Blob: implement the memory buffer interface

This allows us to expose access to the blob's data without the need to copy it into new buffer.
libgit2 · Apr 23, 2014 · 1c76d56 · 1c76d56
1 parent d8bd6f7
commit 1c76d56
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Showing 2 changed files with 65 additions and 2 deletions.
diff --git a/src/blob.c b/src/blob.c
@@ -158,8 +158,58 @@ PyGetSetDef Blob_getseters[] = {
     {NULL}
 };
 
+static int
+Blob_getbuffer(Blob *self, Py_buffer *view, int flags)
+{
+    return PyBuffer_FillInfo(view, (PyObject *) self,
+                             (void *) git_blob_rawcontent(self->blob),
+                             git_blob_rawsize(self->blob), 1, flags);
+}
+
+#if PY_MAJOR_VERSION == 2
 
-PyDoc_STRVAR(Blob__doc__, "Blob objects.");
+static Py_ssize_t
+Blob_getreadbuffer(Blob *self, Py_ssize_t index, const void **ptr)
+{
+    if (index != 0) {
+        PyErr_SetString(PyExc_SystemError,
+                        "accessing non-existent blob segment");
+        return -1;
+    }
+    *ptr = (void *) git_blob_rawcontent(self->blob);
+    return git_blob_rawsize(self->blob);
+}
+
+static Py_ssize_t
+Blob_getsegcount(Blob *self, Py_ssize_t *lenp)
+{
+    if (lenp)
+        *lenp = git_blob_rawsize(self->blob);
+
+    return 1;
+}
+
+static PyBufferProcs Blob_as_buffer = {
+    (readbufferproc)Blob_getreadbuffer,
+    NULL,                       /* bf_getwritebuffer */
+    (segcountproc)Blob_getsegcount,
+    NULL,                       /* charbufferproc */
+    (getbufferproc)Blob_getbuffer,
+};
+
+#else
+
+static PyBufferProcs Blob_as_buffer = {
+    (getbufferproc)Blob_getbuffer,
+};
+
+#endif  /* python 2 vs python 3 buffers */
+
+PyDoc_STRVAR(Blob__doc__, "Blob object.\n"
+  "\n"
+  "Blobs implement the buffer interface, which means you can get access\n"
+  "to its data via `memoryview(blob)` without the need to create a copy."
+);
 
 PyTypeObject BlobType = {
     PyVarObject_HEAD_INIT(NULL, 0)
@@ -180,8 +230,14 @@ PyTypeObject BlobType = {
     0,                                         /* tp_str            */
     0,                                         /* tp_getattro       */
     0,                                         /* tp_setattro       */
-    0,                                         /* tp_as_buffer      */
+    &Blob_as_buffer,                           /* tp_as_buffer      */
+#if PY_MAJOR_VERSION == 2
+    Py_TPFLAGS_DEFAULT |                       /* tp_flags          */
+    Py_TPFLAGS_HAVE_GETCHARBUFFER |
+    Py_TPFLAGS_HAVE_NEWBUFFER,
+#else
     Py_TPFLAGS_DEFAULT,                        /* tp_flags          */
+#endif
     Blob__doc__,                               /* tp_doc            */
     0,                                         /* tp_traverse       */
     0,                                         /* tp_clear          */

diff --git a/test/test_blob.py b/test/test_blob.py
@@ -74,6 +74,13 @@ def test_create_blob(self):
         self.assertEqual(BLOB_NEW_CONTENT, blob.data)
         self.assertEqual(len(BLOB_NEW_CONTENT), blob.size)
         self.assertEqual(BLOB_NEW_CONTENT, blob.read_raw())
+        blob_buffer = memoryview(blob)
+        self.assertEqual(len(BLOB_NEW_CONTENT), len(blob_buffer))
+        self.assertEqual(BLOB_NEW_CONTENT, blob_buffer)
+        def set_content():
+            blob_buffer[:2] = b'hi'
+
+        self.assertRaises(TypeError, set_content)
 
     def test_create_blob_fromworkdir(self):