Failure to send data from client to server in ESP-01 WiFi - server

Question

Using the ESP8266WiFi library, I have two ESP-01's/ESP8266's connected over WiFi. It works perfectly when the client sends a request (all non HTML!) to the server (using port 5000 - to prevent any confusion with HTTP, FTP etc.). But I cannot get the client to receive an answer back from the server. Now, in the ESP8266WiFi library (3.0.2) there is a note that server.write() is not implemented, and that I should use server.accept() instead of server.available(); though I did not see any applicable examples using server.accept(), but I see many examples using client.print() so I try to follow those - to no avail, yet. What I am doing is the following: 1. establish connectivity to the WiFi; 2. have the client connect to the server and send two bytes to the server. 3. Do a digital write to a pin of the server-ESP8266.(this toggles a relay, which works fine) 4. write back from server to client that the digital write has been done. On the client side, after writing to the server, I run in a loop for some 10 seconds trying to receive something from the server, which never comes. Then I cycle back to the beginning, and the client asks to toggle the relay again - this runs nicely for hours.
Any insights here on what I should do differently are highly appreciated. I really want to be able to get some acknowledgement back to the client once the server has toggled the relay. Or if someone has a working example with server.accept() - I would try that too.
Client side code:
int pin_value;
uint8_t ip[4];
void setup()
{
Serial.begin(115200);
ip[0]=10;
ip[1]=0;
ip[2]=0;
ip[3]=6;
//We connect to the WiFi network
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);
//Wait until connected
while (WiFi.status() != WL_CONNECTED){
delay(500);
Serial.print(".");
}
Serial.print("Client - ");
Serial.println("WiFi connected");
}
void loop(){
//Variable that we will use to connect to the server
WiFiClient client;
//if not able to connect, return.
if (!client.connect(ip, SERVER_PORT)){ return; }
// We create a buffer to put the send data
uint8_t buffer[Protocol::BUFFER_SIZE];
//We put the pin number in the buffer
// whose state we want to send
buffer[Protocol::PIN] = RELAY;
//put the current state of the pin in the send buffer
buffer[Protocol::VALUE] = pin_value;
//We send the data to the server
client.write(buffer, Protocol::BUFFER_SIZE);
// try to read the answer from the server for about 10 seconds
int nr_of_tries = 10000;
while (client.connected() && nr_of_tries > 0)
{if (client.available())
{ String line = client.readStringUntil('\n');
nr_of_tries = 0;
Serial.print("line= ");
Serial.println(line);
}
else
{delay(1);
nr_of_tries=nr_of_tries-1;
}
}
Serial.print("nr of tries= ");
Serial.println(nr_of_tries);
Serial.print("connected: ");
Serial.println(client.connected());
client.flush();
client.stop();
Serial.println(" change sent");
if (pin_value == 0)
{pin_value =1;
Serial.println("Pin_value set to 1");
}
else
{pin_value=0;
Serial.println("Pin_value set to 0");}
delay(10000);
}
Server side code:
WiFiServer server(SERVER_PORT);
void setup()
{
Serial.begin(115200); // must have the same baud rate as the serial monitor
pinMode(RELAY,OUTPUT);
digitalWrite(RELAY, LOW);
// Connect to the WiFi network
Serial.println();
Serial.println();
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED){
delay(500);
Serial.print(".");
}
Serial.println("Server - ");
Serial.println("WiFi connected");
// Set this ESP to behave as a WiFi Access Point
// WiFi.mode(WIFI_AP);
// set SSID and Password to connect to this ESP
// WiFi.softAP(SSID, PASSWORD);
// Start the server
server.begin();
Serial.println("Server started");
// Output of the IP address
Serial.print("Use this IP to connect: ");
Serial.println(WiFi.localIP());
}
void loop()
{
// Check if there is any client connecting
WiFiClient client = server.available();
if (client)
{
//Serial.println("Client detected");
//If the client has data he wants to send us
//check for a second or so as transmission can take time
int nr_of_tries = 1000;
while(!client.available() && nr_of_tries > 0)
{ nr_of_tries=nr_of_tries-1;
delay(1);
}
if (client.available())
{
// Serial.println(" Client data");
// create a buffer to put the data to be received
uint8_t buffer[Protocol::BUFFER_SIZE];
// We put the data sent by the client in the buffer
// but do not read more than the buffer length.
int len = client.read(buffer, Protocol::BUFFER_SIZE);
// retrieve which pin number the client sent
int pinNumber = buffer[Protocol::PIN];
Serial.print("Pin Number: ");
Serial.println(pinNumber);
// retrieve the value of this pin
int value = buffer[Protocol::VALUE];
Serial.print("Value: ");
Serial.println(value);
// Set the pin indicated by the received pin number in output mode
// but only if the pin is the GPIO0 pin!
if (pinNumber == RELAY)
{ pinMode(pinNumber, OUTPUT);
// Set the pin indicated by the received pin number to the passed value
digitalWrite(pinNumber, value);
}
// tell the client that the relay has been set or reset.
size_t i;
if (value == 0) {
i=server.println("Set");
Serial.print("i= ");
Serial.println(i);
}
else {
i=server.println("Reset");
Serial.print("i= ");
Serial.println(i);
}
}
}
//Close the connection with the client
//client.stop();
}
Common definitions:
#include <ESP8266WiFi.h>
const char* ssid = "blablabla";
const char* password = "blublublu";
#define SERVER_PORT 5000
#define RELAY 0
//Protocol that the Server and Client will use to communicate
enum Protocol{
PIN, // Pin whose state you want to change
VALUE, // State to which the pin should go (HIGH = 1 or LOW = 0)
BUFFER_SIZE // The size of our protocol. IMPORTANT: always leave it as the last item of the enum
};

Answer 1

Solved! By changing server.println("Set"); into client.println("Set") and doing the same for the transmission of "Reset" a few lines lower in the server side code it works!