From 3ea015db968644c3f4e88fff59b9741b4903d478 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Igor=20Anic=CC=81?= <igor.anic@gmail.com>
Date: Fri, 8 Aug 2025 17:21:45 +0200
Subject: [PATCH] Io.Reader fix defaultReadVec

Running tar.pipeToFileSystem compressed_mingw_includes.tar file from #24732
finishes in infinite loop calling defaultReadVec with:
r.seek = 1024
r.end = 1024
r.buffer.len = 1024
first.len = 512
that combination calls vtable.stream with 0 capacity writer and loops
forever.

Comment is to use whichever has larger capacity, and this fix reflects that.
---
 lib/std/Io/Reader.zig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/std/Io/Reader.zig b/lib/std/Io/Reader.zig
index b8fa6f2313..9e637cf9a3 100644
--- a/lib/std/Io/Reader.zig
+++ b/lib/std/Io/Reader.zig
@@ -426,7 +426,7 @@ pub fn readVec(r: *Reader, data: [][]u8) Error!usize {
 /// Writes to `Reader.buffer` or `data`, whichever has larger capacity.
 pub fn defaultReadVec(r: *Reader, data: [][]u8) Error!usize {
     const first = data[0];
-    if (r.seek == r.end and first.len >= r.buffer.len) {
+    if (first.len >= r.buffer.len - r.end) {
         var writer: Writer = .{
             .buffer = first,
             .end = 0,