Move to kernel style SPDX license identifiers
[babeltrace.git] / tests / bindings / python / bt2 / test_message_iterator.py
index 9c8277b7f6b1ef2e3e0054d9f51c0fffdd7aae0b..54fd232907dadc4c7a51f122844b1d31bb54bbe7 100644 (file)
-from bt2 import value
-import collections
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Copyright (C) 2019 EfficiOS Inc.
+#
+
 import unittest
-import copy
 import bt2
+import sys
+from utils import TestOutputPortMessageIterator
+from bt2 import port as bt2_port
+from bt2 import message_iterator as bt2_message_iterator
 
 
-class UserMessageIteratorTestCase(unittest.TestCase):
-    @staticmethod
-    def _create_graph(src_comp_cls):
-        class MySink(bt2._UserSinkComponent):
-            def __init__(self, params):
-                self._add_input_port('in')
+class SimpleSink(bt2._UserSinkComponent):
+    # Straightforward sink that creates one input port (`in`) and consumes from
+    # it.
 
-            def _consume(self):
-                next(self._msg_iter)
+    def __init__(self, config, params, obj):
+        self._add_input_port('in')
 
-            def _graph_is_configured(self):
-                self._msg_iter = self._input_ports['in'].create_message_iterator()
+    def _user_consume(self):
+        next(self._msg_iter)
 
-        graph = bt2.Graph()
-        src_comp = graph.add_component(src_comp_cls, 'src')
-        sink_comp = graph.add_component(MySink, 'sink')
-        graph.connect_ports(src_comp.output_ports['out'],
-                            sink_comp.input_ports['in'])
-        return graph
+    def _user_graph_is_configured(self):
+        self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+
+def _create_graph(src_comp_cls, sink_comp_cls, flt_comp_cls=None):
+    graph = bt2.Graph()
+
+    src_comp = graph.add_component(src_comp_cls, 'src')
+    sink_comp = graph.add_component(sink_comp_cls, 'sink')
 
+    if flt_comp_cls is not None:
+        flt_comp = graph.add_component(flt_comp_cls, 'flt')
+        graph.connect_ports(src_comp.output_ports['out'], flt_comp.input_ports['in'])
+        graph.connect_ports(flt_comp.output_ports['out'], sink_comp.input_ports['in'])
+    else:
+        graph.connect_ports(src_comp.output_ports['out'], sink_comp.input_ports['in'])
+
+    return graph
+
+
+class UserMessageIteratorTestCase(unittest.TestCase):
     def test_init(self):
         the_output_port_from_source = None
         the_output_port_from_iter = None
 
         class MyIter(bt2._UserMessageIterator):
-            def __init__(self, self_port_output):
+            def __init__(self, config, self_port_output):
                 nonlocal initialized
                 nonlocal the_output_port_from_iter
                 initialized = True
                 the_output_port_from_iter = self_port_output
 
-        class MySource(bt2._UserSourceComponent,
-                       message_iterator_class=MyIter):
-            def __init__(self, params):
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
                 nonlocal the_output_port_from_source
                 the_output_port_from_source = self._add_output_port('out', 'user data')
 
         initialized = False
-        graph = self._create_graph(MySource)
+        graph = _create_graph(MySource, SimpleSink)
         graph.run()
         self.assertTrue(initialized)
-        self.assertEqual(the_output_port_from_source.addr, the_output_port_from_iter.addr)
+        self.assertEqual(
+            the_output_port_from_source.addr, the_output_port_from_iter.addr
+        )
         self.assertEqual(the_output_port_from_iter.user_data, 'user data')
 
