データのストリーミング¶
🌐 AI と人間による翻訳
この翻訳は、人間のガイドに基づいて AI によって作成されました。🤝
原文の意図を取り違えていたり、不自然な表現になっている可能性があります。🤖
AI LLM をより適切に誘導するのを手伝う ことで、この翻訳を改善できます。
JSON として構造化できるデータをストリームしたい場合は、JSON Lines をストリームする を参照してください。
しかし、純粋なバイナリデータや文字列をストリームしたい場合は、次のようにできます。
情報
FastAPI 0.134.0 で追加されました。
ユースケース¶
例えば、AI LLM サービスの出力をそのまま、純粋な文字列としてストリームしたい場合に使えます。
メモリに一度に全て読み込むことなく、読み込みながらチャンクごとに送ることで、巨大なバイナリファイルをストリームすることにも使えます。
同様に、動画や音声をストリームすることもできます。処理しながら生成し、そのまま送信することも可能です。
yield を使った StreamingResponse¶
path operation 関数で response_class=StreamingResponse を宣言すると、yield を使ってデータをチャンクごとに順次送信できます。
from collections.abc import AsyncIterable, Iterable
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
app = FastAPI()
message = """
Rick: (stumbles in drunkenly, and turns on the lights) Morty! You gotta come on. You got--... you gotta come with me.
Morty: (rubs his eyes) What, Rick? What's going on?
Rick: I got a surprise for you, Morty.
Morty: It's the middle of the night. What are you talking about?
Rick: (spills alcohol on Morty's bed) Come on, I got a surprise for you. (drags Morty by the ankle) Come on, hurry up. (pulls Morty out of his bed and into the hall)
Morty: Ow! Ow! You're tugging me too hard!
Rick: We gotta go, gotta get outta here, come on. Got a surprise for you Morty.
"""
@app.get("/story/stream", response_class=StreamingResponse)
async def stream_story() -> AsyncIterable[str]:
for line in message.splitlines():
yield line
# Code below omitted 👇
👀 Full file preview
from collections.abc import AsyncIterable, Iterable
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
app = FastAPI()
message = """
Rick: (stumbles in drunkenly, and turns on the lights) Morty! You gotta come on. You got--... you gotta come with me.
Morty: (rubs his eyes) What, Rick? What's going on?
Rick: I got a surprise for you, Morty.
Morty: It's the middle of the night. What are you talking about?
Rick: (spills alcohol on Morty's bed) Come on, I got a surprise for you. (drags Morty by the ankle) Come on, hurry up. (pulls Morty out of his bed and into the hall)
Morty: Ow! Ow! You're tugging me too hard!
Rick: We gotta go, gotta get outta here, come on. Got a surprise for you Morty.
"""
@app.get("/story/stream", response_class=StreamingResponse)
async def stream_story() -> AsyncIterable[str]:
for line in message.splitlines():
yield line
@app.get("/story/stream-no-async", response_class=StreamingResponse)
def stream_story_no_async() -> Iterable[str]:
for line in message.splitlines():
yield line
@app.get("/story/stream-no-annotation", response_class=StreamingResponse)
async def stream_story_no_annotation():
for line in message.splitlines():
yield line
@app.get("/story/stream-no-async-no-annotation", response_class=StreamingResponse)
def stream_story_no_async_no_annotation():
for line in message.splitlines():
yield line
@app.get("/story/stream-bytes", response_class=StreamingResponse)
async def stream_story_bytes() -> AsyncIterable[bytes]:
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-async-bytes", response_class=StreamingResponse)
def stream_story_no_async_bytes() -> Iterable[bytes]:
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-annotation-bytes", response_class=StreamingResponse)
async def stream_story_no_annotation_bytes():
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-async-no-annotation-bytes", response_class=StreamingResponse)
def stream_story_no_async_no_annotation_bytes():
for line in message.splitlines():
yield line.encode("utf-8")
FastAPI は各データチャンクをそのまま StreamingResponse に渡し、JSON などに変換しようとはしません。
非 async な path operation 関数¶
async なしの通常の def 関数でも同様に yield を使えます。
# Code above omitted 👆
@app.get("/story/stream-no-async", response_class=StreamingResponse)
def stream_story_no_async() -> Iterable[str]:
for line in message.splitlines():
yield line
# Code below omitted 👇
👀 Full file preview
from collections.abc import AsyncIterable, Iterable
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
app = FastAPI()
message = """
Rick: (stumbles in drunkenly, and turns on the lights) Morty! You gotta come on. You got--... you gotta come with me.
