Extract the contents of escaped CDATA sections (#440)#572
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Extract the contents of escaped CDATA sections (#440)#572Labib-Bin-Salam wants to merge 1 commit into
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When a feed XML-escapes a CDATA section -- for example, a <description> whose text content is the literal string '<![CDATA[...]]>' -- the HTML processor handled the marked section with SGMLParser.unknown_decl(), whose default implementation discards it. The character data was therefore dropped and the field was parsed as an empty string. Override unknown_decl() in BaseHTMLProcessor to emit the contents of a CDATA marked section (escaped for the surrounding markup) instead of discarding them. (kurtmckee#440)
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Fixes #440.
The problem
When a feed XML-escapes a CDATA section, feedparser parses the field as an empty string. For example:
>>> feedparser.parse(rss).entries[0].description '' # expected: 'some text'After the document is parsed, the text content of
<description>is the literal string<![CDATA[some text]]>. feedparser treats that content as HTML, so it runs through the SGML-based HTML processor, which recognizes<![CDATA[ ... ]]>as a marked section and hands its body tounknown_decl().BaseHTMLProcessornever overrodeunknown_decl(), so the basesgmllib.SGMLParser.unknown_decl()ran — and its default implementation discards the data. The character data was silently dropped.This has been reported several times against real-world feeds (e.g. the feeds linked in #440).
The fix
Override
unknown_decl()inBaseHTMLProcessorto emit the contents of a CDATA marked section instead of discarding them. The contents of a CDATA section are character data, so the few characters that are special in the surrounding markup (&,<,>) are escaped before being emitted. This keeps a script smuggled inside an escaped CDATA section inert — it is rendered as literal text rather than executed.Real (unescaped) CDATA sections are unaffected: the XML parser strips those before the HTML processor ever sees them.
Tests
tests/wellformed/sgml/escaped_cdata_section.xmlcovering the reported case (runs under both the strict and loose parsers).4307 passed).