Maintain tables from HTML email in when using HTML to Markdown

mcwumbly · 2017 年6 月 13 日 16:27

I was trying to advise a user on how they might import a Google Doc into Discourse as a new topic and suggested trying to copy/paste the doc into an email and then email it in. It mostly worked, but there were a few tables in the doc that got mangled in the process.

When an email into Discourse includes an HTML table, that table gets mangled and turned into plaintext on the Discourse side.

I have the incoming_email_prefer_html on as well as the “allow html tables” setting.

It’d be cool if tables were just skipped and maintained as HTML in that case. (Or perhaps there’s a table extension we’re planning on enabling once the markdown-it is in the mix?)

codinghorror · 2018 年5 月 3 日 08:53

This might work better now that we have more formal Markdown table support @vinothkannans?

vinothkannans · 2018 年5 月 3 日 09:06

Yes, it will work better if the user used copy-paste method instead of email-in workaround.

HTML pasting feature uses client side JavaScript for Markdown conversion. But for incoming emails we converting it in server side using our custom converter which doesn’t support Markdown tables yet.

zogstrip · 2018 年5 月 3 日 14:45

I see no point in duplicating our code in JS and Ruby. I will remove the Ruby version and replace it with the JS version.

brechtm · 2020 年2 月 6 日 15:34

我偶尔会收到包含表格的邮件，但第一个表格及其之后的内容在转换为 Markdown 时会丢失。这导致消息突然中断，让用户感到十分困惑。虽然他们可以点击小信封图标查看原始 HTML 邮件，但这远不够友好，很可能应被视为一个缺陷。

编辑消息并将原始 HTML 表格粘贴进去似乎效果很好。为什么不在 Markdown 转换过程中这样做呢？

zogstrip · 2020 年4 月 29 日 15:35

合并此 PR 后，表格将正确转换：

github.com/discourse/discourse

FIX: server-side HtmlToMarkdown improvements (#9586)

master ← fix-html-to-markdown

merged 10:21AM - 30 Apr 20 UTC

ZogStriP

+422 -207

TLDR; this commit vastly improves how whitespaces are handled when converting fr…om 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 ` ` tags. I know those tiny ` ` don't do much but they can be quite annoying. The ` ` tags are inline elements but they visually work like a block element (ie. they create a new line). If you have the following HTML "`Foo Bar`", it ends up visually similar to "`Foo Bar`". 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 ` ` 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 ` `, and all its children are also inline. The `collapse_spaces!` method will collapse any kind of (white) space into a single space (" ") character, even across tags. For example, if we have "` Foo \n Bar \t42`", it will return "`Foo Bar 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: switched Nokogiri to Nokogumbo for better HTML5 parsing 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: 🍪.

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Maintain tables from HTML email in when using HTML to Markdown

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