docker/README.md

# Dockerfile for EMSDK

This Dockerfile builds a self-contained version of emsdk that enables emscripten to be used without any
other installation on the host system.

It is published at https://hub.docker.com/u/emscripten/emsdk

### Usage

Simple usage of this container to compile a hello-world
```bash
# create helloworld.cpp
cat << EOF > helloworld.cpp
#include <iostream>
int main() {
  std::cout << "Hello World!" << std::endl;
  return 0;
}
EOF
```

```bash
# compile with docker image
docker run \
  --rm \
  -v $(pwd):$(pwd) \
  -u $(id -u):$(id -g) \
  emscripten/emsdk \
  emcc helloworld.cpp -o helloworld.js

# execute on host machine
node helloworld.js
```

Teardown of compilation command:

|part|description|
|---|---|
|`docker run`| A standard command to run a command in a container|
|`--rm`|remove a container after execution (optimization)|
|`-v $(pwd):$(pwd)`|Mounting current folder from the host system into mirrored path on the container<br>TIP: This helps to investigate possible problem as we preserve exactly the same paths like in host. In such case modern editors (like Sublime, Atom, VS Code) let us to CTRL+Click on a problematic file |
|`-u $(id -u):$(id -g)`| Run the container as a non-root user with the same UID and GID as local user. Hence all files produced by this are accessible to non-root users|
|`emscripten/emsdk`|Get the latest tag of this container|
|`emcc helloworld.cpp -o helloworld.js`|Execute `emcc` command with following arguments inside container, effectively compile our source code|



### Building Dockerfile

This image requires to specify following build arguments:

| arg | description |
| --- | --- |
| `EMSCRIPTEN_VERSION` | One of released version of Emscripten. For example `1.38.45`<br/> Can be used with `-upstream` variant like: `1.38.45-upstream`<br /> Minimal supported version is **1.38.40**|

**Building**

This step will build Dockerfile as given tag on local machine
```bash
# using docker
docker build \
    --build-arg=EMSCRIPTEN_VERSION=1.38.43-upstream \
    --tag emscripten/emsdk:1.38.43-upstream \
    .
```
```bash
# using predefined make target
make version=1.38.43-upstream build
```

**Tagging**

In case of using `docker build` command directly, given `--tag` should match version of released Emscripten (you can see list of non-legacy versions by executing `emsdk list`).

**Pushing**

This step will take local image and push to default docker registry. You need to make sure that you logged in docker cli (`docker login`) and you have rights to push to that registry.

```bash
# using docker
docker push emscripten/emsdk:1.38.43-upstream
```
```bash
# using predefined make target
make version=1.38.43-upstream push
```

In case of pushing the most recent version, this version should be also tagged as `latest` or `latest-upstream` and pushed.
```bash
# using docker cli

# in case of fastcomp variant (default backend)
docker tag emscripten/emsdk:1.38.43 emscripten/emsdk:latest
docker push emscripten/emsdk:latest

# in case of upstream variant
docker tag emscripten/emsdk:1.38.43-upstream emscripten/emsdk:latest-upstream
docker push emscripten/emsdk:latest-upstream

```

```bash
# using predefined make target

make version=1.38.43-upstream alias=latest-upstream push

```


### Extending

If your project uses packages that this image doesn't provide you might want to:
* Contribute to this repo: Maybe your dependency is either non-intrusive or could be useful for other people
* Create custom image that bases on this image

1. create own Dockerfile that holds:
    ```dockerfile
    # Point at any base image that you find suitable to extend.
    FROM emscripten/emsdk:1.38.25

    # Install required tools that are useful for your project i.e. ninja-build
    RUN apt update && apt install -y ninja-build

    ```
2. build it
    ```shell
    docker build -t extended_emscripten .
    ```

3. test
    ```shell
    docker run --rm extended_emscripten ninja --version
    # Python 2.7.16
    ```