Markdown: add minimal support for AST to HTML Includes extension support to walk the AST and produce a table of contents from the contained HeaderNodes. Rendered HTML is blessed as SanitizedContent for Soy to include inside of templates without further escaping. Change-Id: Ib53e091617b39e22a230da9ec8a4aa39c3bf5c26

diff --git a/gitiles-servlet/BUCK b/gitiles-servlet/BUCK
index 9fdacae..9e7a1e8 100644
--- a/gitiles-servlet/BUCK
+++ b/gitiles-servlet/BUCK

@@ -2,10 +2,12 @@
 RSRC = glob(['src/main/resources/**/*'])
 DEPS = [
   '//lib:commons-lang',
+  '//lib:grappa',
   '//lib:gson',
   '//lib:guava',
   '//lib:joda-time',
   '//lib:jsr305',
+  '//lib:pegdown',
   '//lib:prettify',
   '//lib/jgit:jgit',
   '//lib/jgit:jgit-servlet',

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownHelper.java b/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownHelper.java
new file mode 100644
index 0000000..6d67505
--- /dev/null
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownHelper.java

@@ -0,0 +1,53 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gitiles.doc;
+
+import com.google.common.base.Strings;
+
+import org.pegdown.ast.Node;
+import org.pegdown.ast.TextNode;
+
+public class MarkdownHelper {
+  /** Check if anchor URL is like {@code /top.md}. */
+  public static boolean isAbsolutePathToMarkdown(String url) {
+    return url.length() >= 5
+        && url.charAt(0) == '/' && url.charAt(1) != '/'
+        && url.endsWith(".md");
+  }
+
+  /** Combine child nodes as string; this must be escaped for HTML. */
+  public static String getInnerText(Node node) {
+    if (node == null || node.getChildren().isEmpty()) {
+      return null;
+    }
+
+    StringBuilder b = new StringBuilder();
+    appendTextFromChildren(b, node);
+    return Strings.emptyToNull(b.toString().trim());
+  }
+
+  private static void appendTextFromChildren(StringBuilder b, Node node) {
+    for (Node child : node.getChildren()) {
+      if (child instanceof TextNode) {
+        b.append(((TextNode) child).getText());
+      } else {
+        appendTextFromChildren(b, child);
+      }
+    }
+  }
+
+  private MarkdownHelper() {
+  }
+}

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownToHtml.java b/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownToHtml.java
new file mode 100644
index 0000000..bad8ab7
--- /dev/null
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/doc/MarkdownToHtml.java

