Compare Pack's tar stream with the build agent's, since gzip's bytes differ between Go versions (issue 1479)

go/buildstep/pack_test.go

@@ -2,8 +2,10 @@ package buildstep
 
 import (
 	"bytes"
+	"compress/gzip"
 	"crypto/sha256"
 	"encoding/hex"
+	"io"
 	"os"
 	"path/filepath"
 	"testing"
@@ -33,11 +35,13 @@ func fixture(t *testing.T) string {
 	return root
 }
 
-// 1479/AC1: the archive equals the bytes mesh-controller's pack makes for this tree. testdata/pack-golden.tar.gz
-// was made once by running mesh-controller internal/builder/builder.go pack (origin/main 073ccc29, :1351-1425)
-// on this fixture (fixture above, modes set by chmod).
+// 1479/AC1: the tar stream inside the archive equals the bytes mesh-controller's pack makes for this tree.
+// testdata/pack-golden.tar is the uncompressed stream, made once by running mesh-controller
+// internal/builder/builder.go pack (origin/main 073ccc29, :1351-1425) on this fixture (above, modes set by chmod)
+// and gunzipping its archive. The gzip layer is not compared byte for byte, since compress/gzip's output differs
+// between Go versions; its header is checked to carry no name, no comment and no time.
 func TestPackEqualsTheBuildAgentsArchive(t *testing.T) {
-	golden, err := os.ReadFile("testdata/pack-golden.tar.gz")
+	golden, err := os.ReadFile("testdata/pack-golden.tar")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -45,12 +49,23 @@ func TestPackEqualsTheBuildAgentsArchive(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if !bytes.Equal(archive, golden) {
-		t.Errorf("the archive is %d bytes, the build agent's %d, and they differ", len(archive), len(golden))
+	zr, err := gzip.NewReader(bytes.NewReader(archive))
+	if err != nil {
+		t.Fatal(err)
 	}
-	sum := sha256.Sum256(golden)
+	if zr.Name != "" || zr.Comment != "" || !zr.ModTime.IsZero() {
+		t.Errorf("gzip header = name %q, comment %q, time %v; want none", zr.Name, zr.Comment, zr.ModTime)
+	}
+	tarBytes, err := io.ReadAll(zr)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(tarBytes, golden) {
+		t.Errorf("the tar stream is %d bytes, the build agent's %d, and they differ", len(tarBytes), len(golden))
+	}
+	sum := sha256.Sum256(archive)
 	if digest != "sha256:"+hex.EncodeToString(sum[:]) {
-		t.Errorf("digest = %s", digest)
+		t.Errorf("digest = %s, not the sha256 of the archive", digest)
 	}
 }