flexmark-java

flexmark-java is a Java implementation of CommonMark (spec 0.28) parser using theblocks first, inlines after Markdown parsing architecture.

Its strengths are speed, flexibility, Markdown source element based AST with details of thesource position down to individual characters of lexemes that make up the element andextensibility.

The API allows granular control of the parsing process and is optimized for parsing with a largenumber of installed extensions. The parser and extensions come with plenty of options for parserbehavior and HTML rendering variations. The end goal is to have the parser and renderer be ableto mimic other parsers with great degree of accuracy. This is now partially complete with theimplementation of Markdown Processor Emulation

Motivation for this project was the need to replace pegdown parser in my Markdown Navigatorplugin for JetBrains IDEs. pegdown has a great feature set but its speed in general is lessthan ideal and for pathological input either hangs or practically hangs during parsing.

⚠️ Version 0.60.0 has breaking changes due to re-organization, renaming, clean up andoptimization of implementation classes. Changes are detailed inVersion-0.60.0-Changes.

master

latest

ℹ️ Thanks to Alex Karezin for setting upFlexmark Architecture and Dependencies Diagrams andhttps://sourcespy.com. You can now get an overview of module dependencies with ability todrill down to packages and classes, updated from the repository sources. ��

Requirements

• Java 8 or above, Java 9+ compatible

• Android compatibility to be added

• The project is on Maven: com.vladsch.flexmark

• The core has no dependencies other than org.jetbrains:annotations:15.0. For extensions, seeextension description below.

  The API is still evolving to accommodate new extensions and functionality.

Quick Start

For Maven, add flexmark-all as a dependency which includes core and all modules to thefollowing sample:

<dependency>
    <groupId>com.vladsch.flexmark</groupId>
    <artifactId>flexmark-all</artifactId>
    <version>0.62.2</version>
</dependency>

Source:BasicSample.java

package com.vladsch.flexmark.samples;

import com.vladsch.flexmark.util.ast.Node;
import com.vladsch.flexmark.html.HtmlRenderer;
import com.vladsch.flexmark.parser.Parser;
import com.vladsch.flexmark.util.data.MutableDataSet;

public class BasicSample {
    public static void main(String[] args) {
        MutableDataSet options = new MutableDataSet();

        // uncomment to set optional extensions
        //options.set(Parser.EXTENSIONS, Arrays.asList(TablesExtension.create(), StrikethroughExtension.create()));

        // uncomment to convert soft-breaks to hard breaks
        //options.set(HtmlRenderer.SOFT_BREAK, "<br />\n");

        Parser parser = Parser.builder(options).build();
        HtmlRenderer renderer = HtmlRenderer.builder(options).build();

        // You can re-use parser and renderer instances
        Node document = parser.parse("This is *Sparta*");
        String html = renderer.render(document);  // "<p>This is <em>Sparta</em></p>\n"
        System.out.println(html);
    }
}

Building via Gradle

compile 'com.vladsch.flexmark:flexmark-all:0.62.2'

Building with Android Studio

Additional settings due to duplicate files:

packagingOptions {
    exclude 'META-INF/LICENSE-LGPL-2.1.txt'
    exclude 'META-INF/LICENSE-LGPL-3.txt'
    exclude 'META-INF/LICENSE-W3C-TEST'
    exclude 'META-INF/DEPENDENCIES'
}

More information can be found in the documentation:
Wiki Home     Usage Examples    Extension Details    Writing Extensions

Pegdown Migration Helper

PegdownOptionsAdapter class converts pegdown Extensions.* flags to flexmark options andextensions list. Pegdown Extensions.java is included for convenience and new options not foundin pegdown 1.6.0. These are located in flexmark-profile-pegdown module but you can grab thesource from this repo: PegdownOptionsAdapter.java, Extensions.java and make your ownversion, modified to your project's needs.