@@ -0,0 +1,418 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gitiles.doc;
+
+import static com.google.common.base.Preconditions.checkState;
+import static com.google.gitiles.doc.MarkdownHelper.getInnerText;
+
+import com.google.gitiles.doc.html.HtmlBuilder;
+import com.google.template.soy.data.SanitizedContent;
+import com.google.template.soy.shared.restricted.EscapingConventions;
+
+import org.pegdown.ast.AbbreviationNode;
+import org.pegdown.ast.AutoLinkNode;
+import org.pegdown.ast.BlockQuoteNode;
+import org.pegdown.ast.BulletListNode;
+import org.pegdown.ast.CodeNode;
+import org.pegdown.ast.DefinitionListNode;
+import org.pegdown.ast.DefinitionNode;
+import org.pegdown.ast.DefinitionTermNode;
+import org.pegdown.ast.ExpImageNode;
+import org.pegdown.ast.ExpLinkNode;
+import org.pegdown.ast.HeaderNode;
+import org.pegdown.ast.HtmlBlockNode;
+import org.pegdown.ast.InlineHtmlNode;
+import org.pegdown.ast.ListItemNode;
+import org.pegdown.ast.MailLinkNode;
+import org.pegdown.ast.Node;
+import org.pegdown.ast.OrderedListNode;
+import org.pegdown.ast.ParaNode;
+import org.pegdown.ast.QuotedNode;
+import org.pegdown.ast.RefImageNode;
+import org.pegdown.ast.RefLinkNode;
+import org.pegdown.ast.ReferenceNode;
+import org.pegdown.ast.RootNode;
+import org.pegdown.ast.SimpleNode;
+import org.pegdown.ast.SpecialTextNode;
+import org.pegdown.ast.StrikeNode;
+import org.pegdown.ast.StrongEmphSuperNode;
+import org.pegdown.ast.SuperNode;
+import org.pegdown.ast.TableBodyNode;
+import org.pegdown.ast.TableCaptionNode;
+import org.pegdown.ast.TableCellNode;
+import org.pegdown.ast.TableColumnNode;
+import org.pegdown.ast.TableHeaderNode;
+import org.pegdown.ast.TableNode;
+import org.pegdown.ast.TableRowNode;
+import org.pegdown.ast.TextNode;
+import org.pegdown.ast.VerbatimNode;
+import org.pegdown.ast.WikiLinkNode;
+
+/**
+ * Formats parsed markdown AST into HTML.
+ * <p>
+ * Callers must create a new instance for each RootNode.
+ */
+public class MarkdownToHtml implements Visitor {
+  private final ReferenceMap references = new ReferenceMap();
+  private final HtmlBuilder html = new HtmlBuilder();
+  private final TocFormatter toc = new TocFormatter(html, 3);
+  private TableState table;
+
+  /** Render the document AST to sanitized HTML. */
+  public SanitizedContent toSoyHtml(RootNode node) {
+    if (node == null) {
+      return null;
+    }
+
+    toc.setRoot(node);
+    node.accept(this);
+    return html.toSoy();
+  }
+
+  @Override
+  public void visit(RootNode node) {
+    references.add(node);
+    visitChildren(node);
+  }
+
+  @Override
+  public void visit(TocNode node) {
+    toc.format();
+  }
+
+  @Override
+  public void visit(HeaderNode node) {
+    String tag = "h" + node.getLevel();
+    html.open(tag);
+    if (toc.include(node)) {
+      html.attribute("id", toc.idFromHeader(node));
+    }
+    visitChildren(node);
+    html.close(tag);
+  }
+
+  @Override
+  public void visit(ParaNode node) {
+    wrapChildren("p", node);
+  }
+
+  @Override
+  public void visit(BlockQuoteNode node) {
+    wrapChildren("blockquote", node);
+  }
+
+  @Override
+  public void visit(OrderedListNode node) {
+    wrapChildren("ol", node);
+  }
+
+  @Override
+  public void visit(BulletListNode node) {
+    wrapChildren("ul", node);
+  }
+
+  @Override
+  public void visit(ListItemNode node) {
+    wrapChildren("li", node);
+  }
+
+  @Override
+  public void visit(DefinitionListNode node) {
+    wrapChildren("dl", node);
+  }
+
+  @Override
+  public void visit(DefinitionNode node) {
+    wrapChildren("dd", node);
+  }
+
+  @Override
+  public void visit(DefinitionTermNode node) {
+    wrapChildren("dt", node);
+  }
+
+  @Override
+  public void visit(VerbatimNode node) {
+    html.open("pre").attribute("class", "code");
+    String text = node.getText();
+    while (text.startsWith("\n")) {
+      html.open("br");
+      text = text.substring(1);
+    }
+    html.appendAndEscape(text);
+    html.close("pre");
+  }
+
+  @Override
+  public void visit(CodeNode node) {
+    wrapText("code", node);
+  }
+
+  @Override
+  public void visit(StrikeNode node) {
+    wrapChildren("del", node);
+  }
+
+  @Override
+  public void visit(StrongEmphSuperNode node) {
+    if (node.isClosed()) {
+      wrapChildren(node.isStrong() ? "strong" : "em", node);
+    } else {
+      // Unclosed (or unmatched) sequence is plain text.
+      html.appendAndEscape(node.getChars());
+      visitChildren(node);
+    }
+  }
+
+  @Override
+  public void visit(AutoLinkNode node) {
+    String url = node.getText();
+    html.open("a").attribute("href", url)
+        .appendAndEscape(url)
+        .close("a");
+  }
+
+  @Override
+  public void visit(MailLinkNode node) {
+    String addr = node.getText();
+    html.open("a").attribute("href", "mailto:" + addr)
+        .appendAndEscape(addr)
+        .close("a");
+  }
+
+  @Override
+  public void visit(WikiLinkNode node) {
+    String text = node.getText();
+    String path = text.replace(' ', '-') + ".md";
+    html.open("a").attribute("href", path)
+        .appendAndEscape(text)
+        .close("a");
+  }
+
+  @Override
+  public void visit(ExpLinkNode node) {
