Use native Go in Docker build

.dockerignore

@@ -5,7 +5,6 @@ tmp/
 imgproxy
 
 docs/
-docker/
 examples/
 LICENSE
 README.md

docker/Dockerfile

@@ -2,8 +2,11 @@ ARG BASE_IMAGE_VERSION="v3.2.1"
 
 FROM darthsim/imgproxy-base:${BASE_IMAGE_VERSION}
 
+ARG BUILDPLATFORM
+ARG TARGETPLATFORM
+
 COPY . .
-RUN ["bash", "-c", "go build -v -o /usr/local/bin/imgproxy"]
+RUN docker/go.sh build -v -o /usr/local/bin/imgproxy
 
 # ==================================================================================================
 # Final image

docker/go.sh

@@ -0,0 +1,52 @@
+#!/bin/bash
+
+set -e
+
+# This is pretty dirty hack. Building imgproxy under Qemu is pretty slow.
+# So we install Go binary native for the BUILDPLATFORM.
+if [[ $BUILDPLATFORM != $TARGETPLATFORM ]]; then
+  case "$BUILDPLATFORM" in
+    amd64 | "linux/amd64")
+      BUILD_ARCH="amd64"
+      ;;
+
+    arm64 | "arm64/v8" | "linux/arm64" | "linux/arm64/v8")
+      BUILDPLATFORM="arm64"
+      ;;
+
+    *)
+      echo "Unknown platform: $BUILDPLATFORM"
+      exit 1
+  esac
+
+  case "$TARGETPLATFORM" in
+    amd64 | "linux/amd64")
+      TARGET_ARCH="amd64"
+      ;;
+
+    arm64 | "arm64/v8" | "linux/arm64" | "linux/arm64/v8")
+      TARGET_ARCH="arm64"
+      ;;
+
+    *)
+      echo "Unknown platform: $TARGETPLATFORM"
+      exit 1
+  esac
+
+  GOLANG_VERSION=$(go version | sed -E 's/.*go([0-9]+\.[0-9]+\.[0-9]+).*/\1/')
+
+  rm -rf /usr/local/go
+
+  dpkg --add-architecture ${BUILD_ARCH}
+  apt-get update
+  apt-get install -y --no-install-recommends libstdc++6:${BUILD_ARCH}
+
+  curl -Ls https://golang.org/dl/go${GOLANG_VERSION}.linux-${BUILD_ARCH}.tar.gz \
+    | tar -xzC /usr/local
+
+  export CGO_ENABLED=1
+  export GOOS=linux
+  export GOARCH=$TARGET_ARCH
+fi
+
+go $@