Add a check that piece request order items are scanned in order

It's not clear from btree documentation that scan should be ordered.

diff --git a/request-strategy/order.go b/request-strategy/order.go
index 3b7284b2f44c2bd8e5670c3431d707a7f80d5b76..b009a10882e84eb9a235345b64f70cd2f2631f15 100644 (file)
--- a/request-strategy/order.go
+++ b/request-strategy/order.go
@@ -4,6 +4,7 @@ import (
        "bytes"
        "expvar"
 
+       "github.com/anacrolix/generics"
        "github.com/anacrolix/multiless"
 
        "github.com/anacrolix/torrent/metainfo"
@@ -54,7 +55,16 @@ func GetRequestablePieces(
                storageLeft = &cap
        }
        var allTorrentsUnverifiedBytes int64
+       var lastItem generics.Option[pieceRequestOrderItem]
        pro.tree.Scan(func(_i pieceRequestOrderItem) bool {
+               // Check that scan emits pieces in priority order.
+               if lastItem.Ok {
+                       if _i.Less(&lastItem.Value) {
+                               panic("scan not in order")
+                       }
+               }
+               lastItem.Set(_i)
+
                ih := _i.key.InfoHash
                var t = input.Torrent(ih)
                pieceLength := t.PieceLength()