Skip checksum validation for multifile downloads where no checksum is provided

Author: kylstevenson

src/main/java/io/github/jpmorganchase/fusion/api/request/PartFetcher.java

@@ -3,6 +3,7 @@
 import static io.github.jpmorganchase.fusion.api.tools.ResponseChecker.checkResponseStatus;
 
 import io.github.jpmorganchase.fusion.FusionConfiguration;
+import io.github.jpmorganchase.fusion.api.exception.FileDownloadException;
 import io.github.jpmorganchase.fusion.api.response.GetPartResponse;
 import io.github.jpmorganchase.fusion.api.response.Head;
 import io.github.jpmorganchase.fusion.api.stream.IntegrityCheckingInputStream;
@@ -55,23 +56,32 @@ public GetPartResponse fetch(PartRequest pr) {
     }
 
     private InputStream getIntegrityCheckingInputStream(HttpResponse<InputStream> response, Head head, PartRequest pr) {
-        if (shouldSkipChecksumValidation(head, pr.getDownloadRequest())) {
-            return response.getBody();
+        String checksum = head.getChecksum();
+        boolean checksumMissing = Objects.isNull(checksum) || checksum.isEmpty();
+        DownloadRequest downloadRequest = pr.getDownloadRequest();
+
+        if (checksumMissing) {
+            if (downloadRequest.isSkipChecksumValidationIfMissing()) {
+                log.debug(
+                        "Skipping checksum validation for download request {}",
+                        downloadRequest);
+                return response.getBody();
+            } else {
+                throw new FileDownloadException(
+                        "Checksum validation failed: checksum is missing for download request: "
+                                + downloadRequest);
+            }
         }
 
+        log.debug("Verifying checksum for download request {} with checksum: {}", downloadRequest, checksum);
         return IntegrityCheckingInputStream.builder()
                 .part(response.getBody())
-                .checksum(head.getChecksum())
+                .checksum(checksum)
                 .partChecker(
                         PartChecker.builder().digestAlgo(getDigestAlgo(head)).build())
                 .build();
     }
 
-    private boolean shouldSkipChecksumValidation(Head head, DownloadRequest downloadRequest) {
-        String checksum = head.getChecksum();
-        return (Objects.isNull(checksum) || checksum.isEmpty()) && downloadRequest.isSkipChecksumValidationIfMissing();
-    }
-
     private String getDigestAlgo(Head head) {
         return head.getChecksumAlgorithm() != null ? head.getChecksumAlgorithm() : configuration.getDigestAlgorithm();
     }