comment

Author: syphar

src/storage/s3.rs

@@ -212,6 +212,15 @@ impl S3Backend {
 
         let etag = if let Some(mut etag) = res.e_tag {
             if let Some(range) = range {
+                // we can generate a strong, unique etag for a range of the remote object too,
+                // by just concatenating the original etag with the range start and end.
+                //
+                // About edge cases:
+                // When the etag of the full archive changes after a rebuild,
+                // all derived etags for files inside the archive will also change.
+                //
+                // This could lead to _changed_ ETags, where the single file inside the archive
+                // is actually the same.
                 etag = format!("\"{}:{}-{}\"", etag, range.start(), range.end())
             }
             match etag.parse::<headers::ETag>() {