channels: Use dynamically allocated memory for callbacks

Fixes ansible#57

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

src/pylibsshext/channel.pxd

@@ -23,3 +23,6 @@ cdef class Channel:
     cdef  _session
     cdef libssh.ssh_channel _libssh_channel
     cdef libssh.ssh_session _libssh_session
+
+cdef class ChannelCallback:
+    cdef callbacks.ssh_channel_callbacks callback

src/pylibsshext/channel.pyx

@@ -20,7 +20,7 @@ import time
 from io import BytesIO
 
 from cpython.bytes cimport PyBytes_AS_STRING
-from libc.string cimport memset
+from cpython.mem cimport PyMem_Calloc, PyMem_Free
 
 from pylibsshext.errors cimport LibsshChannelException
 from pylibsshext.errors import LibsshChannelReadFailure
@@ -45,6 +45,20 @@ cdef int _process_outputs(libssh.ssh_session session,
         result.stdout += data_b
     return len
 
+cdef class ChannelCallback:
+    def __cinit__(self):
+        cb_size = sizeof(callbacks.ssh_channel_callbacks_struct)
+        self.callback = <callbacks.ssh_channel_callbacks>PyMem_Calloc(1, cb_size)
+        if self.callback is NULL:
+            raise LibsshChannelException("Memory allocation error")
+        self.callback.channel_data_function = <callbacks.ssh_channel_data_callback>&_process_outputs
+
+    def __dealloc__(self):
+        PyMem_Free(self.callback)
+
+    def set_user_data(self, userdata):
+        self.callback.userdata = <void *>userdata
+
 cdef class Channel:
     def __cinit__(self, session):
         self._session = session
@@ -166,12 +180,12 @@ 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.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)
+        cb = ChannelCallback()
+        cb.set_user_data(result)
+        callbacks.ssh_callbacks_init(cb.callback)
+        callbacks.ssh_set_channel_callbacks(channel, cb.callback)
+        # keep it around in the session object
+        self._session.push_callback(cb)
 
         libssh.ssh_channel_send_eof(channel)
         result.returncode = libssh.ssh_channel_get_exit_status(channel)

src/pylibsshext/session.pxd

@@ -26,5 +26,6 @@ cdef class Session:
     cdef _hash_py
     cdef _fingerprint_py
     cdef _keytype_py
+    cdef _channel_callbacks
 
 cdef libssh.ssh_session get_libssh_session(Session session)

src/pylibsshext/session.pyx

@@ -107,6 +107,10 @@ cdef class Session(object):
         self._hash_py = None
         self._fingerprint_py = None
         self._keytype_py = None
+        # Due to delayed freeing of channels, some older libssh versions might expect
+        # the callbacks to be around even after we free the underlying channels so
+        # we should free them only when we terminate the session.
+        self._channel_callbacks = []
 
     def __cinit__(self, host=None, **kwargs):
         self._libssh_session = libssh.ssh_new()
@@ -123,6 +127,9 @@ cdef class Session(object):
             libssh.ssh_free(self._libssh_session)
             self._libssh_session = NULL
 
+    def push_callback(self, callback):
+        self._channel_callbacks.push(callback)
+
     @property
     def port(self):
         cdef unsigned int port_i