Restrict output of inspect() function

Particularly, trim recursive or overly nested structures.

Replicates some ideas from graphql/graphql-js#1771
but truncates strings like in pytest, and puts an
ellipsis in the middle of long lists, dicts, sets etc.

This is done to avoid server memory and performance issues.

README.md

@@ -13,7 +13,7 @@ a query language for APIs created by Facebook.
 [![Code Style](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/ambv/black)
 
 The current version 1.0.1 of GraphQL-core-next is up-to-date with GraphQL.js version
-14.1.1. All parts of the API are covered by an extensive test suite of currently 1701
+14.1.1. All parts of the API are covered by an extensive test suite of currently 1723
 unit tests.
 
 

graphql/pyutils/inspect.py

@@ -9,47 +9,89 @@
     isasyncgenfunction,
     isasyncgen,
 )
-from typing import Any
+from typing import Any, List
 
 from ..error import INVALID
 
+__all__ = ["inspect"]
 
-def inspect(value: Any) -> str:
+
+def inspect(value: Any, max_depth: int = 2, depth: int = 0) -> str:
     """Inspect value and a return string representation for error messages.
 
     Used to print values in error messages. We do not use repr() in order to not
     leak too much of the inner Python representation of unknown objects, and we
     do not use json.dumps() because not all objects can be serialized as JSON and
     we want to output strings with single quotes like Python repr() does it.
+
+    We also restrict the size of the representation by truncating strings and
+    collections and allowing only a maximum recursion depth.
     """
-    if isinstance(value, (bool, int, float, str)) or value in (None, INVALID):
+    if value is None or value is INVALID or isinstance(value, (bool, float, complex)):
         return repr(value)
-    # check if we have a custom inspect method
-    try:
-        inspect_method = value.__inspect__
-        if callable(inspect_method):
-            value = inspect_method()
-            return value if isinstance(value, str) else inspect(value)
-    except AttributeError:
-        pass
-    if isinstance(value, list):
-        return f"[{', '.join(map(inspect, value))}]"
-    if isinstance(value, tuple):
-        if len(value) == 1:
-            return f"({inspect(value[0])},)"
-        return f"({', '.join(map(inspect, value))})"
-    if isinstance(value, dict):
-        return (
-            "{"
-            + ", ".join(
-                map(lambda i: f"{inspect(i[0])}: {inspect(i[1])}", value.items())
-            )
-            + "}"
-        )
-    if isinstance(value, set):
-        if not len(value):
-            return "<empty set>"
-        return "{" + ", ".join(map(inspect, value)) + "}"
+    if isinstance(value, (int, str, bytes, bytearray)):
+        return trunc_str(repr(value))
+    if depth < max_depth:
+        try:
+            # check if we have a custom inspect method
+            inspect_method = value.__inspect__
+            if callable(inspect_method):
+                s = inspect_method()
+                return (
+                    trunc_str(s)
+                    if isinstance(s, str)
+                    else inspect(s, max_depth, depth + 1)
+                )
+        except AttributeError:
+            pass
+        if isinstance(value, (list, tuple, dict, set, frozenset)):
+            if not value:
+                return repr(value)
+            if isinstance(value, list):
+                items = value
+            elif isinstance(value, dict):
+                items = list(value.items())
+            else:
+                items = list(value)
+            items = trunc_list(items)
+            depth += 1
+            if isinstance(value, dict):
+                s = ", ".join(
+                    "..."
+                    if v is ELLIPSIS
+                    else inspect(v[0], max_depth, depth)
+                    + ": "
+                    + inspect(v[1], max_depth, depth)
+                    for v in items
+                )
+            else:
+                s = ", ".join(
+                    "..." if v is ELLIPSIS else inspect(v, max_depth, depth)
+                    for v in items
+                )
+            if isinstance(value, tuple):
+                if len(items) == 1:
+                    return f"({s},)"
+                return f"({s})"
+            if isinstance(value, (dict, set)):
+                return "{" + s + "}"
+            if isinstance(value, frozenset):
+                return f"frozenset({{{s}}})"
+            return f"[{s}]"
+    else:
+        if isinstance(value, (list, tuple, dict, set, frozenset)):
+            if not value:
+                return repr(value)
+            if isinstance(value, list):
+                return "[...]"
+            if isinstance(value, tuple):
+                return "(...)"
+            if isinstance(value, dict):
+                return "{...}"
+            if isinstance(value, set):
+                return "set(...)"
+            if isinstance(value, frozenset):
+                return "frozenset(...)"
     if isinstance(value, Exception):
         type_ = "exception"
         value = type(value)
@@ -95,3 +137,28 @@ def inspect(value: Any) -> str:
         return f"<{type_}>"
     else:
         return f"<{type_} {name}>"
+
+
+def trunc_str(s: str, max_string=240) -> str:
+    """Truncate strings to maximum length."""
+    if len(s) > max_string:
+        i = max(0, (max_string - 3) // 2)
+        j = max(0, max_string - 3 - i)
+        s = s[:i] + "..." + s[-j:]
+    return s
+
+
+def trunc_list(s: List, max_list=10) -> List:
+    """Truncate lists to maximum length."""
+    if len(s) > max_list:
+        i = max_list // 2
+        j = i - 1
+        s = s[:i] + [ELLIPSIS] + s[-j:]
+    return s
+
+
+class InspectEllipsisType:
+    """Singleton class for indicating ellipses in sequences."""
+
+
+ELLIPSIS = InspectEllipsisType()