Arduino hangs during multiple http requests on Linux but not on Windows - c++

Question

i have a problem when i send http requests from the arduino to linux mysql server. It randomly hangs after some requests (~150) but on windows it runs smoothly.
Because of this i am thinking that the problem is not on the arduino code but somewhere else.
The linux server runs on a raspberry pi (Raspbian).
Any suggestions?
The arduino code HERE
if(!getPage(server,serverPort)) Serial.print(F("Fail "));
byte getPage(IPAddress ipBuf,int thisPort)
{
int inChar;
Serial.print(F("connecting..."));
if(client.connect(ipBuf,thisPort))
{
Serial.println(F("connected"));
strcpy(outBuf,"GET /write3.php?value0=");
itoa(value0,tBuf,10);
strcat(outBuf,tBuf);
strcat(outBuf,"&value1=");
itoa(dht_humidity,tBuf,10);
strcat(outBuf,tBuf);
strcat(outBuf,"&value2=");
itoa(temperature,tBuf,10);
strcat(outBuf,tBuf);
strcat(outBuf,"&value3=");
itoa(pressure,tBuf,10);
strcat(outBuf,tBuf);
strcat(outBuf,"&value4=");
itoa(altitude,tBuf,10);
strcat(outBuf,tBuf);
strcat(outBuf,"&value5=");
itoa(gust,tBuf,10);
strcat(outBuf,tBuf);
strcat(outBuf,"&value6=");
itoa(dir,tBuf,10);
strcat(outBuf,tBuf);
strcat(outBuf,"&value7=");
itoa(rain,tBuf,10);
strcat(outBuf,tBuf);
strcat(outBuf,"&value8=");
itoa(knots,tBuf,10);
strcat(outBuf,tBuf);
client.write(outBuf);
client.println(" HTTP/1.1");
client.println("Host: 192.168.1.3");
client.println("Connection: close");
client.println();
EDIT: Just hanged at DEBUG___3
Serial.println("DEBUG___2");
client.write(outBuf);
Serial.println("DEBUG___3");
client.println(" HTTP/1.1");
Serial.println("DEBUG___4");
client.println("Host: 192.168.1.3");
Serial.println("DEBUG___5");
client.println("Connection: close");
client.println();
I captured the network traffic with wireshark when it hanged:
(Large pics: hanged http request ---- successfull http request)
Here is the http request that hanged
And here is a successful request:
Any ideas guys? Still stuck there !!!

Answer 1

Presuming you are certain the outBuf is not overflowed (it is smaller than maximum possible request string size and you are using strcat (source of all evil))
The server may timeout in the long time between when the connection is opened, and when you actually send any bytes. Preconstruct the outBuf so that it is ready to go when the connection opens.
strncat(outBuf,...,127);
... request is fully constructed
if(client.connect(ipBuf,thisPort)) {
client.write(outBuf);
client.println(" HTTP/1.1");
client.println("Host: 192.168.1.3");
...
To the server, the connection that is SYN'd but not used is a resource to be recovered. The Arduino will be so slow, it will look like an idle connection. Also a SYN flood is an old denial of service vector that most servers will protect against.
A difference in the timeout values would explain why the Linux and Win based server act different. You could confirm this by running Wireshark on the traffic. If the server is timing out on the Arduino, you will see this sequence:
the SYN handshake proceed between server and Arduino
a little time passes
a RST from the server indicating the connection is dead
the Arduino sends the request string to the now dead connection
the Arduino program hangs at the client.write() because the connection state is out of
sync
the client will probably be retrying - you should see some retransmissions