You can pass your extension flags to static PegdownOptionsAdapter.flexmarkOptions(int) or youcan instantiate PegdownOptionsAdapter and use convenience methods to set, add and removeextension flags. PegdownOptionsAdapter.getFlexmarkOptions() will return a fresh copy ofDataHolder every time with the options reflecting pegdown extension flags.

import com.vladsch.flexmark.html.HtmlRenderer;
import com.vladsch.flexmark.parser.Parser;
import com.vladsch.flexmark.profile.pegdown.Extensions;
import com.vladsch.flexmark.profile.pegdown.PegdownOptionsAdapter;
import com.vladsch.flexmark.util.data.DataHolder;

public class PegdownOptions {
     final private static DataHolder OPTIONS = PegdownOptionsAdapter.flexmarkOptions(
            Extensions.ALL
    );

    static final Parser PARSER = Parser.builder(OPTIONS).build();
    static final HtmlRenderer RENDERER = HtmlRenderer.builder(OPTIONS).build();

    // use the PARSER to parse and RENDERER to render with pegdown compatibility
}

Default flexmark-java pegdown emulation uses less strict HTML block parsing which interrupts anHTML block on a blank line. Pegdown only interrupts an HTML block on a blank line if all tags inthe HTML block are closed.

To get closer to original pegdown HTML block parsing behavior use the method which takes aboolean strictHtml argument:

import com.vladsch.flexmark.html.HtmlRenderer;
import com.vladsch.flexmark.parser.Parser;
import com.vladsch.flexmark.profile.pegdown.Extensions;
import com.vladsch.flexmark.profile.pegdown.PegdownOptionsAdapter;
import com.vladsch.flexmark.util.data.DataHolder;

public class PegdownOptions {
     final private static DataHolder OPTIONS = PegdownOptionsAdapter.flexmarkOptions(true,
            Extensions.ALL
    );

    static final Parser PARSER = Parser.builder(OPTIONS).build();
    static final HtmlRenderer RENDERER = HtmlRenderer.builder(OPTIONS).build();

    // use the PARSER to parse and RENDERER to render with pegdown compatibility
}

A sample with acustom link resolveris also available, which includes link resolver for changing URLs or attributes of links and acustom node renderer if you need to override the generated link HTML.

ℹ️ flexmark-java has many more extensions and configuration options thanpegdown in addition to extensions available in pegdown 1.6.0.Available Extensions via PegdownOptionsAdapter

Latest Additions and Changes

• Major reorganization and code cleanup of implementation in version 0.60.0, seeVersion-0.60.0-Changes

• Flexmark Architecture and Dependencies Diagramsthanks to great work by Alex Karezin you can get an overviewof module dependencies with ability to drill down to packages and classes.

• Merge API to merge multiple markdown documents into a singledocument.

• Docx Renderer Extension: Limited Attributes Node Handling

• Extensible HTML to Markdown Converter module:flexmark-html2md-converter.Sample: HtmlToMarkdownCustomizedSample.java

• Java9+ module compatibility

• Compound Enumerated ReferencesEnumerated References Extension for creatinglegal numbering for elements and headings.

• Macros Extension to allow arbitrary markdown content to beinserted as block or inline elements, allowing block elements to be used where only inlineelements are allowed by syntax.

• Extensions: Gitlab Flavoured Markdown forparsing and rendering GitLab markdown extensions.

• OSGi module courtesy Dan Klco (GitHub @klcodanr)

• Extensions: Media Tags Media link transformer extensioncourtesy Cornelia Schultz (GitHub @CorneliaXaos) transformslinks using custom prefixes to Audio, Embed, Picture, and Video HTML5 tags.

• Translation Helper API to make translating markdowndocuments easier.

• Admonition Extension Tocreate block-styled side content. For complete documentation please see theAdmonition Extension, Material for MkDocs documentation.

• Enumerated Referenceto create enumerated references for figures, tables and other markdown elements.

• Attributes Extension toparse attributes of the form {name name=value name='value' name="value" #id .class-name}attributes.

• YouTube Embedded Link Transformerthanks to Vyacheslav N. Boyko (GitHub @bvn13) transforms simple links to youtube videos toembedded video iframe HTML.

• Docx Converter Moduleusing the docx4j library. How to use: DocxConverter Sample, how to customize:Customizing Docx Rendering

  Development of this module was sponsored byJohner Institut GmbH.