+    html.open("a")
+        .attribute("href", node.url)
+        .attribute("title", node.title);
+    visitChildren(node);
+    html.close("a");
+  }
+
+  @Override
+  public void visit(RefLinkNode node) {
+    ReferenceNode ref = references.get(node.referenceKey, getInnerText(node));
+    if (ref != null) {
+      html.open("a")
+          .attribute("href", ref.getUrl())
+          .attribute("title", ref.getTitle());
+      visitChildren(node);
+      html.close("a");
+    } else {
+      // Treat a broken RefLink as plain text.
+      visitChildren(node);
+    }
+  }
+
+  @Override
+  public void visit(ExpImageNode node) {
+    html.open("img")
+        .attribute("src", node.url)
+        .attribute("title", node.title)
+        .attribute("alt", getInnerText(node));
+  }
+
+  @Override
+  public void visit(RefImageNode node) {
+    String alt = getInnerText(node);
+    String url, title = alt;
+    ReferenceNode ref = references.get(node.referenceKey, alt);
+    if (ref != null) {
+      url = ref.getUrl();
+      title = ref.getTitle();
+    } else {
+      // If reference is missing, insert a broken image.
+      url = EscapingConventions.FilterImageDataUri.INSTANCE.getInnocuousOutput();
+    }
+    html.open("img")
+        .attribute("src", url)
+        .attribute("title", title)
+        .attribute("alt", alt);
+  }
+
+  @Override
+  public void visit(TableNode node) {
+    table = new TableState(node);
+    wrapChildren("table", node);
+    table = null;
+  }
+
+  private void mustBeInsideTable(Node node) {
+    checkState(table != null, "%s must be in table", node);
+  }
+
+  @Override
+  public void visit(TableHeaderNode node) {
+    mustBeInsideTable(node);
+    table.inHeader = true;
+    wrapChildren("thead", node);
+    table.inHeader = false;
+  }
+
+  @Override
+  public void visit(TableBodyNode node) {
+    wrapChildren("tbody", node);
+  }
+
+  @Override
+  public void visit(TableCaptionNode node) {
+    wrapChildren("caption", node);
+  }
+
+  @Override
+  public void visit(TableRowNode node) {
+    mustBeInsideTable(node);
+    table.startRow();
+    wrapChildren("tr", node);
+  }
+
+  @Override
+  public void visit(TableCellNode node) {
+    mustBeInsideTable(node);
+    String tag = table.inHeader ? "th" : "td";
+    html.open(tag)
+        .attribute("align", table.getAlign());
+    if (node.getColSpan() > 1) {
+      html.attribute("colspan", Integer.toString(node.getColSpan()));
+    }
+    visitChildren(node);
+    html.close(tag);
+    table.done(node);
+  }
+
+  @Override
+  public void visit(TableColumnNode node) {
+    // Not for output; should not be in the Visitor API.
+  }
+
+  @Override
+  public void visit(TextNode node) {
+    html.appendAndEscape(node.getText());
+    // TODO(sop) printWithAbbreviations
+  }
+
+  @Override
+  public void visit(SpecialTextNode node) {
+    html.appendAndEscape(node.getText());
+  }
+
+  @Override
+  public void visit(QuotedNode node) {
+    switch (node.getType()) {
+      case DoubleAngle:
+        html.entity("&laquo;");
+        visitChildren(node);
+        html.entity("&raquo;");
+        break;
+      case Double:
+        html.entity("&ldquo;");
+        visitChildren(node);
+        html.entity("&rdquo;");
+        break;
+      case Single:
+        html.entity("&lsquo;");
+        visitChildren(node);
+        html.entity("&rsquo;");
+        break;
+      default:
+        checkState(false, "unsupported quote %s", node.getType());
+    }
+  }
+
+  @Override
+  public void visit(SimpleNode node) {
+    switch (node.getType()) {
+      case Apostrophe:
+        html.entity("&rsquo;");
+        break;
+      case Ellipsis:
+        html.entity("&hellip;");
+        break;
+      case Emdash:
+        html.entity("&mdash;");
+        break;
+      case Endash:
+        html.entity("&ndash;");
+        break;
+      case HRule:
+        html.open("hr");
+        break;
+      case Linebreak:
+        html.open("br");
+        break;
+      case Nbsp:
+        html.entity("&nbsp;");
+        break;
+      default:
+        checkState(false, "unsupported node %s", node.getType());
+    }
+  }
+
+  @Override
+  public void visit(SuperNode node) {
+    visitChildren(node);
+  }
+
+  @Override
+  public void visit(Node node) {
+    checkState(false, "node %s unsupported", node.getClass());
+  }
+
+  @Override
+  public void visit(HtmlBlockNode node) {
+    // Drop all HTML nodes.
+  }
+
+  @Override
+  public void visit(InlineHtmlNode node) {
+    // Drop all HTML nodes.
+  }
+
+  @Override
+  public void visit(ReferenceNode node) {
+    // Reference nodes are not printed; they only declare an item.
+  }
+
+  @Override
+  public void visit(AbbreviationNode node) {
+    // Abbreviation nodes are not printed; they only declare an item.
+  }
+
+  private void wrapText(String tag, TextNode node) {
+    html.open(tag).appendAndEscape(node.getText()).close(tag);
+  }
+
+  private void wrapChildren(String tag, SuperNode node) {
+    html.open(tag);
+    visitChildren(node);
+    html.close(tag);
+  }
+
+  private void visitChildren(Node node) {
+    for (Node child : node.getChildren()) {
+      child.accept(this);
+    }
+  }
+}

