feat: refreshing images

[dalechyn]

This PR is a result of a research on why the frames with Cache-Control: max-age=0 are not refreshing.

First of all, the passed Cache-Control header must be lowercased. What happens is that @vercel/og is setting a lowercased cache-control header key to "public, immutable, no-transform, max-age=31536000" , yet hono-og sets Cache-Control (different case) to "public, immutable, no-transform, max-age=31536000" (same value as prev one). Even if a user doesn't pass any headers in imageOptions, what ends up being under the hood there – is an object with both cache-control and Cache-Control headers set, and it looks like that the lowercased header takes a precedence over the uppercased one, since it started working correctly without patches when I've passed a lowercased header key.

Secondly, WC caches the initial image url and expects you to update it under the same URL. However, since the image, imageOptions and headers are serialized and passed inside search params, the initial /image?=image... link will always change if the image is changing. So I've decided to add an internal frog:image (maybe change to frog:initial_image?) meta tag that stores the full link to the image with search params. This allows to serve the image for initial frame request under /image route without any search params whatsoever by fetching the original frame, retrieving frog:image and redirecting user to it. It's not ideal – as it adds up an additional request for image retrieval (breaks idempotency), uneffectively re-rendering the frame twice: first time when the frame is accessed (i.e. /), and then to retrieve frog:image from the image route (i.e. /image), which could cause some slow frames to time out. I cannot figure another way to persist the image state yet. However it doesn't seem as a huge problem as "usually" initial frames are resolved fast, as there is no frameData to perform expensive operations with.

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As I write this long description, I think that what can be done though – is explicitly asking a user to opt out to a "refreshing" frame or not, warning him that the initial frame render will force it to render twice and setting cache-control:max-age=0 in headers and performing this trick only if the flag is set.

[vercel[bot]]

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Name	Status	Preview	Comments	Updated (UTC)
frog	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Apr 3, 2024 6:50pm
frog-frame	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Apr 3, 2024 6:50pm

[vercel[bot]]

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[dalechyn]

This also needs a test in Warpcast but it crashes today due to some internal server errors.

[dalechyn]

This also needs a test in Warpcast but it crashes today due to some internal server errors.

https://warpcast.com/dalechyn.eth/0xf0ae1ed7

tested, works as expected