Issue #21448: Fixed FeedParser feed() to avoid O(N**2) behavior when parsing long line.

Original patch by Raymond Hettinger.

Lib/test/test_email/test_email.py

@@ -10,6 +10,7 @@ import textwrap
 
 from io import StringIO, BytesIO
 from itertools import chain
+from random import choice
 
 import email
 import email.policy
@@ -3353,16 +3354,70 @@ Do you like this message?
             bsf.push(il)
             nt += n
             n1 = 0
-            while True:
-                ol = bsf.readline()
-                if ol == NeedMoreData:
-                    break
+            for ol in iter(bsf.readline, NeedMoreData):
                 om.append(ol)
                 n1 += 1
             self.assertEqual(n, n1)
         self.assertEqual(len(om), nt)
         self.assertEqual(''.join([il for il, n in imt]), ''.join(om))
 
+    def test_push_random(self):
+        from email.feedparser import BufferedSubFile, NeedMoreData
+
+        n = 10000
+        chunksize = 5
+        chars = 'abcd \t\r\n'
+
+        s = ''.join(choice(chars) for i in range(n)) + '\n'
+        target = s.splitlines(True)
+
+        bsf = BufferedSubFile()
+        lines = []
+        for i in range(0, len(s), chunksize):
+            chunk = s[i:i+chunksize]
+            bsf.push(chunk)
+            lines.extend(iter(bsf.readline, NeedMoreData))
+        self.assertEqual(lines, target)
+
+
+class TestFeedParsers(TestEmailBase):
+
+    def parse(self, chunks):
+        from email.feedparser import FeedParser
+        feedparser = FeedParser()
+        for chunk in chunks:
+            feedparser.feed(chunk)
+        return feedparser.close()
+
+    def test_newlines(self):
+        m = self.parse(['a:\nb:\rc:\r\nd:\n'])
+        self.assertEqual(m.keys(), ['a', 'b', 'c', 'd'])
+        m = self.parse(['a:\nb:\rc:\r\nd:'])
+        self.assertEqual(m.keys(), ['a', 'b', 'c', 'd'])
+        m = self.parse(['a:\rb', 'c:\n'])
+        self.assertEqual(m.keys(), ['a', 'bc'])
+        m = self.parse(['a:\r', 'b:\n'])
+        self.assertEqual(m.keys(), ['a', 'b'])
+        m = self.parse(['a:\r', '\nb:\n'])
+        self.assertEqual(m.keys(), ['a', 'b'])
+        m = self.parse(['a:\x85b:\u2028c:\n'])
+        self.assertEqual(m.items(), [('a', '\x85'), ('b', '\u2028'), ('c', '')])
+        m = self.parse(['a:\r', 'b:\x85', 'c:\n'])
+        self.assertEqual(m.items(), [('a', ''), ('b', '\x85'), ('c', '')])
+
+    def test_long_lines(self):
+        M, N = 1000, 100000
+        m = self.parse(['a:b\n\n'] + ['x'*M] * N)
+        self.assertEqual(m.items(), [('a', 'b')])
+        self.assertEqual(m.get_payload(), 'x'*M*N)
+        m = self.parse(['a:b\r\r'] + ['x'*M] * N)
+        self.assertEqual(m.items(), [('a', 'b')])
+        self.assertEqual(m.get_payload(), 'x'*M*N)
+        m = self.parse(['a:b\r\r'] + ['x'*M+'\x85'] * N)
+        self.assertEqual(m.items(), [('a', 'b')])
+        self.assertEqual(m.get_payload(), ('x'*M+'\x85')*N)
+        m = self.parse(['a:\r', 'b: '] + ['x'*M] * N)
+        self.assertEqual(m.items(), [('a', ''), ('b', 'x'*M*N)])
 
 
 class TestParsers(TestEmailBase):