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/doc/ReferenceMap.java b/gitiles-servlet/src/main/java/com/google/gitiles/doc/ReferenceMap.java
new file mode 100644
index 0000000..65fe86e
--- /dev/null
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/doc/ReferenceMap.java

@@ -0,0 +1,61 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gitiles.doc;
+
+import static com.google.gitiles.doc.MarkdownHelper.getInnerText;
+
+import org.pegdown.ast.ReferenceNode;
+import org.pegdown.ast.RootNode;
+import org.pegdown.ast.SuperNode;
+
+import java.util.HashMap;
+import java.util.Map;
+
+class ReferenceMap {
+  private final Map<String, ReferenceNode> references = new HashMap<>();
+
+  void add(RootNode node) {
+    for (ReferenceNode ref : node.getReferences()) {
+      String id = getInnerText(ref);
+      references.put(key(id), ref);
+    }
+  }
+
+  ReferenceNode get(SuperNode keyNode, String text) {
+    String id = keyNode != null ? getInnerText(keyNode) : text;
+    return references.get(key(id));
+  }
+
+  private static String key(String in) {
+    // Strip whitespace and normalize to lower case. Pegdown's default
+    // HTML formatter also applies this type of normalization to make
+    // it easier for document authors to reference links. Links should
+    // be case insensitive to allow for easier formatting of title case
+    // in prose vs. in the reference table, especially if a link is used
+    // both at the start of a sentence and later in the middle of sentence.
+    //
+    // Whitespace stripping is also performed by pegdown's default code.
+    // This allows references to to be declared as "foobar" but prose to
+    // mention it as "Foo Bar".
+    StringBuilder r = new StringBuilder(in.length());
+    for (int i = 0; i < in.length(); i++) {
+      char c = in.charAt(i);
+      if (!Character.isWhitespace(c)) {
+        r.append(Character.toLowerCase(c));
+      }
+    }
+    return r.toString();
+  }
+}

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/doc/TableState.java b/gitiles-servlet/src/main/java/com/google/gitiles/doc/TableState.java
new file mode 100644
index 0000000..80276d2
--- /dev/null
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/doc/TableState.java

@@ -0,0 +1,59 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gitiles.doc;
+
+import org.pegdown.ast.TableCellNode;
+import org.pegdown.ast.TableColumnNode;
+import org.pegdown.ast.TableNode;
+
+import java.util.List;
+
+class TableState {
+  private final List<TableColumnNode> columns;
+
+  boolean inHeader;
+  int column;
+
+  TableState(TableNode node) {
+    columns = node.getColumns();
+  }
+
+  void startRow() {
+    column = 0;
+  }
+
+  String getAlign() {
+    int pos = Math.min(column, columns.size() - 1);
+    TableColumnNode c = columns.get(pos);
+    switch (c.getAlignment()) {
+      case None:
+        return null;
+      case Left:
+        return "left";
+      case Right:
+        return "right";
+      case Center:
+        return "center";
+      default:
+        throw new IllegalStateException(String.format(
+            "unsupported alignment %s on column %d",
+            c.getAlignment(), pos));
+    }
+  }
+
+  void done(TableCellNode cell) {
+    column += cell.getColSpan();
+  }
+}
\ No newline at end of file

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/doc/TocFormatter.java b/gitiles-servlet/src/main/java/com/google/gitiles/doc/TocFormatter.java
new file mode 100644
index 0000000..5dcfc77
--- /dev/null
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/doc/TocFormatter.java

