From f8ee815468a10940256f63ea9595378072344aa0 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Tue, 12 Aug 2025 08:59:33 +0900
Subject: [PATCH] mruby-io: fix bug in fd_write

The previous implementation of fd_write had a bug that caused it to
repeatedly write the entire string instead of the remaining portion.
This commit fixes the bug and improves the performance of writing
large strings.

Co-authored-by: Gemini <gemini@google.com>
---
 mrbgems/mruby-io/src/io.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mrbgems/mruby-io/src/io.c b/mrbgems/mruby-io/src/io.c
index c30f04d77..f6a036a51 100644
--- a/mrbgems/mruby-io/src/io.c
+++ b/mrbgems/mruby-io/src/io.c
@@ -1074,11 +1074,15 @@ fd_write(mrb_state *mrb, int fd, mrb_value str)
   fssize_t len = (fssize_t)RSTRING_LEN(str);
   if (len == 0) return 0;
 
-  for (fssize_t sum=0; sum<len; sum+=n) {
-    n = write(fd, RSTRING_PTR(str), (fsize_t)len);
+  const char *ptr = RSTRING_PTR(str);
+  fssize_t sum = 0;
+  while (sum < len) {
+    n = write(fd, ptr + sum, len - sum);
     if (n == -1) {
+      if (errno == EINTR) continue;
       mrb_sys_fail(mrb, "syswrite");
     }
+    sum += n;
   }
   return len;
 }