os.environ.get("HERMES_DASHBOARD_PUBLIC_URL", "")
+    env_clean = _normalise_public_url(env_raw)
+    if env_clean:
+        return env_clean
+    _warn_if_malformed("HERMES_DASHBOARD_PUBLIC_URL env var", env_raw)
+    cfg_raw = str(_load_dashboard_section().get("public_url", ""))
+    cfg_clean = _normalise_public_url(cfg_raw)
+    if not cfg_clean:
+        _warn_if_malformed("dashboard.public_url in config.yaml", cfg_raw)
+    return cfg_clean