Morty: (rubs his eyes) What, Rick? What's going on?
Rick: I got a surprise for you, Morty.
Morty: It's the middle of the night. What are you talking about?
Rick: (spills alcohol on Morty's bed) Come on, I got a surprise for you. (drags Morty by the ankle) Come on, hurry up. (pulls Morty out of his bed and into the hall)
Morty: Ow! Ow! You're tugging me too hard!
Rick: We gotta go, gotta get outta here, come on. Got a surprise for you Morty.
"""
@app.get("/story/stream", response_class=StreamingResponse)
async def stream_story() -> AsyncIterable[str]:
for line in message.splitlines():
yield line
@app.get("/story/stream-no-async", response_class=StreamingResponse)
def stream_story_no_async() -> Iterable[str]:
for line in message.splitlines():
yield line
@app.get("/story/stream-no-annotation", response_class=StreamingResponse)
async def stream_story_no_annotation():
for line in message.splitlines():
yield line
@app.get("/story/stream-no-async-no-annotation", response_class=StreamingResponse)
def stream_story_no_async_no_annotation():
for line in message.splitlines():
yield line
@app.get("/story/stream-bytes", response_class=StreamingResponse)
async def stream_story_bytes() -> AsyncIterable[bytes]:
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-async-bytes", response_class=StreamingResponse)
def stream_story_no_async_bytes() -> Iterable[bytes]:
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-annotation-bytes", response_class=StreamingResponse)
async def stream_story_no_annotation_bytes():
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-async-no-annotation-bytes", response_class=StreamingResponse)
def stream_story_no_async_no_annotation_bytes():
for line in message.splitlines():
yield line.encode("utf-8")
アノテーションなし¶
バイナリデータをストリームする場合、戻り値の型アノテーションを宣言する必要は実際にはありません。
この場合、FastAPI はデータを Pydantic で JSON 化したり、何らかの方法でシリアライズしようとしないため、型アノテーションはエディタやツール向けの補助にすぎず、FastAPI 自体では使用されません。
# Code above omitted 👆
@app.get("/story/stream-no-annotation", response_class=StreamingResponse)
async def stream_story_no_annotation():
for line in message.splitlines():
yield line
# Code below omitted 👇
👀 Full file preview
from collections.abc import AsyncIterable, Iterable
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
app = FastAPI()
message = """
Rick: (stumbles in drunkenly, and turns on the lights) Morty! You gotta come on. You got--... you gotta come with me.
Morty: (rubs his eyes) What, Rick? What's going on?
Rick: I got a surprise for you, Morty.
Morty: It's the middle of the night. What are you talking about?
Rick: (spills alcohol on Morty's bed) Come on, I got a surprise for you. (drags Morty by the ankle) Come on, hurry up. (pulls Morty out of his bed and into the hall)
Morty: Ow! Ow! You're tugging me too hard!
Rick: We gotta go, gotta get outta here, come on. Got a surprise for you Morty.
