Function normalizeGatewayStreamUsage

src/node/utils/gatewayStreamNormalization.ts:107–137

()

 * Only transforms "finish" events; all other chunks pass through unchanged.
 */
export function normalizeGatewayStreamUsage(): TransformStream {
  return new TransformStream({
    transform(chunk: unknown, controller: TransformStreamDefaultController) {
      if (typeof chunk !== "object" || chunk == null) {
        controller.enqueue(chunk);
        return;
      }

      const c = chunk as Record<string, unknown>;
      if (c.type !== "finish") {
        controller.enqueue(chunk);
        return;
      }

      // Normalize usage: convert flat → v3 nested if needed
      let usage = c.usage;
      if (usage != null && !isV3Usage(usage)) {
        usage = flatUsageToV3(usage as Record<string, unknown>);
      }

      // Normalize finishReason: convert string → { unified, raw } if needed
      const finishReason = normalizeFinishReason(c.finishReason);

      controller.enqueue({
        ...c,
        ...(usage != null && { usage }),
        ...(finishReason != null && { finishReason }),
      });
    },
  });
}