如何解决400错误的请求

Question

I am running a program that reports data about a pump runtime and amps to a server using a POST request to a PHP page. The system is running fine on several Arduino Pro Minis. I am testing it out on a board that I built using a 328 and Arduino Uno bootloader, and of the 4 different POST requests, two work and two fail.

I believe this to be caused by the Arduino poorly forming the POST request, but I have no way to verify this since the Arduino Serial.prints the correct string. If I manually hard code the string, it also works.

I form the data this way:

byte runtime = analogRead(A3); // generates random data
float amps = analogRead(A2) / 100;
char cruntime[4]; // create char array for runtime
char camps[5];
dtostrf(runtime, 4, 0, cruntime);
dtostrf(amps, 2, 1, camps);
String sruntime = String(cruntime);
sruntime.trim();
String samps = String(camps);
samps.trim();
String cwpdata = "serial=test&runtime=" + sruntime + "&amps=" + samps; // posted to server

I've check my server for errors, but couldn't find records of these. Is there anyway I can see what is being posted each time so I can see where the request is not forming properly?

Here is the code in the Arduino to post data:

void postData(String inputData, String filename) {
  if (client.connect(server, 80)) {
    Serial.println("connected");
    // Make a HTTP request:
    client.println("POST /dev/telemetry/test/" + filename + ".php HTTP/1.1");
    client.println("Host: www.SERVER.com"); // changed for privacy
    client.println("Content-Type: application/x-www-form-urlencoded");
    client.print("Content-Length: "); 
    client.println(inputData.length()); 
    Serial.println(inputData);
    Serial.print("Data Length: ");
    Serial.println(inputData.length());
    client.println("Connection: close");
    client.println(); 
    client.println(inputData);
    client.println();
  } // close if client

  wdt_reset();
  unsigned long startMillis = millis();
  unsigned long endMillis = startMillis + timeout;
  while(client.connected() && (millis() < endMillis)) {
    wdt_reset();
    while(client.available()) {
      char ch = client.read();
      Serial.print(ch);
      wdt_reset();
    } 
  }
  // if the server's disconnected, stop the client:
  Serial.println();
  client.stop();
  int memory = freeMemory();
  if (memory < 125) {
    delay(15000);
  }
}

Answer 1

I would hazard a guess that, sometimes, your inputData contains unescaped characters that are not properly encoded before they are sent in the POST body.

Within "serial=test&runtime=" + sruntime + "&amps=" + samps , if either sruntime or samps contains unescaped characters, it could very well throw the server-side parsing off. Are there any "unprintable" control bytes hiding in the Serial.println(inputData) that might have been overlooked?

"Safe" characters, by the way, are AZ, az, 0-9, dash, underscore, dot, tilde, and the plus sign (which means space). Everything else would have to be percent-encoded before being sent. It gets a little hairier if the data happens to be Unicode.