Problem reading channel. HTTP error code -304

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Amanj Abdollah Zadeh
评论： Niels 2025-2-19
when i want to read data from thingspeak, i get the below messege :
Problem reading channel. HTTP error code -304
how can i solve this?
  2 个评论
Vinod
Vinod 2020-9-8
How are you reading the data from your ThingSpeak channel?
  • A HTML page using the ThingSpeak API and Javascript?
  • MATLAB code using thingSpeakRead?
  • From an embedded device?
  • Something else?

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回答（2 个）

Christopher Stapels
移动：Christopher Stapels 2024-1-5
The negative errors are from the communication library, not standard HTTP responses. From the ThingSpeak communication library readme, -304 is Timeout waiting for server to respond. This seems to either be a network issue, or you are sending an incomplete message to ThingSpeak. Are you using one of the standard examples form the library or your own code?
Niels
Niels 2025-2-18
The same problem appeared here when accessing a university server, except I was writing not reading a field. I solved this by trying to write the field up to 10 times during 5 seconds. Now I always get a success with error code 200. I guess the same idea would work for reading a field. Why it works, I've got no clue.
int returnCode;
for (int i=0; i<10; ++i) {
returnCode = ThingSpeak.writeField(channelId, field, value, pw);
if (returnCode == 200) break;
delay(500);
}
Serial.println("writeField " + String(field) + " " + String(value,2) + " " + String(returnCode));
  2 个评论
Vinod
Vinod 2025-2-18
The suggestion I would make is to apply some sort of (exponential?) backoff to the delay in the loop. You don't want to inadvertantly trigger a DoS attack from your device. A simple backoff might be:
delay(500 + i*(i+100));
Niels
Niels 2025-2-19
That's neat, thanks. The danger of triggering a DoS attack detector did not occur to me. Thinking more about the problem, I guess that the university IoT server has gotten quite busy due to a proliferation of connected things. So, every time that I try to connect through it to ThingSpeak, there is a probability of it being busy and denying my request. Then, it is simply a matter of trying repeatedly until by chance I get through.

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