feat(core): islands

<!--- Provide a general summary of your changes in the title above -->

## Types of changes
<!--- What types of changes does your code introduce? Put an `x` in all the boxes that apply: -->
- [ ] Bug fix (a non-breaking change which fixes an issue)
- [x] New feature (a non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)

## Description
<!--- Describe your changes in detail -->
<!--- Why is this change required? What problem does it solve? -->
<!--- If it resolves an open issue, please link to the issue here. For example "Resolves: #137" -->

Closes #494

This PR introduces support for Nuxt Server Components (a.k.a Islands).

## Checklist:
<!--- Put an `x` in all the boxes that apply. -->
<!--- If your change requires a documentation PR, please link it appropriately -->
<!--- If you're unsure about any of these, don't hesitate to ask. We're here to help! -->
- [ ] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.
- [ ] I have added tests to cover my changes (if not applicable, please state why)

package.json

@@ -67,8 +67,8 @@
     "@types/node": "^18.18.1",
     "eslint": "^8.50.0",
     "nuxt": "^3.11.2",
-    "vitest": "^1.3.1",
-    "typescript": "^5.4.5"
+    "typescript": "^5.4.5",
+    "vitest": "^1.3.1"
   },
   "stackblitz": {
     "installDependencies": false,

playground/components/ServerComponent.server.vue

@@ -0,0 +1,3 @@
+<template>
+  <div>Server component</div>
+</template>

playground/pages/island.vue

@@ -0,0 +1,6 @@
+<template>
+  <div>
+    Island Page
+    <ServerComponent />
+  </div>
+</template>

src/runtime/nitro/plugins/50-updateCsp.ts

@@ -7,16 +7,18 @@ import type { ContentSecurityPolicyValue } from '../../../types/headers'
  */
 export default defineNitroPlugin((nitroApp) => {
   nitroApp.hooks.hook('render:html', (response, { event }) => {
-    const rules = resolveSecurityRules(event)
-    if (rules.enabled && rules.headers) {
-      const headers = rules.headers
-
-      if (headers.contentSecurityPolicy) {
-        const csp = headers.contentSecurityPolicy
-        const nonce = event.context.security?.nonce
-        const scriptHashes = event.context.security?.hashes?.script
-        const styleHashes = event.context.security?.hashes?.style
-        headers.contentSecurityPolicy = updateCspVariables(csp, nonce, scriptHashes, styleHashes)
+    if (!response.island) {
+      const rules = resolveSecurityRules(event)
+      if (rules.enabled && rules.headers) {
+        const headers = rules.headers
+
+        if (headers.contentSecurityPolicy) {
+          const csp = headers.contentSecurityPolicy
+          const nonce = event.context.security?.nonce
+          const scriptHashes = event.context.security?.hashes?.script
+          const styleHashes = event.context.security?.hashes?.style
+          headers.contentSecurityPolicy = updateCspVariables(csp, nonce, scriptHashes, styleHashes)
+        }
       }
     }
   })

src/runtime/nitro/plugins/60-recombineHtml.ts

@@ -24,11 +24,13 @@ export default defineNitroPlugin((nitroApp) => {
 
       // Let's insert the CSP meta tag just after the first tag which should be the charset meta
       let insertIndex = 0
-      const metaCharsetMatch = html.head[0].match(/^<meta charset="(.*?)">/mdi)
-      if (metaCharsetMatch && metaCharsetMatch.indices) {
-        insertIndex = metaCharsetMatch.indices[0][1]
+      if (html.head.length > 0) {
+        const metaCharsetMatch = html.head[0].match(/^<meta charset="(.*?)">/mdi)
+        if (metaCharsetMatch && metaCharsetMatch.indices) {
+          insertIndex = metaCharsetMatch.indices[0][1]
+        }
+        html.head[0] = html.head[0].slice(0, insertIndex) + `<meta http-equiv="Content-Security-Policy" content="${headerValue}">` + html.head[0].slice(insertIndex) 
       }
-      html.head[0] = html.head[0].slice(0, insertIndex) + `<meta http-equiv="Content-Security-Policy" content="${headerValue}">` + html.head[0].slice(insertIndex) 
     }
   })
 })