return empty string on length=0

This matches behavior of all the core Ruby methods.

2 files changed, 27 insertions, 7 deletions

diff --git a/ext/kgio/read_write.c b/ext/kgio/read_write.c
index 0ee7866..141b078 100644
--- a/ext/kgio/read_write.c
+++ b/ext/kgio/read_write.c
@@ -92,11 +92,14 @@ static VALUE my_read(int io_wait, int argc, VALUE *argv, VALUE io)
         long n;
 
         prepare_read(&a, argc, argv, io);
-        set_nonblocking(a.fd);
+
+        if (a.len > 0) {
+                set_nonblocking(a.fd);
 retry:
-        n = (long)read(a.fd, a.ptr, a.len);
-        if (read_check(&a, n, "read", io_wait) != 0)
-                goto retry;
+                n = (long)read(a.fd, a.ptr, a.len);
+                if (read_check(&a, n, "read", io_wait) != 0)
+                        goto retry;
+        }
         return a.buf;
 }
 
@@ -159,10 +162,13 @@ static VALUE my_recv(int io_wait, int argc, VALUE *argv, VALUE io)
         long n;
 
         prepare_read(&a, argc, argv, io);
+
+        if (a.len > 0) {
 retry:
-        n = (long)recv(a.fd, a.ptr, a.len, MSG_DONTWAIT);
-        if (read_check(&a, n, "recv", io_wait) != 0)
-                goto retry;
+                n = (long)recv(a.fd, a.ptr, a.len, MSG_DONTWAIT);
+                if (read_check(&a, n, "recv", io_wait) != 0)
+                        goto retry;
+        }
         return a.buf;
 }
 
diff --git a/test/lib_read_write.rb b/test/lib_read_write.rb
index 6296586..6f90041 100644
--- a/test/lib_read_write.rb
+++ b/test/lib_read_write.rb
@@ -18,6 +18,20 @@ module LibReadWriteTest
     end
   end
 
+  def test_read_zero
+    assert_equal "", @rd.kgio_read(0)
+    buf = "foo"
+    assert_equal buf.object_id, @rd.kgio_read(0, buf).object_id
+    assert_equal "", buf
+  end
+
+  def test_tryread_zero
+    assert_equal "", @rd.kgio_tryread(0)
+    buf = "foo"
+    assert_equal buf.object_id, @rd.kgio_tryread(0, buf).object_id
+    assert_equal "", buf
+  end
+
   def test_read_eof
     @wr.close
     assert_nil @rd.kgio_read(5)