fix for edge condition with connections smaller than total size

Author: LesnyRumcajs

src/utils/net/download_file.rs

@@ -282,7 +282,10 @@ async fn download_http_parallel(
         .await
         .context("couldn't allocate file space")?;
 
-    let chunk_size = total_size / num_connections as u64;
+    // Prevent underflow when file is smaller than connection count
+    // Use at most as many connections as there are bytes
+    let effective_connections = (num_connections as u64).min(total_size.max(1));
+    let chunk_size = total_size / effective_connections;
 
     // Progress tracking - log every 5 seconds like the forest::progress system
     let bytes_downloaded = Arc::new(std::sync::atomic::AtomicU64::new(0));
@@ -292,7 +295,7 @@ async fn download_http_parallel(
     const UPDATE_FREQUENCY: Duration = Duration::from_secs(5);
 
     // Download chunks in parallel
-    let download_tasks = (0..num_connections).map(|i| {
+    let download_tasks = (0..effective_connections).map(|i| {
         let client = client.clone();
         let url = url.clone();
         let tmp_path = tmp_dst_path.clone();
@@ -301,11 +304,11 @@ async fn download_http_parallel(
         let last_logged_time = Arc::clone(&last_logged_time);
         let callback = callback.clone();
 
-        let start = i as u64 * chunk_size;
-        let end = if i == num_connections - 1 {
+        let start = i * chunk_size;
+        let end = if i == effective_connections - 1 {
             total_size - 1
         } else {
-            (i + 1) as u64 * chunk_size - 1
+            ((i + 1) * chunk_size - 1).min(total_size - 1)
         };
 
         async move {
@@ -405,7 +408,7 @@ async fn download_http_parallel(
 
     // Execute all downloads in parallel and collect results
     let results: Vec<_> = stream::iter(download_tasks)
-        .buffer_unordered(num_connections)
+        .buffer_unordered(effective_connections as usize)
         .collect()
         .await;
 
@@ -885,4 +888,25 @@ mod test {
         let content = std::fs::read(&result).unwrap();
         assert_eq!(content, TEST_FILE_CONTENT);
     }
+
+    #[tokio::test]
+    async fn test_small_file_with_many_connections() {
+        // Test edge case: file smaller than connection count
+        // This tests the underflow prevention when chunk_size would be 0
+        let small_content: &[u8] = b"Hi!"; // 3 bytes
+        let server = TestServer::start_with_content(small_content).await;
+        let temp_dir = tempfile::tempdir().unwrap();
+        let url = server.url("/test-file");
+
+        // Try to download with more connections than bytes
+        let result = download_http_parallel(&url, temp_dir.path(), "tiny.dat", 5, None)
+            .await
+            .unwrap();
+
+        assert!(result.exists());
+
+        // Verify content is correct
+        let downloaded = std::fs::read(&result).unwrap();
+        assert_eq!(downloaded, small_content);
+    }
 }