[Flask] Why is a small response broken into 3 TCP segments?

[Ben Kinsella]

 I am working with a very limited client in an embedded device, and I would
like the HTTP response from my Flask app to be contained in one IP packet.

I know a response will be automatically segmented if the size exceeds my
TCP MSS (1460 bytes).
But I find that, even with a minimal “Hello World” response (112 bytes),
the response is sent in multiple IP packets (each containing one TCP
segment).

With Flask's builtin server, the response comes in 3 segments: start line,
headers, body.
With Gevent as the server, the same response comes in 2 segments: start
line & headers, body.

Is this behaviour configurable at any level? (Werkzeug, Flask, Gevent, any
another server?).

Thanks,
Ben.
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