serverFetch causes infinite loop (Maximum call stack size exceeded) when route doesn't exist

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Description

When using serverFetch() inside an HTML template (e.g., index.html) to fetch a route that doesn't exist, it causes an infinite recursion loop resulting in RangeError: Maximum call stack size exceeded.

Reproduction

1. Create a new Nitro project with the default starter template
2. The index.html contains: {{{ serverFetch("/api") }}}
3. But there's no /api route defined (only routes/index.ts which maps to /)
4. Run bun run build && bun run preview
5. Visit http://localhost:3000/api

What happens

/api request
    ↓
No route found → fallback /** → renderer-template
    ↓
Template calls serverFetch("/api")
    ↓
/api request (again)
    ↓
No route found → fallback /** → renderer-template
    ↓
... infinite loop → Maximum call stack size exceeded

Error output

[request error] [unhandled] [GET] http://localhost/api
 RangeError: Maximum call stack size exceeded
    at hasTrailingSlash (file:///.output/server/chunks/nitro/app.mjs:713:26)
    at withoutTrailingSlash$1 (file:///.output/server/chunks/nitro/app.mjs:718:40)
    at serverFetch (file:///.output/server/chunks/nitro/app.mjs:1574:26)
    at template (file:///.output/server/chunks/nitro/renderer-template.mjs:187:7)
    ...

Root cause

The serverFetch() function in nitro/dist/runtime/internal/app.mjs has no recursion protection:

export function serverFetch(resource, init, context) {
    const req = toRequest(resource, init);
    req.context = {
        ...req.context,
        ...context
    };
    const appHandler = useNitroApp().fetch;
    try {
        return Promise.resolve(appHandler(req));
    } catch (error) {
        return Promise.reject(error);
    }
}

Suggested fix

Add recursion depth tracking to prevent infinite loops:

export function serverFetch(resource, init, context) {
    const req = toRequest(resource, init);
    
    // Recursion guard
    const depth = (context?._serverFetchDepth || 0) + 1;
    if (depth > 10) {
        throw new Error(`serverFetch: maximum recursion depth exceeded for "${resource}". This usually means the requested route doesn't exist and falls back to a template that calls serverFetch again.`);
    }
    
    req.context = {
        ...req.context,
        ...context,
        _serverFetchDepth: depth
    };
    
    const appHandler = useNitroApp().fetch;
    try {
        return Promise.resolve(appHandler(req));
    } catch (error) {
        return Promise.reject(error);
    }
}

Environment

• Nitro version: v3 (latest)
• Runtime: Bun
• OS: macOS

Additional context

This is a defensive programming issue. While the immediate workaround is to ensure all routes called by serverFetch() exist, the framework should protect against infinite recursion with a clear error message.

[productdevbook]

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