Validate IPv6 prefix field in VPC create form

app/forms/vpc-create.tsx

@@ -7,6 +7,7 @@
  */
 import { useForm } from 'react-hook-form'
 import { useNavigate } from 'react-router'
+import type { SetNonNullable } from 'type-fest'
 
 import { api, q, queryClient, useApiMutation, type VpcCreate } from '@oxide/api'
 
@@ -19,13 +20,15 @@ import { titleCrumb } from '~/hooks/use-crumbs'
 import { useProjectSelector } from '~/hooks/use-params'
 import { addToast } from '~/stores/toast'
 import { SideModalFormDocs } from '~/ui/lib/ModalLinks'
+import { validateVpcIpv6Prefix } from '~/util/ip'
 import { docLinks } from '~/util/links'
 import { pb } from '~/util/path-builder'
 
-const defaultValues: VpcCreate = {
+const defaultValues: SetNonNullable<Required<VpcCreate>> = {
   name: '',
   description: '',
   dnsName: '',
+  ipv6Prefix: '',
 }
 
 export const handle = titleCrumb('New VPC')
@@ -56,15 +59,30 @@ export default function CreateVpcSideModalForm() {
       form={form}
       formType="create"
       resourceName="VPC"
-      onSubmit={(values) => createVpc.mutate({ query: projectSelector, body: values })}
+      onSubmit={({ ipv6Prefix, ...rest }) =>
+        createVpc.mutate({
+          query: projectSelector,
+          body: { ...rest, ipv6Prefix: ipv6Prefix.trim() || undefined },
+        })
+      }
       onDismiss={() => navigate(pb.vpcs(projectSelector))}
       loading={createVpc.isPending}
       submitError={createVpc.error}
     >
       <NameField name="name" control={form.control} />
       <DescriptionField name="description" control={form.control} />
       <NameField name="dnsName" label="DNS name" control={form.control} />
-      <TextField name="ipv6Prefix" label="IPV6 prefix" control={form.control} />
+      <TextField
+        name="ipv6Prefix"
+        label="IPv6 prefix"
+        control={form.control}
+        validate={(value) => {
+          const prefix = value.trim()
+          // field is optional — API generates a prefix if none is given
+          if (!prefix) return
+          return validateVpcIpv6Prefix(prefix)
+        }}
+      />
       <SideModalFormDocs docs={[docLinks.vpcs]} />
     </SideModalForm>
   )

app/util/ip.spec.ts

@@ -10,7 +10,13 @@ import { describe, expect, test } from 'vitest'
 
 import type { ExternalIp, IpVersion, UnicastIpPool } from '~/api'
 
-import { getEphemeralIpSlots, toUrlCheckableIpv6, parseIp, parseIpNet } from './ip'
+import {
+  getEphemeralIpSlots,
+  toUrlCheckableIpv6,
+  parseIp,
+  parseIpNet,
+  validateVpcIpv6Prefix,
+} from './ip'
 
 const makePool = (ipVersion: IpVersion, name = `pool-${ipVersion}`): UnicastIpPool => ({
   id: `id-${name}`,
@@ -336,3 +342,34 @@ test.each([
 ])('parseIpNet message: %s', (input, message) => {
   expect(parseIpNet(input)).toEqual({ type: 'error', message })
 })
+
+describe('validateVpcIpv6Prefix', () => {
+  test.each([
+    'fd00::/48',
+    'fd2d:4569:88b2::/48',
+    'fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff/48',
+    'fd00::1/48', // host bits are fine, matching oxnet
+    'fc00::/48', // std's is_unique_local covers fc00::/7
+  ])('valid: %s', (s) => {
+    expect(validateVpcIpv6Prefix(s)).toBeUndefined()
+  })
+
+  const notV6 = 'Must be an IPv6 prefix'
+  const notUla = 'Must be a unique local address (fc00::/7)'
+  const badPrefixWidth = 'Width must be 48'
+
+  test.each([
+    ['nonsense', nonsense],
+    ['fd00::', nonsense],
+    ['10.0.0.0/8', notV6],
+    ['::/48', notUla],
+    ['fbff:ffff:ffff:ffff:ffff:ffff:ffff:ffff/48', notUla],
+    ['2001:db8::/48', notUla],
+    ['fe00::/48', notUla],
+    ['fd00::/64', badPrefixWidth],
+    ['fd00::/40', badPrefixWidth],
+    ['fd00::/129', ipv6Width],
+  ])('invalid: %s', (input, message) => {
+    expect(validateVpcIpv6Prefix(input)).toEqual(message)
+  })
+})

app/util/ip.ts

@@ -137,6 +137,32 @@ export function validateIpNet(ipNet: string): string | undefined {
   if (result.type === 'error') return result.message
 }
 
