Function decodeAction

packages/react-server/src/ReactFlightActionServer.js:107–164

(
  body: FormData,
  serverManifest: ServerManifest,
)

}

export function decodeAction<T>(
  body: FormData,
  serverManifest: ServerManifest,
): Promise<() => T> | null {
  // We're going to create a new formData object that holds all the fields except
  // the implementation details of the action data.
  const formData = new FormData();

  let action: Promise<(formData: FormData) => T> | null = null;
  const seenActions = new Set<string>();

  // $FlowFixMe[prop-missing]
  body.forEach((value: string | File, key: string) => {
    if (!key.startsWith('$ACTION_')) {
      // $FlowFixMe[incompatible-call]
      formData.append(key, value);
      return;
    }
    // Later actions may override earlier actions if a button is used to
    // override the default form action. However, we don't expect the same
    // action ref field to be sent multiple times in legitimate form data.
    if (key.startsWith('$ACTION_REF_')) {
      if (seenActions.has(key)) {
        return;
      }
      seenActions.add(key);
      const formFieldPrefix = '$ACTION_' + key.slice(12) + ':';
      const metaData = decodeBoundActionMetaData(
        body,
        serverManifest,
        formFieldPrefix,
      );
      action = loadServerReference(serverManifest, metaData);
      return;
    }
    // A simple action with no bound arguments may appear twice in the form data
    // if a button specifies the same action as the default form action. We only
    // load the first one, as they're guaranteed to be identical.
    if (key.startsWith('$ACTION_ID_')) {
      if (seenActions.has(key)) {
        return;
      }
      seenActions.add(key);
      const id = key.slice(11);
      action = loadServerReference(serverManifest, {
        id,
        bound: null,
      });
      return;
    }
  });

  if (action === null) {
    return null;
  }
  // Return the action with the remaining FormData bound to the first argument.
  return action.then(fn => fn.bind(null, formData));
}