ESP8266 receive problem

Projects Programming
1

I have built a udp server for receiving udp messages. i tried to implement a type or homemade ack.

  int packetSize = Udp.parsePacket();
  if (packetSize) {
        char verifyStart[7];
    char verifyEnd[7];
    Serial.printf("Received %d bytes from %s, port %d\n", packetSize, Udp.remoteIP().toString().c_str(), Udp.remotePort());
    int len = Udp.read(incomingPacket, 800);
    strncpy (verifyStart, (char*)incomingPacket, 7 );
    strncpy (verifyEnd, (char *)incomingPacket + len - 6 , 7 );
    Serial.println(packetSize);
    if (strcmp(verifyStart, "NODECM") == 0) {
      Serial.println("NODECM");
    }
    if (strcmp(verifyEnd, "CMNODE") == 0) {
      Serial.println("CMNODE");

    }

if i send bytes NODECM it prints NODECM in the serial console as i expected also the same result if i send NODECMCMNODE both if statements print, but if i send the wrong command after a recognized byte string it still prints the if statements as if i was sending the expect NODECM or NODECMCMNODE. am i forgetting to flush the incomingPacket? how do i do this?

2

If i send NODECM it prints NODECM at the serial console. If i send NODEC it prints NODECM at the erial console. if i send N to the server it also prints NODECM at the serial console. this only happens if i first send NDOECM to the udp server. if i send the wrong command first it wont print anything in the console as expected. but if i send NODECM then any time i send anything that starts with N it prints NODECM at the serial console. why is this happening sorry if this is hard to understand

3

Udp.read () does not null terminate received pkt like Cstr functions require

either add the null yourself or use memset to clear the incomingPacket buffer

4

racpi:
Udp.read () does not null terminate received pkt like Cstr functions require

either add the null yourself or use memset to clear the incomingPacket buffer

How do i use memset to clear the incoming packet buffer. i think i know what you mean by null terminated "NODECM0" but either way if it wasnt null terminated and it expected a null terminated string then why does it work in the first place?

5

memset(incomingPacket, 0, sizeof(incomingPacket)); Seems to fix the problem

6

Can anyone tell me how i can get the data from between the first and last 7 bytes?

  int packetSize = Udp.parsePacket();
  if (packetSize) {
    char verifyStart[7];
    char verifyEnd[7];
    Serial.printf("Received %d bytes from %s, port %d\n", packetSize, Udp.remoteIP().toString().c_str(), Udp.remotePort());
    int len = Udp.read(incomingPacket, 800);
    strncpy (verifyStart, (char*)incomingPacket, 6);
    strncpy (verifyEnd, (char *)incomingPacket + len - 6 , 7 );
    if (strcmp(verifyStart, "NODECM") == 0) {
    if (strcmp(verifyEnd, "CMNODE") == 0) {
      Serial.println(data_between_bytes);
    }
    }
    memset(incomingPacket, 0, sizeof(incomingPacket));
  }
7

Maybe there is a better way, this is what i ended up doing. someone please chime in if you see something critically wrong here,

  int packetSize = Udp.parsePacket();
  if (packetSize) {
    char verifyStart[7];
    char verifyEnd[7];
    char _data[5];
    Serial.printf("Received %d bytes from %s, port %d\n", packetSize, Udp.remoteIP().toString().c_str(), Udp.remotePort());
    int len = Udp.read(incomingPacket, 800);
    strncpy (verifyStart, (char*)incomingPacket, 6);
    strncpy (verifyEnd, (char *)incomingPacket + len - 6 , 7 );
    strncpy (_data, (char*)incomingPacket + 6,len - 12);
    int value = atoi(_data);
    if (strcmp(verifyStart, "NODECM") == 0) {
    if (strcmp(verifyEnd, "CMNODE") == 0) {
      Serial.println(value);

    }
    }
    memset(incomingPacket, 0, sizeof(incomingPacket));
  }
8

how come when i send NODEC1100C1NODE value prints as 1000 but when i send NODEC110C1NODE value prints as 10?

  int packetSize = Udp.parsePacket();
  if (packetSize) {
    char verifyStart[7];
    char verifyEnd[7];
    char _data[10];
    Serial.printf("Received %d bytes from %s, port %d\n", packetSize, Udp.remoteIP().toString().c_str(), Udp.remotePort());
    int len = Udp.read(incomingPacket, 800);
    strncpy (verifyStart, (char*)incomingPacket, 6);
    strncpy (verifyEnd, (char *)incomingPacket + len - 6 , 7 );
    strncpy (_data, (char*)incomingPacket + 6, len - 12);
    unsigned long value = atol(_data);
    if (strcmp(verifyStart, "NODEC1") == 0) {
      if (strcmp(verifyEnd, "C1NODE") == 0) {
        Serial.println("command_1");
        dutycycle1 = value;
      }
    }
9

I suspect that you need to null terminate _data.

10

I changed len -12 to -11 and it seemed to have took care of the problem. i dont know why and for some reason i cant wrap my head around how to terminate the string besides adding \0 to the end of the string when i send the message? as i understand the end of a string has a trailing '0' byte

strncpy (_data, (char*)incomingPacket + 6, len - 11);

11

Like this:

_data[len - 12]=0;
12

wildbill:
Like this:

_data[len - 12]=0;

Is this for the strncpy expression or the strcmp? What i see if were inserting 0 at position len-12 'end' in data. By adding a 0 to the end of the string it will remove a 0? sorry i'm still a bit confused.

13

strncpy does not necessarily null terminate the target string so you need to do it manually after copying digits into _data.

If it's not null terminated, you will print what you copied, plus whatever is hanging around in memory until you get to a NULL, in your case apparently that's an extra '0'.

14

wildbill:
strncpy does not necessarily null terminate the target string so you need to do it manually after copying digits into _data.

If it's not null terminated, you will print what you copied, plus whatever is hanging around in memory until you get to a NULL, in your case apparently that's an extra '0'.

null terminating the string did solve the problem. Im going to try to use an ESP8266 to control multiple PWM controlled devices. now i just have to figure out how many PWM signals the ESP8266 can generate simultaneously at the same freq and different duty cycles