add Dockerfile

Signed-off-by: Florian Brandes <florian.brandes@posteo.de>

Dockerfile

@@ -0,0 +1,41 @@
+# syntax=docker/dockerfile:1
+
+FROM python:3.13.8-slim as base
+# Prevents Python from writing pyc files.
+ENV PYTHONDONTWRITEBYTECODE=1
+# Keeps Python from buffering stdout and stderr to avoid situations where
+# the application crashes without emitting any logs due to buffering.
+ENV PYTHONUNBUFFERED=1
+
+WORKDIR /app
+
+# Create a non-privileged user that the app will run under.
+# See https://docs.docker.com/go/dockerfile-user-best-practices/
+ARG UID=10001
+RUN adduser \
+    --disabled-password \
+    --gecos "" \
+    --home "/nonexistent" \
+    --shell "/sbin/nologin" \
+    --no-create-home \
+    --uid "${UID}" \
+    appuser
+
+RUN apt-get update
+RUN apt-get install -y build-essential libssl-dev python3-dev swig
+
+# Download dependencies as a separate step to take advantage of Docker's caching.
+# Leverage a cache mount to /root/.cache/pip to speed up subsequent builds.
+# Leverage a bind mount to requirements.txt to avoid having to copy them into
+# into this layer.
+RUN --mount=type=cache,target=/root/.cache/pip \
+    --mount=type=bind,source=requirements.txt,target=requirements.txt \
+    python -m pip install -r requirements.txt
+
+# Switch to the non-privileged user to run the application.
+USER appuser
+
+ADD smtprd_ng /app/smtprd_ng
+
+EXPOSE 8025
+CMD python smtprd_ng/smtprd.py --config /app/config.ini