commit 79d840443b6079952acc16765ecfe5ff62df32ab
Author: Lawrence D'Oliveiro <ldo@geek-central.gen.nz>
Date:   Sun Oct 11 01:44:00 2020 +0000

    Simplify Context.getxattr() to only allocate needed space for
    attributes buffer.

diff --git a/smbc/context.c b/smbc/context.c
index fa37af4..2e8eaf1 100644
--- a/smbc/context.c
+++ b/smbc/context.c
@@ -576,64 +576,41 @@ Context_chmod (Context *self, PyObject *args)
  */
 static PyObject *
 Context_getxattr (Context *self, PyObject *args)
-{
-  int ret;
-  char *uri = NULL;
-  char *name = NULL;
-  char *buffer = NULL;
-  static smbc_getxattr_fn fn;
-
-  // smbc_getxattr takes two string parameters
-  if (!PyArg_ParseTuple (args, "ss", &uri, &name))
-    {
-      return NULL;
-    }
-
-  /* The security descriptor string returned by this call will vary depending on the requested attribute
-   * A call with system.nt_sec_desc.* will return the longest string which would be in the following format:
-   *
-   * REVISION:<revision number>,OWNER:<sid>,GROUP:<sid>,ACL:<sid>:<type>/<flags>/<mask>
-   *
-   * There could be multiple ACL entries up to a reasonable maximum of 1820.
-   *
-   * <revision number> : 3 chars
-   * <sid> :  184 chars
-   * <type>:  1 char
-   * <flags>: 3 chars
-   * <mask>:  10 chars
-   *
-   * The maximum size of the security descriptor string returned can be
-   * derived as follows (includes space for terminating null):
-   * Sec Desc = 13 + 2 x (7 + <sid>) + 1820 * (5 + <acl>) = 375315
-   *
-   * References: https://msdn.microsoft.com/en-us/library/cc246018.aspx
-   *             https://technet.microsoft.com/en-us/library/cc961995.aspx
-   *             https://technet.microsoft.com/en-us/library/cc961986.aspx
-   */
-
-  size_t size = 375315;
-  buffer = (char *)malloc (size);
-  if(!buffer)
-    return PyErr_NoMemory ();
-
-  bzero(buffer, size);
-
-  errno = 0;
-  fn = smbc_getFunctionGetxattr(self->context);
-  ret = (*fn)(self->context, uri, name, buffer, size);
-
-  if (ret < 0)
-    {
-      pysmbc_SetFromErrno ();
-      free(buffer);
-      return NULL;
-    }
-
-  PyObject *value = PyUnicode_FromString(buffer);
-  free(buffer);
-
-  return value;
-}
+  {
+    PyObject * result = NULL;
+    char *uri = NULL;
+    char *name = NULL;
+    char *buffer = NULL;
+    do /*once*/
+      {
+        if (!PyArg_ParseTuple(args, "ss", &uri, &name))
+            break;
+        const smbc_getxattr_fn fn = smbc_getFunctionGetxattr(self->context);
+        errno = 0;
+        const int bufsize = fn(self->context, uri, name, NULL, 0);
+        if (bufsize < 0)
+          {
+            pysmbc_SetFromErrno();
+            break;
+          } /*if*/
+        buffer = (char *)malloc(bufsize);
+        if (buffer == NULL)
+          {
+            PyErr_NoMemory();
+            break;
+          } /*if*/
+        const int ret = fn(self->context, uri, name, buffer, bufsize);
+        if (ret < 0)
+          {
+            pysmbc_SetFromErrno();
+            break;
+          } /*if*/
+        result = PyUnicode_FromString(buffer);
+      }
+    while (false);
+    free(buffer);
+    return result;
+  } /*Context_getxattr*/
 
 
 /**