Cache remote JSON schemas

CHANGELOG.md

@@ -1,3 +1,7 @@
+## Unreleased
+
+- Cache remote JSON schemas for extensions (#155, @avbentem)
+
 ## 3.1.0 (2024-05-21)
 
 - Allow extra fields in Links (#144, @jonhealy1)

README.md

@@ -91,7 +91,7 @@ assert catalog.links[0].href == "item.json"
 
 ### Extensions
 
-STAC defines many extensions which let the user customize the data in their catalog. `stac-pydantic.extensions.validate_extensions` will validate a `dict`, `Item`, `Collection` or `Catalog` against the schema urls provided in the `stac_extensions` property:
+STAC defines many extensions which let the user customize the data in their catalog. `stac-pydantic.extensions.validate_extensions` gets the JSON schemas from the URLs provided in the `stac_extensions` property (caching the last fetched ones), and will validate a `dict`, `Item`, `Collection` or `Catalog` against those fetched schemas:
 
 ```python
 from stac_pydantic import Item

stac_pydantic/extensions.py

@@ -1,4 +1,5 @@
 import json
+from functools import lru_cache
 from typing import Any, Dict, Union
 
 import jsonschema
@@ -9,10 +10,21 @@
 from stac_pydantic.item import Item
 
 
+@lru_cache(maxsize=128)
+def _fetch_schema(url: str) -> dict:
+    """Fetch the remote JSON schema, if not already cached."""
+    req = requests.get(url)
+    return req.json()
+
+
 def validate_extensions(
     stac_obj: Union[Item, Collection, Catalog, Dict[str, Any]],
     reraise_exception: bool = False,
 ) -> bool:
+    """
+    Fetch the remote JSON schema, if not already cached, and validate the STAC
+    object against that schema.
+    """
     if isinstance(stac_obj, dict):
         stac_dict = stac_obj
     else:
@@ -23,8 +35,7 @@ def validate_extensions(
     try:
         if stac_dict["stac_extensions"]:
             for ext in stac_dict["stac_extensions"]:
-                req = requests.get(ext)
-                schema = req.json()
+                schema = _fetch_schema(ext)
                 jsonschema.validate(instance=stac_dict, schema=schema)
     except Exception:
         if reraise_exception:

tests/test_models.py

@@ -6,7 +6,7 @@
 from shapely.geometry import shape
 
 from stac_pydantic import Collection, Item, ItemProperties
-from stac_pydantic.extensions import validate_extensions
+from stac_pydantic.extensions import _fetch_schema, validate_extensions
 from stac_pydantic.links import Link, Links
 from stac_pydantic.shared import MimeTypes, StacCommonMetadata
 
@@ -116,6 +116,22 @@ def test_explicit_extension_validation() -> None:
     validate_extensions(test_item)
 
 
+def test_extension_validation_schema_cache() -> None:
+    # Defines 3 extensions, but one is a non-existing URL
+    test_item = request(EO_EXTENSION)
+
+    _fetch_schema.cache_clear()
+
+    assert not validate_extensions(test_item)
+    assert _fetch_schema.cache_info().hits == 0
+    assert _fetch_schema.cache_info().misses == 3
+
+    assert not validate_extensions(test_item)
+    assert _fetch_schema.cache_info().hits == 2
+    # The non-existing URL will have failed, hence retried
+    assert _fetch_schema.cache_info().misses == 4
+
+
 @pytest.mark.parametrize(
     "infile,model",
     [(EO_EXTENSION, Item), (COLLECTION, Collection)],