Add dockerfile for nat testing

.gitignore

@@ -6,6 +6,7 @@
 !LICENSE*
 !Makefile
 !Jenkinsfile
+!Dockerfile
 
 nimcache/
 

tests/integration/nat/Dockerfile

@@ -0,0 +1,54 @@
+FROM ubuntu:24.04
+
+ARG NIM_VERSION=2.2.10
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    gcc g++ make cmake git curl ca-certificates xz-utils \
+    libc-dev ccache \
+    iproute2 \
+    && rm -rf /var/lib/apt/lists/*
+
+# Build miniupnpd with stub redirector: no iptables/nftables needed, always
+# returns success for port mapping requests — safe for isolated test containers.
+COPY tests/integration/nat/miniupnpd_stub_rdr.c /tmp/stub_rdr.c
+RUN git clone --depth=1 --branch miniupnpd_2_3_9 \
+        https://github.com/miniupnp/miniupnp.git /tmp/miniupnp \
+    && cd /tmp/miniupnp/miniupnpd \
+    && ./configure \
+    && cp /tmp/stub_rdr.c . \
+    && make NETFILTEROBJS=stub_rdr.o miniupnpd \
+    && install -m 755 miniupnpd /usr/local/sbin/miniupnpd \
+    && rm -rf /tmp/miniupnp /tmp/stub_rdr.c
+
+# Install Nim
+RUN curl -fsSL "https://nim-lang.org/download/nim-${NIM_VERSION}-linux_x64.tar.xz" \
+    | tar -xJ -C /opt && \
+    ln -s "/opt/nim-${NIM_VERSION}/bin/nim" /usr/local/bin/nim
+
+WORKDIR /app
+
+# Copy project source (build context must be the project root)
+COPY vendor/ vendor/
+COPY storage/ storage/
+COPY library/ library/
+COPY tests/ tests/
+COPY build.nims config.nims storage.nim ./
+
+# Build libplum C library and Nim binaries.
+# ccache caches C compilation across builds; nimcache caches Nim's generated C files.
+RUN --mount=type=cache,target=/root/.ccache \
+    --mount=type=cache,target=/app/nimcache \
+    export PATH="/usr/lib/ccache:$PATH" && \
+    rm -rf vendor/nim-libplum/vendor/libplum/build && \
+    cmake -B vendor/nim-libplum/vendor/libplum/build \
+        -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=OFF \
+        vendor/nim-libplum/vendor/libplum && \
+    make -j$(nproc) -C vendor/nim-libplum/vendor/libplum/build && \
+    cp vendor/nim-libplum/vendor/libplum/build/libplum.a \
+        vendor/nim-libplum/vendor/libplum/libplum.a && \
+    USE_SYSTEM_NIM=1 vendor/nimbus-build-system/scripts/env.sh \
+    nim buildNatPortMappingBinaries -d:debug -d:disable_libbacktrace build.nims
+
+COPY tests/integration/nat/docker-entrypoint.sh /entrypoint.sh
+RUN chmod +x /entrypoint.sh
+ENTRYPOINT ["/entrypoint.sh"]