@@ -0,0 +1,170 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gitiles.doc;
+
+import com.google.gitiles.doc.html.HtmlBuilder;
+
+import org.apache.commons.lang3.StringUtils;
+import org.pegdown.ast.HeaderNode;
+import org.pegdown.ast.Node;
+import org.pegdown.ast.RootNode;
+
+/** Outputs outline from HeaderNodes in the AST. */
+class TocFormatter {
+  private final HtmlBuilder html;
+  private final int maxLevel;
+
+  private RootNode root;
+  private Boolean hasToc;
+  private int countH1;
+
+  private int level;
+
+  TocFormatter(HtmlBuilder html, int maxLevel) {
+    this.html = html;
+    this.maxLevel = maxLevel;
+  }
+
+  void setRoot(RootNode doc) {
+    root = doc;
+    hasToc = null;
+  }
+
+  boolean include(HeaderNode h) {
+    init();
+    if (!hasToc) {
+      return false;
+    } else if (h.getLevel() == 1) {
+      return countH1 > 1;
+    }
+    return h.getLevel() <= maxLevel;
+  }
+
+  String idFromHeader(HeaderNode header) {
+    String t = MarkdownHelper.getInnerText(header);
+    return t != null ? idFromTitle(t) : null;
+  }
+
+  void format() {
+    init();
+
+    int startLevel = countH1 > 1 ? 1 : 2;
+    hasToc = true;
+    level = startLevel;
+
+    html.open("div")
+        .attribute("class", "toc")
+        .attribute("role", "navigation")
+      .open("h2").appendAndEscape("Contents").close("h2")
+      .open("div").attribute("class", "toc-aux")
+      .open("ul");
+    outline(root);
+    while (level >= startLevel) {
+      html.close("ul");
+      level--;
+    }
+    html.close("div").close("div");
+  }
+
+  private void outline(Node node) {
+    if (node instanceof HeaderNode) {
+      outline((HeaderNode) node);
+    } else {
+      for (Node child : node.getChildren()) {
+        outline(child);
+      }
+    }
+  }
+
+  private void outline(HeaderNode h) {
+    if (!include(h)) {
+      return;
+    }
+
+    String title = MarkdownHelper.getInnerText(h);
+    if (title == null) {
+      return;
+    }
+
+    while (level > h.getLevel()) {
+      html.close("ul");
+      level--;
+    }
+    while (level < h.getLevel()) {
+      html.open("ul");
+      level++;
+    }
+
+    html.open("li")
+      .open("a").attribute("href", "#" + idFromTitle(title))
+      .appendAndEscape(title)
+      .close("a")
+      .close("li");
+  }
+
+  private static String idFromTitle(String title) {
+    StringBuilder b = new StringBuilder(title.length());
+    for (char c : StringUtils.stripAccents(title).toCharArray()) {
+      if (('a' <= c && c <= 'z')
+          || ('A' <= c && c <= 'Z')
+          || ('0' <= c && c <= '9')) {
+        b.append(c);
+      } else if (c == ' ') {
+        if (b.length() > 0
+            && b.charAt(b.length() - 1) != '-'
+            && b.charAt(b.length() - 1) != '_') {
+          b.append('-');
+        }
+      } else if (b.length() > 0
+          && b.charAt(b.length() - 1) != '-'
+          && b.charAt(b.length() - 1) != '_') {
+        b.append('_');
+      }
+    }
+    while (b.length() > 0) {
+      char c = b.charAt(b.length() - 1);
+      if (c == '-' || c == '_') {
+        b.setLength(b.length() - 1);
+        continue;
+      }
+      break;
+    }
+    return b.toString();
+  }
+
+  private void init() {
+    if (hasToc == null) {
+      hasToc = false;
+      init(root);
+    }
+  }
+
+  private void init(Node node) {
+    if (node instanceof TocNode) {
+      hasToc = true;
+      return;
+    } else if (node instanceof HeaderNode
+        && ((HeaderNode) node).getLevel() == 1) {
+      countH1++;
+      return;
+    }
+    for (Node child : node.getChildren()) {
+      init(child);
+      if (hasToc && countH1 > 1) {
+        break;
+      }
+    }
+  }
+}

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/doc/TocNode.java b/gitiles-servlet/src/main/java/com/google/gitiles/doc/TocNode.java
new file mode 100644
index 0000000..33dd31c
--- /dev/null
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/doc/TocNode.java

@@ -0,0 +1,34 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gitiles.doc;
+
+import org.pegdown.ast.AbstractNode;
+import org.pegdown.ast.Node;
+
+import java.util.Collections;
+import java.util.List;
+
+/** Block node {@code [TOC]} to display table of contents. */
+public class TocNode extends AbstractNode {
+  @Override
+  public void accept(org.pegdown.ast.Visitor visitor) {
+    ((Visitor) visitor).visit(this);
+  }
+
+  @Override
+  public List<Node> getChildren() {
+    return Collections.emptyList();
+  }
+}

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/doc/Visitor.java b/gitiles-servlet/src/main/java/com/google/gitiles/doc/Visitor.java
new file mode 100644
index 0000000..b8cf64e
--- /dev/null
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/doc/Visitor.java

@@ -0,0 +1,19 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gitiles.doc;
+
+public interface Visitor extends org.pegdown.ast.Visitor {
+  void visit(TocNode node);
+}