Empty and return the buffer if zero size is given [Bug #18421]

In `IO#readpartial` and `IO#read_nonblock`, as well as `IO#read`.

1 files changed, 6 insertions, 2 deletions

diff --git a/io.c b/io.c
index dc883f36b4..8ac29083ae 100644
--- a/io.c
+++ b/io.c
@@ -3161,8 +3161,10 @@ io_getpartial(int argc, VALUE *argv, VALUE io, int no_exception, int nonblock)
     GetOpenFile(io, fptr);
     rb_io_check_byte_readable(fptr);
 
-    if (len == 0)
+    if (len == 0) {
+	io_set_read_length(str, 0, shrinkable);
 	return str;
+    }
 
     if (!nonblock)
         READ_CHECK(fptr);
@@ -3305,8 +3307,10 @@ io_read_nonblock(rb_execution_context_t *ec, VALUE io, VALUE length, VALUE str,
     GetOpenFile(io, fptr);
     rb_io_check_byte_readable(fptr);
 
-    if (len == 0)
+    if (len == 0) {
+	io_set_read_length(str, 0, shrinkable);
 	return str;
+    }
 
     n = read_buffered_data(RSTRING_PTR(str), len, fptr);
     if (n <= 0) {