POST requests without Content-Length or Transfer-Encoding return 400 Bad Request

[o7si]

I created a POST endpoint using the following code:

#include <httplib.h>
using namespace httplib;
int main(void) {
  Server svr;
  svr.Post("/test", [](const Request &req, Response &res) {
    res.set_content("", "text/plain");
  });
  svr.listen("0.0.0.0", 7777);
}

Then I accessed it using curl:

# curl -X POST "http://localhost:7777/test" -v
* Host localhost:7777 was resolved.
* IPv6: ::1
* IPv4: 127.0.0.1
*   Trying [::1]:7777...
* connect to ::1 port 7777 from ::1 port 59000 failed: Connection refused
*   Trying 127.0.0.1:7777...
* Connected to localhost (127.0.0.1) port 7777
> POST /test HTTP/1.1
> Host: localhost:7777
> User-Agent: curl/8.7.1
> Accept: */*
> 
* Request completely sent off
< HTTP/1.1 400 Bad Request
< Connection: close
< Content-Length: 0
< 
* Closing connection

After analyzing the code, I found that the issue occurs at this location:

cpp-httplib/httplib.h

Lines 7934 to 7941 in 27ee115

	if (req.method == "DELETE" && !req.has_header("Content-Length")) {
	return true;
	}
	if (!detail::read_content(strm, req, payload_max_length_, res.status, nullptr,
	out, true)) {
	return false;
	}

Based on my reading of RFC 7231, POST requests don't seem to require a message body, but I could be wrong about this. Should POST requests without Content-Length or Transfer-Encoding headers be accepted?

[o7si]

To verify the expected behavior, I tested the same request against a Flask server:

from flask import Flask

app = Flask(__name__)

@app.route('/test', methods=['POST'])
def test():
    return "", 200, {'Content-Type': 'text/plain'}

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=7777)

Same curl request:

# curl -X POST "http://localhost:7777/test" -v
* Host localhost:7777 was resolved.
* IPv6: ::1
* IPv4: 127.0.0.1
*   Trying [::1]:7777...
* connect to ::1 port 7777 from ::1 port 60645 failed: Connection refused
*   Trying 127.0.0.1:7777...
* Connected to localhost (127.0.0.1) port 7777
> POST /test HTTP/1.1
> Host: localhost:7777
> User-Agent: curl/8.7.1
> Accept: */*
> 
* Request completely sent off
< HTTP/1.1 200 OK
< Server: Werkzeug/3.1.3 Python/3.12.8
< Date: Sat, 22 Nov 2025 12:53:50 GMT
< Content-Type: text/plain
< Content-Length: 0
< Connection: close
< 
* Closing connection

The Flask server successfully handles the same POST request without Content-Length or Transfer-Encoding headers, returning a 200 OK response.