Viewer fix: invalid html_widget resource paths

[ElianHugh]

Resolves#665

Adds a mutation observer to the webview body, which watches for changes in the DOM. Specifically, the filescheme vscode-webview:// is tested for 'URLness' and (if true) is converted to an https:// request.

This PR also defines some (minimal) content security policies for the webview.

Screenshot

How can I check this pull request?

Prior to the PR, the following led to a blank viewer page, which should now be fixed:

library(leaflet)
leaflet() |> addTiles()

Dynamic loading of resources is supported too:

library(mapview)
mapview(breweries)

[renkun-ken]

Thanks for working on this! Works nicely already.

When I test the mapview example, it actually works, but I found the following error in the log:

fgb.js:103 Refused to connect to 'vscode-webview://8fe576af-ef9f-4237-9417-cd8966ff7eef/lib/breweries-0.0.1/breweries_layer.fgb' because it violates the following Content Security Policy directive: "default-src https: data: filesystem:". Note that 'connect-src' was not explicitly set, so 'default-src' is used as a fallback.
LeafletWidget.methods.addFlatGeoBuf @ fgb.js:103
fgb.js:103 Refused to connect to 'vscode-webview://8fe576af-ef9f-4237-9417-cd8966ff7eef/lib/breweries-0.0.1/breweries_layer.fgb' because it violates the document's Content Security Policy.
LeafletWidget.methods.addFlatGeoBuf @ fgb.js:103
fgb.js:103 Uncaught (in promise) TypeError: Failed to fetch
at e.LeafletWidget.methods.addFlatGeoBuf (fgb.js:103)
at Object.doRenderValue (leaflet.js:812)
at Object.renderValue (leaflet.js:714)
at Object.renderValue (htmlwidgets.js:886)
at htmlwidgets.js:653
at Array.forEach (<anonymous>)
at forEach (htmlwidgets.js:55)
at htmlwidgets.js:576
at Array.forEach (<anonymous>)
at forEach (htmlwidgets.js:55)

Not sure if it has any impact on the functionality. Anything we should do about this or we could ignore it?

[ElianHugh]

Thanks for working on this! Works nicely already.

When I test the mapview example, it actually works, but I found the following error in the log:

fgb.js:103 Refused to connect to 'vscode-webview://8fe576af-ef9f-4237-9417-cd8966ff7eef/lib/breweries-0.0.1/breweries_layer.fgb' because it violates the following Content Security Policy directive: "default-src https: data: filesystem:". Note that 'connect-src' was not explicitly set, so 'default-src' is used as a fallback.
LeafletWidget.methods.addFlatGeoBuf @ fgb.js:103
fgb.js:103 Refused to connect to 'vscode-webview://8fe576af-ef9f-4237-9417-cd8966ff7eef/lib/breweries-0.0.1/breweries_layer.fgb' because it violates the document's Content Security Policy.
LeafletWidget.methods.addFlatGeoBuf @ fgb.js:103
fgb.js:103 Uncaught (in promise) TypeError: Failed to fetch
at e.LeafletWidget.methods.addFlatGeoBuf (fgb.js:103)
at Object.doRenderValue (leaflet.js:812)
at Object.renderValue (leaflet.js:714)
at Object.renderValue (htmlwidgets.js:886)
at htmlwidgets.js:653
at Array.forEach (<anonymous>)
at forEach (htmlwidgets.js:55)
at htmlwidgets.js:576
at Array.forEach (<anonymous>)
at forEach (htmlwidgets.js:55)

Not sure if it has any impact on the functionality. Anything we should do about this or we could ignore it?

Very weird, this doesn't occur on WSL, but does on Linux. Removing the CSP policies shows a fetch attempt to a non-existent filepath for some reason... I think it does effect the blue dots on the map, but is fixed if you type mapviewOptions(fgb = FALSE). In looking into this I came across this thread which appears to suggest this isn't just a VS Code thing.

[renkun-ken]

Very weird, this doesn't occur on WSL, but does on Linux. Removing the CSP policies shows a fetch attempt to a non-existent filepath for some reason... I think it does effect the blue dots on the map, but is fixed if you type mapviewOptions(fgb = FALSE). In looking into this I came across this thread which appears to suggest this isn't just a VS Code thing.

Do you think if there is anything we could do about it?

[ElianHugh]

Do you think if there is anything we could do about it?

I found this, so I guess it might be something that can be fixed. I'll have a look

[renkun-ken]

Works nicely now.

LGTM