From 5de3be1bee65bf6df1336eaee5979afadd54a937 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Wed, 2 Aug 2023 19:23:48 +0900
Subject: [PATCH] mruby-dir/dir.c (mrb_di_getwd): reduce buffer allocation size

Instead of allocating `MAXPATHLEN` buffer string at the beginning,
allocate smaller (64 bytes) buffer, then resize it if needed. The
allocating max size is safe but consumes more memory.
---
 mrbgems/mruby-dir/src/dir.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/mrbgems/mruby-dir/src/dir.c b/mrbgems/mruby-dir/src/dir.c
index 80f70df19..52d100f2b 100644
--- a/mrbgems/mruby-dir/src/dir.c
+++ b/mrbgems/mruby-dir/src/dir.c
@@ -34,6 +34,7 @@
 #include <stdlib.h>
 #include <signal.h>
 #include <string.h>
+#include <errno.h>
 
 #define E_IO_ERROR mrb_exc_get_id(mrb, MRB_SYM(IOError))
 
@@ -128,10 +129,16 @@ static mrb_value
 mrb_dir_getwd(mrb_state *mrb, mrb_value klass)
 {
   mrb_value path;
+  mrb_int size = 64;
 
-  path = mrb_str_buf_new(mrb, MAXPATHLEN);
-  if (getcwd(RSTRING_PTR(path), MAXPATHLEN) == NULL) {
-    mrb_sys_fail(mrb, "getcwd(2)");
+  path = mrb_str_buf_new(mrb, size);
+  while (getcwd(RSTRING_PTR(path), size) == NULL) {
+    int e = errno;
+    if (e != ERANGE) {
+      mrb_sys_fail(mrb, "getcwd(2)");
+    }
+    size *= 2;
+    mrb_str_resize(mrb, path, size);
   }
   mrb_str_resize(mrb, path, strlen(RSTRING_PTR(path)));
   return path;