@ai-sdk/amazon-bedrock/src/amazon-bedrock-event-stream-decoder.ts

The **[Amazon Bedrock provider](https://ai-sdk.dev/providers/ai-sdk-providers/amazon-bedrock)** for the [AI SDK](https://ai-sdk.dev/docs) contains language model support for the Amazon Bedrock [converse API](https://docs.aws.amazon.com/bedrock/latest/APIR

import { EventStreamCodec } from '@smithy/eventstream-codec';
import { toUtf8, fromUtf8 } from '@smithy/util-utf8';

export interface DecodedEvent {
  messageType: string;
  eventType: string;
  data: string;
}

export function createAmazonBedrockEventStreamDecoder<T>(
  body: ReadableStream<Uint8Array>,
  processEvent: (
    event: DecodedEvent,
    controller: TransformStreamDefaultController<T>,
  ) => void | Promise<void>,
): ReadableStream<T> {
  const codec = new EventStreamCodec(toUtf8, fromUtf8);
  let buffer = new Uint8Array(0);
  const textDecoder = new TextDecoder();

  return body.pipeThrough(
    new TransformStream<Uint8Array, T>({
      async transform(chunk, controller) {
        const newBuffer = new Uint8Array(buffer.length + chunk.length);
        newBuffer.set(buffer);
        newBuffer.set(chunk, buffer.length);
        buffer = newBuffer;

        while (buffer.length >= 4) {
          const totalLength = new DataView(
            buffer.buffer,
            buffer.byteOffset,
            buffer.byteLength,
          ).getUint32(0, false);

          if (buffer.length < totalLength) {
            break;
          }

          try {
            const subView = buffer.subarray(0, totalLength);
            const decoded = codec.decode(subView);

            buffer = buffer.slice(totalLength);

            const messageType = decoded.headers[':message-type']
              ?.value as string;
            const eventType = decoded.headers[':event-type']?.value as string;
            const data = textDecoder.decode(decoded.body);

            await processEvent({ messageType, eventType, data }, controller);
          } catch {
            break;
          }
        }
      },
    }),
  );
}