add mqtt-telegram page

input/projects/smarthome/mqtt_telegram.md

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+title: MQTT Telegram Bot
+description: Go server to control stuff from anywhere in the world
+parent: smarthome
+position: 500
+git: https://git.xythobuz.de/thomas/lights-telegram
+date: 2022-08-23
+comments: true
+---
+
+<!--% backToParent() %-->
+
+After creating my [MQTT Web UI](mqtt_web.html) I had some troubles getting it to work on all devices.
+My server at home is using a self-signed SSL certificate.
+I imported the certificate authority into my desktop, which Chromium accepts fine there.
+But on Android the connection is still considered insecure, even with the CA cert imported, so the JS can not communicate with the MQTT broker.
+
+To work around that problem I decided to create a simple Telegram Bot that can fulfill the same task of switching the lights.
+
+<!--%
+lightgallery([
+    [ "img/mqtt_telegram.png", "Screenshot of chat with bot" ],
+])
+%-->
+
+You can [find the source code on my Gitea](https://git.xythobuz.de/thomas/lights-telegram), as well as installation and setup instructions.
+
+This was my first time doing something with Go.
+I think the language is interesting and I will probably continue using it in the future.
+On one hand it was quite easy to find some suitable libraries that simplified the main tasks of the application greatly!
+But also the language features I found out about impressed me.
+
+One good example is reading the config file.
+You can simply define a struct that holds all configuration variables, with additional markup to control how it is marshalled and unmarshalled into different formats, in my case yaml.
+
+<pre class="sh_go">
+type Mqtt struct {
+    Url string `yaml:"url"`
+    User string `yaml:"username"`
+    Pass string `yaml:"password"`
+}
+
+type Registration struct {
+    Name string `yaml:"name"`
+    Topic string `yaml:"topic"`
+    Values []string `yaml:"values"`
+}
+
+type Config struct {
+    // Telegram Bot API key
+    Key string `yaml:"api_key"`
+
+    // Telegram UserID (int64) of admin account
+    Admin int64 `yaml:"admin_id"`
+
+    // MQTT credentials
+    Mqtt Mqtt
+
+    // Telegram UserIDs (int64) of allowed users
+    // (does not need to be modified manually)
+    Users []int64 `yaml:"authorized_users"`
+
+    // Available MQTT topics
+    // (does not need to be modified manually)
+    Registration []Registration
+}
+
+// default values
+var config = Config {
+    Key: "API_KEY_GOES_HERE",
+    Admin: 0,
+    Mqtt: Mqtt {
+        Url: "wss://MQTT_HOST:MQTT_PORT",
+        User: "MQTT_USERNAME",
+        Pass: "MQTT_PASSWORD",
+    },
+}
+</pre>
+
+Using simple functions to read and write files according to this format, you can then get a file looking something like this.
+
+<pre class="sh_yaml">
+api_key: API_KEY_REDACTED
+admin_id: ADMIN_ID_REDACTED
+mqtt:
+    url: wss://iot.fritz.box:8083
+    username: USERNAME_REDACTED
+    password: PASSWORD_REDACTED
+authorized_users: []
+registration:
+    - name: kitchen
+      topic: livingroom/light_kitchen
+      values:
+        - "on"
+        - "off"
+    - name: bathroom
+      topic: bathroom/force_light
+      values:
+        - none
+        - big
+        - small
+        - "off"
+    - name: pc
+      topic: livingroom/light_pc
+      values:
+        - "on"
+        - "off"
+    - name: workbench
+      topic: livingroom/light_bench
+      values:
+        - "on"
+        - "off"
+    - name: box
+      topic: livingroom/light_box
+      values:
+        - "on"
+        - "off"
+    - name: amp
+      topic: livingroom/light_amp
+      values:
+        - "on"
+        - "off"
+</pre>
+
+I'm using this file both to store static configuration data, like the API key, as well as runtime configuration data entered by the admin user, like available MQTT topics.
+
+All in all I was able to implement a basic working prototype in less than 500 LOC and in just a single evening!

static/js/sh/sh_go.min.js

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static/js/sh/sh_yaml.min.js

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