+    def test_create_from_message_iterator(self):
+        class MySourceIter(bt2._UserMessageIterator):
+            def __init__(self, config, self_port_output):
+                nonlocal src_iter_initialized
+                src_iter_initialized = True
+
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MySourceIter):
+            def __init__(self, config, params, obj):
+                self._add_output_port('out')
+
+        class MyFilterIter(bt2._UserMessageIterator):
+            def __init__(self, config, self_port_output):
+                nonlocal flt_iter_initialized
+                flt_iter_initialized = True
+                self._up_iter = self._create_message_iterator(
+                    self._component._input_ports['in']
+                )
+
+            def __next__(self):
+                return next(self._up_iter)
+
+        class MyFilter(bt2._UserFilterComponent, message_iterator_class=MyFilterIter):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+                self._add_output_port('out')
+
+        src_iter_initialized = False
+        flt_iter_initialized = False
+        graph = _create_graph(MySource, SimpleSink, MyFilter)
+        graph.run()
+        self.assertTrue(src_iter_initialized)
+        self.assertTrue(flt_iter_initialized)
+
+    def test_create_user_error(self):
+        # This tests both error handling by
+        # _UserSinkComponent._create_message_iterator
+        # and _UserMessageIterator._create_message_iterator, as they
+        # are both used in the graph.
+        class MySourceIter(bt2._UserMessageIterator):
+            def __init__(self, config, self_port_output):
+                raise ValueError('Very bad error')
+
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MySourceIter):
+            def __init__(self, config, params, obj):
+                self._add_output_port('out')
+
+        class MyFilterIter(bt2._UserMessageIterator):
+            def __init__(self, config, self_port_output):
+                # This is expected to raise because of the error in
+                # MySourceIter.__init__.
+                self._create_message_iterator(self._component._input_ports['in'])
+
+        class MyFilter(bt2._UserFilterComponent, message_iterator_class=MyFilterIter):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+                self._add_output_port('out')
+
+        graph = _create_graph(MySource, SimpleSink, MyFilter)
+
+        with self.assertRaises(bt2._Error) as ctx:
+            graph.run()
+
+        exc = ctx.exception
+        cause = exc[0]
+
+        self.assertIsInstance(cause, bt2._MessageIteratorErrorCause)
+        self.assertEqual(cause.component_name, 'src')
+        self.assertEqual(cause.component_output_port_name, 'out')
+        self.assertIn('ValueError: Very bad error', cause.message)
+
     def test_finalize(self):
         class MyIter(bt2._UserMessageIterator):
-            def _finalize(self):
+            def _user_finalize(self):
                 nonlocal finalized
                 finalized = True
 
-        class MySource(bt2._UserSourceComponent,
-                       message_iterator_class=MyIter):
-            def __init__(self, params):
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
                 self._add_output_port('out')
 
         finalized = False
-        graph = self._create_graph(MySource)
+        graph = _create_graph(MySource, SimpleSink)
         graph.run()
         del graph
         self.assertTrue(finalized)
 
+    def test_config_parameter(self):
+        class MyIter(bt2._UserMessageIterator):
+            def __init__(self, config, port):
+                nonlocal config_type
+                config_type = type(config)
+
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
+                self._add_output_port('out')
+
+        config_type = None
+        graph = _create_graph(MySource, SimpleSink)
+        graph.run()
+        self.assertIs(config_type, bt2_message_iterator._MessageIteratorConfiguration)
+
+    def _test_config_can_seek_forward(self, set_can_seek_forward):
+        class MyIter(bt2._UserMessageIterator):
+            def __init__(self, config, port):
+                if set_can_seek_forward:
+                    config.can_seek_forward = True
+
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
+                self._add_output_port('out')
+
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                nonlocal can_seek_forward
+                can_seek_forward = self._msg_iter.can_seek_forward
+
+        can_seek_forward = None
+        graph = _create_graph(MySource, MySink)
+        graph.run_once()
+        self.assertIs(can_seek_forward, set_can_seek_forward)
+
+    def test_config_can_seek_forward_default(self):
+        self._test_config_can_seek_forward(False)
+
+    def test_config_can_seek_forward(self):
+        self._test_config_can_seek_forward(True)
+
+    def test_config_can_seek_forward_wrong_type(self):
+        class MyIter(bt2._UserMessageIterator):
+            def __init__(self, config, port):
+                config.can_seek_forward = 1
+
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
+                self._add_output_port('out')
+
+        graph = _create_graph(MySource, SimpleSink)
+        with self.assertRaises(bt2._Error) as ctx:
+            graph.run()
+
+        root_cause = ctx.exception[0]
+        self.assertIn("TypeError: 'int' is not a 'bool' object", root_cause.message)
+
     def test_component(self):
         class MyIter(bt2._UserMessageIterator):
-            def __init__(self, self_port_output):
+            def __init__(self, config, self_port_output):
                 nonlocal salut
                 salut = self._component._salut
 
