From 72d356e3584ebfb8e813a8e9f2cd3dccf233c0d9 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Sun, 13 Nov 2022 11:00:25 -0800
Subject: [PATCH] gh-99418: Make urllib.parse.urlparse enforce that a scheme
 must begin with an alphabetical ASCII character. (GH-99421)

Prevent urllib.parse.urlparse from accepting schemes that don't begin with an alphabetical ASCII character.

RFC 3986 defines a scheme like this: `scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )`
RFC 2234 defines an ALPHA like this: `ALPHA = %x41-5A / %x61-7A`

The WHATWG URL spec defines a scheme like this:
`"A URL-scheme string must be one ASCII alpha, followed by zero or more of ASCII alphanumeric, U+002B (+), U+002D (-), and U+002E (.)."`
(cherry picked from commit 439b9cfaf43080e91c4ad69f312f21fa098befc7)

Co-authored-by: Ben Kallus <49924171+kenballus@users.noreply.github.com>
---
 Lib/test/test_urlparse.py                      | 18 ++++++++++++++++++
 Lib/urllib/parse.py                            |  2 +-
 ...22-11-12-15-45-51.gh-issue-99418.FxfAXS.rst |  2 ++
 3 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2022-11-12-15-45-51.gh-issue-99418.FxfAXS.rst

diff --git a/Lib/test/test_urlparse.py b/Lib/test/test_urlparse.py
index 4d28646d5ffff4..b4261107235f81 100644
--- a/Lib/test/test_urlparse.py
+++ b/Lib/test/test_urlparse.py
@@ -668,6 +668,24 @@ def test_attributes_bad_port(self):
                         with self.assertRaises(ValueError):
                             p.port
 
+    def test_attributes_bad_scheme(self):
+        """Check handling of invalid schemes."""
+        for bytes in (False, True):
+            for parse in (urllib.parse.urlsplit, urllib.parse.urlparse):
+                for scheme in (".", "+", "-", "0", "http&", "६http"):
+                    with self.subTest(bytes=bytes, parse=parse, scheme=scheme):
+                        url = scheme + "://www.example.net"
+                        if bytes:
+                            if url.isascii():
+                                url = url.encode("ascii")
+                            else:
+                                continue
+                        p = parse(url)
+                        if bytes:
+                            self.assertEqual(p.scheme, b"")
+                        else:
+                            self.assertEqual(p.scheme, "")
+
     def test_attributes_without_netloc(self):
         # This example is straight from RFC 3261.  It looks like it
         # should allow the username, hostname, and port to be filled
diff --git a/Lib/urllib/parse.py b/Lib/urllib/parse.py
index 12fe0112e4fe2b..69631cbb810b54 100644
--- a/Lib/urllib/parse.py
+++ b/Lib/urllib/parse.py
@@ -460,7 +460,7 @@ def urlsplit(url, scheme='', allow_fragments=True):
     allow_fragments = bool(allow_fragments)
     netloc = query = fragment = ''
     i = url.find(':')
-    if i > 0:
+    if i > 0 and url[0].isascii() and url[0].isalpha():
         for c in url[:i]:
             if c not in scheme_chars:
                 break
diff --git a/Misc/NEWS.d/next/Library/2022-11-12-15-45-51.gh-issue-99418.FxfAXS.rst b/Misc/NEWS.d/next/Library/2022-11-12-15-45-51.gh-issue-99418.FxfAXS.rst
new file mode 100644
index 00000000000000..0a06e7c5c6ac48
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-11-12-15-45-51.gh-issue-99418.FxfAXS.rst
@@ -0,0 +1,2 @@
+Fix bug in :func:`urllib.parse.urlparse` that causes URL schemes that begin
+with a digit, a plus sign, or a minus sign to be parsed incorrectly.