internetarchive: fix corrupted files being created when the source ends early

If the source supplied fewer bytes than its declared size, the upload
request failed but a retry could report success even though the stored
file was truncated, because the retry re-sent an already exhausted
reader.

Count the bytes actually read from the source and if they do not match
the declared size return an error.

This was found by the new FsPutShortEOF integration test.

backend/internetarchive/internetarchive.go

@@ -30,6 +30,7 @@ import (
 	"github.com/rclone/rclone/lib/encoder"
 	"github.com/rclone/rclone/lib/pacer"
 	"github.com/rclone/rclone/lib/random"
+	"github.com/rclone/rclone/lib/readers"
 	"github.com/rclone/rclone/lib/rest"
 )
 
@@ -854,11 +855,12 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 	}
 
 	// make a PUT request at (IAS3)/encoded(:item/:path)
+	counter := readers.NewCountingReader(in)
 	var resp *http.Response
 	opts := rest.Opts{
 		Method:        "PUT",
 		Path:          "/" + url.PathEscape(path.Join(bucket, bucketPath)),
-		Body:          in,
+		Body:          counter,
 		ContentLength: &size,
 		ExtraHeaders:  headers,
 	}
@@ -868,6 +870,12 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 		return o.fs.shouldRetry(resp, err)
 	})
 
+	// Check the source supplied the number of bytes it declared
+	// otherwise a truncated file would be stored as a good upload
+	if err == nil && size >= 0 && int64(counter.BytesRead()) != size {
+		err = fmt.Errorf("expected %d bytes in input, but got %d: %w", size, counter.BytesRead(), io.ErrUnexpectedEOF)
+	}
+
 	// we can't update/find metadata here as IA will "ingest" uploaded file(s)
 	// upon uploads. (you can find its progress at https://archive.org/history/ItemNameHere )
 	// or we have to wait for finish? (needs polling (frontend)/metadata/:item or scraping (frontend)/history/:item)