#1486713: Add a tolerant mode to HTMLParser.

The motivation for adding this option is that the the functionality it
provides used to be provided by sgmllib in Python2, and was used by,
for example, BeautifulSoup.  Without this option, the Python3 version
of BeautifulSoup and the many programs that use it are crippled.

The original patch was by 'kxroberto'.  I modified it heavily but kept his
heuristics and test.  I also added additional heuristics to fix #975556,
#1046092, and part of #6191.  This patch should be completely backward
compatible:  the behavior with the default strict=True is unchanged.

1 files changed, 83 insertions, 16 deletions

diff --git a/Lib/html/parser.py b/Lib/html/parser.py
index c2c7f6b..8d275ab 100644
--- a/Lib/html/parser.py
+++ b/Lib/html/parser.py
@@ -24,10 +24,14 @@ starttagopen = re.compile('<[a-zA-Z]')
 piclose = re.compile('>')
 commentclose = re.compile(r'--\s*>')
 tagfind = re.compile('[a-zA-Z][-.a-zA-Z0-9:_]*')
+# Note, the strict one of this pair isn't really strict, but we can't
+# make it correctly strict without breaking backward compatibility.
 attrfind = re.compile(
     r'\s*([a-zA-Z_][-.:a-zA-Z_0-9]*)(\s*=\s*'
     r'(\'[^\']*\'|"[^"]*"|[-a-zA-Z0-9./,:;+*%?!&$\(\)_#=~@]*))?')
-
+attrfind_tolerant = re.compile(
+    r'\s*([a-zA-Z_][-.:a-zA-Z_0-9]*)(\s*=\s*'
+    r'(\'[^\']*\'|"[^"]*"|[^>\s]*))?')
 locatestarttagend = re.compile(r"""
   <[a-zA-Z][-.a-zA-Z0-9:_]*          # tag name
   (?:\s+                             # whitespace before attribute name
@@ -42,6 +46,21 @@ locatestarttagend = re.compile(r"""
    )*
   \s*                                # trailing whitespace
 """, re.VERBOSE)
+locatestarttagend_tolerant = re.compile(r"""
+  <[a-zA-Z][-.a-zA-Z0-9:_]*          # tag name
+  (?:\s*                             # optional whitespace before attribute name
+    (?:[a-zA-Z_][-.:a-zA-Z0-9_]*     # attribute name
+      (?:\s*=\s*                     # value indicator
+        (?:'[^']*'                   # LITA-enclosed value
+          |\"[^\"]*\"                # LIT-enclosed value
+          |[^'\">\s]+                # bare value
+         )
+         (?:\s*,)*                   # possibly followed by a comma
+       )?
+     )
+   )*
+  \s*                                # trailing whitespace
+""", re.VERBOSE)
 endendtag = re.compile('>')
 endtagfind = re.compile('</\s*([a-zA-Z][-.a-zA-Z0-9:_]*)\s*>')
 
@@ -86,9 +105,15 @@ class HTMLParser(_markupbase.ParserBase):
 
     CDATA_CONTENT_ELEMENTS = ("script", "style")
 
+    def __init__(self, strict=True):
+        """Initialize and reset this instance.
 
-    def __init__(self):
-        """Initialize and reset this instance."""
+        If strict is set to True (the default), errors are raised when invalid
+        HTML is encountered.  If set to False, an attempt is instead made to
+        continue parsing, making "best guesses" about the intended meaning, in
+        a fashion similar to what browsers typically do.
+        """
+        self.strict = strict
         self.reset()
 
