Improve Docker build

* Improves code readability.
* Improve documentation.
* Fix "docker stop" doesn't terminate qbt gracefully which could lead to
  data corruption.
* Provide correct/working bittorrent listening port by default.
* Make use of qbt profile option instead of hacking environment
  variables.
* Simplify build steps.

PR #16976.

dist/docker/Readme.md

@@ -1,68 +1,71 @@
-# Docker Container Name
+# qBittorrent-nox Docker Image
 
-This Dockerfile allows you to build a qBittorrent-nox container
+This Dockerfile allows you to build a docker image containing qBittorrent-nox
 
-## Getting Started
+## Prerequisities
 
-### Prerequisities
+In order to build/run this image you'll need docker installed: https://docs.docker.com/get-docker/
 
+## Building docker image
 
-In order to run this container you'll need docker installed.
-
-* [Windows](https://docs.docker.com/windows/started)
-* [OS X](https://docs.docker.com/mac/started/)
-* [Linux](https://docs.docker.com/linux/started/)
-
-
-## Built
-
-in the docker folder run
-
+In this docker folder run:
 ```shell
-release="4.2.0" ; sudo docker build --build-arg BUILD_TYPE=Release --build-arg RELEASE=$release -t qbittorrent-nox:$release --rm  .
+export \
+  QBT_VERSION=devel
+docker build \
+  --build-arg QBT_VERSION \
+  -t qbittorrent-nox:"$QBT_VERSION" \
+  .
 ```
 
-where:
+### Parameters
 
-* the `release` variable is the specific tagged version you want to build
-* the `BUILD_TYPE` argument is the build you want to create `Debug` or `Release`
-* the `RELEASE` argument works as the but is the actual argument given to docker, in the above script is defined by the `release` variable
+* `QBT_VERSION`
+  This environment variable specifies the version of qBittorrent-nox to be built. \
+  For example, `4.4.0` is a valid entry. You can find all tagged versions [here](https://github.com/qbittorrent/qBittorrent/tags). \
+  Or you can put `devel` to build the latest development version.
 
+## Running docker image
 
-### Usage
+* To start the the docker image simply run:
+  ```shell
+  export \
+    QBT_VERSION=devel \
+    QBT_EULA=accept \
+    QBT_WEBUI_PORT=8080
+  docker run \
+    -it \
+    --rm \
+    --name qbittorrent-nox \
+    -e QBT_EULA \
+    -e QBT_WEBUI_PORT \
+    -p "$QBT_WEBUI_PORT":"$QBT_WEBUI_PORT" \
+    -p 6881:6881/tcp \
+    -p 6881:6881/udp \
+    -v /your_path/config:/config \
+    -v /your_path/downloads:/downloads \
+    qbittorrent-nox:"$QBT_VERSION"
+  ```
+  Then you can login at: `http://127.0.0.1:8080`
 
-#### Container Variables
+* To stop the container:
+  ```shell
+  docker stop -t 1800 qbittorrent-nox
+  ```
 
-there is one important variable to run the container:
+### Parameters
 
-* the `LEGAL` varible defines if you accept the Legal Notice, put accept as a value only if you understand and accept the Legal Notice
+* `QBT_VERSION` \
+  The same as [above](#variables).
+* `QBT_EULA` \
+  This environment variable defines whether you accept the end-user license agreement (EULA) of qBittorrent. \
+  Put `accept` only if you understand and accepted the EULA. You can find
+  the EULA [here](https://github.com/qbittorrent/qBittorrent/blob/56667e717b82c79433ecb8a5ff6cc2d7b315d773/src/app/main.cpp#L320-L323).
+* `QBT_WEBUI_PORT` \
+  This environment variable sets the port number which qBittorrent WebUI will be binded to.
 
-#### Volumes
+### Volumes
 
-there are three main locations:
-
-* `config` contains qBittorrent configurations
-* `data` contains qBittorrent application data
-* `downloads` contains the files downloaded by qBittorrent
-
-```shell
-docker run give.example.org/of/your/container:v0.2.1 parameters
-```
-
-#### Network
-
-on the port `8080` the webinterface is run
-
-#### RUN
-
-To start the the docker image simply run
-
-```shell
-docker run --env LEGAL=accept -p 8080:8080 -v /your/path/config:/config -v /your/path/data:/data -v /your/path/download:/downloads --name qBittorrent qbittorrent-nox:4.2.0
-```
-
-to stop the container
-
-```shell
-docker stop qBittorrent
-```
+There are some paths involved:
+* `/your_path/config` on your host machine will contain qBittorrent configurations
+* `/your_path/downloads` on your host machine will contain the files downloaded by qBittorrent