Initial commit: basic working version

The firmware currently has the following features:

- Start a webserver on port 80, serving the measurement data as JSON
- Read WLAN credentials from LittleFS
- Asynchronous reading of the BME680 every 10 seconds

.gitignore

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+.pio
+.vscode/.browse.c_cpp.db*
+.vscode/c_cpp_properties.json
+.vscode/launch.json
+.vscode/ipch
+
+data/etc/*
+!data/etc/.*

include/Config.h

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+#pragma once
+
+#include <vector>
+#include <string>
+
+class Config
+{
+    public:
+        struct WLAN
+        {
+            std::string ssid;
+            std::string password;
+        };
+
+        typedef std::vector<WLAN> WLANList;
+
+        static Config &instance()
+        {
+            static Config theConfig;
+            return theConfig;
+        }
+
+        void load(void);
+
+        const WLANList& getWLANList(void) { return m_wlans; }
+
+        const std::string& getCRPassword(void) { return m_crPassword; }
+        const std::string& getCRSalt(void) { return m_crSalt; }
+
+    private:
+        Config();
+
+        WLANList    m_wlans;
+        std::string m_crPassword;
+        std::string m_crSalt;
+};

include/README

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+
+This directory is intended for project header files.
+
+A header file is a file containing C declarations and macro definitions
+to be shared between several project source files. You request the use of a
+header file in your project source file (C, C++, etc) located in `src` folder
+by including it, with the C preprocessing directive `#include'.
+
+```src/main.c
+
+#include "header.h"
+
+int main (void)
+{
+ ...
+}
+```
+
+Including a header file produces the same results as copying the header file
+into each source file that needs it. Such copying would be time-consuming
+and error-prone. With a header file, the related declarations appear
+in only one place. If they need to be changed, they can be changed in one
+place, and programs that include the header file will automatically use the
+new version when next recompiled. The header file eliminates the labor of
+finding and changing all the copies as well as the risk that a failure to
+find one copy will result in inconsistencies within a program.
+
+In C, the usual convention is to give header files names that end with `.h'.
+It is most portable to use only letters, digits, dashes, and underscores in
+header file names, and at most one dot.
+
+Read more about using header files in official GCC documentation:
+
+* Include Syntax
+* Include Operation
+* Once-Only Headers
+* Computed Includes
+
+https://gcc.gnu.org/onlinedocs/cpp/Header-Files.html

lib/README

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+
+This directory is intended for project specific (private) libraries.
+PlatformIO will compile them to static libraries and link into executable file.
+
+The source code of each library should be placed in a an own separate directory
+("lib/your_library_name/[here are source files]").
+
+For example, see a structure of the following two libraries `Foo` and `Bar`:
+
+|--lib
+|  |
+|  |--Bar
+|  |  |--docs
+|  |  |--examples
+|  |  |--src
+|  |     |- Bar.c
+|  |     |- Bar.h
+|  |  |- library.json (optional, custom build options, etc) https://docs.platformio.org/page/librarymanager/config.html
+|  |
+|  |--Foo
+|  |  |- Foo.c
+|  |  |- Foo.h
+|  |
+|  |- README --> THIS FILE
+|
+|- platformio.ini
+|--src
+   |- main.c
+
+and a contents of `src/main.c`:
+```
+#include <Foo.h>
+#include <Bar.h>
+
+int main (void)
+{
+  ...
+}
+
+```
+
+PlatformIO Library Dependency Finder will find automatically dependent
+libraries scanning project source files.
+
+More information about PlatformIO Library Dependency Finder
+- https://docs.platformio.org/page/librarymanager/ldf.html

platformio.ini

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+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[env:esp12e]
+platform = espressif8266
+board = d1_mini
+framework = arduino
+lib_deps = 
+    adafruit/Adafruit BME680 Library@^1.1.1
+    adafruit/Adafruit Unified Sensor@^1.1.4
+    SPI
+    Wire
+
+monitor_speed = 115200
+board_build.filesystem = littlefs

src/Config.cpp

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+#include <LittleFS.h>
+
+#include "Config.h"
+
+Config::Config()
+{}
+
+void Config::load(void)
+{
+    // load WLANs
+    File wlanFile = LittleFS.open("/etc/wlan", "r");
+
+    while(wlanFile.available()) {
+        String ssid = wlanFile.readStringUntil('\n');
+
+        if(!wlanFile.available()) {
+            Serial.println("/etc/wlan terminated early. Last entry ignored.");
+            break;
+        }
+
+        String passwd = wlanFile.readStringUntil('\n');
+
+        m_wlans.emplace_back(WLAN{ssid.c_str(), passwd.c_str()});
+    }
+
+    wlanFile.close();
+
+    // load Challenge-Response data
+    File authFile = LittleFS.open("/etc/auth", "r");
+
+    if(authFile.available()) {
+        String passwd = authFile.readStringUntil('\n');
+        m_crPassword = passwd.c_str();
+
+        if(!authFile.available()) {
+            m_crSalt = "";
+        } else {
+            String salt = authFile.readStringUntil('\n');
+            m_crSalt = salt.c_str();
+        }
+    }
+
+    authFile.close();
+}

