Take review comments into account.

quickwit/quickwit-indexing/src/source/file_source.rs

@@ -17,7 +17,7 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program. If not, see <http://www.gnu.org/licenses/>.
 
-use std::ops::Range;
+use std::ffi::OsStr;
 use std::path::Path;
 use std::sync::Arc;
 use std::time::Duration;
@@ -153,29 +153,21 @@ impl TypedSourceFactory for FileSourceFactory {
             let (dir_uri, file_name) = dir_and_filename(filepath)?;
             let storage = ctx.storage_resolver.resolve(&dir_uri).await?;
             let file_size = storage.file_num_bytes(file_name).await?.try_into().unwrap();
+            if offset > file_size {
+                return Err(anyhow::anyhow!(
+                    "offset {} can't be greater than the file size {}",
+                    offset,
+                    file_size
+                ));
+            }
             // If it's a gzip file, we can't seek to a specific offset, we need to start from the
             // beginning of the file, decompress and skip the first `offset` bytes.
-            if filepath.extension().map_or(false, |ext| ext == "gz") {
-                let stream = storage
-                    .get_slice_stream(
-                        file_name,
-                        Range {
-                            start: 0,
-                            end: file_size,
-                        },
-                    )
-                    .await?;
-                assert!(file_size >= offset, "file size should be >= offset");
+            if filepath.extension() == Some(OsStr::new("gz")) {
+                let stream = storage.get_slice_stream(file_name, 0..file_size).await?;
                 FileSourceReader::new(Box::new(GzipDecoder::new(BufReader::new(stream))), offset)
             } else {
                 let stream = storage
-                    .get_slice_stream(
-                        file_name,
-                        Range {
-                            start: offset,
-                            end: file_size,
-                        },
-                    )
+                    .get_slice_stream(file_name, offset..file_size)
                     .await?;
                 FileSourceReader::new(stream, 0)
             }
@@ -210,6 +202,8 @@ impl FileSourceReader {
         }
     }
 
+    // This function is only called for GZIP file.
+    // Because they cannot be seeked into, we have to scan them to the right initial position.
     async fn skip(&mut self) -> io::Result<()> {
         // Allocate once a 64kb buffer.
         let mut buf = [0u8; 64000];