pkg/image: make Decompress easier to use

Change DecompressWriter to DecompressCheck: checking validity
of the image is the only useful use of DecompressWriter.

Change Decompress to MustDecompress which does not return an error.
We check validity during program deserialization, so all other
uses already panic on errors.
Also add dtor return value in preparation for subsequent changes.

1 files changed, 2 insertions, 4 deletions

diff --git a/prog/mutation.go b/prog/mutation.go
index 100c47a91..5a38cfa88 100644
--- a/prog/mutation.go
+++ b/prog/mutation.go
@@ -396,10 +396,8 @@ func (r *randGen) mutateImage(compressed []byte) (data []byte, retry bool) {
 	// Reconsider when/if we move mutation to the host process.
 	imageMu.Lock()
 	defer imageMu.Unlock()
-	data, err := image.Decompress(compressed)
-	if err != nil {
-		panic(fmt.Sprintf("could not decompress data: %v", err))
-	}
+	data, dtor := image.MustDecompress(compressed)
+	defer dtor()
 	if len(data) == 0 {
 		return compressed, true // Do not mutate empty data.
 	}