async def sse_items_string():
    yield ServerSentEvent(data="plain text data")


@app.post("/items/stream-post", response_class=EventSourceResponse)
async def sse_items_post() -> AsyncIterable[Item]:
    for item in items:
        yield item


@app.get("/items/stream-raw", response_class=EventSourceResponse)
async def sse_items_raw():
    yield ServerSentEvent(raw_data="plain text without quotes")

    request.addHeader("Accept", "text/plain")

    @Suppress("DEPRECATION")
    httpClient.execute(request).use { response ->
      assertThat(response.code).isEqualTo(200)
      assertThat(EntityUtils.toString(response.entity)).isEqualTo("hello, Apache HttpClient 5.x")
    }

    val recorded = server.takeRequest()
    assertThat(recorded.headers["Accept"]).isEqualTo("text/plain")
    assertThat(

import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicBoolean;
import org.jspecify.annotations.Nullable;

/**
 * Utilities necessary for working with libraries that supply plain {@link Future} instances. Note
 * that, whenever possible, it is strongly preferred to modify those libraries to return {@code
 * ListenableFuture} directly.
 *

      .assertNoMoreLogs()
  }

  private fun request(): Request.Builder = Request.Builder().url(url)

  companion object {
    private val PLAIN = "text/plain".toMediaType()
  }

      client
        .newRequest(server.url("/").toUri())
        .header("Accept", "text/plain")
    val response = request.send()
    assertThat(response.status).isEqualTo(200)
    assertThat(response.contentAsString).isEqualTo("hello, Jetty HTTP Client")

    val recorded = server.takeRequest()
    assertThat(recorded.headers["Accept"]).isEqualTo("text/plain")
    assertThat(recorded.headers["Accept-Encoding"]).isEqualTo("gzip")

  /** Support for {@link Iterator#remove()}. */
  SUPPORTS_REMOVE,
  /**
   * Support for {@link ListIterator#add(Object)}; ignored for plain {@link Iterator}
   * implementations.
   */
  SUPPORTS_ADD,
  /**
   * Support for {@link ListIterator#set(Object)}; ignored for plain {@link Iterator}
   * implementations.
   */
  SUPPORTS_SET;

  /**

/** A utility method to perform unchecked casts to suppress errors produced by nullness analyses. */
@GwtCompatible
final class NullnessCasts {
  /**
   * Accepts a {@code @Nullable T} and returns a plain {@code T}, without performing any check that
   * that conversion is safe.
   *
   * <p>This method is intended to help with usages of type parameters that have {@linkplain

        .header("Accept", "text/plain")
        .build()

    val response = httpClient.send(request, BodyHandlers.ofString())
    assertThat(response.statusCode()).isEqualTo(200)
    assertThat(response.body()).isEqualTo("hello, Java HTTP Client")

    val recorded = server.takeRequest()
    assertThat(recorded.headers["Accept"]).isEqualTo("text/plain")

    for item in items:
        yield item
```

## Server-Sent Events (SSE)

To stream Server-Sent Events, use `response_class=EventSourceResponse` and `yield` items from the endpoint.

Plain objects are automatically JSON-serialized as `data:` fields, declare the return type so the serialization is done by Pydantic:

```python
from collections.abc import AsyncIterable

from fastapi import FastAPI

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