Connection: close and Connection: keep-alive both present in the header

[enjoyneering]

Basic Infos

• [x ] This issue complies with the issue POLICY doc.
• [x ] I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• [x ] I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• [x ] I have filled out all fields below.

Platform

• Hardware: [ESP-12]
• Core Version: [3.0.1]
• Development Env: [Arduino IDE]
• Operating System: [Windows]

Settings in IDE

• Module: [Wemos D1 mini r2]
• Flash Mode: [qio]
• Flash Size: [4MB]
• lwip Variant: [v2 Higher Bandwidth]
• Reset Method: [nodemcu]
• Flash Frequency: [80Mhz]
• CPU Frequency: [80Mhz]
• Upload Using: [OTA]
• Upload Speed: [115200] (serial upload only)

Problem Description

Accordind to the comment in ESP8266WebServer.h - if the client sends the "Connection" header, the value given by the header is used. But in fact, both server.keepAlive(true); and server.sendHeader(F("Connection"), F("close")); server.send(200); is present in the header.

HTTP/1.1 200 OK
Content-Type:
Connection: close
Content-Length: 0
Connection: keep-alive
Keep-Alive: timeout=2000

UDP:
For some reason short version server.send(200, F("Connection"), F("close")); doesn't work (only keep-alive is present).

[mcspr]

Accordind to the comment in ESP8266WebServer.h - if the client sends the "Connection" header, the value given by the header is used. But in fact, both server.keepAlive(true); and server.sendHeader(F("Connection"), F("close")); server.send(200); is present in the header.

Works as intended per #7414?

Connection: {Keep-Alive,close} is not meant to be sent by the user, but by the server internals through setting keep alive flag. But, I suppose we may add some code to reject such internal header(s). Internally, keep-alive is first sourced from the HTTP version, then checks whether the request contains Connection: and again updates the flag when it equals to keep-alive and otherwise defaults to close

Plus, I don't see how multiple 'Connection's may sneak into the response headers string; server code only sends it once. But, we don't check for unique / duplicates / internal header fields, so it is possible for user to inject something unexpected (and the spec technically allows it)

For some reason short version server.send(200, F("Connection"), F("close")); doesn't work (only keep-alive is present).

Invalid? Call will respond with 'content-type: connection' and 'close' in the body

Arduino/libraries/ESP8266WebServer/src/ESP8266WebServer.h

Line 160 in c12a6b4

void send(int code, const String& content_type, const String& content);