fix: improve config path checks

cubicweb_api/util.py

@@ -39,9 +39,9 @@
     path_prefix: str = (
         repo.get_option_value("api-path-prefix") or API_PATH_DEFAULT_PREFIX
     )
-    match = re.match("^[a-zA-Z0-9-_@.&+!*(),/]{1,30}$", path_prefix)
+    match = re.match("^/[a-zA-Z0-9-_@.&+!*(),/]{1,29}$", path_prefix)
     if match:
         return path_prefix.rstrip("/")
     else:
         if len(path_prefix) > 30:
             raise ConfigurationError(
@@ -43,9 +43,16 @@
     if match:
         return path_prefix.rstrip("/")
     else:
         if len(path_prefix) > 30:
             raise ConfigurationError(
-                "api-path-prefix is too long. Max size allowed is 30 characters."
+                f"api-path-prefix '{path_prefix}' is too long. "
+                f"Max size allowed is 30 characters. "
+                f"Current size is {len(path_prefix)}."
+            )
+        if not path_prefix.startswith("/"):
+            raise ConfigurationError(
+                f"api-path-prefix '{path_prefix}' does not start with '/'. "
+                "Prefix should start with '/' to be validated by openapi"
             )
 
         raise ConfigurationError(
@@ -49,6 +56,6 @@
             )
 
         raise ConfigurationError(
-            "api-path-prefix contains invalid characters."
+            f"api-path-prefix '{path_prefix}' contains invalid characters. "
             "Allowed characters are: a-zA-Z0-9-_@.&+!*(),/"
         )