Refactor the error handling further

Use defer, a nested function, and early returns.

Besides being a bit more directly related to what
we want to achieve, this now does not call decompressed.Close()
on a nil value if DecompressStream fails.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

pkg/blobcache/dest.go

@@ -79,6 +79,7 @@ func (d *blobCacheDestination) IgnoresEmbeddedDockerReference() bool {
 // and this new file.
 func (d *blobCacheDestination) saveStream(wg *sync.WaitGroup, decompressReader io.ReadCloser, tempFile *os.File, compressedFilename string, compressedDigest digest.Digest, isConfig bool, alternateDigest *digest.Digest) {
 	defer wg.Done()
+	defer decompressReader.Close()
 
 	succeeded := false
 	defer func() {
@@ -90,28 +91,30 @@ func (d *blobCacheDestination) saveStream(wg *sync.WaitGroup, decompressReader i
 		}
 	}()
 
-	// Decompress from and digest the reading end of that pipe.
-	decompressed, err3 := archive.DecompressStream(decompressReader)
 	digester := digest.Canonical.Digester()
-	if err3 == nil {
+	if err := func() error { // A scope for defer
+		defer tempFile.Close()
+
+		// Decompress from and digest the reading end of that pipe.
+		decompressed, err := archive.DecompressStream(decompressReader)
+		if err != nil {
+			// Drain the pipe to keep from stalling the PutBlob() thread.
+			if _, err2 := io.Copy(io.Discard, decompressReader); err2 != nil {
+				logrus.Debugf("error draining the pipe: %v", err2)
+			}
+			return err
+		}
+		defer decompressed.Close()
 		// Read the decompressed data through the filter over the pipe, blocking until the
 		// writing end is closed.
-		_, err3 = io.Copy(io.MultiWriter(tempFile, digester.Hash()), decompressed)
-	} else {
-		// Drain the pipe to keep from stalling the PutBlob() thread.
-		if _, err := io.Copy(io.Discard, decompressReader); err != nil {
-			logrus.Debugf("error draining the pipe: %v", err)
-		}
+		_, err = io.Copy(io.MultiWriter(tempFile, digester.Hash()), decompressed)
+		return err
+	}(); err != nil {
+		return
 	}
-	decompressReader.Close()
-	decompressed.Close()
-	tempFile.Close()
 
 	// Determine the name that we should give to the uncompressed copy of the blob.
 	decompressedFilename := d.reference.blobPath(digester.Digest(), isConfig)
-	if err3 != nil {
-		return
-	}
 	// Rename the temporary file.
 	if err := os.Rename(tempFile.Name(), decompressedFilename); err != nil {
 		logrus.Debugf("error renaming new decompressed copy of blob %q into place at %q: %v", digester.Digest().String(), decompressedFilename, err)