• Update library to be CommonMark (spec 0.28) compliant and addParserEmulationProfile.COMMONMARK_0_27 and ParserEmulationProfile.COMMONMARK_0_28 to allowselecting a specific spec version options.

• Custom node rendering API with ability to invoke standard rendering for an overridden node,allowing custom node renders that only handle special cases and let the rest be rendered asusual.PegdownCustomLinkResolverOptions

• Gfm Issues andGfm Users extensions forparsing and rendering #123 and @user-name respectively.

• Deep HTML block parsing option for better handling of raw text tags that come after other tagsand for pegdown HTML block parsing compatibility.

• flexmark-all module that includes: core, all extensions, formatter, JIRA and YouTrackconverters, pegdown profile module and HTML to Markdown conversion.

• PDF converter moduleUsage: PDF Output usingOpen HTML To PDF

• Typographic Extension Moduleimplemented

• XWiki Macros Extension Module

• Jekyll tags Extension Module

• HTML to Markdown Converter Module

• Maven Markdown Page Generator Plugin

• Markdown Formatter module tooutput AST as markdown with formatting options.

• Table Extension forMarkdown Formatter withcolumn width and alignment of markdown tables:

  Input	Output
  day|time|spent :---|:---:|--: nov. 2. tue|10:00|4h 40m nov. 3. thu|11:00|4h nov. 7. mon|10:20|4h 20m total:|| 13h	| day | time | spent | |:------------|:-----:|--------:| | nov. 2. tue | 10:00 | 4h 40m | | nov. 3. thu | 11:00 | 4h | | nov. 7. mon | 10:20 | 4h 20m | | total: || 13h |

Releases, Bug Fixes, Enhancements and Support

I use flexmark-java as the parser for Markdown Navigator plugin for JetBrains IDEs. I tend touse the latest, unreleased version to fix bugs or get improvements. So if you find a bug that isa show stopper for your project or see a bug in github issues page marked fixed for next release that is affecting your project then please let me know and I may be able to promptlymake a new release to address your issue. Otherwise, I will let bug fixes and enhancementsaccumulate thinking no one is affected by what is already fixed.

Extension points in the API are many and numerous

There are many extension options in the API with their intended use. A good soft-start is theflexmark-java-samplesmodule which has simple samples for asked for extensions. The next best place is the source ofan existing extension that has similar syntax to what you want to add.

If your extension lines up with the right API, the task is usually very short and sweet. If yourextension uses the API in an unintended fashion or does not follow expected housekeepingprotocols, you may find it an uphill battle with a rat's nest of if/else condition handling andfixing one bug only leading to creating another one.

Generally, if it takes more than a few dozen lines to add a simple extension, then either youare going about it wrong or the API is missing an extension point. If you look at all theimplemented extensions you will see that most are a few lines of code other than boiler platedictated by the API. That is the goal for this library: provide an extensible core that makeswriting extensions a breeze.

The larger extensions are flexmark-ext-tables and flexmark-ext-spec-example, the meat ofboth is around 200 lines of code. You can use them as a guide post for size estimating yourextension.

My own experience adding extensions shows that sometimes a new type of extension is bestaddressed with an API enhancement to make its implementation seamless, or by fixing a bug thatwas not visible before the extension stressed the API in just the right way. Your intendedextension may just be the one requiring such an approach.

Don't hesitate to open an issue if you can't find the answer

The takeaway is: if you want to implement an extension or a feature please don't hesitate toopen an issue and I will give you pointers on the best way to go about it. It may save you a lotof time by letting me improve the API to address your extension's needs before you put a lot offruitless effort into it.

I do ask that you realize that I am chief cook and bottle washer on this project, without aniota of Vulcan Mind Melding skills. I do ask that you describe what you want to implementbecause I can't read your mind. Please do some reconnaissance background work around the sourcecode and documentation because I cannot transfer what I know to you, without your willingeffort.

Consulting is available

If you have a commercial application and don't want to write the extension(s) yourself or wantto reduce the time and effort of implementing extensions and integrating flexmark-java, feelfree to contact me. I am available on a consulting/contracting basis, All about me.

