How to return and download Excel file using FastAPI?

Question

How do I return an excel file (version: Office365) using FastAPI? The documentation seems pretty straightforward. But, I don't know what media_type to use. Here's my code:

import os
from fastapi import FastAPI
from fastapi.responses import FileResponse
from pydantic import BaseModel
from typing import Optional

excel_file_path = r"C:\Users\some_path\the_excel_file.xlsx"

app = FastAPI()

class ExcelRequestInfo(BaseModel):
    client_id: str


@app.post("/post_for_excel_file/")
async def serve_excel(item: ExcelRequestInfo):
    # (Generate excel using item.)
    # For now, return a fixed excel.
    return FileResponse(
        path=excel_file_path,

        # Swagger UI says 'cannot render, look at console', but console shows nothing.
        media_type='application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'

        # Swagger renders funny chars with this argument:
        # 'application/vnd.ms-excel'
    )

Assuming I get it right, how to download the file? Can I use Swagger UI generated by FastAPI to view the sheet? Or, curl? Ideally, I'd like to be able to download and view the file in Excel.

Answer 1

You could set the Content-Disposition header using the attachment parameter, indicating to the browser that the file should be downloaded, as described in the answers here and here. Swagger UI will provide a Download file link for you to download the file, as soon as you execute the request.

headers = {'Content-Disposition': 'attachment; filename="Book.xlsx"'}
return FileResponse(excel_file_path, headers=headers)

To have the file viewed in the browser, one can use the inline, instead of attachment, parameter in the Content-Disposition header, as explained in the linked answers earlier. However, for the browser to be able to display the Excel file, one should set the correct media_type in the FileResponse (for Excel files see here), as well as .xlsx (or .xls) must be a known file extension to the browser (this is usually achieved through browser extensions/plug-ins).