Function serializeAsyncIterable

packages/react-server/src/ReactFlightServer.js:1191–1329

(
  request: Request,
  task: Task,
  iterable: $AsyncIterable<ReactClientValue, ReactClientValue, void>,
  iterator: $AsyncIterator<ReactClientValue, ReactClientValue, void>,
)

}

function serializeAsyncIterable(
  request: Request,
  task: Task,
  iterable: $AsyncIterable<ReactClientValue, ReactClientValue, void>,
  iterator: $AsyncIterator<ReactClientValue, ReactClientValue, void>,
): string {
  // Generators/Iterators are Iterables but they're also their own iterator
  // functions. If that's the case, we treat them as single-shot. Otherwise,
  // we assume that this iterable might be a multi-shot and allow it to be
  // iterated more than once on the client.
  const isIterator = iterable === iterator;

  // This task won't actually be retried. We just use it to attempt synchronous renders.
  const streamTask = createTask(
    request,
    task.model,
    task.keyPath,
    task.implicitSlot,
    task.formatContext,
    request.abortableTasks,
    enableProfilerTimer &&
      (enableComponentPerformanceTrack || enableAsyncDebugInfo)
      ? task.time
      : 0,
    __DEV__ ? task.debugOwner : null,
    __DEV__ ? task.debugStack : null,
    __DEV__ ? task.debugTask : null,
  );

  if (__DEV__) {
    const debugInfo: ?ReactDebugInfo = (iterable: any)._debugInfo;
    if (debugInfo) {
      forwardDebugInfo(request, streamTask, debugInfo);
    }
  }

  // The task represents the Stop row. This adds a Start row.
  request.pendingChunks++;
  const startStreamRow =
    streamTask.id.toString(16) + ':' + (isIterator ? 'x' : 'X') + '\n';
  request.completedRegularChunks.push(stringToChunk(startStreamRow));

  function progress(
    entry:
      | {done: false, +value: ReactClientValue, ...}
      | {done: true, +value: ReactClientValue, ...},
  ) {
    if (streamTask.status !== PENDING) {
      return;
    }

    if (entry.done) {
      streamTask.status = COMPLETED;
      let endStreamRow;
      if (entry.value === undefined) {
        endStreamRow = streamTask.id.toString(16) + ':C\n';
      } else {
        // Unlike streams, the last value may not be undefined. If it's not