If you declare a `response_class=StreamingResponse` in your *path operation function*, you can use `yield` to send each chunk of data in turn.

{* ../../docs_src/stream_data/tutorial001_py310.py ln[1:23] hl[20,23] *}

FastAPI will give each chunk of data to the `StreamingResponse` as is, it won't try to convert it to JSON or anything similar.

### Non-async *path operation functions* { #non-async-path-operation-functions }

 *
 * <p>{@link #processBytes} will be called for each chunk of data that is read, and should return
 * {@code false} when you want to stop processing.
 *
 * @author Chris Nokleberg
 * @since 1.0
 */
@DoNotMock("Implement it normally")
@J2ktIncompatible
@GwtIncompatible
public interface ByteProcessor<T extends @Nullable Object> {
  /**
   * This method will be called for each chunk of bytes in an input stream. The implementation

        final PrintWriter writer = new PrintWriter(stringWriter);

        chatApiManager.sendSseEvent(writer, "chunk", Map.of("content", "Hello "));

        final String output = stringWriter.toString();
        assertTrue(output.contains("event: chunk"));
        assertTrue(output.contains("\"content\":\"Hello \""));
    }

    @Test
    public void test_sendSseEvent_error() {

但如果你想串流純二進位資料或字串，以下是做法。

/// info

已在 FastAPI 0.134.0 新增。

///

## 使用情境 { #use-cases }

當你想串流純字串時可以用這個機制，例如直接轉發來自 AI LLM 服務的輸出。

你也可以用它來串流大型二進位檔案，邊讀邊將每個區塊（chunk）串流出去，而不必一次把整個檔案載入記憶體。

你也可以用同樣方式串流視訊或音訊，甚至可以在處理的同時即時產生並傳送。

## 使用 `yield` 的 `StreamingResponse` { #a-streamingresponse-with-yield }

如果在你的路徑操作函式中宣告 `response_class=StreamingResponse`，就可以用 `yield` 逐一送出每個資料區塊。

    public SrvCopyChunkCopyResponse() {
    }

    private int chunksWritten;
    private int chunkBytesWritten;
    private int totalBytesWritten;

    /**
     * Gets the number of bytes written in the last chunk
     * @return the chunkBytesWritten
     */
    public int getChunkBytesWritten() {
        return this.chunkBytesWritten;
    }

    /**
     * Gets the number of chunks successfully written

   * @param last when true, there is no response data.
   */
  fun onHeaders(
    streamId: Int,
    responseHeaders: List<Header>,
    last: Boolean,
  ): Boolean

  /**
   * A chunk of response data corresponding to a pushed request.  This data must either be read or
   * skipped.
   *
   * @param streamId server-initiated stream ID: an even number.

        // Write 11MB of data
        try (FileOutputStream fos = new FileOutputStream(largeFile)) {
            final byte[] chunk = new byte[1024 * 1024]; // 1MB
            for (int i = 0; i < 11; i++) { // Write 11MB
                fos.write(chunk);
            }
        }

        try {
            FileUtil.readBytes(largeFile);
            fail("Expected IORuntimeException for large file");

    /**
     * Function code to transceive data on a named pipe
     */
    public static final int FSCTL_PIPE_TRANSCEIVE = 0x0011C017;
    /**
     * Function code for server-side copy chunk operation
     */
    public static final int FSCTL_SRV_COPYCHUNK = 0x001440F2;
    /**
     * Function code to enumerate volume shadow copy snapshots
     */

      throw new UnsupportedOperationException();
    }

    @Override
    public String toString() {
      StringBuilder sb = new StringBuilder(length);
      for (CharSequence chunk : chunks) {
        sb.append(chunk);
      }
      return sb.toString();
    }
  }

  /**
   * Puts an array of bytes into this sink.
   *
   * @param bytes a byte array
   * @return this instance
   */
  @CanIgnoreReturnValue
  PrimitiveSink putBytes(byte[] bytes);

  /**
   * Puts a chunk of an array of bytes into this sink. {@code bytes[off]} is the first byte written,
   * {@code bytes[off + len - 1]} is the last.
   *
   * @param bytes a byte array
   * @param off the start offset in the array