The code for testing content that has potentially been modified between btpd

runs was quite broken. Pieces stayed marked as ok event though the hash test
failed for pieces in modified files. Oops!

btpd/content.c

@@ -562,6 +562,10 @@ test_torrent(struct torrent *tp, volatile sig_atomic_t *cancel)
             break;
         if (test_hash(tp, hash, piece) == 0)
             set_bit(tp->cm->piece_field, piece);
+        else {
+            clear_bit(tp->cm->piece_field, piece);
+            bzero(cm->block_field + piece * cm->bppbf, cm->bppbf);
+        }
         if (*cancel) {
             err = EINTR;
             break;
@@ -684,25 +688,20 @@ cm_td_start(struct cm_op *op)
         memset(cm->pos_field, 0xff, ceil(tp->meta.npieces / 8.0));
         off_t off = 0;
         for (int i = 0; i < tp->meta.nfiles; i++) {
-            if (sbs[i].size == -1 || sbs[i].size == 0) {
-                uint32_t start = off / tp->meta.piece_length;
-                uint32_t end = (off + tp->meta.files[i].length - 1) /
-                    tp->meta.piece_length;
+            if (sbs[i].size != tp->meta.files[i].length) {
+                uint32_t start, end;
+                end = (off + tp->meta.files[i].length - 1)
+                    / tp->meta.piece_length;
+                if (sbs[i].size == -1)
+                    start = off / tp->meta.piece_length;
+                else
+                    start = (off + sbs[i].size) / tp->meta.piece_length;
                 while (start <= end) {
                     clear_bit(cm->pos_field, start);
                     clear_bit(cm->piece_field, start);
                     bzero(cm->block_field + start * cm->bppbf, cm->bppbf);
                     start++;
                 }
-            } else if (sbs[i].size < tp->meta.files[i].length) {
-                uint32_t start = (off + sbs[i].size) /
-                    tp->meta.piece_length;
-                uint32_t end = (off + tp->meta.files[i].length - 1) /
-                    tp->meta.piece_length;
-                while (start <= end) {
-                    clear_bit(cm->pos_field, start);
-                    start++;
-                }
             }
             off += tp->meta.files[i].length;
         }