add OKF conformance validator

surfsense_backend/app/services/okf/validator.py

@@ -0,0 +1,90 @@
+"""Minimal OKF v0.1 conformance checks.
+
+A bundle conforms if every non-reserved ``.md`` file has a parseable YAML
+frontmatter block whose ``type`` is a non-empty string. Reserved files
+(``index.md``, ``log.md``) are exempt from the frontmatter requirement.
+Consumers must stay permissive, so this is for producers to self-check what they
+emit, not to reject foreign bundles.
+
+Spec: https://github.com/GoogleCloudPlatform/knowledge-catalog/blob/main/okf/SPEC.md
+"""
+
+from __future__ import annotations
+
+import yaml
+
+from app.services.okf.serializer import INDEX_FILENAME, LOG_FILENAME
+
+_DELIMITER = "---"
+RESERVED_FILENAMES = frozenset({INDEX_FILENAME, LOG_FILENAME})
+
+# The OKF v0.1 frontmatter contract, shared by serializer and validator. Only
+# ``type`` is mandatory; the rest are recommended.
+REQUIRED_FRONTMATTER_KEYS: tuple[str, ...] = ("type",)
+RECOMMENDED_FRONTMATTER_KEYS: tuple[str, ...] = (
+    "title",
+    "description",
+    "resource",
+    "tags",
+    "timestamp",
+)
+
+
+def parse_frontmatter(text: str) -> tuple[dict | None, str | None]:
+    """Split an OKF concept into ``(frontmatter_dict, error)``.
+
+    Returns ``(dict, None)`` on success or ``(None, reason)`` if the frontmatter
+    block is missing or not a parseable YAML mapping.
+    """
+    if not text.startswith(_DELIMITER + "\n"):
+        return None, "missing opening '---' frontmatter delimiter"
+    rest = text[len(_DELIMITER) + 1 :]
+    end = rest.find("\n" + _DELIMITER)
+    if end == -1:
+        return None, "missing closing '---' frontmatter delimiter"
+    block = rest[:end]
+    try:
+        data = yaml.safe_load(block)
+    except yaml.YAMLError as exc:
+        return None, f"frontmatter is not valid YAML: {exc}"
+    if not isinstance(data, dict):
+        return None, "frontmatter is not a YAML mapping"
+    return data, None
+
+
+def validate_concept(text: str) -> list[str]:
+    """Return conformance errors for a single concept document (empty == conforms)."""
+    frontmatter, error = parse_frontmatter(text)
+    if error:
+        return [error]
+    errors: list[str] = []
+    for key in REQUIRED_FRONTMATTER_KEYS:
+        value = frontmatter.get(key)
+        if not isinstance(value, str) or not value.strip():
+            errors.append(f"frontmatter '{key}' is missing or empty")
+    return errors
+
+
+def is_conformant_concept(text: str) -> bool:
+    """True if a single concept document conforms to OKF v0.1."""
+    return not validate_concept(text)
+
+
+def validate_bundle(files: dict[str, str]) -> dict[str, list[str]]:
+    """Validate a bundle given a mapping of relative path -> file contents.
+
+    Only non-reserved ``.md`` files are checked for concept conformance. Returns
+    a mapping of path -> errors for every non-conformant file (an empty mapping
+    means the whole bundle conforms).
+    """
+    problems: dict[str, list[str]] = {}
+    for path, contents in files.items():
+        if not path.endswith(".md"):
+            continue
+        filename = path.rsplit("/", 1)[-1]
+        if filename in RESERVED_FILENAMES:
+            continue
+        errors = validate_concept(contents)
+        if errors:
+            problems[path] = errors
+    return problems