feat(openapi): form-data helpers (#951)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Exposed Form Data helpers in the OpenAPI client to parse nested form
submissions and retrieve validation messages via bracket notation.

* **Documentation**
  * Added a “Form Data” guide with usage examples and a sidebar link.
  * Streamlined server-action docs to reference the re-exported helpers.
  * Fixed formatting in the bracket-notation complex example.

* **Tests**
  * Added a test to verify the helpers entry is available.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: dinwwwh

apps/content/.vitepress/config.ts

@@ -154,6 +154,7 @@ export default withMermaid(defineConfig({
             { text: 'Base64Url', link: '/docs/helpers/base64url' },
             { text: 'Cookie', link: '/docs/helpers/cookie' },
             { text: 'Encryption', link: '/docs/helpers/encryption' },
+            { text: 'Form Data', link: '/docs/helpers/form-data' },
             { text: 'Signing', link: '/docs/helpers/signing' },
           ],
         },

apps/content/docs/helpers/form-data.md

@@ -0,0 +1,96 @@
+---
+title: Form Data Helpers
+description: Utilities for parsing form data and handling validation errors with bracket notation support.
+---
+
+# Form Data Helpers
+
+Form data helpers provide utilities for parsing HTML form data and extracting validation error messages, with full support for [bracket notation](/docs/openapi/bracket-notation) to handle complex nested structures.
+
+## `parseFormData`
+
+Parses HTML form data using [bracket notation](/docs/openapi/bracket-notation) to deserialize complex nested objects and arrays.
+
+```ts twoslash
+import { parseFormData } from '@orpc/openapi-client/helpers'
+
+const form = new FormData()
+form.append('name', 'John')
+form.append('user[email]', 'john@example.com')
+form.append('user[hobbies][]', 'reading')
+form.append('user[hobbies][]', 'gaming')
+
+const parsed = parseFormData(form)
+// Result:
+// {
+//   name: 'John',
+//   user: {
+//     email: 'john@example.com',
+//     hobbies: ['reading', 'gaming']
+//   }
+// }
+```
+
+## `getIssueMessage`
+
+Extracts validation error messages from [standard schema](https://github.com/standard-schema/standard-schema) issues using [bracket notation](/docs/openapi/bracket-notation) paths.
+
+```ts twoslash
+import { getIssueMessage } from '@orpc/openapi-client/helpers'
+
+const error = {
+  data: {
+    issues: [
+      {
+        path: ['user', 'email'],
+        message: 'Invalid email format'
+      }
+    ]
+  }
+}
+
+const emailError = getIssueMessage(error, 'user[email]')
+// Returns: 'Invalid email format'
+
+const tagError = getIssueMessage(error, 'user[tags][]')
+// Returns error message for any array item
+
+const anyError = getIssueMessage('anything', 'path')
+// Returns undefined if cannot find issue
+```
+
+::: warning
+The `getIssueMessage` utility works with any data type but requires validation errors to follow the [standard schema issue format](https://github.com/standard-schema/standard-schema?tab=readme-ov-file#the-interface). It looks for issues in the `data.issues` property. If you use custom [validation errors](/docs/advanced/validation-errors), store them elsewhere, or modify the issue format, `getIssueMessage` may not work as expected.
+:::
+
+## Usage Example
+
+```tsx
+import { getIssueMessage, parseFormData } from '@orpc/openapi-client/helpers'
+
+export function ContactForm() {
+  const [error, setError] = useState()
+
+  const handleSubmit = (form: FormData) => {
+    try {
+      const data = parseFormData(form)
+      // Process structured data
+    }
+    catch (error) {
+      setError(error)
+    }
+  }
+
+  return (
+    <form action={handleSubmit}>
+      <input name="user[name]" type="text" />
+      <span>{getIssueMessage(error, 'user[name]')}</span>
+
+      <input name="user[emails][]" type="email" />
+      <span>{getIssueMessage(error, 'user[emails][]')}</span>
+
+      <button type="submit">Submit</button>
+    </form>
+  )
+}
+```

apps/content/docs/openapi/bracket-notation.md

@@ -107,15 +107,4 @@ This form data is parsed as:
     "files": ["<binary data>", "<binary data>"]
   }
 }
-```
-
-    "files": ["<binary data>", "<binary data>"]
-
-}
-}
-}
-}
-
-```
-
 ```

apps/content/docs/server-action.md

@@ -273,10 +273,9 @@ By moving the `redirect('/some-where')` logic into `createFormAction` rather tha
 When using `createFormAction`, any `ORPCError` with a status of `401`, `403`, or `404` is automatically converted into the corresponding Next.js error responses: [unauthorized](https://nextjs.org/docs/app/api-reference/functions/unauthorized), [forbidden](https://nextjs.org/docs/app/api-reference/functions/forbidden), and [not found](https://nextjs.org/docs/app/api-reference/functions/not-found).
 :::
 
-### `parseFormData` and `getIssueMessage` utilities
+### Form Data Utilities
 
-- `parseFormData` parse a form data with [Bracket Notation](/docs/openapi/bracket-notation)
-- `getIssueMessage` get the [standard schema](https://github.com/standard-schema/standard-schema?tab=readme-ov-file#the-interface) issue message with [Bracket Notation](/docs/openapi/bracket-notation) path
+The `@orpc/react` package re-exports [Form Data Helpers](/docs/helpers/form-data) for seamless form data parsing and validation error handling with [bracket notation](/docs/openapi/bracket-notation) support.
 
 ```tsx
 import { getIssueMessage, parseFormData } from '@orpc/react'
@@ -311,7 +310,3 @@ export function MyComponent() {
   )
 }
 ```
-
-::: info
-The `getIssueMessage` utility works with any data type but requires validation errors to follow the [standard schema issue format](https://github.com/standard-schema/standard-schema?tab=readme-ov-file#the-interface). It looks for issues in the `data.issues` property. If you use custom [validation errors](/docs/advanced/validation-errors), store them elsewhere, or modify the issue format, `getIssueMessage` may not work as expected.
-:::

packages/openapi-client/package.json

@@ -20,6 +20,11 @@
         "import": "./dist/index.mjs",
         "default": "./dist/index.mjs"
       },
+      "./helpers": {
+        "types": "./dist/helpers/index.d.mts",
+        "import": "./dist/helpers/index.mjs",
+        "default": "./dist/helpers/index.mjs"
+      },
       "./standard": {
         "types": "./dist/adapters/standard/index.d.mts",
         "import": "./dist/adapters/standard/index.mjs",
@@ -34,6 +39,7 @@
   },
   "exports": {
     ".": "./src/index.ts",
+    "./helpers": "./src/helpers/index.ts",
     "./standard": "./src/adapters/standard/index.ts",
     "./fetch": "./src/adapters/fetch/index.ts"
   },

packages/openapi-client/src/helpers/index.test.ts

@@ -0,0 +1,3 @@
+it('exports something', async () => {
+  expect(await import('./index')).toHaveProperty('getIssueMessage')
+})

packages/openapi-client/src/helpers/index.ts

@@ -0,0 +1 @@
+export { getIssueMessage, parseFormData } from '../adapters/standard'