"""
@app.get("/story/stream", response_class=StreamingResponse)
async def stream_story() -> AsyncIterable[str]:
for line in message.splitlines():
yield line
@app.get("/story/stream-no-async", response_class=StreamingResponse)
def stream_story_no_async() -> Iterable[str]:
for line in message.splitlines():
yield line
@app.get("/story/stream-no-annotation", response_class=StreamingResponse)
async def stream_story_no_annotation():
for line in message.splitlines():
yield line
@app.get("/story/stream-no-async-no-annotation", response_class=StreamingResponse)
def stream_story_no_async_no_annotation():
for line in message.splitlines():
yield line
@app.get("/story/stream-bytes", response_class=StreamingResponse)
async def stream_story_bytes() -> AsyncIterable[bytes]:
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-async-bytes", response_class=StreamingResponse)
def stream_story_no_async_bytes() -> Iterable[bytes]:
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-annotation-bytes", response_class=StreamingResponse)
async def stream_story_no_annotation_bytes():
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-async-no-annotation-bytes", response_class=StreamingResponse)
def stream_story_no_async_no_annotation_bytes():
for line in message.splitlines():
yield line.encode("utf-8")
つまり、StreamingResponse では型アノテーションに依存せず、送信したい形式に合わせてバイト列を生成・エンコードする「自由」と「責任」があなたにあります。 🤓
バイト列をストリームする¶
主なユースケースの一つは、文字列ではなく bytes をストリームすることです。もちろん可能です。
# Code above omitted 👆
@app.get("/story/stream-bytes", response_class=StreamingResponse)
async def stream_story_bytes() -> AsyncIterable[bytes]:
for line in message.splitlines():
yield line.encode("utf-8")
# Code below omitted 👇
👀 Full file preview
from collections.abc import AsyncIterable, Iterable
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
app = FastAPI()
message = """
Rick: (stumbles in drunkenly, and turns on the lights) Morty! You gotta come on. You got--... you gotta come with me.
Morty: (rubs his eyes) What, Rick? What's going on?
Rick: I got a surprise for you, Morty.
Morty: It's the middle of the night. What are you talking about?
Rick: (spills alcohol on Morty's bed) Come on, I got a surprise for you. (drags Morty by the ankle) Come on, hurry up. (pulls Morty out of his bed and into the hall)
Morty: Ow! Ow! You're tugging me too hard!
Rick: We gotta go, gotta get outta here, come on. Got a surprise for you Morty.
"""
@app.get("/story/stream", response_class=StreamingResponse)
async def stream_story() -> AsyncIterable[str]:
for line in message.splitlines():
yield line
@app.get("/story/stream-no-async", response_class=StreamingResponse)
def stream_story_no_async() -> Iterable[str]:
for line in message.splitlines():
yield line
@app.get("/story/stream-no-annotation", response_class=StreamingResponse)
async def stream_story_no_annotation():
for line in message.splitlines():
yield line
@app.get("/story/stream-no-async-no-annotation", response_class=StreamingResponse)
def stream_story_no_async_no_annotation():
for line in message.splitlines():
yield line
@app.get("/story/stream-bytes", response_class=StreamingResponse)
async def stream_story_bytes() -> AsyncIterable[bytes]:
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-async-bytes", response_class=StreamingResponse)
def stream_story_no_async_bytes() -> Iterable[bytes]:
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-annotation-bytes", response_class=StreamingResponse)
async def stream_story_no_annotation_bytes():
for line in message.splitlines():
yield line.encode("utf-8")
@app.get("/story/stream-no-async-no-annotation-bytes", response_class=StreamingResponse)
def stream_story_no_async_no_annotation_bytes():
for line in message.splitlines():
yield line.encode("utf-8")
カスタム PNGStreamingResponse¶
上記の例ではバイト列をストリームしましたが、レスポンスに Content-Type ヘッダがないため、クライアントは受け取るデータの種類を認識できませんでした。
StreamingResponse を継承したカスタムクラスを作成し、ストリームするデータに応じて Content-Type ヘッダを設定できます。
例えば、media_type 属性で Content-Type を image/png に設定する PNGStreamingResponse を作成できます:
# Code above omitted 👆
from fastapi.responses import StreamingResponse
# Code here omitted 👈
class PNGStreamingResponse(StreamingResponse):
media_type = "image/png"
