File upload & streamed response not working through NGINX

[xxcodianxx]

First Check

• I added a very descriptive title to this issue.
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Example Code

@app.post("/uploadfile")
async def upload_something(file: UploadFile = File(...)):
    return {'filename': file.filename}

Description

Streamed file requests, like the example above do not work when passing through nginx.

For some reason, whenever the above example is tried with the server before a NGINX proxy, with the proxy_pass directive, streamed requests do not get received by FastAPI.

eg.

location /api/ {
    proxy_pass http://127.0.0.1:8000/;
}

Contacting the server with a file upload directly works:

$ curl -F 'file=@somefile.txt' http://directly_to_fastapi/uploadfile

but this does not:

$ curl -F 'file=@somefile.txt' http://through_nginx/api/uploadfile

Exiting with error:

WARNING:  Invalid HTTP request received.
Traceback (most recent call last):
  File "/home/user/.local/lib/python3.10/site-packages/uvicorn/protocols/http/httptools_impl.py", line 132, in data_received
    self.parser.feed_data(data)
  File "httptools/parser/parser.pyx", line 212, in httptools.parser.parser.HttpParser.feed_data
httptools.parser.errors.HttpParserInvalidMethodError: Invalid method encountered

I have searched far and wide for a solution to this, however it seems that no one has come up with any sane solution.

Furthermore, streamed requests also break when passing through NGINX, eg.

@app.post("/stream")
async def stream_something(request: Request):
    chunks = 0 
    print("starting to stream")
    async for _ in request.stream():
        chunks += 1
        print(f"got chunk {chunks}")

does not work with the same error returned, unless the FastAPI server is contacted directly (not through NGINX).

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.74.0

Python Version

Python 3.10.1

Additional Context

$ nginx -V
nginx version: nginx/1.21.6
built by gcc 10.2.1 20210110 (Debian 10.2.1-6) 
built with OpenSSL 1.1.1k  25 Mar 2021
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib/nginx/modules --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-log-path=/var/log/nginx/access.log --pid-path=/var/run/nginx.pid --lock-path=/var/run/nginx.lock --http-client-body-temp-path=/var/cache/nginx/client_temp --http-proxy-temp-path=/var/cache/nginx/proxy_temp --http-fastcgi-temp-path=/var/cache/nginx/fastcgi_temp --http-uwsgi-temp-path=/var/cache/nginx/uwsgi_temp --http-scgi-temp-path=/var/cache/nginx/scgi_temp --user=nginx --group=nginx --with-compat --with-file-aio --with-threads --with-http_addition_module --with-http_auth_request_module --with-http_dav_module --with-http_flv_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_mp4_module --with-http_random_index_module --with-http_realip_module --with-http_secure_link_module --with-http_slice_module --with-http_ssl_module --with-http_stub_status_module --with-http_sub_module --with-http_v2_module --with-mail --with-mail_ssl_module --with-stream --with-stream_realip_module --with-stream_ssl_module --with-stream_ssl_preread_module --with-cc-opt='-g -O2 -ffile-prefix-map=/data/builder/debuild/nginx-1.21.6/debian/debuild-base/nginx-1.21.6=. -fstack-protector-strong -Wformat -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fPIC' --with-ld-opt='-Wl,-z,relro -Wl,-z,now -Wl,--as-needed -pie'

I am running NGINX with the following Docker command line (for development):

$ docker run -it --rm --network host -v /somewhere/nginx.conf:/etc/nginx/nginx.conf:ro nginx

My Docker version is:

$ docker --version
Docker version 20.10.12, build e91ed5707e

And my full NGINX conf I am using to test this:

http {
    server_tokens off;

    client_max_body_size 128M;

    server {
        listen 80;
        root /mnt;

        location / {
            # where my hot reload frontend is (irrelevant to this)
            proxy_pass http://127.0.0.1:8080/;
        }

        location /api/ {
            # where my server is
            proxy_pass http://127.0.0.1:8000/;
        }
    }
}

events {}

Logs from NGINX whenever request attempts to reach FastAPI server:

2022/02/20 11:09:42 [error] 31#31: *3 writev() failed (104: Connection reset by peer) while sending request to upstream, client: 127.0.0.1, server: , request: "POST /api/uploadfile HTTP/1.1", upstream: "http://127.0.0.1:8000/uploadfile", host: "localhost"
127.0.0.1 - - [20/Feb/2022:11:09:42 +0000] "POST /api/uploadfile HTTP/1.1" 502 175 "-" "curl/7.81.0"

[frankie567]

Are you serving your application with uvicorn? I had a similar issue some days ago; it seems it was related to a bug in uvicorn. Upgrade to uvicorn==0.17.5 fixed the issue for me.

[xxcodianxx]

Yep! This indeed fixes it! Thanks for the help! 👍