Hext — Extract Data from HTML

Hext is a domain-specific language for extracting structured data from HTML documents.

Hext is written in C++ but language bindings are available for Python, Node, JavaScript, Ruby and PHP.

See https://hext.thomastrapp.com for documentation, installation instructions and a live demo.

The Hext project is released under the terms of the Apache License v2.0.

Example

Suppose you want to extract all hyperlinks from a web page. Hyperlinks have an anchor tag <a>, an attribute called href and a text that visitors can click. The following Hext template will produce a dictionary for every matched element. Each dictionary will contain the keys link and title which refer to the href attribute and the text content of the matched <a>.

# Extract links and their text
<a href:link @text:title />

» Load example in editor

Visit Hext's project page to learn more about Hext. For examples that use the libhext C++ library check out /libhext/examples and libhext's C++ library overview.

Components of this Project

• htmlext: Command line utility that applies Hext templates to an HTML document and produces JSON.
• libhext: C++ library that contains a Hext parser but also allows for customization.
• libhext-test: Unit tests for libhext.
• Hext bindings: Bindings for scripting languages. There are extensions for Node.js, Python, Ruby and PHP that are able to parse Hext and extract values from HTML.

Project layout

├── build             Build directory for htmlext
├── cmake             CMake modules used by the project
├── htmlext           Source for the htmlext command line tool
├── libhext           The libhext project
│   ├── bindings      Hext bindings for scripting languages
│   ├── build         Build directory for libhext
│   ├── doc           Doxygen documentation for libhext
│   ├── examples      Examples making use of libhext
│   ├── include       Public libhext API
│   ├── ragel         Ragel input files
│   ├── scripts       Helper scripts for libhext
│   ├── src           libhext implementation files
│   └── test          The libhext-test project
│       ├── build     Build directory for libhext-test
│       └── src       Source for libhext-test
├── man               Htmlext man page
├── scripts           Scripts for building and testing releases
├── syntaxhl          Syntax highlighters for Vim and ACE
└── test              Blackbox tests for htmlext

Dependencies for development

• Ragel generates the state machine that is used to parse Hext
• The unit tests for libhext are written with Google Test
• libhext's public API documentation is generated by Doxygen
• libhext's scripting language bindings are generated by Swig

Tests

There are unit tests for libhext and blackbox tests for Hext as a language, whose main purpose is to detect unwanted change in syntax or behavior.
The libhext-test project is located in /libhext/test and depends on Google Test. Nothing fancy, just build the project and run the executable libhext-test. How to write test cases with Google Test is described here.
The blackbox tests are located in /test. There you'll find a shell script called blackbox.sh. This script applies Hext templates to HTML documents and compares the result to a third file that contains the expected output. For example, there is a test case icase-quoted-regex that consists of three files: icase-quoted-regex.hext, icase-quoted-regex.html, and icase-quoted-regex.expected. To run this test case you would do the following:

$ ./blackbox.sh case/icase-quoted-regex.hext

blackbox.sh will then look for the corresponding .html and .expected files of the same name in the directory of icase-quoted-regex.hext. Then it will invoke htmlext with the given Hext template and HTML document and compare the result to icase-quoted-regex.expected. To run all blackbox tests in succession:

$ ./blackbox.sh case/*.hext

By default blackbox.sh will look for the htmlext binary in $PATH. Failing that, it looks for the binary in the default build directory. You can tell blackbox.sh which command to use by setting HTMLEXT. For example, to run all tests through valgrind you'd run the following:

$ HTMLEXT="valgrind -q ../build/htmlext" ./blackbox.sh case/*.hext

Acknowledgements

• Gumbo — An HTML5 parsing library in pure C99
  Gumbo is used as the HTML parser behind hext::Html. It's fast, easy to integrate and even fixes invalid HTML.
• Ragel — Ragel State Machine Compiler
  The state machine that is used to parse Hext templates is generated by Ragel. You can find the definition of this machine in /libhext/ragel/hext-machine.rl.
• RapidJSON — A fast JSON parser/generator for C++
  RapidJSON powers the JSON output of the htmlext command line utility.
• jq — A lightweight and flexible command-line JSON processor
  An indispensable tool when dealing with JSON in the shell. Piping the output of htmlext into jq lets you do all sorts of crazy things.
• Ace — A Code Editor for the Web
  Used as the code editor in the "Try Hext in your Browser!" section and as a highlighter for all code examples. The highlighting rules for Hext are included in this project in /syntaxhl/ace. Also, there's a script in /libhext/scripts/syntax-hl-ace that uses Ace to transform a code template into highlighted HTML.
• Boost.Beast — HTTP and WebSocket built on Boost.Asio in C++11
  The Websocket server behind the "Try Hext in your Browser!" section is built with Beast. See github.com/html-extract/hext-on-websockets for more.