From 14c16992b563a77330478bcc6fecdb54df4300b5 Mon Sep 17 00:00:00 2001
From: Prashanth Pai <ppai@redhat.com>
Date: Tue, 23 Jun 2015 20:04:30 +0530
Subject: Add readinto() API

readinto()
This method is useful when you have to read a large file over multiple
read calls. While read() allocates a buffer every time it's invoked,
readinto() copies data to an already allocated buffer passed to it.

Change-Id: Ic8a3aa0e544e09e05101c983b329c91864832e4a
Signed-off-by: Prashanth Pai <ppai@redhat.com>
---
 gluster/gfapi.py                         | 23 +++++++++++++++++++++++
 test/functional/libgfapi-python-tests.py | 18 ++++++++++++++++++
 test/unit/gluster/test_gfapi.py          | 11 +++++++++++
 3 files changed, 52 insertions(+)

diff --git a/gluster/gfapi.py b/gluster/gfapi.py
index fa0e1b3..d6f847d 100755
--- a/gluster/gfapi.py
+++ b/gluster/gfapi.py
@@ -328,6 +328,29 @@ class File(object):
             err = ctypes.get_errno()
             raise OSError(err, os.strerror(err))
 
+    def readinto(self, buf):
+        """
+        Read up to len(buf) bytes into buf which must be a bytearray.
+        (buf cannot be a string as strings are immutable in python)
+
+        This method is useful when you have to read a large file over
+        multiple read calls. While read() allocates a buffer every time
+        it's invoked, readinto() copies data to an already allocated
+        buffer passed to it.
+
+        Returns the number of bytes read (0 for EOF).
+        """
+        if type(buf) is bytearray:
+            buf_ptr = (ctypes.c_ubyte * len(buf)).from_buffer(buf)
+        else:
+            # TODO: Allow reading other types such as array.array
+            raise TypeError("buffer must of type bytearray")
+        nread = api.glfs_read(self.fd, buf_ptr, len(buf_ptr), 0)
+        if nread < 0:
+            err = ctypes.get_errno()
+            raise OSError(err, os.strerror(err))
+        return nread
+
     def write(self, data, flags=0):
         """
         Write data to the file.
diff --git a/test/functional/libgfapi-python-tests.py b/test/functional/libgfapi-python-tests.py
index 6840d18..3a0b89e 100644
--- a/test/functional/libgfapi-python-tests.py
+++ b/test/functional/libgfapi-python-tests.py
@@ -502,6 +502,24 @@ class FileOpsTest(unittest.TestCase):
         self.vol.symlink(file_name, link_name)
         self.assertEqual(self.vol.readlink(link_name), file_name)
 
+    def test_readinto(self):
+        file_name = uuid4().hex
+        with File(self.vol.open(file_name, os.O_WRONLY | os.O_CREAT)) as f:
+            s = ''.join([str(i) for i in xrange(10)])
+            f.write(s)
+            f.fsync()
+
+        buf = bytearray(1)
+        with File(self.vol.open(file_name, os.O_RDONLY)) as f:
+            for i in xrange(10):
+                # Read one character at a time into buf
+                f.readinto(buf)
+                self.assertEqual(len(buf), 1)
+                self.assertEqual(buf, bytearray(str(i)))
+
+        with File(self.vol.open(file_name, os.O_RDONLY)) as f:
+            self.assertRaises(TypeError, f.readinto, str("buf"))
+
 
 class DirOpsTest(unittest.TestCase):
 
diff --git a/test/unit/gluster/test_gfapi.py b/test/unit/gluster/test_gfapi.py
index 5551235..4be2346 100644
--- a/test/unit/gluster/test_gfapi.py
+++ b/test/unit/gluster/test_gfapi.py
@@ -192,6 +192,17 @@ class TestFile(unittest.TestCase):
                 with patch("gluster.gfapi.File.fgetsize", _mock_fgetsize):
                     self.fd.read(buflen)
 
+    def test_readinto(self):
+        mock_glfs_read = Mock()
+        mock_glfs_read.return_value = 5
+
+        with patch("gluster.gfapi.api.glfs_read", mock_glfs_read):
+            buf = bytearray(10)
+            ret = self.fd.readinto(buf)
+            self.assertEqual(ret, 5)
+
+        self.assertRaises(TypeError, self.fd.readinto, str("hello"))
+
     def test_write_success(self):
         mock_glfs_write = Mock()
         mock_glfs_write.return_value = 5
-- 
cgit