Ensure readonly-modules when installing tools

Signed-off-by: Knut Ahlers <knut@ahlers.me>

Dockerfile

@@ -1,5 +1,7 @@
 FROM golang:alpine as builder
 
+ENV GO111MODULE=on
+
 COPY . /src
 WORKDIR /src
 
@@ -9,10 +11,7 @@ RUN set -ex \
       curl \
       git \
       make \
- && go get -v \
+ && bash /src/gotools.sh \
-      github.com/Luzifer/bind-log-metrics \
-      github.com/Luzifer/named-blacklist \
-      github.com/Luzifer/rootzone \
  && rootzone >named.stubs \
  && make blacklist
 

gotools.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+set -euxo pipefail
+
+packages=(
+	github.com/Luzifer/bind-log-metrics
+	github.com/Luzifer/named-blacklist
+	github.com/Luzifer/rootzone
+)
+
+for pkg in "${packages[@]}"; do
+	targetdir="/go/src/${pkg}"
+
+	# Get sources
+	git clone "https://${pkg}.git" "${targetdir}"
+
+	# Go to directory and install util
+	pushd "${targetdir}"
+	go install -mod=readonly
+	popd
+done