Set socket to MAX_SOCK_NUM if connection fails

[goccert25]

I've been experiencing a bug using the Arduino to communicate over ethernet when using multiple EthernetClients, and as far as I can tell this line is the culprit. The exact steps of how the bug happens:

• Initialize two EthernetClients A and B to talk to HOST at PORT1 and PORT2
• A.connect(HOST, PORT1); is called first. Inside the connect function, the function socketBegin is called, which according to the code here finds the first unused socket number and returns it. Lets say in this case the first unused socket number is 0. This means that A._socketIndex ends up being 0.
• For some reason, A.connect(HOST, PORT1); fails on line 63. However, note that A._socketIndex is NOT reset back to MAX_SOCK_NUM and stays at the initialized value (for this example we'll stick with 0).
• B.connect(HOST, PORT2); is called second. The process as above happens, and B._socketIndex is set to 0. However, for some reason B.connect(HOST, PORT2); works, and B is able to connect.
• Note that now B._socketIndex == A._socketIndex == 0. However, since A.connect(HOST, PORT1) returned 0 (which stands for false), calls to A.available(), A.read() shouldn't work. Instead, they do work, and even worse A.write() will write data to the socket that B is connected to.

This change should fix the bug, because instead of returning 0 on line 63 we break, we set _socketIndex back to MAX_SOCK_NUM and everything behaves as expected.

[goccert25]

@karlsoderby @per1234 , this is my first time contributing to the Arduino ecosystem. Please let me know if there's anything missing from the PR or anything else you'd like to see from me :)

[github-actions]

Memory usage change @ ec1ed04

Board	flash	%	RAM for global variables	%
arduino:avr:leonardo	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:avr:mega	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:avr:nano	💚 -2 - 0	-0.01 - 0.0	0 - 0	0.0 - 0.0
arduino:megaavr:nona4809	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:megaavr:uno2018	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:sam:arduino_due_x_dbg	🔺 0 - +8	0.0 - 0.0	N/A	N/A
arduino:samd:arduino_zero_edbg	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkr1000	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrfox1200	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrgsm1400	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrnb1500	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrvidor4000	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrwan1300	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrwan1310	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrwifi1010	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrzero	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:nano_33_iot	🔺 0 - +4	0.0 - 0.0	0 - 0	0.0 - 0.0

Click for full report table

Board	examples/AdvancedChatServer flash	%	examples/AdvancedChatServer RAM for global variables	%	examples/BarometricPressureWebServer flash	%	examples/BarometricPressureWebServer RAM for global variables	%	examples/ChatServer flash	%	examples/ChatServer RAM for global variables	%	examples/DhcpAddressPrinter flash	%	examples/DhcpAddressPrinter RAM for global variables	%	examples/DhcpChatServer flash	%	examples/DhcpChatServer RAM for global variables	%	examples/LinkStatus flash	%	examples/LinkStatus RAM for global variables	%	examples/PagerServer flash	%	examples/PagerServer RAM for global variables	%	examples/TelnetClient flash	%	examples/TelnetClient RAM for global variables	%	examples/UDPSendReceiveString flash	%	examples/UDPSendReceiveString RAM for global variables	%	examples/UdpNtpClient flash	%	examples/UdpNtpClient RAM for global variables	%	examples/WebClient flash	%	examples/WebClient RAM for global variables	%	examples/WebClientRepeating flash	%	examples/WebClientRepeating RAM for global variables	%	examples/WebServer flash	%	examples/WebServer RAM for global variables	%
arduino:avr:leonardo	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
arduino:avr:mega	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
arduino:avr:nano	-2	-0.01	0	0.0	-2	-0.01	0	0.0	-2	-0.01	0	0.0	0	0.0	0	0.0	-2	-0.01	0	0.0	0	0.0	0	0.0	-2	-0.01	0	0.0	-2	-0.01	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	-2	-0.01	0	0.0	-2	-0.01	0	0.0	-2	-0.01	0	0.0
arduino:megaavr:nona4809	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
arduino:megaavr:uno2018	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
arduino:sam:arduino_due_x_dbg	0	0.0	N/A	N/A	8	0.0	N/A	N/A	0	0.0	N/A	N/A	0	0.0	N/A	N/A	8	0.0	N/A	N/A	0	0.0	N/A	N/A	0	0.0	N/A	N/A	8	0.0	N/A	N/A	0	0.0	N/A	N/A	0	0.0	N/A	N/A	0	0.0	N/A	N/A	0	0.0	N/A	N/A	0	0.0	N/A	N/A
arduino:samd:arduino_zero_edbg	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:mkr1000	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:mkrfox1200	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:mkrgsm1400	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:mkrnb1500	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:mkrvidor4000	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:mkrwan1300	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:mkrwan1310	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:mkrwifi1010	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:mkrzero	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0
arduino:samd:nano_33_iot	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0	4	0.0	0	0.0