src/main.cpp

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+#include <sstream>
+
+#include <Arduino.h>
+
+#include <ESP8266WiFi.h>
+#include <ESP8266WiFiMulti.h>
+
+#include <LittleFS.h>
+
+#include <Adafruit_BME680.h>
+
+#include <ESP8266WebServer.h>
+
+#include "Config.h"
+
+#define ENDLESS_LOOP() while(true) { delay(100); }
+
+#define BME680_UPDATE_INTERVAL 10000 // milliseconds
+
+ESP8266WiFiMulti wiFiMulti;
+
+ESP8266WebServer httpServer(80);
+
+Adafruit_BME680 bme680;
+
+unsigned long bme680LastReadingTime;
+unsigned long bme680ReadingDuration;
+
+String bme680_json_cache;
+
+void httpHandleIndex(void)
+{
+  httpServer.send(200, F("application/json"), bme680_json_cache);
+}
+
+void httpHandle404(void)
+{
+  httpServer.send(404, F("text/plain"), F("This is not the page you are looking for."));
+}
+
+
+void wifi_setup(void)
+{
+  Serial.println(F("Trying to connect..."));
+
+  //WiFi.setHostname(F("mlmini");
+
+  bool led_on = true;
+  for(size_t tries = 0; tries < 300; tries++)
+  {
+    if(wiFiMulti.run() == WL_CONNECTED) {
+      Serial.println(F(""));
+      Serial.println(F("WiFi connected"));
+      Serial.println(F("IP address: "));
+      Serial.println(WiFi.localIP());
+      break;
+    }
+
+    led_on = !led_on;
+    digitalWrite(LED_BUILTIN, led_on);
+    delay(100);
+
+    Serial.print(F("."));
+  }
+
+  if(WiFi.status() != WL_CONNECTED) {
+    Serial.println(F("Connection failed, setting up access point..."));
+
+    IPAddress apIP(192, 168, 42, 1);
+
+    WiFi.mode(WIFI_AP);
+    WiFi.softAPConfig(apIP, apIP, IPAddress(255, 255, 255, 0));
+    WiFi.softAP(F("☀️🌧️🌩️"), F("How'sTheWeather?"));
+    WiFi.enableAP(true);
+
+    digitalWrite(LED_BUILTIN, false); // LED ON (active low)
+  } else {
+    digitalWrite(LED_BUILTIN, true); // LED OFF (active low)
+  }
+
+}
+
+void bme680_setup(void)
+{
+  if(!bme680.begin()) {
+    Serial.println(F("Could not initialize BME680 sensor!"));
+    ENDLESS_LOOP();
+  }
+
+  // Set up oversampling and filter initialization
+  bme680.setTemperatureOversampling(BME680_OS_8X);
+  bme680.setHumidityOversampling(BME680_OS_2X);
+  bme680.setPressureOversampling(BME680_OS_4X);
+  bme680.setIIRFilterSize(BME680_FILTER_SIZE_3);
+  bme680.setGasHeater(320, 150); // 320*C for 150 ms
+}
+
+void httpserver_setup()
+{
+  httpServer.on("/", httpHandleIndex);
+  httpServer.onNotFound(httpHandle404);
+
+  httpServer.begin();
+}
+
+void setup()
+{
+  Serial.begin(115200);
+
+  pinMode(LED_BUILTIN, OUTPUT);
+
+  Serial.println(F("Hello World!"));
+
+  if(!LittleFS.begin()) {
+    Serial.println(F("LittleFS setup failed!"));
+    ENDLESS_LOOP();
+  }
+
+  bme680_setup();
+
+  Config::instance().load();
+
+  // Connect the WiFi network (or start an AP if that doesn't work)
+  for (auto &net : Config::instance().getWLANList())
+  {
+    Serial.print(F("Adding network "));
+    Serial.println(net.ssid.c_str());
+    wiFiMulti.addAP(net.ssid.c_str(), net.password.c_str());
+  }
+
+  wifi_setup();
+
+  httpserver_setup();
+
+  bme680LastReadingTime = millis() + 10000;
+  bme680ReadingDuration = 0;
+
+  bme680_json_cache = F("{}");
+}
+
+void update_bme680_json(void)
+{
+  std::ostringstream oss;
+
+  oss << "{\n";
+
+  oss << "\"temperature\": {\"value\": " << bme680.temperature << ", \"unit\": \"°C\"},\n";
+  oss << "\"pressure\": {\"value\": " << (bme680.pressure / 100.0) << ", \"unit\": \"hPa\"},\n";
+  oss << "\"humidity\": {\"value\": " << bme680.humidity << ", \"unit\": \"%rH\"},\n";
+  oss << "\"gas_resistance\": {\"value\": " << bme680.gas_resistance << ", \"unit\": \"Ohm\"},\n";
+  oss << "\"generated_at_millis\": " << millis() << "\n";
+
+  oss << "}";
+
+  bme680_json_cache = oss.str().c_str();
+}
+
+void loop() {
+  unsigned long now = millis();
+  if((now - bme680LastReadingTime) >= BME680_UPDATE_INTERVAL) {
+    // Tell BME680 to begin measurement.
+    bme680ReadingDuration = bme680.beginReading();
+    if (bme680ReadingDuration == 0) {
+      Serial.println(F("Failed to begin BME680 reading :(F("));
+      return;
+    }
+
+    bme680LastReadingTime = now;
+    bme680ReadingDuration -= now; // so far, the "duration" contained the absolute end time. Make it relative to the current timestamp
+  }
+
+  if((bme680ReadingDuration != 0) && ((millis() - bme680LastReadingTime) >= bme680ReadingDuration)) {
+    if(!bme680.endReading()) {
+      Serial.println(F("Could not finalize BME680 reading."));
+    } else {
+      // reading is good
+      update_bme680_json();
+    }
+
+    bme680ReadingDuration = 0;
+  }
+
+  // TODO: do something else?
+  httpServer.handleClient();
+}

test/README

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+
+This directory is intended for PlatformIO Unit Testing and project tests.
+
+Unit Testing is a software testing method by which individual units of
+source code, sets of one or more MCU program modules together with associated
+control data, usage procedures, and operating procedures, are tested to
+determine whether they are fit for use. Unit testing finds problems early
+in the development cycle.
+
+More information about PlatformIO Unit Testing:
+- https://docs.platformio.org/page/plus/unit-testing.html