Preserve quoted commas in Accept media ranges

mimeparse/__init__.py

@@ -175,7 +175,7 @@ def quality(mime_type: str, ranges: str) -> float:
                   text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5')
     0.7
     """
-    parsed_ranges = [parse_media_range(r) for r in ranges.split(',')]
+    parsed_ranges = [parse_media_range(r) for r in _split_media_ranges(ranges)]
 
     return quality_parsed(mime_type, parsed_ranges)
 
@@ -194,7 +194,7 @@ def best_match(supported: Iterable[str], header: str) -> str:
                    'text/*;q=0.5,*/*; q=0.1')
     'text/xml'
     """
-    split_header = _filter_blank(header.split(','))
+    split_header = _filter_blank(_split_media_ranges(header))
     parsed_header = [parse_media_range(r) for r in split_header]
     weighted_matches = []
     pos = 0
@@ -210,6 +210,28 @@ def best_match(supported: Iterable[str], header: str) -> str:
     return weighted_matches[-1][0][0] and weighted_matches[-1][2] or ''
 
 
+def _split_media_ranges(header: str) -> Generator[str, None, None]:
+    """Split an Accept list without splitting quoted parameter values."""
+    if '"' not in header:
+        yield from header.split(',')
+        return
+
+    start = 0
+    quoted = False
+    escaped = False
+    for index, char in enumerate(header):
+        if escaped:
+            escaped = False
+        elif quoted and char == '\\':
+            escaped = True
+        elif char == '"':
+            quoted = not quoted
+        elif char == ',' and not quoted:
+            yield header[start:index]
+            start = index + 1
+    yield header[start:]
+
+
 def _filter_blank(i: Iterable[str]) -> Generator[str, None, None]:
     """Return all non-empty items in the list."""
     for s in i:

mimeparse_test.py

@@ -68,6 +68,30 @@ def test_best_match(self):
         for args, expected, description in self.test_data['best_match']:
             self._test_best_match(args, expected, description)
 
+    def test_quoted_commas(self):
+        values = (
+            r'"a,b"',
+            r'"a\",b"',
+            r'"a\\,b"',
+            r'"a,b\\"',
+            r'"a;b,c"',
+            r'"a,\"b,c\""',
+        )
+        for value in values:
+            with self.subTest(value=value):
+                media_type = f'text/plain;note={value}'
+                header = f'{media_type},application/json;q=0.2'
+                self.assertEqual(mimeparse.quality(media_type, header), 1)
+                self.assertEqual(
+                    mimeparse.best_match([media_type, 'application/json'], header),
+                    media_type,
+                )
+
+    def test_quoted_commas_with_blank_ranges(self):
+        media_type = 'text/plain;note="a,b"'
+        header = f', {media_type}, , '
+        self.assertEqual(mimeparse.best_match([media_type], header), media_type)
+
     def test_parse_mime_type(self):
         for args, expected in self.test_data['parse_mime_type']:
             self._test_parse_mime_type(args, expected)

testdata.json

@@ -14,6 +14,20 @@
     ],
 
     "quality": [
+        [
+            [
+                "text/plain;profile=\"a,b\"",
+                "text/plain;profile=\"a,b\";q=0.8, application/json;q=0.2"
+            ],
+            0.8
+        ],
+        [
+            [
+                "application/json",
+                "text/plain;profile=\"a,b\";q=0.8, application/json;q=0.2"
+            ],
+            0.2
+        ],
         [
             [
                 "text/html;level=1",
@@ -66,6 +80,22 @@
     ],
 
     "best_match": [
+        [
+            [
+                ["text/plain;profile=\"a,b\"", "application/json"],
+                "text/plain;profile=\"a,b\";q=0.8, application/json;q=0.2"
+            ],
+            "text/plain;profile=\"a,b\"",
+            "preserve a comma within a quoted parameter value"
+        ],
+        [
+            [
+                ["text/plain;profile=\"a,b\"", "application/json"],
+                "text/plain;profile=\"a,b\";q=0.2, application/json;q=0.8"
+            ],
+            "application/json",
+            "compare quality factors after a quoted parameter containing a comma"
+        ],
         [
             [
                 ["application/json", "text/html"],