Add digest property to parent and nested java package metadata (#941)

syft/file/digest_cataloger.go

@@ -77,30 +77,39 @@ func (i *DigestsCataloger) catalogLocation(resolver source.FileResolver, locatio
 	}
 	defer internal.CloseAndLogError(contentReader, location.VirtualPath)
 
+	digests, err := DigestsFromFile(contentReader, i.hashes)
+	if err != nil {
+		return nil, internal.ErrPath{Context: "digests-cataloger", Path: location.RealPath, Err: err}
+	}
+
+	return digests, nil
+}
+
+func DigestsFromFile(closer io.ReadCloser, hashes []crypto.Hash) ([]Digest, error) {
 	// create a set of hasher objects tied together with a single writer to feed content into
-	hashers := make([]hash.Hash, len(i.hashes))
-	writers := make([]io.Writer, len(i.hashes))
-	for idx, hashObj := range i.hashes {
+	hashers := make([]hash.Hash, len(hashes))
+	writers := make([]io.Writer, len(hashes))
+	for idx, hashObj := range hashes {
 		hashers[idx] = hashObj.New()
 		writers[idx] = hashers[idx]
 	}
 
-	size, err := io.Copy(io.MultiWriter(writers...), contentReader)
+	size, err := io.Copy(io.MultiWriter(writers...), closer)
 	if err != nil {
-		return nil, internal.ErrPath{Context: "digests-cataloger", Path: location.RealPath, Err: err}
+		return nil, err
 	}
 
 	if size == 0 {
 		return make([]Digest, 0), nil
 	}
 
-	result := make([]Digest, len(i.hashes))
+	result := make([]Digest, len(hashes))
 	// only capture digests when there is content. It is important to do this based on SIZE and not
 	// FILE TYPE. The reasoning is that it is possible for a tar to be crafted with a header-only
 	// file type but a body is still allowed.
 	for idx, hasher := range hashers {
 		result[idx] = Digest{
-			Algorithm: DigestAlgorithmName(i.hashes[idx]),
+			Algorithm: DigestAlgorithmName(hashes[idx]),
 			Value:     fmt.Sprintf("%+x", hasher.Sum(nil)),
 		}
 	}