Refactor Helix Flow to give Content Repository Precedence for all Request

[trieloff]

I've been discussing this with @davidnuescheler and since we have the new drawings in docs (https://github.com/adobe/helix-publish/tree/master/docs), I can outline the change I'd like to achieve.

Old:

New:

What changes:

1. all normal requests get the raw request type first (this used to be called `image)
2. only when the extension is supported by the image optimizer, we will enable image optimization
3. otherwise the raw request type works like the old image type, it tries to fetch the content directly from the content repository, even when it is a html, js, or css file.

• this means you can create a static index.html and get it served @filmaj
• this means you can have custom CSS for Helix Pages @koraa and @kptdobe
• this means you can have a 404.html @tripodsan @ramboz (but more about that later)

4. when this request (which is very cheap for us) fails, we fall back to the regular pipeline request type, i.e. try to call the runtime action.

• note: the most frequent failure cases, i.e. no action for css, js, etc. is very cheap and fast for us, because no action gets called

5. when the pipeline request fails, we fall back to static, which can (as before yield content, or a redirect, or a static_url, each with a restart.
6. when that request fails, we start a new request type error, which changes the internal URL to 404.html and tries to get it from the content repository

Examples of requests and resolution:

Request	Content repo	Static repo	Comment
/index.html	index.md ✅		Default md processing
/index.html	index.html ✅; index.md		Static html file stronger than md processed file
/index.html	index.html ✅	index.html
/index.html	index.html ✅	htdocs/index.html
/index.html		htdocs/index.html ✅
/index.html		htdocs/index.md :	❌ 404 - no pipeline processing from static
/index.html		index.html :	❌ 404 - static action mapped to htdocs
/style.css		htdocs/style.css ✅	Default style handling
/style.css	style.css ✅		Strange but supported
/style.css	style.css ✅	htdocs/style.css	Style override inside content repo

[trieloff]

This is the maximum number of restarts (3) that Fastly supports, so going back to static for 404.html is not an option.

[kptdobe]

If I summarise, each request will go through: content repo via raw API -> content repo via pipeline action -> static repo via static action via raw API

It would be great to create an exhaustive list of all the cases we want to support (especially with the overrides) and check if they are covered by this new flow.

In step 6, isn't possible to do a redirect to 404.html (something like changing the external url) which would follow the same complete logic ? (treated like a normal request).

[trieloff]

Yes, we could redirect instead of restarting for 404.html, but I'd like to avoid this because it will mask all 404 errors as 301 or 302 non-errors.

[adobe-bot]

🎉 This issue has been resolved in version 2.0.0 🎉

The release is available on GitHub release

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