Return a better error message if a file: URL is not found (#10263)

Co-authored-by: Tzu-ping Chung <[email protected]>
Co-authored-by: Pradyun Gedam <[email protected]>

news/10263.bugfix.rst

@@ -0,0 +1 @@
+Present a better error message, when a ``file:`` URL is not found.

src/pip/_internal/network/session.py

@@ -3,6 +3,7 @@
 """
 
 import email.utils
+import io
 import ipaddress
 import json
 import logging
@@ -207,8 +208,11 @@ def send(
  try:
  stats = os.stat(pathname)
  except OSError as exc:
+ # format the exception raised as a io.BytesIO object,
+ # to return a better error message:
  resp.status_code = 404
- resp.raw = exc
+ resp.reason = type(exc).__name__
+ resp.raw = io.BytesIO(f"{resp.reason}: {exc}".encode("utf8"))
  else:
  modified = email.utils.formatdate(stats.st_mtime, usegmt=True)
  content_type = mimetypes.guess_type(pathname)[0] or "text/plain"

tests/functional/test_bad_url.py

@@ -0,0 +1,16 @@
+# test the error message returned by pip when
+# a bad "file:" URL is passed to it.
+
+from typing import Any
+
+
+def test_filenotfound_error_message(script: Any) -> None:
+ # Test the error message returned when using a bad 'file:' URL.
+ # make pip to fail and get an error message
+ # by running "pip install -r file:nonexistent_file"
+ proc = script.pip("install", "-r", "file:unexistent_file", expect_error=True)
+ assert proc.returncode == 1
+ expect = (
+ "ERROR: 404 Client Error: FileNotFoundError for url: file:///unexistent_file"
+ )
+ assert proc.stderr.rstrip() == expect