# Code below omitted 👇
👀 Full file preview
import base64
from collections.abc import AsyncIterable, Iterable
from io import BytesIO
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
image_base64 = "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"
binary_image = base64.b64decode(image_base64)
def read_image() -> BytesIO:
return BytesIO(binary_image)
app = FastAPI()
class PNGStreamingResponse(StreamingResponse):
media_type = "image/png"
@app.get("/image/stream", response_class=PNGStreamingResponse)
async def stream_image() -> AsyncIterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async", response_class=PNGStreamingResponse)
def stream_image_no_async() -> Iterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-yield-from", response_class=PNGStreamingResponse)
def stream_image_no_async_yield_from() -> Iterable[bytes]:
with read_image() as image_file:
yield from image_file
@app.get("/image/stream-no-annotation", response_class=PNGStreamingResponse)
async def stream_image_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-no-annotation", response_class=PNGStreamingResponse)
def stream_image_no_async_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk
その後、path operation 関数で response_class=PNGStreamingResponse としてこの新しいクラスを使用できます:
# Code above omitted 👆
@app.get("/image/stream", response_class=PNGStreamingResponse)
async def stream_image() -> AsyncIterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
# Code below omitted 👇
👀 Full file preview
import base64
from collections.abc import AsyncIterable, Iterable
from io import BytesIO
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
image_base64 = "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"
binary_image = base64.b64decode(image_base64)
def read_image() -> BytesIO:
return BytesIO(binary_image)
app = FastAPI()
class PNGStreamingResponse(StreamingResponse):
media_type = "image/png"
@app.get("/image/stream", response_class=PNGStreamingResponse)
async def stream_image() -> AsyncIterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async", response_class=PNGStreamingResponse)
def stream_image_no_async() -> Iterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-yield-from", response_class=PNGStreamingResponse)
def stream_image_no_async_yield_from() -> Iterable[bytes]:
with read_image() as image_file:
yield from image_file
@app.get("/image/stream-no-annotation", response_class=PNGStreamingResponse)
async def stream_image_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-no-annotation", response_class=PNGStreamingResponse)
def stream_image_no_async_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk
ファイルを模擬する¶
この例では io.BytesIO でファイルを模擬しています。これはメモリ上だけに存在するファイルライクオブジェクトですが、通常のファイルと同じインターフェースを提供します。
例えば、ファイルと同様にイテレートして内容を読み出せます。
import base64
from collections.abc import AsyncIterable, Iterable
from io import BytesIO
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
image_base64 = "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"
binary_image = base64.b64decode(image_base64)
def read_image() -> BytesIO:
return BytesIO(binary_image)
app = FastAPI()
class PNGStreamingResponse(StreamingResponse):
media_type = "image/png"
@app.get("/image/stream", response_class=PNGStreamingResponse)
async def stream_image() -> AsyncIterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
# Code below omitted 👇
👀 Full file preview
import base64
from collections.abc import AsyncIterable, Iterable
from io import BytesIO
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
image_base64 = "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"
binary_image = base64.b64decode(image_base64)
def read_image() -> BytesIO:
return BytesIO(binary_image)
app = FastAPI()
class PNGStreamingResponse(StreamingResponse):
media_type = "image/png"
@app.get("/image/stream", response_class=PNGStreamingResponse)
async def stream_image() -> AsyncIterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async", response_class=PNGStreamingResponse)
def stream_image_no_async() -> Iterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-yield-from", response_class=PNGStreamingResponse)
def stream_image_no_async_yield_from() -> Iterable[bytes]:
with read_image() as image_file:
yield from image_file
@app.get("/image/stream-no-annotation", response_class=PNGStreamingResponse)
async def stream_image_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-no-annotation", response_class=PNGStreamingResponse)
def stream_image_no_async_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk
技術詳細
他の2つの変数 image_base64 と binary_image は、画像を Base64 でエンコードし、それを bytes に変換してから io.BytesIO に渡したものです。
この例では1つのファイル内に完結させ、コピーしてそのまま実行できるようにするためだけのものです。 🥚
with ブロックを使うことで、ジェネレータ関数（yield を持つ関数）が終了した後、つまりレスポンス送信が完了した後に、そのファイルライクオブジェクトが確実にクローズされます。
この例では io.BytesIO によるメモリ内の疑似ファイルなので重要度は高くありませんが、実ファイルの場合は処理後に確実にクローズすることが重要です。
ファイルと非同期¶
多くの場合、ファイルライクオブジェクトはデフォルトでは async/await と互換性がありません。
例えば、await file.read() や async for chunk in file のような操作は提供されていません。
また、多くの場合、ディスクやネットワークから読み出すため、読み取りはブロッキング（イベントループをブロックし得る）処理になります。
情報
上記の例は例外で、io.BytesIO は既にメモリ上にあるため、読み取りが何かをブロックすることはありません。
しかし多くの場合、ファイルやファイルライクオブジェクトの読み取りはブロッキングになります。
イベントループのブロッキングを避けるには、path operation 関数を async def ではなく通常の def で宣言してください。そうすると FastAPI はその関数をスレッドプールワーカー上で実行し、メインループのブロッキングを避けます。
# Code above omitted 👆
@app.get("/image/stream-no-async", response_class=PNGStreamingResponse)
def stream_image_no_async() -> Iterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
# Code below omitted 👇
👀 Full file preview
import base64
from collections.abc import AsyncIterable, Iterable
from io import BytesIO
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
image_base64 = "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"
binary_image = base64.b64decode(image_base64)
def read_image() -> BytesIO:
return BytesIO(binary_image)
app = FastAPI()
class PNGStreamingResponse(StreamingResponse):
media_type = "image/png"
@app.get("/image/stream", response_class=PNGStreamingResponse)
async def stream_image() -> AsyncIterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async", response_class=PNGStreamingResponse)
def stream_image_no_async() -> Iterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-yield-from", response_class=PNGStreamingResponse)
def stream_image_no_async_yield_from() -> Iterable[bytes]:
with read_image() as image_file:
yield from image_file
@app.get("/image/stream-no-annotation", response_class=PNGStreamingResponse)
async def stream_image_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-no-annotation", response_class=PNGStreamingResponse)
def stream_image_no_async_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk
豆知識
async 関数内からブロッキングなコードを呼び出す必要がある場合、あるいはブロッキングな関数内から async 関数を呼び出す必要がある場合は、FastAPI の兄弟ライブラリである Asyncer を利用できます。
yield from¶
ファイルライクオブジェクトのようなものをイテレートして各要素に対して yield している場合、for ループを省略して、yield from で各要素をそのまま送ることもできます。
これは FastAPI 固有ではなく単なる Python の機能ですが、知っておくと便利な小ワザです。 😎
# Code above omitted 👆
@app.get("/image/stream-no-async-yield-from", response_class=PNGStreamingResponse)
def stream_image_no_async_yield_from() -> Iterable[bytes]:
with read_image() as image_file:
yield from image_file
# Code below omitted 👇
👀 Full file preview
import base64
from collections.abc import AsyncIterable, Iterable
from io import BytesIO
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
image_base64 = "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"
binary_image = base64.b64decode(image_base64)
def read_image() -> BytesIO:
return BytesIO(binary_image)
app = FastAPI()
class PNGStreamingResponse(StreamingResponse):
media_type = "image/png"
@app.get("/image/stream", response_class=PNGStreamingResponse)
async def stream_image() -> AsyncIterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async", response_class=PNGStreamingResponse)
def stream_image_no_async() -> Iterable[bytes]:
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-yield-from", response_class=PNGStreamingResponse)
def stream_image_no_async_yield_from() -> Iterable[bytes]:
with read_image() as image_file:
yield from image_file
@app.get("/image/stream-no-annotation", response_class=PNGStreamingResponse)
async def stream_image_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk
@app.get("/image/stream-no-async-no-annotation", response_class=PNGStreamingResponse)
def stream_image_no_async_no_annotation():
with read_image() as image_file:
for chunk in image_file:
yield chunk