-        class MySource(bt2._UserSourceComponent,
-                       message_iterator_class=MyIter):
-            def __init__(self, params):
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
                 self._add_output_port('out')
                 self._salut = 23
 
         salut = None
-        graph = self._create_graph(MySource)
+        graph = _create_graph(MySource, SimpleSink)
         graph.run()
         self.assertEqual(salut, 23)
 
+    def test_port(self):
+        class MyIter(bt2._UserMessageIterator):
+            def __init__(self_iter, config, self_port_output):
+                nonlocal called
+                called = True
+                port = self_iter._port
+                self.assertIs(type(self_port_output), bt2_port._UserComponentOutputPort)
+                self.assertIs(type(port), bt2_port._UserComponentOutputPort)
+                self.assertEqual(self_port_output.addr, port.addr)
+
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
+                self._add_output_port('out')
+
+        called = False
+        graph = _create_graph(MySource, SimpleSink)
+        graph.run()
+        self.assertTrue(called)
+
     def test_addr(self):
         class MyIter(bt2._UserMessageIterator):
-            def __init__(self, self_port_output):
+            def __init__(self, config, self_port_output):
                 nonlocal addr
                 addr = self.addr
 
-        class MySource(bt2._UserSourceComponent,
-                       message_iterator_class=MyIter):
-            def __init__(self, params):
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
                 self._add_output_port('out')
 
         addr = None
-        graph = self._create_graph(MySource)
+        graph = _create_graph(MySource, SimpleSink)
         graph.run()
         self.assertIsNotNone(addr)
         self.assertNotEqual(addr, 0)
 
-
-class OutputPortMessageIteratorTestCase(unittest.TestCase):
-    def test_component(self):
+    # Test that messages returned by _UserMessageIterator.__next__ remain valid
+    # and can be re-used.
+    def test_reuse_message(self):
         class MyIter(bt2._UserMessageIterator):
-            def __init__(self, self_port_output):
-                self._at = 0
+            def __init__(self, config, port):
+                tc, sc, ec = port.user_data
+                trace = tc()
+                stream = trace.create_stream(sc)
+                packet = stream.create_packet()
+
+                # This message will be returned twice by __next__.
+                event_message = self._create_event_message(ec, packet)
+
+                self._msgs = [
+                    self._create_stream_beginning_message(stream),
+                    self._create_packet_beginning_message(packet),
+                    event_message,
+                    event_message,
+                ]
 
             def __next__(self):
-                if self._at == 7:
-                    raise bt2.Stop
-
-                if self._at == 0:
-                    msg = self._create_stream_beginning_message(test_obj._stream)
-                elif self._at == 1:
-                    msg = self._create_packet_beginning_message(test_obj._packet)
-                elif self._at == 5:
-                    msg = self._create_packet_end_message(test_obj._packet)
-                elif self._at == 6:
-                    msg = self._create_stream_end_message(test_obj._stream)
-                else:
-                    msg = self._create_event_message(test_obj._event_class, test_obj._packet)
-                    msg.event.payload_field['my_int'] = self._at * 3
+                return self._msgs.pop(0)
 
-                self._at += 1
-                return msg
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
+                tc = self._create_trace_class()
+                sc = tc.create_stream_class(supports_packets=True)
+                ec = sc.create_event_class()
+                self._add_output_port('out', (tc, sc, ec))
+
+        graph = bt2.Graph()
+        src = graph.add_component(MySource, 'src')
+        it = TestOutputPortMessageIterator(graph, src.output_ports['out'])
+
+        # Skip beginning messages.
+        msg = next(it)
+        self.assertIs(type(msg), bt2._StreamBeginningMessageConst)
+        msg = next(it)
+        self.assertIs(type(msg), bt2._PacketBeginningMessageConst)
 
