From b9765eec5cbc149120acb50646256cffde94d74f Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Tue, 3 Feb 2015 14:57:49 +0200
Subject: [PATCH] Issue #15381: Try to fix refcount bug. Empty and 1-byte
 buffers are always shared.

---
 Modules/_io/bytesio.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index ca5156b84b..1638f943d0 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -38,7 +38,8 @@ typedef struct {
         return NULL; \
     }
 
-#define SHARED_BUF(self) (Py_REFCNT((self)->buf) > 1)
+#define SHARED_BUF(self) (Py_REFCNT((self)->buf) > 1 || \
+                          PyBytes_GET_SIZE((self)->buf) <= 1)
 
 
 /* Internal routine to get a line from the buffer of a BytesIO
@@ -308,6 +309,7 @@ read_bytes(bytesio *self, Py_ssize_t size)
     char *output;
 
     assert(self->buf != NULL);
+    assert(size <= self->string_size);
     if (size > 1 &&
         self->pos == 0 && size == PyBytes_GET_SIZE(self->buf) &&
         self->exports == 0) {
-- 
2.40.0