Large Data URI Encoded images cause subsequent components to be rendered multiple times

[dabbers]

Describe the bug When inserting an image with a large data uri encoded image, any subsequent components being included in the response will get rendered twice. This is easiest to reproduce when fetching and inserting content via fetch. I noticed this bug by having a link to the same page (/news/[slug].svelte) with a different slug. This caused the components after the large image to be rendered twice.

To Reproduce

• In src/routes/blog/_posts.js Add an img alt="sample" src="" tag to any blog post you'd like where the value of src is from https://onlineimagetools.com/convert-image-to-data-uri
• In _layout.svelte Add a second <Nav /> below the . Any component will work, but with a base template, Nav is readily available.
• npm run dev
• Visit the /blog/ of the blog post you added the to.
• Hit refresh (ctrl+r) on your browser.

• If possible, we recommend creating a small repo that illustrates the problem. See: https://github.com/dabbers/test-content

• npm install
• npm run dev
• load /blog/what-is-sapper in your browser
• Hit refresh

Expected behavior I expect the subsequent components not to be rendered again. Since they aren't changing and the page hasn't changed.

Information about your Sapper Installation:

• The output of npx envinfo --system --npmPackages svelte,sapper,rollup,webpack --binaries --browsers npx: installed 1 in 0.918s

  System: OS: Windows 10 10.0.19041 Memory: 17.22 GB / 31.95 GB Binaries: Node: 12.18.3 - C:\Program Files\nodejs\node.EXE npm: 6.14.6 - C:\Program Files\nodejs\npm.CMD Browsers: Edge: Spartan (44.19041.423.0), Chromium (87.0.664.47) Internet Explorer: 11.0.19041.1 npmPackages: rollup: ^2.3.4 => 2.33.3 sapper: ^0.28.0 => 0.28.10 svelte: ^3.17.3 => 3.30.0

• Your browser Edge Chromium Version 87.0.664.47 (Official build) (64-bit)

• Your hosting environment (i.e. Local, GCP/AWS/Azure, Vercel/Begin, etc...) Windows 10

Severity This is moderate impact. It's adding a second footer and sometimes duplicated related articles to my page that persist until the server is restarted or a hard refresh (haven't nailed down which one actually clears it).

[dabbers]

I tried reproducing this on the standard Svelte template, but could not get it to reproduce. So I suspect it has something to do with Sapper's client vs server side rendering.

[dabbers]

By dropping my template svelte and sapper versions to:

        "sapper": "^0.27.16",
        "svelte": "^3.0.0",

The issue went away. This might help narrow down a potential issue. When I keep svelte to 3.0.0, but move sapper back to 0.28.0, the issue returns, indicating an issue occuring between those 2 versions. I also tested with 0.28.10 but the issue remains. I'd drop down to 27.16 but I'm already pretty far along with Typescript so cannot drop down.