Throw error if fetching from relative URL on the server

[shuding]

Feature Request

Description

If running on the server, you cannot use <img src="/my-img.png"/> because there is no domain provided. We should throw a specific error message in that case.

[wong2]

node-fetch already throw such an error: Can't load image /aaa.jpg: Only absolute URLs are supported

Node.js 18: Can't load image /aaa.jpg: Failed to parse URL from /aaa.jpg

[shuding]

We need to unify that error message, also I think some fetch polyfills won't throw in that case.

[KiwiKilian]

Not quite exactly on the topic, but is there any other option to fix this error other than inlining the image?

[shuding]

You can fetch the image with an absolute URL such as <img src="https://example.com/my-img.png"/>.

[KiwiKilian]

Thanks for the answer, I should have been more clear. I was thinking about other solutions to local usage on the server. Is there currently any, aside of inlining?

If not, would it be in scope for satori to extend towards this sever usage? For example a resolveResource function one could pass as an option? I guess it would be called at the same place this error occurs.

[multipletwigs]

Hey! I'd love to take this issue (for my first OSS contribution) if it hasn't been assigned yet 🥳

[multipletwigs]

Hey there, spent some time tinkering around the codebase, and I was wondering if the enhancement is as simple as checking the image src with the following code. First checking if the code is running on a server environment, then checking if it's using an absolute url.

// In src/handler/image.ts

// Check if on server
  if (typeof window === 'undefined') {
    // Check if src is absolute url
    if (!src.startsWith('http') && !src.startsWith('data:')) {
      throw new Error(`Image source must be an absolute URL: ${src}`)
    }
  }

[shuding]

@multipletwigs that fix makes sense to me! Feel free to open a PR :)

[shuding]

Fixed with #447.