Click for full report CSV

Board,examples/AdvancedChatServer<br>flash,%,examples/AdvancedChatServer<br>RAM for global variables,%,examples/BarometricPressureWebServer<br>flash,%,examples/BarometricPressureWebServer<br>RAM for global variables,%,examples/ChatServer<br>flash,%,examples/ChatServer<br>RAM for global variables,%,examples/DhcpAddressPrinter<br>flash,%,examples/DhcpAddressPrinter<br>RAM for global variables,%,examples/DhcpChatServer<br>flash,%,examples/DhcpChatServer<br>RAM for global variables,%,examples/LinkStatus<br>flash,%,examples/LinkStatus<br>RAM for global variables,%,examples/PagerServer<br>flash,%,examples/PagerServer<br>RAM for global variables,%,examples/TelnetClient<br>flash,%,examples/TelnetClient<br>RAM for global variables,%,examples/UDPSendReceiveString<br>flash,%,examples/UDPSendReceiveString<br>RAM for global variables,%,examples/UdpNtpClient<br>flash,%,examples/UdpNtpClient<br>RAM for global variables,%,examples/WebClient<br>flash,%,examples/WebClient<br>RAM for global variables,%,examples/WebClientRepeating<br>flash,%,examples/WebClientRepeating<br>RAM for global variables,%,examples/WebServer<br>flash,%,examples/WebServer<br>RAM for global variables,%
arduino:avr:leonardo,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0
arduino:avr:mega,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0
arduino:avr:nano,-2,-0.01,0,0.0,-2,-0.01,0,0.0,-2,-0.01,0,0.0,0,0.0,0,0.0,-2,-0.01,0,0.0,0,0.0,0,0.0,-2,-0.01,0,0.0,-2,-0.01,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,-2,-0.01,0,0.0,-2,-0.01,0,0.0,-2,-0.01,0,0.0
arduino:megaavr:nona4809,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0
arduino:megaavr:uno2018,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0
arduino:sam:arduino_due_x_dbg,0,0.0,N/A,N/A,8,0.0,N/A,N/A,0,0.0,N/A,N/A,0,0.0,N/A,N/A,8,0.0,N/A,N/A,0,0.0,N/A,N/A,0,0.0,N/A,N/A,8,0.0,N/A,N/A,0,0.0,N/A,N/A,0,0.0,N/A,N/A,0,0.0,N/A,N/A,0,0.0,N/A,N/A,0,0.0,N/A,N/A
arduino:samd:arduino_zero_edbg,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:mkr1000,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:mkrfox1200,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:mkrgsm1400,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:mkrnb1500,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:mkrvidor4000,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:mkrwan1300,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:mkrwan1310,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:mkrwifi1010,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:mkrzero,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0
arduino:samd:nano_33_iot,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0,4,0.0,0,0.0

[goccert25]

Hey @karlsoderby @per1234, bumping this. Is there anyway to move this PR forward?

[per1234]

There is an alternative proposal at #176