WiFi: fetch the weather, on an ESP32-C3

/*
 * WiFi: fetch the weather.
 *
 * SIMULATED, all of it. The radio is simulated, and so is the internet: the
 * only names that resolve are time.mokxi, weather.mokxi, echo.mokxi, api.mokxi
 * and the board's own address. Nothing here reaches the network your browser
 * is on, ever. Open the Cloud panel to watch the requests go out and to
 * change the numbers weather.mokxi answers with.
 *
 * The code is the code you would write for a real board.
 */
#include <HTTPClient.h>
#include <WiFi.h>
#include <WiFiClient.h>

const char *SSID = "Mokxi-Lab";
const char *PASSWORD = "breadboard";

/* Pull one number out of a JSON body without a JSON library: find the key,
   step over the colon, copy what follows. Good enough for a lesson, and it
   keeps the sketch to the one thing it is about. */
static bool jsonValue(const char *body, const char *key, char *out, int size) {
  String text(body);
  int at = text.indexOf(key);
  if (at < 0) return false;
  at += (int)strlen(key);
  while (text[(size_t)at] == '"' || text[(size_t)at] == ':' || text[(size_t)at] == ' ') at++;
  int used = 0;
  while (used + 1 < size) {
    char c = text[(size_t)at + (size_t)used];
    if (c == ',' || c == '}' || c == '\0') break;
    out[used++] = c;
  }
  out[used] = '\0';
  return used > 0;
}

void fetchWeather() {
  WiFiClient client;
  HTTPClient http;
  http.begin(client, "http://weather.mokxi/");
  int code = http.GET();
  if (code <= 0) {
    Serial.print("request failed: ");
    Serial.println(HTTPClient::errorToString(code));
    http.end();
    return;
  }
  Serial.print("HTTP ");
  Serial.println(code);
  String body = http.getString();
  Serial.print("body: ");
  Serial.println(body);

  char value[24];
  if (jsonValue(body.c_str(), "temperatureC", value, sizeof value)) {
    Serial.print("temperature: ");
    Serial.print(value);
    Serial.println(" C");
  }
  if (jsonValue(body.c_str(), "humidity", value, sizeof value)) {
    Serial.print("humidity: ");
    Serial.print(value);
    Serial.println(" %");
  }
  http.end();
}

void setup() {
  Serial.begin(115200);
  Serial.println("Simulated WiFi and a simulated internet: .mokxi names only.");
  WiFi.begin(SSID, PASSWORD);
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print(".");
    delay(250);
  }
  Serial.println();
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  /* A name that is not under .mokxi does not resolve, and says so. */
  HTTPClient outside;
  outside.begin("http://example.com/");
  int code = outside.GET();
  Serial.print("example.com -> ");
  Serial.println(HTTPClient::errorToString(code));
  outside.end();
}

void loop() {
  fetchWeather();
  delay(5000);
}