Mongoose prematurely closes connections when the second request in a pipeline is invalid

[Ben Kallus]

Describe the bug

From RFC 9112, section 9.6:

A server that receives a "close" connection option MUST initiate closure of the connection (see below) after it sends the final response to the request that contained the "close" connection option. The server SHOULD send a "close" connection option in its final response on that connection. The server MUST NOT process any further requests received on that connection.

When Mongoose receives a pipeline with a request containing Connection: close, followed by an invalid request, it closes the connection prematurely, without responding to the first request in the pipeline.

To Reproduce

1. Start the http-server example.
2. Send it a pipeline consisting of a valid request with Connection: close set, followed by an invalid request:

printf 'GET / HTTP/1.1\r\nConnection: close\r\n\r\nInvalid\r\n\r\n' | nc localhost 8000

3. Observe that the server does not respond, and immediately closes the connection,

Expected behavior

The server should respond to the first request, and then close the connection.

Logs

17e1fd9 2 main.c:32:cb                  GET / 200 2257
17e1fd9 1 mongoose.c:1359:mg_error      2 5 HTTP parse, 48 bytes
0000   47 45 54 20 2f 20 48 54 54 50 2f 31 2e 31 0d 0a   GET / HTTP/1.1..
17e1fd9 2 main.c:32:cb                  GET / 200 2257

Weirdly, the log indicates that the GET request was processed twice. This might be indicative of a deeper problem?