[GitHub] [arrow-rs] tustvold commented on a diff in pull request #1807: Don't trample existing data on snappy decompress (#1806)

[GitBox <gi...@apache.org>]

tustvold commented on code in PR #1807:
URL: https://github.com/apache/arrow-rs/pull/1807#discussion_r891044017


##########
parquet/src/compression.rs:
##########
@@ -340,26 +341,46 @@ mod tests {
             .expect("Error when compressing");
 
         // Decompress with c2
-        let mut decompressed_size = c2
+        let decompressed_size = c2
             .decompress(compressed.as_slice(), &mut decompressed)
             .expect("Error when decompressing");
         assert_eq!(data.len(), decompressed_size);
-        decompressed.truncate(decompressed_size);
         assert_eq!(data, decompressed.as_slice());
 
+        decompressed.clear();
         compressed.clear();
 
         // Compress with c2
         c2.compress(data, &mut compressed)
             .expect("Error when compressing");
 
         // Decompress with c1
-        decompressed_size = c1
+        let decompressed_size = c1
             .decompress(compressed.as_slice(), &mut decompressed)
             .expect("Error when decompressing");
         assert_eq!(data.len(), decompressed_size);
-        decompressed.truncate(decompressed_size);

Review Comment:
   This test was actually incorrect, it never cleared `decompressed` and so this was effectively just checking the same bytes it checked in the test above (except for Snappy which would truncate and trample)



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