501b19b6e0
TLDR; this commit vastly improves how whitespaces are handled when converting from HTML to Markdown. It also adds support for converting HTML <tables> to markdown tables. The previous 'remove_whitespaces!' method was traversing the whole HTML tree and used a heuristic to remove leading and trailing whitespaces whenever it was appropriate (ie. mostly before and after HTML block elements) It was a good idea, but it was very limited and leaded to bad conversion when the html had leading whitespaces on several lines for example. One such example can be found [here](https://meta.discourse.org/t/86782). For various reasons, most of the whitespaces in a HTML file is ignored when the page is being displayed in a browser. The rules that the browsers follow are the [CSS' White Space Processing Rules](https://www.w3.org/TR/css-text-3/#white-space-rules). They can be quite complicated when you take into account RTL languages and other various tidbits but they boils down to the following: - Collapse whitespaces down to one space (0x20) inside an inline context (ie. nodes/tags that are being displaying on the same line) - Remove any leading/trailing whitespaces inside an inline context One quick & dirty way of getting this 90% solved would be to do 'HTML.gsub!(/[[:space:]]+/, " ")'. We would also need to hoist <pre> elements in order to not mess with their whitespaces. Unfortunately, this solution let some whitespaces creep around HTML tags which leads to more '.strip!' calls than I can bear. I decided to "emulate" the browser's handling of whitespaces and came up with a solution in 4 parts 1. remove_not_allowed! The HtmlToMarkdown library is recursively "visiting" all the nodes in the HTML in order to convert them to Markdown. All the nodes that aren't handled by the library (eg. <script>, <style> or any non-textual HTML tags) are "swallowed". In order to reduce the number of nodes visited, the method 'remove_not_allowed!' will automatically delete all the nodes that have no "visitor" (eg. a 'visit_<tag>' method) defined. 2. remove_hidden! Similar purpose as the previous method (eg. reducing number of nodes visited), there's no point trying to convert something that is hidden. The 'remove_hidden!' method removes any nodes that was hidden using the "hidden" HTML attribute, some CSS or with a width or height equal to 0. 3. hoist_line_breaks! The 'hoist_line_breaks!' method is there to handle <br> tags. I know those tiny <br> don't do much but they can be quite annoying. The <br> tags are inline elements but they visually work like a block element (ie. they create a new line). If you have the following HTML "<i>Foo<br>Bar</i>", it ends up visually similar to "<i>Foo</i><br><i>Bar</i>". The latter being much more easy to process than the former, so that's what this method is doing. The "hoist_line_breaks" will hoist <br> tags out of inline tags until their parent is a block element. 4. remove_whitespaces! The "remove_whitespaces!" is where all the whitespace removal is happening. It's broken down into 4 methods as well - remove_whitespaces! - is_inline? - collapse_spaces! - remove_trailing_space! The 'remove_whitespace!' method is recursively walking the HTML tree (skipping <pre> tags). If a node has any children, they will be chunked into groups of inline elements vs block elements. For each chunks of inline elements, it will call the "collapse_space!" and "remove_trailing_space!" methods. For each chunks of block elements, it will call "remote_whitespace!" to keep walking the HTML tree recursively. The "is_inline?" method determines whether a node is part of a inline context. A node is inline iif it's a text node or it's an inline tag, but not <br>, and all its children are also inline. The "collapse_spaces!" method will collapse any kind of (white) space into a single space (" ") character, even accros tags. For example, if we have " Foo \n<i> Bar </i>\t42", it will return "Foo <i>Bar </i>42". Finally, the "remove_trailing_space!" method is there to remove any trailing space that might creep in at the end of the inline chunk. This solution is not 100% bullet-proof. It does not support RTL languages at all and has some caveats that I felt were not worth the work to get properly fixed. FIX: better detection of hidden elements when converting HTML to Markdown FIX: take into account the 'allowed_href_schemes' site setting when converting HTML <a> to Markdown FIX: added support for 'mailto:' scheme when converting <a> from HTML to Markdown FIX: added support for <img> dimensions when converting from HTML to Markdown FIX: added support for <dl>, <dd> and <dt> when converting from HTML to Markdown FIX: added support for multilines emphases, strongs and strikes when converting from HTML to Markdown FIX: added support for <acronym> when converting from HTML to Markdown DEV: remove unused 'sanitize' gem Wow, did you just read all that?! Congratz, here's a cookie: 🍪.
Discourse is the 100% open source discussion platform built for the next decade of the Internet. Use it as a:
- mailing list
- discussion forum
- long-form chat room
To learn more about the philosophy and goals of the project, visit discourse.org.
Screenshots
Browse lots more notable Discourse instances.
Development
To get your environment setup, follow the community setup guide for your operating system.
- If you're on macOS, try the macOS development guide.
- If you're on Ubuntu, try the Ubuntu development guide.
- If you're on Windows, try the Windows 10 development guide.
If you're familiar with how Rails works and are comfortable setting up your own environment, you can also try out the Discourse Advanced Developer Guide, which is aimed primarily at Ubuntu and macOS environments.
Before you get started, ensure you have the following minimum versions: Ruby 2.6+, PostgreSQL 10+, Redis 4.0+. If you're having trouble, please see our TROUBLESHOOTING GUIDE first!
Setting up Discourse
If you want to set up a Discourse forum for production use, see our Discourse Install Guide.
If you're looking for business class hosting, see discourse.org/buy.
Requirements
Discourse is built for the next 10 years of the Internet, so our requirements are high.
Discourse supports the latest, stable releases of all major browsers and platforms:
| Browsers | Tablets | Phones |
|---|---|---|
| Apple Safari | iPadOS | iOS |
| Google Chrome | Android | Android |
| Microsoft Edge | ||
| Mozilla Firefox |
Built With
- Ruby on Rails — Our back end API is a Rails app. It responds to requests RESTfully in JSON.
- Ember.js — Our front end is an Ember.js app that communicates with the Rails API.
- PostgreSQL — Our main data store is in Postgres.
- Redis — We use Redis as a cache and for transient data.
Plus lots of Ruby Gems, a complete list of which is at /master/Gemfile.
Contributing
Discourse is 100% free and open source. We encourage and support an active, healthy community that accepts contributions from the public – including you!
Before contributing to Discourse:
- Please read the complete mission statements on discourse.org. Yes we actually believe this stuff; you should too.
- Read and sign the Electronic Discourse Forums Contribution License Agreement.
- Dig into CONTRIBUTING.MD, which covers submitting bugs, requesting new features, preparing your code for a pull request, etc.
- Always strive to collaborate with mutual respect.
- Not sure what to work on? We've got some ideas.
We look forward to seeing your pull requests!
Security
We take security very seriously at Discourse; all our code is 100% open source and peer reviewed. Please read our security guide for an overview of security measures in Discourse, or if you wish to report a security issue.
The Discourse Team
The original Discourse code contributors can be found in AUTHORS.MD. For a complete list of the many individuals that contributed to the design and implementation of Discourse, please refer to the official Discourse blog and GitHub's list of contributors.
Copyright / License
Copyright 2014 - 2020 Civilized Discourse Construction Kit, Inc.
Licensed under the GNU General Public License Version 2.0 (or later); you may not use this work except in compliance with the License. You may obtain a copy of the License in the LICENSE file, or at:
https://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
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.
Discourse logo and “Discourse Forum” ®, Civilized Discourse Construction Kit, Inc.
Dedication
Discourse is built with love, Internet style.