cap scrollback to avoid unbounded memory usage

3 files changed, 33 insertions, 6 deletions

diff --git a/src/config.c b/src/config.c
index 3a4ae4a..689f042 100644
--- a/src/config.c
+++ b/src/config.c
@@ -312,6 +312,7 @@ static void runes_config_set_defaults(RunesTerm *t)
     config->default_cols = 80;
 
     config->scroll_lines = 3;
+    config->scrollback_length = 4096;
 }
 
 static FILE *runes_config_get_config_file()
@@ -499,6 +500,9 @@ static void runes_config_set(RunesTerm *t, char *key, char *val)
     else if (!strcmp(key, "scroll_lines")) {
         config->scroll_lines = runes_config_parse_uint(val);
     }
+    else if (!strcmp(key, "scrollback_length")) {
+        config->scrollback_length = runes_config_parse_uint(val);
+    }
     else if (!strcmp(key, "command")) {
         config->cmd = runes_config_parse_string(val);
     }
diff --git a/src/config.h b/src/config.h
index a98d9d0..58b781b 100644
--- a/src/config.h
+++ b/src/config.h
@@ -13,6 +13,7 @@ struct runes_config {
     int default_cols;
 
     int scroll_lines;
+    int scrollback_length;
 
     char *cmd;
     char *font_name;
diff --git a/src/screen.c b/src/screen.c
index 3681eb4..86a29c0 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -810,13 +810,35 @@ static void runes_screen_scroll_down(RunesTerm *t, int count)
         }
     }
     else {
-        runes_screen_ensure_capacity(t, scr->grid->row_count + count);
-        for (i = 0; i < count; ++i) {
-            row = runes_screen_row_at(t, i + scr->grid->max.row);
-            row->cells = calloc(scr->grid->max.col, sizeof(struct runes_cell));
+        int scrollback = t->config.scrollback_length;
+
+        if (scr->grid->row_count + count > scrollback) {
+            int overflow = scr->grid->row_count + count - scrollback;
+
+            runes_screen_ensure_capacity(t, scrollback);
+            for (i = 0; i < overflow; ++i) {
+                free(scr->grid->rows[i].cells);
+            }
+            memmove(
+                &scr->grid->rows[0], &scr->grid->rows[overflow],
+                (scrollback - overflow) * sizeof(struct runes_row));
+            for (i = scrollback - count; i < scrollback; ++i) {
+                scr->grid->rows[i].cells = calloc(
+                    scr->grid->max.col, sizeof(struct runes_cell));
+            }
+            scr->grid->row_count = scrollback;
+            scr->grid->row_top = scrollback - scr->grid->max.row;
+        }
+        else {
+            runes_screen_ensure_capacity(t, scr->grid->row_count + count);
+            for (i = 0; i < count; ++i) {
+                row = runes_screen_row_at(t, i + scr->grid->max.row);
+                row->cells = calloc(
+                    scr->grid->max.col, sizeof(struct runes_cell));
+            }
+            scr->grid->row_count += count;
+            scr->grid->row_top += count;
         }
-        scr->grid->row_count += count;
-        scr->grid->row_top += count;
     }
 }