Fix uppercase scheme (mitmproxy#8174)

* fix: lowercase scheme

* fix: add uppercase proto test

* [autofix.ci] apply automated fixes

* Add RFC reference

Add comments to clarify scheme handling in URL parsing

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Maximilian Hils <git@maximilianhils.com>

Author: 3 people

CHANGELOG.md

@@ -7,6 +7,8 @@
 
 ## Unreleased: mitmproxy next
 
+- Fix 400 Bad Request for HTTP requests with uppercase scheme (e.g. `HTTP://`).
+  ([#8174](https://github.com/mitmproxy/mitmproxy/pull/8174), @emanuele-em)
 - Fix console command panel losing focus due to incoming traffic (e.g. websocket messages).
   ([#8173](https://github.com/mitmproxy/mitmproxy/pull/8173), @emanuele-em)
 - mitmdump: Fix failed CONNECT requests not being displayed.

mitmproxy/net/http/http1/read.py

@@ -180,6 +180,11 @@ def _read_request_line(
                 raise ValueError
         else:
             scheme, rest = target.split(b"://", maxsplit=1)
+            # https://www.rfc-editor.org/rfc/rfc3986.html#section-3.1
+            # An implementation should accept uppercase letters as equivalent to lowercase in scheme names
+            # (e.g., allow "HTTP" as well as "http") for the sake of robustness but should only produce
+            # lowercase scheme names for consistency.
+            scheme = scheme.lower()
             authority, _, path_ = rest.partition(b"/")
             path = b"/" + path_
             host, port = url.parse_authority(authority, check=True)

test/mitmproxy/net/http/http1/test_read.py

@@ -203,6 +203,15 @@ def t(b):
         b"/",
         b"HTTP/1.1",
     )
+    assert t(b"GET HTTP://foo:42/bar HTTP/1.1") == (
+        "foo",
+        42,
+        b"GET",
+        b"http",
+        b"foo:42",
+        b"/bar",
+        b"HTTP/1.1",
+    )
 
     with pytest.raises(ValueError):
         t(b"GET / WTF/1.1")