     def reset(self):
@@ -160,9 +185,18 @@ class HTMLParser(_markupbase.ParserBase):
                 else:
                     break
                 if k < 0:
-                    if end:
+                    if not end:
+                        break
+                    if self.strict:
                         self.error("EOF in middle of construct")
-                    break
+                    k = rawdata.find('>', i + 1)
+                    if k < 0:
+                        k = rawdata.find('<', i + 1)
+                        if k < 0:
+                            k = i + 1
+                    else:
+                        k += 1
+                    self.handle_data(rawdata[i:k])
                 i = self.updatepos(i, k)
             elif startswith("&#", i):
                 match = charref.match(rawdata, i)
@@ -193,7 +227,12 @@ class HTMLParser(_markupbase.ParserBase):
                 if match:
                     # match.group() will contain at least 2 chars
                     if end and match.group() == rawdata[i:]:
-                        self.error("EOF in middle of entity or char ref")
+                        if self.strict:
+                            self.error("EOF in middle of entity or char ref")
+                        else:
+                            if k <= i:
+                                k = n
+                            i = self.updatepos(i, i + 1)
                     # incomplete
                     break
                 elif (i + 1) < n:
@@ -240,7 +279,10 @@ class HTMLParser(_markupbase.ParserBase):
         self.lasttag = tag = rawdata[i+1:k].lower()
 
         while k < endpos:
-            m = attrfind.match(rawdata, k)
+            if self.strict:
+                m = attrfind.match(rawdata, k)
+            else:
+                m = attrfind_tolerant.search(rawdata, k)
             if not m:
                 break
             attrname, rest, attrvalue = m.group(1, 2, 3)
@@ -262,8 +304,11 @@ class HTMLParser(_markupbase.ParserBase):
                          - self.__starttag_text.rfind("\n")
             else:
                 offset = offset + len(self.__starttag_text)
-            self.error("junk characters in start tag: %r"
-                       % (rawdata[k:endpos][:20],))
+            if self.strict:
+                self.error("junk characters in start tag: %r"
+                           % (rawdata[k:endpos][:20],))
+            self.handle_data(rawdata[i:endpos])
+            return endpos
         if end.endswith('/>'):
             # XHTML-style empty tag: <span attr="value" />
             self.handle_startendtag(tag, attrs)
@@ -277,7 +322,10 @@ class HTMLParser(_markupbase.ParserBase):
     # or -1 if incomplete.
     def check_for_whole_start_tag(self, i):
         rawdata = self.rawdata
-        m = locatestarttagend.match(rawdata, i)
+        if self.strict:
+            m = locatestarttagend.match(rawdata, i)
+        else:
+            m = locatestarttagend_tolerant.match(rawdata, i)
         if m:
             j = m.end()
             next = rawdata[j:j+1]
@@ -290,8 +338,13 @@ class HTMLParser(_markupbase.ParserBase):
                     # buffer boundary
                     return -1
                 # else bogus input
-                self.updatepos(i, j + 1)
-                self.error("malformed empty start tag")
+                if self.strict:
+                    self.updatepos(i, j + 1)
+                    self.error("malformed empty start tag")
+                if j > i:
+                    return j
+                else:
+                    return i + 1
             if next == "":
                 # end of input
                 return -1
@@ -300,8 +353,13 @@ class HTMLParser(_markupbase.ParserBase):
                 # end of input in or before attribute value, or we have the
                 # '/' from a '/>' ending
                 return -1
-            self.updatepos(i, j)
-            self.error("malformed start tag")
+            if self.strict:
+                self.updatepos(i, j)
+                self.error("malformed start tag")
+            if j > i:
+                return j
+            else:
+                return i + 1
         raise AssertionError("we should not get here!")
 
     # Internal -- parse endtag, return end or -1 if incomplete
@@ -314,7 +372,15 @@ class HTMLParser(_markupbase.ParserBase):
         j = match.end()
         match = endtagfind.match(rawdata, i) # </ + tag + >
         if not match:
-            self.error("bad end tag: %r" % (rawdata[i:j],))
+            if self.strict:
+                self.error("bad end tag: %r" % (rawdata[i:j],))
+            k = rawdata.find('<', i + 1, j)
+            if k > i:
+                j = k
+            if j <= i:
+                j = i + 1
+            self.handle_data(rawdata[i:j])
+            return j
         tag = match.group(1)
         self.handle_endtag(tag.lower())
         self.clear_cdata_mode()
@@ -358,7 +424,8 @@ class HTMLParser(_markupbase.ParserBase):
         pass
 
     def unknown_decl(self, data):
-        self.error("unknown declaration: %r" % (data,))
+        if self.strict:
+            self.error("unknown declaration: %r" % (data,))
 
     # Internal -- helper to remove special character quoting
     entitydefs = None