Treat carriage return as whitespace in strutils.is_xml (#8243)

* Treat carriage return as whitespace in strutils.is_xml

is_xml() skipped only tab, LF and space before checking for the
opening "<", so a response body that started with a leading CR
or CRLF (which is what HTTP frames look like, and what some
Windows-side XML producers emit) was not detected as XML.
The XML/HTML content view's auto-detection score then dropped
to 0 instead of the usual 0.4 for those bodies.

XML 1.0 §2.3 defines whitespace as (#x20 | #x9 | #xD | #xA), so
\r (0x0D) belongs in the skip set alongside the other three.
Adds the missing byte plus three assertions in the existing
test_is_xml: \r<foo and \r\n<foo are now recognised, and a
sanity check that \r\nfoo is still rejected.

* [autofix.ci] apply automated fixes

* simplify wording

---------

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

CHANGELOG.md

@@ -7,6 +7,8 @@
 
 ## Unreleased: mitmproxy next
 
+- Fix contentview detection for XML files that start with CRLF.
+  ([#8243](https://github.com/mitmproxy/mitmproxy/pull/8243), @ADiTyaRaj8969)
 - mitmweb: Fix the filter input losing half-typed text on unrelated parent re-renders.
   ([#8234](https://github.com/mitmproxy/mitmproxy/pull/8234), @ariel42)
 - mitmweb: Fix an infinite update cycle in `FlowTable` by only recomputing the virtual-scroll window in `componentDidUpdate` when `flowView` or `rowHeight` actually change.

mitmproxy/utils/strutils.py

@@ -163,8 +163,10 @@ def is_mostly_bin(s: bytes) -> bool:
 
 
 def is_xml(s: bytes) -> bool:
+    # XML 1.0 §2.3 defines whitespace as (#x20 | #x9 | #xD | #xA), so a
+    # leading \r before "<" should also be skipped here.
     for char in s:
-        if char in (9, 10, 32):  # is space?
+        if char in (9, 10, 13, 32):  # is whitespace?
             continue
         return char == 60  # is a "<"?
     return False

test/mitmproxy/utils/test_strutils.py

@@ -106,6 +106,11 @@ def test_is_xml():
     assert not strutils.is_xml(b"foo")
     assert strutils.is_xml(b"<foo")
     assert strutils.is_xml(b"  \n<foo")
+    # XML 1.0 §2.3 lists CR as whitespace, so bodies that arrive with
+    # CRLF (or a stray \r) before the root element must still be detected.
+    assert strutils.is_xml(b"\r<foo")
+    assert strutils.is_xml(b"\r\n<foo")
+    assert not strutils.is_xml(b"\r\nfoo")
 
 
 def test_clean_hanging_newline():