Add helper script to verify release binaries

The script checks that the released binaries and the container binaries
can be reproduced.

helpers/verify-release-binaries.sh

@@ -0,0 +1,133 @@
+#!/bin/bash
+
+set -euo pipefail
+
+if [[ $# -lt 2 ]]; then
+    echo "Usage: $0 restic_version go_version"
+    exit 1
+fi
+
+restic_version="$1"
+go_version="$2"
+
+# invalid if zero
+is_valid=1
+
+tmpdir="$(mktemp -d -p .)"
+cd "${tmpdir}"
+echo -e "Running checks in ${tmpdir}\n"
+
+highlight() {
+    echo "@@${1//?/@}@@"
+    echo "@ ${1} @"
+    echo "@@${1//?/@}@@"
+}
+
+
+highlight "Verifying release self-consistency"
+
+curl -OLSs https://github.com/restic/restic/releases/download/v${restic_version}/restic-${restic_version}.tar.gz.asc
+# tarball is downloaded while processing the SHA256SUMS
+curl -OLSs https://github.com/restic/restic/releases/download/v${restic_version}/SHA256SUMS.asc
+curl -OLSs https://github.com/restic/restic/releases/download/v${restic_version}/SHA256SUMS
+
+export GNUPGHOME=$PWD/gnupg
+mkdir -p 700 $GNUPGHOME
+curl -OLSs https://restic.net/gpg-key-alex.asc
+gpg --import gpg-key-alex.asc
+gpg --verify SHA256SUMS.asc SHA256SUMS
+
+for i in $(cat SHA256SUMS | cut -d " "  -f 3 ) ; do
+    echo "Downloading $i"
+    curl -OLSs https://github.com/restic/restic/releases/download/v${restic_version}/"$i"
+done
+shasum -a256 -c SHA256SUMS || echo "WARNING: RELEASE BINARIES DO NOT MATCH SHA256SUMS!" && is_valid=0
+gpg --verify restic-${restic_version}.tar.gz.asc restic-${restic_version}.tar.gz
+# TODO verify that the release does not contain any unexpected files
+
+
+highlight "Verifying tarball matches tagged commit"
+
+tar xzf "restic-${restic_version}.tar.gz"
+git clone -b "v${restic_version}" https://github.com/restic/restic.git
+rm -rf restic/.git
+diff -r restic restic-${restic_version}
+
+
+highlight "Regenerating builder container"
+
+git clone https://github.com/restic/builder.git
+docker pull debian:stable
+docker build --no-cache -t restic/builder:tmp --build-arg GO_VERSION=${go_version} builder
+
+
+highlight "Reproducing release binaries"
+
+mkdir output
+docker run --rm \
+    --volume "$PWD/restic-${restic_version}:/restic" \
+    --volume "$PWD/output:/output" \
+    restic/builder:tmp \
+    go run helpers/build-release-binaries/main.go --version "${restic_version}"
+
+cp "restic-${restic_version}.tar.gz" output
+cp SHA256SUMS output
+
+# check that all release binaries have been reproduced successfully
+(cd output && shasum -a256 -c SHA256SUMS) || echo "WARNING: REPRODUCED BINARIES DO NOT MATCH RELEASE BINARIES!" && is_valid=0
+# and that the SHA256SUMS files does not miss binaries
+for i in output/restic* ; do grep "$(basename "$i")" SHA256SUMS > /dev/null || echo "WARNING: $i MISSING FROM RELEASE SHA256SUMS FILE!" && is_valid=0 ; done
+
+
+extract_docker() {
+    image=$1
+    docker_platform=$2
+    restic_platform=$3
+    out=restic_${restic_version}_linux_${restic_platform}.bz2
+
+    docker image pull --platform "linux/${docker_platform}" ${image}:${restic_version} > /dev/null
+    docker image save ${image}:${restic_version} -o docker.tar
+
+    mkdir img
+    tar xvf docker.tar -C img --wildcards \*/layer.tar > /dev/null
+    rm docker.tar
+    for i in img/*/layer.tar; do
+        tar -xvf "$i" -C img usr/bin/restic 2> /dev/null 1>&2 || true
+        if [[ -f img/usr/bin/restic ]]; then
+            if [[ -f restic-docker ]]; then
+                echo "WARNING: CONTAINER CONTAINS MULTIPLE RESTIC BINARIES"
+                is_valid=0
+            fi
+            mv img/usr/bin/restic restic-docker
+        fi
+    done
+    
+    rm -rf img
+    bzip2 restic-docker
+    mv restic-docker.bz2 docker/${out}
+    grep ${out} SHA256SUMS >> docker/SHA256SUMS
+}
+
+ctr=0
+for img in restic/restic ghcr.io/restic/restic; do
+    highlight "Verifying binaries in docker containers from $img"
+    mkdir docker
+
+    extract_docker "$img" arm/v7 arm
+    extract_docker "$img" arm64 arm64
+    extract_docker "$img" 386 386
+    extract_docker "$img" amd64 amd64
+
+    (cd docker && shasum -a256 -c SHA256SUMS) || echo "WARNING: DOCKER CONTAINER DOES NOT CONTAIN RELEASE BINARIES!" && is_valid=0
+
+    mv docker docker-$(( ctr++ ))
+done
+
+
+if [[ $is_valid -ne 1 ]]; then
+    highlight "Failed to reproduce some binaries, check the script output for details"
+    exit 1
+else
+    cd ..
+    rm -rf "${tmpdir}"
+fi