cmd: add helper for seed generation

To ensure that manifests get random(ish) and stable UUIDs we set the rng seed arg based on the filename.

This should fix the issue discovered in
osbuild/manifest-db#124

that duplicated UUIDs for xfs/btrfs can trigger random(ish) and hard to diagnose errors.

This is the same as
osbuild/osbuild-composer#4124 hopefully for the right place this time.

cmd/build/main.go

@@ -42,7 +42,6 @@ func makeManifest(
 	distribution distro.Distro,
 	repos []rpmmd.RepoConfig,
 	archName string,
-	seedArg int64,
 	cacheRoot string,
 ) (manifest.OSBuildManifest, error) {
 	cacheDir := filepath.Join(cacheRoot, archName+distribution.Name())
@@ -58,6 +57,10 @@ func makeManifest(
 	if config.Blueprint != nil {
 		bp = blueprint.Blueprint(*config.Blueprint)
 	}
+	seedArg, err := cmdutil.SeedArgFor(config, imgType, distribution, archName)
+	if err != nil {
+		return nil, err
+	}
 
 	manifest, warnings, err := imgType.Manifest(&bp, options, repos, seedArg)
 	if err != nil {
@@ -209,9 +212,6 @@ func main() {
 		os.Exit(1)
 	}
 
-	rngSeed, err := cmdutil.NewRNGSeed()
-	check(err)
-
 	testedRepoRegistry, err := reporegistry.NewTestedDefault()
 	if err != nil {
 		panic(fmt.Sprintf("failed to create repo registry with tested distros: %v", err))
@@ -258,7 +258,7 @@ func main() {
 	}
 
 	fmt.Printf("Generating manifest for %s: ", config.Name)
-	mf, err := makeManifest(config, imgType, distribution, repos, archName, rngSeed, rpmCacheRoot)
+	mf, err := makeManifest(config, imgType, distribution, repos, archName, rpmCacheRoot)
 	check(err)
 	fmt.Print("DONE\n")
 

cmd/gen-manifests/main.go

@@ -179,7 +179,6 @@ func makeManifestJob(
 	distribution distro.Distro,
 	repos []rpmmd.RepoConfig,
 	archName string,
-	seedArg int64,
 	cacheRoot string,
 	path string,
 	content map[string]bool,
@@ -190,6 +189,12 @@ func makeManifestJob(
 	filename := fmt.Sprintf("%s-%s-%s-%s.json", u(distroName), u(archName), u(imgType.Name()), u(name))
 	cacheDir := filepath.Join(cacheRoot, archName+distribution.Name())
 
+	// ensure that each file has a unique seed based on filename
+	seedArg, err := cmdutil.SeedArgFor(bc, imgType, distribution, archName)
+	if err != nil {
+		panic(err)
+	}
+
 	options := bc.Options
 
 	var bp blueprint.Blueprint
@@ -508,11 +513,6 @@ func main() {
 
 	flag.Parse()
 
-	rngSeed, err := cmdutil.NewRNGSeed()
-	if err != nil {
-		panic(err)
-	}
-
 	testedRepoRegistry, err := reporegistry.NewTestedDefault()
 	if err != nil {
 		panic(fmt.Sprintf("failed to create repo registry with tested distros: %v", err))
@@ -598,7 +598,7 @@ func main() {
 				}
 
 				for _, itConfig := range imgTypeConfigs {
-					job := makeManifestJob(itConfig, imgType, distribution, repos, archName, rngSeed, cacheRoot, outputDir, contentResolve, metadata)
+					job := makeManifestJob(itConfig, imgType, distribution, repos, archName, cacheRoot, outputDir, contentResolve, metadata)
 					jobs = append(jobs, job)
 				}
 			}

internal/cmdutil/export_test.go

@@ -0,0 +1,3 @@
+package cmdutil
+
+var NewRNGSeed = newRNGSeed

internal/cmdutil/rand.go

@@ -3,17 +3,20 @@ package cmdutil
 import (
 	"crypto/rand"
 	"fmt"
+	"hash/fnv"
 	"math"
 	"math/big"
 	"os"
 	"strconv"
+
+	"github.com/osbuild/images/internal/buildconfig"
 )
 
 const RNG_SEED_ENV_KEY = "OSBUILD_TESTING_RNG_SEED"
 
-// NewRNGSeed generates a random seed value unless the env var
+// newRNGSeed generates a random seed value unless the env var
 // OSBUILD_TESTING_RNG_SEED is set.
-func NewRNGSeed() (int64, error) {
+func newRNGSeed() (int64, error) {
 	if envSeedStr := os.Getenv(RNG_SEED_ENV_KEY); envSeedStr != "" {
 		envSeedInt, err := strconv.ParseInt(envSeedStr, 10, 64)
 		if err != nil {
@@ -28,3 +31,22 @@ func NewRNGSeed() (int64, error) {
 	}
 	return randSeed.Int64(), nil
 }
+
+type namer interface {
+	Name() string
+}
+
+func SeedArgFor(bc *buildconfig.BuildConfig, imgType namer, distribution namer, archName string) (int64, error) {
+	rngSeed, err := newRNGSeed()
+	if err != nil {
+		return 0, err
+	}
+
+	h := fnv.New64()
+	h.Write([]byte(distribution.Name()))
+	h.Write([]byte(archName))
+	h.Write([]byte(imgType.Name()))
+	h.Write([]byte(bc.Name))
+
+	return rngSeed + int64(h.Sum64()), nil
+}

internal/cmdutil/rand_test.go

@@ -7,6 +7,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
+	"github.com/osbuild/images/internal/buildconfig"
 	"github.com/osbuild/images/internal/cmdutil"
 )
 
@@ -38,3 +39,31 @@ func TestNewRNGSeed(t *testing.T) {
 		require.EqualError(t, err, fmt.Sprintf(`failed to parse %s: strconv.ParseInt: parsing "NaN": invalid syntax`, cmdutil.RNG_SEED_ENV_KEY))
 	})
 }
+
+type fakeNamer struct {
+	fakeName string
+}
+
+func (fn fakeNamer) Name() string {
+	return fn.fakeName
+}
+
+func TestSeedArgFor(t *testing.T) {
+	t.Setenv(cmdutil.RNG_SEED_ENV_KEY, "1234")
+
+	for _, tc := range []struct {
+		bcName, imgType, distro, archName string
+		expectedSeed                      int64
+	}{
+		{"bcName", "fakeImgType", "fakeDistro", "x86_64", 9170052743323116054},
+		{"bcName1", "fakeImgType", "fakeDistro", "x86_64", -7134826073208782961},
+		{"bcName", "fakeImgType1", "fakeDistro", "x86_64", 4026045880862600579},
+		{"bcName", "fakeImgType", "fakeDistro1", "x86_64", 3669869122697339647},
+		{"bcName", "fakeImgType", "fakeDistro1", "aarch64", 47752167762999679},
+	} {
+		bc := &buildconfig.BuildConfig{Name: tc.bcName}
+		seedArg, err := cmdutil.SeedArgFor(bc, fakeNamer{tc.imgType}, fakeNamer{tc.distro}, tc.archName)
+		assert.NoError(t, err)
+		assert.Equal(t, tc.expectedSeed, seedArg)
+	}
+}