Refs #33865 -- Improved implementation of FakePayload.

FakePayload is a wrapper around io.BytesIO and is expected to
masquerade as though it is a file-like object. For that reason it makes
sense that it should inherit the correct signatures from io.BytesIO
methods.

Crucially an implementation of .readline() is added which will be
necessary for this to behave more like the expected file-like objects as
LimitedStream will be changed to defer to the wrapped stream object
rather than rolling its own implementation for improved performance.

It should be safe to adjust these signatures because FakePayload is
only used internally within test client helpers, is undocumented, and
thus private.

django/test/client.py

@@ -6,7 +6,7 @@ from copy import copy
 from functools import partial
 from http import HTTPStatus
 from importlib import import_module
-from io import BytesIO
+from io import BytesIO, IOBase
 from urllib.parse import unquote_to_bytes, urljoin, urlparse, urlsplit
 
 from asgiref.sync import sync_to_async
@@ -55,7 +55,7 @@ class RedirectCycleError(Exception):
         self.redirect_chain = last_response.redirect_chain
 
 
-class FakePayload:
+class FakePayload(IOBase):
     """
     A wrapper around BytesIO that restricts what can be read since data from
     the network can't be sought and cannot be read outside of its content
@@ -63,39 +63,49 @@ class FakePayload:
     that wouldn't work in real life.
     """
 
-    def __init__(self, content=None):
+    def __init__(self, initial_bytes=None):
         self.__content = BytesIO()
         self.__len = 0
         self.read_started = False
-        if content is not None:
-            self.write(content)
+        if initial_bytes is not None:
+            self.write(initial_bytes)
 
     def __len__(self):
         return self.__len
 
-    def read(self, num_bytes=None):
+    def read(self, size=-1, /):
         if not self.read_started:
             self.__content.seek(0)
             self.read_started = True
-        if num_bytes is None:
-            num_bytes = self.__len or 0
+        if size == -1 or size is None:
+            size = self.__len
         assert (
-            self.__len >= num_bytes
+            self.__len >= size
         ), "Cannot read more than the available bytes from the HTTP incoming data."
-        content = self.__content.read(num_bytes)
-        self.__len -= num_bytes
+        content = self.__content.read(size)
+        self.__len -= len(content)
         return content
 
-    def write(self, content):
+    def readline(self, size=-1, /):
+        if not self.read_started:
+            self.__content.seek(0)
+            self.read_started = True
+        if size == -1 or size is None:
+            size = self.__len
+        assert (
+            self.__len >= size
+        ), "Cannot read more than the available bytes from the HTTP incoming data."
+        content = self.__content.readline(size)
+        self.__len -= len(content)
+        return content
+
+    def write(self, b, /):
         if self.read_started:
             raise ValueError("Unable to write a payload after it's been read")
-        content = force_bytes(content)
+        content = force_bytes(b)
         self.__content.write(content)
         self.__len += len(content)
 
-    def close(self):
-        pass
-
 
 def closing_iterator_wrapper(iterable, close):
     try: