feat: Add a flag to allow for uploading chunks from the end of the li…

…st (#335)

This adds a flag to the uploader binary to allow for choosing whether
the upload starts from the first chunk (default) or the last chunk. This
can be handy to speed up the upload of state since once can start two
instance in parallel, one uploading from the first chunk and the other
from the last one.

bootstrap/uploader/src/upload.rs

@@ -37,6 +37,9 @@ struct Args {
     /// The canister to upload the state to.
     #[clap(long)]
     canister_id: Principal,
+
+    #[clap(long, default_value_t = false)]
+    upload_from_end: bool,
 }
 
 #[derive(CandidType)]
@@ -84,7 +87,15 @@ async fn main() {
 
     // Upload the missing chunks.
     let mut reader = BufReader::new(f);
-    for chunk_index in missing_chunk_indices {
+    // Compute the chunk indices in the order they should be uploaded
+    // either from the beginning or from the end, depending on the
+    // `upload_from_end` flag.
+    let chunk_indices: Vec<u64> = if args.upload_from_end {
+        missing_chunk_indices.into_iter().rev().collect()
+    } else {
+        missing_chunk_indices.into_iter().collect()
+    };
+    for chunk_index in chunk_indices {
         let offset = chunk_index * PAGE_SIZE_IN_BYTES;
         let mut buf = vec![0; CHUNK_SIZE_IN_BYTES as usize];
         reader