+// The API requires a VPC IPv6 prefix to be a unique local address (fc00::/7)
+// with a width of exactly 48. Anything else is rejected on create.
+// https://github.com/oxidecomputer/omicron/blob/6db4c7e/common/src/api/external/mod.rs#L1287-L1288
+// https://github.com/oxidecomputer/omicron/blob/6db4c7e/nexus/db-model/src/vpc.rs#L86-L98
+export const VPC_IPV6_PREFIX_WIDTH = 48
+
+/** First hextet of a valid IPv6 address, e.g. 0xfd00 for `fd00::1` or `fd00::` */
+function firstHextet(address: string): number {
+  // a leading `::` means the first hextet is zero
+  if (address.startsWith(':')) return 0
+  return parseInt(address.split(':', 1)[0], 16)
+}
+
+export function validateVpcIpv6Prefix(value: string): string | undefined {
+  const result = parseIpNet(value)
+  if (result.type === 'error') return result.message
+  if (result.type !== 'v6') return 'Must be an IPv6 prefix'
+  // Rust's `Ipv6Addr::is_unique_local` checks fc00::/7
+  if ((firstHextet(result.address) & 0xfe00) !== 0xfc00) {
+    return 'Must be a unique local address (fc00::/7)'
+  }
+  if (result.width !== VPC_IPV6_PREFIX_WIDTH) {
+    return `Width must be ${VPC_IPV6_PREFIX_WIDTH}`
+  }
+}
+
 /**
  * Get compatible IP versions from an instance's NICs. External IPs route
  * through the primary interface, so only its IP stack matters.

test/e2e/vpcs.e2e.ts

@@ -74,6 +74,61 @@ test('can edit VPC', async ({ page }) => {
   })
 })
 
+test('IPv6 prefix is validated on VPC create', async ({ page }) => {
+  await page.goto('/projects/mock-project/vpcs')
+  await page.getByRole('link', { name: 'New VPC' }).click()
+
+  const dialog = page.getByRole('dialog', { name: 'Create VPC' })
+  await expect(dialog).toBeVisible()
+
+  await dialog.getByRole('textbox', { name: 'Name', exact: true }).fill('vpc-v6')
+  await dialog.getByRole('textbox', { name: 'DNS name' }).fill('vpc-v6')
+
+  const prefixField = dialog.getByRole('textbox', { name: 'IPv6 prefix' })
+  const submitButton = dialog.getByRole('button', { name: 'Create VPC' })
+
+  await prefixField.fill('not a prefix 🎉')
+  await submitButton.click()
+  await expect(
+    dialog.getByText('Must contain an IP address and a width, separated by a /')
+  ).toBeVisible()
+
+  // field revalidates on change after the first submit attempt
+  await prefixField.fill('10.0.0.0/8')
+  await expect(dialog.getByText('Must be an IPv6 prefix')).toBeVisible()
+
+  await prefixField.fill('2001:db8::/48')
+  await expect(dialog.getByText('Must be a unique local address (fc00::/7)')).toBeVisible()
+
+  await prefixField.fill('fd00::/64')
+  await expect(dialog.getByText('Width must be 48')).toBeVisible()
+
+  // empty is fine — the field is optional
+  await prefixField.clear()
+  await expect(dialog.getByText('Width must be 48')).toBeHidden()
+
+  await prefixField.fill('  fd2d:4569:88b2::/48  ')
+  await submitButton.click()
+
+  await expect(dialog).toBeHidden()
+  await expect(page.getByRole('heading', { name: 'vpc-v6' })).toBeVisible()
+  await expect(page.getByText('fd2d:4569:88b2::/48')).toBeVisible()
+})
+
+test('whitespace-only IPv6 prefix is omitted on VPC create', async ({ page }) => {
+  await page.goto('/projects/mock-project/vpcs')
+  await page.getByRole('link', { name: 'New VPC' }).click()
+
+  const dialog = page.getByRole('dialog', { name: 'Create VPC' })
+  await dialog.getByRole('textbox', { name: 'Name', exact: true }).fill('vpc-generated-v6')
+  await dialog.getByRole('textbox', { name: 'DNS name' }).fill('vpc-generated-v6')
+  await dialog.getByRole('textbox', { name: 'IPv6 prefix' }).fill('   ')
+  await dialog.getByRole('button', { name: 'Create VPC' }).click()
+
+  await expect(dialog).toBeHidden()
+  await expect(page.getByRole('heading', { name: 'vpc-generated-v6' })).toBeVisible()
+})
+
 test('can create and delete subnet', async ({ page }) => {
   await page.goto('/projects/mock-project/vpcs/default')
   await page.getByRole('tab', { name: 'VPC Subnets' }).click()