channels: Use dynamically allocated memory for callbacks

Fixes ansible#57

Signed-off-by: Jakub Jelen <[email protected]>

src/pylibsshext/channel.pyx

@@ -20,6 +20,7 @@ import time
 from io import BytesIO
 
 from cpython.bytes cimport PyBytes_AS_STRING
+from cpython.mem cimport PyMem_Free, PyMem_Malloc
 from libc.string cimport memset
 
 from pylibsshext.errors cimport LibsshChannelException
@@ -166,19 +167,23 @@ cdef class Channel:
             raise LibsshChannelException("Failed to execute command [{0}]: [{1}]".format(command, rc))
         result = CompletedProcess(args=command, returncode=-1, stdout=b'', stderr=b'')
 
-        cdef callbacks.ssh_channel_callbacks_struct cb
-        memset(&cb, 0, sizeof(cb))
+        cb_size = sizeof(callbacks.ssh_channel_callbacks_struct)
+        cdef callbacks.ssh_channel_callbacks_struct *cb = <callbacks.ssh_channel_callbacks_struct *>PyMem_Malloc(cb_size)
+        if cb is NULL:
+            raise LibsshChannelException("Memory allocation error")
+        memset(cb, 0, cb_size)
         cb.channel_data_function = <callbacks.ssh_channel_data_callback>&_process_outputs
         cb.userdata = <void *>result
-        callbacks.ssh_callbacks_init(&cb)
-        callbacks.ssh_set_channel_callbacks(channel, &cb)
+        callbacks.ssh_callbacks_init(cb)
+        callbacks.ssh_set_channel_callbacks(channel, cb)
 
         libssh.ssh_channel_send_eof(channel)
         result.returncode = libssh.ssh_channel_get_exit_status(channel)
         if channel is not NULL:
             libssh.ssh_channel_close(channel)
             libssh.ssh_channel_free(channel)
 
+        """ XXX leaking the memory of the callbacks """
         return result
 
     def send_eof(self):