follow on updates to new MarkdownParser (#2926)

Author: tballison

tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-text-module/src/main/java/org/apache/tika/parser/markdown/MarkdownParser.java

@@ -97,8 +97,13 @@ public class MarkdownParser extends AbstractEncodingDetectorParser {
     private static final List<Extension> EXTENSIONS =
             List.of(TablesExtension.create(), StrikethroughExtension.create());
 
-    //immutable and thread-safe
-    private static final Parser COMMONMARK = Parser.builder().extensions(EXTENSIONS).build();
+    //immutable and thread-safe.
+    //maxOpenBlockParsers caps block nesting: deeper blocks are parsed as flat paragraph text
+    //rather than nested structure, so a pathologically deep block document still extracts.
+    //Kept below SecureContentHandler's 100-level element-nesting cap so the flattened output
+    //stays under that limit and is emitted rather than rejected as a suspected zip bomb.
+    private static final Parser COMMONMARK =
+            Parser.builder().extensions(EXTENSIONS).maxOpenBlockParsers(64).build();
 
     public MarkdownParser() {
         super();
@@ -123,6 +128,9 @@ public void parse(TikaInputStream tis, ContentHandler handler, Metadata metadata
             metadata.set(Metadata.CONTENT_TYPE, new MediaType(MARKDOWN, charset).toString());
             metadata.set(Metadata.CONTENT_ENCODING, charset.name());
             document = COMMONMARK.parseReader(reader);
+        } catch (StackOverflowError e) {
+            //for reasons
+            throw new TikaException("Markdown is too deeply nested to parse", e);
         }
 
         XHTMLContentHandler xhtml = new XHTMLContentHandler(handler, metadata, context);

tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-text-module/src/test/java/org/apache/tika/parser/markdown/MarkdownParserTest.java

@@ -115,6 +115,14 @@ public void testDataURIsBecomeEmbeddedDocuments() throws Exception {
                 metadataList.get(1).get(TikaCoreProperties.EMBEDDED_RESOURCE_TYPE));
     }
 
+    @Test
+    public void testDeeplyNestedBlocksAreFlattenedNotFailed() throws Exception {
+        //maxOpenBlockParsers caps block nesting below SecureContentHandler's 100-level limit,
+        //so a pathologically deep block document extracts (deeper nesting flattened to text)
+        //rather than being rejected as a suspected zip bomb or overflowing the stack.
+        assertContains("deep", parseString("> ".repeat(5000) + "deep\n").xml);
+    }
+
     @Test
     public void testRoundTripsBackToMarkdown() throws Exception {
         String markdown = "# Title\n\nSome **bold** and *italic* and ~~struck~~ `inline`.\n";