HTTPClient times out, but unclear as to why

[the-maldridge]

I'm running an http.Get() in a tight loop pulling frames of control data from a server down to a small robot and then setting PWM values based on the retrieved data. This works relatively well with the Raspberry Pi Pico W I'm testing with, but I notice that every once in a while I get a response code of -11 which appears to be client timeout.

Given that the client timeout is the default 5000 and the server is on the local network approximately 2ms away, I can't see any reasonable case in which this should time out. I'd appreciate any thoughts or advice as to what's going on here.

Source code as shown below:

#include <WiFi.h>
#include <WiFiMulti.h>
#include <HTTPClient.h>
#include <ArduinoJson.h>
#include <Servo.h>

#ifndef STASSID
#define STASSID "***"
#define STAPSK "*****"
#endif

WiFiMulti WiFiMulti;

HTTPClient http;
DynamicJsonDocument cstate(384);

Servo DriveL;
Servo DriveR;

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);

  Serial.begin(9600);

  Serial.println();
  Serial.println();
  Serial.println("Connecting to WiFi...");

  WiFi.mode(WIFI_STA);
  WiFiMulti.addAP(STASSID, STAPSK);

  // wait for WiFi connection
  while ((WiFiMulti.run() != WL_CONNECTED)) {
    Serial.write('.');
    delay(500);
  }
  Serial.println(" connected to WiFi");

  DriveL.attach(0);
  DriveR.attach(1);
  DriveL.write(90);
  DriveR.write(90);

  // Dumb hack, but you need to wait for PWM to settle for the motor
  // controller to enable.
  delay(5000);

  // allow reuse (if server supports it)
  http.setReuse(true);
  http.setInsecure();
  http.begin("http://192.168.16.10:8080/robot/data/1234");
  http.setTimeout(100);
}

void loop() {
  int httpCode = http.GET();
  digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
  if (httpCode > 0) {
    // file found at server
    if (httpCode == HTTP_CODE_OK) {
      deserializeJson(cstate, http.getStream());
      DriveL.write(map(cstate["AxisLY"], -32768, 32768, 180, 0));
      DriveR.write(map(cstate["AxisRY"], -32768, 32768, 0, 180));
    }
  } else {
    // Something went wrong with the connection, try to reconnect
    Serial.printf("ERROR: %d\r\n", httpCode);
    http.end();
    http.begin("http://192.168.16.10:8080/robot/data/1234");
  }
}