Check the size of build_path

Fixes conda-incubator#649.

conda-store-server/conda_store_server/orm.py

@@ -190,15 +190,22 @@ def build_path(self, conda_store):
         """
         store_directory = os.path.abspath(conda_store.store_directory)
         namespace = self.environment.namespace.name
-        name = self.specification.name
-        return (
+        res = (
             pathlib.Path(
                 conda_store.build_directory.format(
-                    store_directory=store_directory, namespace=namespace, name=name
+                    store_directory=store_directory,
+                    namespace=namespace,
                 )
             )
             / self.build_key
         )
+        # conda prefix must be less or equal to 255 chars
+        # https://github.com/conda-incubator/conda-store/issues/649
+        if len(str(res)) > 255:
+            raise ValueError(
+                f"build_path too long: {res} must be <= 255 chars, got {len(str(res))}"
+            )
+        return res
 
     def environment_path(self, conda_store):
         """Environment path is the path for the symlink to the build

conda-store-server/tests/test_db_api.py

@@ -134,3 +134,13 @@ def test_get_set_keyvaluestore(db):
     # test updating a prefix
     api.set_kvstore_key_values(db, "pytest", {"c": 999, "d": 999}, update=False)
     assert {**setting_1, **setting_2} == api.get_kvstore_key_values(db, "pytest")
+
+
+def test_build_path_too_long(db, conda_store, simple_specification):
+    conda_store.store_directory = 'A' * 800
+    build_id = conda_store.register_environment(
+        db, specification=simple_specification, namespace="pytest"
+    )
+    build = api.get_build(db, build_id=build_id)
+    with pytest.raises(ValueError, match=r"build_path too long: .* must be <= 255 chars"):
+        build.build_path(conda_store)