Markdown Processor Emulation

Despite its name, commonmark is neither a superset nor a subset of other markdown flavors.Rather, it proposes a standard, unambiguous syntax specification for the original, "core"Markdown, thus effectively introducing yet another flavor. While flexmark is by defaultcommonmark compliant, its parser can be tweaked in various ways. The sets of tweaks required toemulate the most commonly used markdown parsers around are available in flexmark asParserEmulationProfiles.

As the name ParserEmulationProfile implies, it's only the parser that is adjusted to thespecific markdown flavor. Applying the profile does not add features beyond those available incommonmark. If you want to use flexmark to fully emulate another markdown processor's behavior,you have to adjust the parser and configure the flexmark extensions that provide the additionalfeatures available in the parser that you want to emulate.

A rewrite of the list parser to better control emulation of other markdown processors as perMarkdown Processors Emulation is complete. Addition ofprocessor presets to emulate specific markdown processing behaviour of these parsers is on ashort to do list.

Some emulation families do a better better job of emulating their target than others. Most ofthe effort was directed at emulating how these processors parse standard Markdown and listrelated parsing specifically. For processors that extend original Markdown, you will need to addthose extensions that are already implemented in flexmark-java to the Parser/Renderer builderoptions.

Extensions will be modified to include their own presets for specific processor emulation, ifthat processor has an equivalent extension implemented.

If you find a discrepancy please open an issue so it can be addressed.

Major processor families are implemented and some family members also:

• Jekyll
• CommonMark for latest implemented spec, currently CommonMark (spec 0.28)
  • League/CommonMark
  • CommonMark (spec 0.27) for specific version compatibility
  • CommonMark (spec 0.28) for specific version compatibility
  • GitHub Comments
• Markdown.pl
  • Php Markdown Extra
  • GitHub Docs (old GitHub markdown parser)
• Kramdown
• FixedIndent
  • MultiMarkdown
  • Pegdown

ℹ️ profiles to encapsulate configuration details for variants within thefamily were added in 0.11.0:

• CommonMark (default for family): ParserEmulationProfile.COMMONMARK
• FixedIndent (default for family): ParserEmulationProfile.FIXED_INDENT
• GitHub Comments (just CommonMark): ParserEmulationProfile.COMMONMARK
• Old GitHub Docs: ParserEmulationProfile.GITHUB_DOC
• Kramdown (default for family): ParserEmulationProfile.KRAMDOWN
• Markdown.pl (default for family): ParserEmulationProfile.MARKDOWN
• MultiMarkdown: ParserEmulationProfile.MULTI_MARKDOWN
• Pegdown, with pegdown extensions use PegdownOptionsAdapter in flexmark-profile-pegdown
• Pegdown, without pegdown extensions ParserEmulationProfile.PEGDOWN
• Pegdown HTML block parsing rules, without pegdown extensionsParserEmulationProfile.PEGDOWN_STRICT

History and Motivation

flexmark-java is a fork of commonmark-java project, modified to generate an AST whichreflects all the elements in the original source, full source position tracking for all elementsin the AST and easier JetBrains Open API PsiTree generation.

The API was changed to allow more granular control of the parsing process and optimized forparsing with a large number of installed extensions. The parser and extensions come with manytweaking options for parser behavior and HTML rendering variations. The end goal is to have theparser and renderer be able to mimic other parsers with great degree of accuracy.

Motivation for this was the need to replace pegdown parser in Markdown Navigator plugin.pegdown has a great feature set but its speed in general is less than ideal and forpathological input either hangs or practically hangs during parsing.

commonmark-java has an excellent parsing architecture that is easy to understand and extend.The goal was to ensure that adding source position tracking in the AST would not change the easeof parsing and generating the AST more than absolutely necessary.

Reasons for choosing commonmark-java as the parser are: speed, ease of understanding, ease ofextending and speed. More detailed description inPegdown - Achilles heel of the Markdown Navigator plugin. Now that I have reworked the coreand added a few extensions I am extremely satisfied with my choice.

Another goal was to improve the ability of extensions to modify parser behavior so that anydialect of markdown could be implemented through the extension mechanism. An extensible optionsAPI was added to allow setting of all options in one place. Parser, renderer and extensions usethese options for configuration, including disabling some core block parsers.

