ServerFn

ERSC.ServerFn.make({ input, handler }) creates a native React Server Function reference. input decodes the invocation payload and infers the handler parameter; do not annotate it. The handler returns an Effect whose requirements fit the ERSC service universe. The client reference accepts the Schema's encoded type and resolves Promise<Output>; the handler receives its decoded type.

For multiple positional arguments, supply a readonly schema list as input. Each caller argument uses its Schema's encoded type; each handler argument uses its decoded type, in the same order. Inline lists infer their tuple shape without as const. Use input: [] for no arguments. input: Schema.Array(...) and input: Schema.Tuple(...) still describe one argument, not a positional argument list.

const followAuthor = ERSC.ServerFn.make({
  input: Schema.Struct({ authorId: Schema.NonEmptyString }),
  handler: ({ authorId }) => Effect.succeed({ authorId, following: true }),
});

Schema transformations may use a different encoded type. To pass a Server Function directly to form.action, decode FormData and return void:

const followAuthorForm = ERSC.ServerFn.make({
  input: Schema.fromFormData(Schema.Struct({ authorId: Schema.NonEmptyString })),
  handler: ({ authorId }) => Effect.logInfo('Followed author', { authorId }),
});

<form action={followAuthorForm}>
  <input name='authorId' />
  <button type='submit'>Follow</button>
</form>;

A ServerFn created from a derived view activates its middleware for the POST. The Middleware reference defines refresh reach and ordering.

For a useActionState form, declare both the previous state and submitted FormData:

const StateSchema = Schema.Struct({ message: Schema.String });
const FormSchema = Schema.fromFormData(Schema.Struct({ name: Schema.NonEmptyString }));

const greet = ERSC.ServerFn.make({
  input: [StateSchema, FormSchema],
  handler: (_previousState, { name }) => Effect.succeed({ message: `Hello, ${name}` }),
});

Pass the native reference directly to useActionState(greet, { message: '' }) and its returned action to <form action>. React supplies previous state and FormData for hydrated and progressive submissions. Previous state is client input: validate it, but never trust it for authorization or authoritative application state. Native .bind can prefill leading arguments.

Direct server invocation throws. Encode expected failure in a discriminated output union; unexpected failures reject the Promise. Browser requests require an Origin matching the application host and may contain at most 10 MiB. See the known limitations for the typed failure channel and progressive bound arguments.

Related

• Middleware