Slightly change download process to be more verbose in error situations

crunchy-cli-core/src/cli/utils.rs

@@ -93,13 +93,16 @@ pub async fn download_segments(
             Ok(())
         });
     }
+    // drop the sender already here so it does not outlive all (download) threads which are the only
+    // real consumers of it
+    drop(sender);
 
+    // this is the main loop which writes the data. it uses a BTreeMap as a buffer as the write
+    // happens synchronized. the download consist of multiple segments. the map keys are representing
+    // the segment number and the values the corresponding bytes
     let mut data_pos = 0usize;
     let mut buf: BTreeMap<usize, Vec<u8>> = BTreeMap::new();
-    loop {
+    for (pos, bytes) in receiver.iter() {
-        // is always `Some` because `sender` does not get dropped when all threads are finished
-        let (pos, bytes) = receiver.recv().unwrap();
-
         if let Some(p) = &progress {
             let progress_len = p.length().unwrap();
             let estimated_segment_len = (variant_data.bandwidth / 8)
@@ -115,26 +118,44 @@ pub async fn download_segments(
             p.inc(bytes_len)
         }
 
+        // check if the currently sent bytes are the next in the buffer. if so, write them directly
+        // to the target without first adding them to the buffer.
+        // if not, add them to the buffer
         if data_pos == pos {
             writer.write_all(bytes.borrow())?;
             data_pos += 1;
         } else {
             buf.insert(pos, bytes);
         }
+        // check if the buffer contains the next segment(s)
         while let Some(b) = buf.remove(&data_pos) {
             writer.write_all(b.borrow())?;
             data_pos += 1;
         }
-
-        if *count.lock().unwrap() >= total_segments && buf.is_empty() {
-            break;
-        }
     }
 
+    // write the remaining buffer, if existent
+    while let Some(b) = buf.remove(&data_pos) {
+        writer.write_all(b.borrow())?;
+        data_pos += 1;
+    }
+
+    // if any error has occured while downloading it gets returned here. maybe a little late, if one
+    // out of, for example 12, threads has the error
     while let Some(joined) = join_set.join_next().await {
         joined??
     }
 
+    if !buf.is_empty() {
+        bail!(
+            "Download buffer is not empty. Remaining segments: {}",
+            buf.into_keys()
+                .map(|k| k.to_string())
+                .collect::<Vec<String>>()
+                .join(", ")
+        )
+    }
+
     Ok(())
 }