--docker-host flag does not work with Docker sockets

[DiffuseHyperion]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I am running Nixpacks in a Docker container, with the Docker socket exposed to the container as a volume. However, Nixpacks does not recognize the socket and believes that Docker is not installed, even when --docker-host is used.

To reproduce

1. Run a Docker container with any image that Nixpacks can be installed onto, for example debian:slim.
2. Ensure that the Docker socket is exposed to the container with -v /var/run/docker.sock:/var/run/docker.sock
3. Open a shell within the container with exec -it bash
4. Install Nixpacks as shown in the documentation
5. Attempt to build a Docker image with the flag --docker-host.
6. Notice that Nixpacks believes Docker is not installed.

Here is an example of me trying to build an image in a Docker container.

root@b061154b24e6:/deploydeploydeploy# nixpacks build --docker-host unix:///var/run/docker.sock -n test /deploydeploydeploy/data/projects/528253b8-b153-4cf8-82ff-96356311bb6c/

╔════════════ Nixpacks v1.33.0 ════════════╗
║ setup      │ nodejs_18, npm-9_x, openssl ║
║──────────────────────────────────────────║
║ install    │ npm ci                      ║
║──────────────────────────────────────────║
║ build      │ npm run build               ║
║──────────────────────────────────────────║
║ start      │ npm run start               ║
╚══���═══════════════════════════════════════╝

Error: Please install Docker to build the app https://docs.docker.com/engine/install/
root@b061154b24e6:/deploydeploydeploy#

Expected behavior

The Docker image is built normally. I believe building Docker images via Docker sockets is possible as Docker's Python SDK allows this

Environment

• Docker Image: python:3.12-slim
  • Base OS: Debian Bookworm Slim (i believe)
• Nixpacks version: 1.33.0

[DiffuseHyperion]

Just fixed this, I didn't realize you had to install Docker too within the container, not just expose the socket.