How to preprocess markdown?

[GildedHonour]

Say, I have a tag audio, video, image or whatever and I want to dynamically adjust it's "source" before rendering it on an html page. Does comrak provide an api for an element to do so?

[kivikakk]

You can walk the returned AST until you find the InlineHtml or BlockHtml representing the tag in question. It doesn't parse HTML — that's a non-goal of CommonMark — so you'll still have quite a bit of work to do.

[GildedHonour]

thx

does the library support <audio ... and <video markdown tags?

[kivikakk]

No problem!

And unfortunately not; there’s no syntax in CommonMark for those tags, nor any extension implemented.

[GildedHonour]

If I want to extend it for myself, something like this:

[audio](/path/file.mp4)
which will be parsed into the real html audio tag , how will I add that tag? Is there a similar example in the library?

[brson]

@GildedHonour my downstream branch does something like that, commandeering the image syntax like ![video](<hashcode>) (we use hash identifiers instead of paths. I can't share the full code off hand, but here's a snippet:

https://gist.github.com/brson/b180839aa4a236bc78e7b86eca3f7877

I'm not saying this is the cleanest way to do it, but it's what we do - note that when we're in our custom mode, indicated by the 'rtjson' flag - we use a totally new AST node, NodeMeda, to indicate it's special. Elsewhere we have further validation that the text of that node is 'video', 'image', 'gif', etc. - Depending on your needs you might check for those 'keywords' right there to make the decision to use the custom node.

From there you just have to edit html.rs, which should be pretty obvious since it's a small repetitive file.

Hope that helps.

[GildedHonour]

@brson Thanks. But I can't understand how that can be useful for my case because that's quite a small part of code. Can you share more?

Also, there's "}" missing in the very end, or somewhere else.

[brson]

@GildedHonour sorry for the lack of detail. I meant to give a hint of a reasonable place to reinterpret the link syntax. The rest I'd expect to fall out of that via compiler errors.

In close_bracket_match (the function to finish a successfully parsed link) you can use logic to, instead of creating a NodeLink, create your own custom node (like my NodeMedia), perhaps when url equals "audio". You'll need to add the new node in nodes.rs. From there you can extend the renderer in html.rs to emit the audio tag (and maybe the one in cm.rs). That's about all that's needed, afaicr offhand.

Another way to do it is to have an AST post-processing pass that walks the AST and looks for NodeLink and changes them as appropriate to NodeWhatever. Cleaner but slower.

[GildedHonour]

@brson yes, I can. That's why I asked for more code.

[kivikakk]

I'll close this issue out now; thanks @brson for dropping in with pointers from your own work!