This is a work in progress with many API changes. No attempt is made to keep backward APIcompatibility to the original project and until the feature set is mostly complete, not even toearlier versions of this project.

Feature Comparison

(1)

flexmark-java pathological input of 100,000 [ parses in 68ms, 100,000 ] in 57ms, 100,000nested [ ] parse in 55ms

(2)

commonmark-java pathological input of 100,000 [ parses in 30ms, 100,000 ] in 30ms, 100,000nested [ ] parse in 43ms

(3)

pegdown pathological input of 17 [ parses in 650ms, 18 [ in 1300ms

Progress

• Parser options, items marked as a task item are to be implemented the rest are complete:
  • Typographic
    • Quotes
    • Smarts
  • GitHub Extensions
    • Fenced code blocks
    • Anchor links for headers with auto id generation
    • Table Spans option to be implemented for tables extension
    • Wiki Links with GitHub and Creole syntax
    • Emoji Shortcuts with use GitHub emoji URL option
  • GitHub Syntax
    • Strikethrough
    • Task Lists
    • No Atx Header Space
    • No Header indents
    • Hard Wraps (achieved with SOFT_BREAK option changed to "<br />")
    • Relaxed HR Rules Option
    • Wiki links
  • Publishing
    • Abbreviations
    • Footnotes
    • Definitions
    • Table of Contents
  • Suppress
    • inline HTML: all, non-comments, comments
    • HTML blocks: all, non-comments, comments
  • Processor Extensions
    • Jekyll front matter
    • Jekyll tag elements, with support for {% include file %},Include Markdown and HTML File Content
    • GitBook link URL encoding. Not applicable
    • HTML comment nodes: Block and Inline
    • Multi-line Image URLs
    • Spec Example Element
  • Commonmark Syntax suppression
    • Manual loose lists
    • Numbered lists always start with 1.
    • Fixed list item indent, items must be indented by at least 4 spaces
    • Relaxed list start option, allow lists to start when not preceded by a blank line.

I am very pleased with the decision to switch to commonmark-java based parser for my ownprojects. Even though I had to do major surgery on its innards to get full source positiontracking and AST that matches source elements, it is a pleasure to work with and is now apleasure to extend. If you don't need source level element AST or the rest of what flexmark-javaadded and CommonMark is your target markdown parser then I encourage you to usecommonmark-java as it is an excellent choice for your needs and its performance does notsuffer for the overhead of features that you will not use.

Benchmarks

Latest, Jan 28, 2017 flexmark-java 0.13.1, intellij-markdown from CE EAP 2017, commonmark-java0.8.0:

Ratios of above:

Because these two files represent the pathological input for pegdown, I no longer run them aspart of the benchmark to prevent skewing of the results. The results are here for posterity.

Ratios of above:

• VERSION.md is the version log file I use for Markdown Navigator
• commonMarkSpec.md is a 33k line file used in intellij-markdown test suite for performanceevaluation.
• spec.txt commonmark spec markdown file in the commonmark-java project
• hang-pegdown.md is a file containing a single line of 17 characters [[[[[[[[[[[[[[[[[which causes pegdown to go into a hyper-exponential parse time.
• hang-pegdown2.md a file containing a single line of 18 characters [[[[[[[[[[[[[[[[[[ whichcauses pegdown to go into a hyper-exponential parse time.
• wrap.md is a file I was using to test wrap on typing performance only to discover that ithas nothing to do with the wrap on typing code when 0.1 seconds is taken by pegdown to parsethe file. In the plugin the parsing may happen more than once: syntax highlighter pass, psitree building pass, external annotator.
• markdown_example.md a file with 10,000+ lines containing 500kB+ of text.

Contributing

Pull requests, issues and comments welcome �� . For pull requests:

• Add tests for new features and bug fixes, preferably in theast_spec.md format
• Follow the existing style to make merging easier, as much as possible: 4 space indent,trailing spaces trimmed.

License

Copyright (c) 2015-2016 Atlassian and others.

Copyright (c) 2016-2020, Vladimir Schneider,

BSD (2-clause) licensed, see LICENSE.txt file.