Return multiple files from fastapi

Question

Using fastapi, I can't figure out how to send multiple files as a response. For example, to send a single file, I'll use something like this

from fastapi import FastAPI, Response

app = FastAPI()

@app.get("/image_from_id/")
async def image_from_id(image_id: int):

    # Get image from the database
    img = ...
    return Response(content=img, media_type="application/png")

However, I'm not sure what it looks like to send a list of images. Ideally, I'd like to do something like this:

@app.get("/images_from_ids/")
async def image_from_id(image_ids: List[int]):

    # Get a list of images from the database
    images = ...
    return Response(content=images, media_type="multipart/form-data")

However, this returns the error

    def render(self, content: typing.Any) -> bytes:
        if content is None:
            return b""
        if isinstance(content, bytes):
            return content
>       return content.encode(self.charset)
E       AttributeError: 'list' object has no attribute 'encode'

Answer 1

Zipping is the best option that will have same results on all browsers. you can zip files dynamically.

import os
import zipfile
import StringIO


def zipfiles(filenames):
    zip_subdir = "archive"
    zip_filename = "%s.zip" % zip_subdir

    # Open StringIO to grab in-memory ZIP contents
    s = StringIO.StringIO()
    # The zip compressor
    zf = zipfile.ZipFile(s, "w")

    for fpath in filenames:
        # Calculate path for file in zip
        fdir, fname = os.path.split(fpath)
        zip_path = os.path.join(zip_subdir, fname)

        # Add file, at correct path
        zf.write(fpath, zip_path)

    # Must close zip for all contents to be written
    zf.close()

    # Grab ZIP file from in-memory, make response with correct MIME-type
    resp = Response(s.getvalue(), mimetype = "application/x-zip-compressed")
    # ..and correct content-disposition
    resp['Content-Disposition'] = 'attachment; filename=%s' % zip_filename

    return resp


@app.get("/image_from_id/")
async def image_from_id(image_id: int):

    # Get image from the database
    img = ...
    return zipfiles(img)

As alternative you can use base64 encoding to embed an (very small) image into json response. but i don't recommend it.

You can also use MIME/multipart but keep in mind that i was created for email messages and/or POST transmission to the HTTP server. It was never intended to be received and parsed on the client side of a HTTP transaction. Some browsers support it, some others don't. (so i think you shouldn't use this either)

Answer 2

I've got some problems with @kia's answer on Python3 and latest fastapi so here is a fix that I got working it includes BytesIO instead of Stringio, fixes for response attribute and removal of top level archive folder

import os
import zipfile
import io


def zipfiles(filenames):
    zip_filename = "archive.zip"

    s = io.BytesIO()
    zf = zipfile.ZipFile(s, "w")

    for fpath in filenames:
        # Calculate path for file in zip
        fdir, fname = os.path.split(fpath)

        # Add file, at correct path
        zf.write(fpath, fname)

    # Must close zip for all contents to be written
    zf.close()

    # Grab ZIP file from in-memory, make response with correct MIME-type
    resp = Response(s.getvalue(), media_type="application/x-zip-compressed", headers={
        'Content-Disposition': f'attachment;filename={zip_filename}'
    })

    return resp

@app.get("/image_from_id/")
async def image_from_id(image_id: int):

    # Get image from the database
    img = ...
    return zipfiles(img)

Answer 3

Furthermore, you can create the zip on-the-fly and stream it back to the user using a StreamingResponse object:

import os
import zipfile
import StringIO
from fastapi.responses import StreamingResponse

def zipfile(filenames):
    zip_io = BytesIO()
    with zipfile.ZipFile(zip_io, mode='w', compression=zipfile.ZIP_DEFLATED) as temp_zip:
        for fpath in filenames:
            # Calculate path for file in zip
            fdir, fname = os.path.split(fpath)
            zip_path = os.path.join(zip_subdir, fname)
            # Add file, at correct path
            temp_zip.write((fpath, zip_path))
    return StreamingResponse(
        iter([zip_io.getvalue()]), 
        media_type="application/x-zip-compressed", 
        headers = { "Content-Disposition": f"attachment; filename=images.zip"}
    )