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Josh StoryandGitHub
d5dc166f42
When creating spans with OTel random values must be created to follow the OTel spec and is expected in practical implementations. While it is a loose concession Next.js will allow spans to be created while prerendering that have ids generated with random values. and by reading the current time from the system clock. This is pragmatic but potentially risky because if you are not careful and for instance wrap a "use cache" function in a span it is possible you will accidentally pass the span into the cache function causing it to miss on every invocation due to the random nature of one of it's arguments. To defend against this we do check whether `startActiveSpan` is being passed a Cache Function. However it is easy to circumvent by wrapping it in an intermediate function or by using startSpan and context.with yourself. In the long run we should consider tainting the Span objects created in these scopes so they cannot be sent through to a cache. I will consider a follow up PR to land this if we determine taint is likely to be stabilized in React. The pratical implementation of this change is to patch the tracer provider so that it always provides a patched tracer which exits the workUnitStorage on span start/creation and re-enters the scope on inner function exectuion.
42 lines
1.4 KiB
TypeScript
42 lines
1.4 KiB
TypeScript
export default function Page() {
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return (
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<main>
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<h1>OTel Cache Components Compat Test</h1>
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<p>
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Span generation causes random IDs to be created. There is a tradeoff
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with this while prerendering since sync IO like Math.random() should be
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excluded from static prerenders but spans are so widely used for
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providing telemetry for rendering and they would ideally be side effect
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free. Next.js now allows random id generation and current time reading
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while OTel spans are constructed. However it is possible for the span
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object to be passed to a Cache Component where the random ID will cause
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cache misses while prerendering. It is important that Span objects not
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be passed into Cache Functions for proper functioning of Cache
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Components.
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</p>
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<ul>
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<li>
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<a href="/novel/cache">
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"use cache" Page without build-time prerendering
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</a>
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</li>
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<li>
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<a href="/prerendered/cache">
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"use cache" Page with build-time prerendering
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</a>
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</li>
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<li>
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<a href="/novel/server">
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Server Page without build-time prerendering
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</a>
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</li>
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<li>
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<a href="/prerendered/server">
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Server Page with build-time prerendering
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</a>
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</li>
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</ul>
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</main>
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)
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}
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