[network protocol] problems and solutions in the use of LwIP

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Preface

Doing it IOT Equipment is often used LWIP Open source TCP/IP Protocol library , The problem is hereby recorded and the solution

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1. LWIP-HTTP Unable to maintain long connection

1.1 problem

        Developing http When the server provides data to the front end , Web page loading will fail , stay http_accepet In the function, you will see , The browser will always make requests , Cause protocol stack overflow .
        The front end initiates a js There is no problem when requesting , But launching more than a dozen requests is different in succession js request , It's always reconnecting , And there is almost no time to wait , This will cause http Server busy , Resources are exhausted and then down .

1. Solution retention http A long connection ,http_accept Just enter once
2. Solve the problem that the browser requests the next time after receiving the complete static page data

1.2 analysis

1. understand http Protocol and how the front-end browser works , The following two articles document how the server side and browser side work , It's what I want .

HTTP Protocol request header and response header
Talking about Http Long connection and Keep-Alive as well as Tcp Of Keepalive

2. according to 1 Chinese saying , To understand the browser, you need to know how much text is transmitted at a time , To determine whether this connection is over .
3. To maintain a long connection , The response header must contain connetion:persistant, It seems that mine doesn't

1.3 knowledge

Remember a Content-Length The murder that started

2. a large number of TIMEWAIT Cause resource exhaustion

2.1 problem

In the use of LWIP Development IOTdev when , I assigned 10 individual PCB, But because TIMEWAIT stay LWIP Wait for 60 second , It's too long , Because my equipment may be in 16 Use quickly in seconds 16 Different PCB block , This always leads to insufficient resources , Cannot connect to program .

2.2 reason

1. It is found that the web page has not established a long connection , Because there is RTC Every time 1s Polling consumes each time PCB, stay TIMEWIAT Waiting in the 60s, Obviously it took too long , Not enough resources .
2. TIMEOUT It's too long , I think in the LAN 10s sufficient .
   

2.3 Solution

1. take TCP_MSL Change to 100000UL/10s/
2. increase MEMP_NUM_TCP_PCB To 30 individual

2.4 knowledge

2.4.1 TCP/IP Detailed explanation –TCP Connecting TIME_WAIT Too many states

TCP/IP Detailed explanation –TCP Connecting TIME_WAIT Too many states

2.4.2 TCP stay FIN_WAIT1 How long can the state last and TCP False connection problem

TCP stay FIN_WAIT1 How long can the state last and TCP False connection problem

2.4.3 TCP agreement RST：RST Introduce 、 When to send RST package

TCP agreement RST：RST Introduce 、 When to send RST package

2.4.4 Why does the server suddenly reply RST—— Be careful of the security devices in the network

Why does the server suddenly reply RST—— Be careful of the security devices in the network

2.4.5 Graphic network ｜ received RST, It will disconnect TCP Is it connected ？

Graphic network ｜ received RST, It will disconnect TCP Is it connected ？

summary