-        class MySource(bt2._UserSourceComponent,
-                       message_iterator_class=MyIter):
-            def __init__(self, params):
+        msg_ev1 = next(it)
+        msg_ev2 = next(it)
+
+        self.assertIs(type(msg_ev1), bt2._EventMessageConst)
+        self.assertIs(type(msg_ev2), bt2._EventMessageConst)
+        self.assertEqual(msg_ev1.addr, msg_ev2.addr)
+
+    # Try consuming many times from an iterator that always returns TryAgain.
+    # This verifies that we are not missing an incref of Py_None, making the
+    # refcount of Py_None reach 0.
+    def test_try_again_many_times(self):
+        class MyIter(bt2._UserMessageIterator):
+            def __next__(self):
+                raise bt2.TryAgain
+
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MyIter):
+            def __init__(self, config, params, obj):
                 self._add_output_port('out')
 
-                trace_class = self._create_trace_class()
-                stream_class = trace_class.create_stream_class()
+        class MyFilterIter(bt2._UserMessageIterator):
+            def __init__(self, port):
+                input_port = port.user_data
+                self._upstream_iter = self._create_message_iterator(input_port)
 
-                # Create payload field class
-                my_int_ft = trace_class.create_signed_integer_field_class(32)
-                payload_ft = trace_class.create_structure_field_class()
-                payload_ft += collections.OrderedDict([
-                    ('my_int', my_int_ft),
-                ])
+            def __next__(self):
+                return next(self._upstream_iter)
 
-                event_class = stream_class.create_event_class(name='salut', payload_field_class=payload_ft)
+            def _user_seek_beginning(self):
+                self._upstream_iter.seek_beginning()
 
-                trace = trace_class()
-                stream = trace.create_stream(stream_class)
-                packet = stream.create_packet()
+            def _user_can_seek_beginning(self):
+                return self._upstream_iter.can_seek_beginning()
 
-                test_obj._event_class = event_class
-                test_obj._stream = stream
-                test_obj._packet = packet
+        class MyFilter(bt2._UserFilterComponent, message_iterator_class=MyFilterIter):
+            def __init__(self, config, params, obj):
+                input_port = self._add_input_port('in')
+                self._add_output_port('out', input_port)
 
-        test_obj = self
         graph = bt2.Graph()
         src = graph.add_component(MySource, 'src')
-        msg_iter = graph.create_output_port_message_iterator(src.output_ports['out'])
-
-        for at, msg in enumerate(msg_iter):
-            if at == 0:
-                self.assertIsInstance(msg, bt2.message._StreamBeginningMessage)
-            elif at == 1:
-                self.assertIsInstance(msg, bt2.message._PacketBeginningMessage)
-            elif at == 5:
-                self.assertIsInstance(msg, bt2.message._PacketEndMessage)
-            elif at == 6:
-                self.assertIsInstance(msg, bt2.message._StreamEndMessage)
+        it = TestOutputPortMessageIterator(graph, src.output_ports['out'])
+
+        # Three times the initial ref count of `None` iterations should
+        # be enough to catch the bug even if there are small differences
+        # between configurations.
+        none_ref_count = sys.getrefcount(None) * 3
+
+        for i in range(none_ref_count):
+            with self.assertRaises(bt2.TryAgain):
+                next(it)
+
+    def test_error_in_iterator_with_cycle_after_having_created_upstream_iterator(self):
+        # Test a failure that triggered an abort in libbabeltrace2, in this situation:
+        #
+        #   - The filter iterator creates an upstream iterator.
+        #   - The filter iterator creates a reference cycle, including itself.
+        #   - An exception is raised, causing the filter iterator's
+        #     initialization method to fail.
+        class MySourceIter(bt2._UserMessageIterator):
+            pass
+
+        class MySource(bt2._UserSourceComponent, message_iterator_class=MySourceIter):
+            def __init__(self, config, params, obj):
+                self._add_output_port('out')
+
+        class MyFilterIter(bt2._UserMessageIterator):
+            def __init__(self, config, port):
+                # First, create an upstream iterator.
+                self._upstream_iter = self._create_message_iterator(
+                    self._component._input_ports['in']
+                )
+
+                # Then, voluntarily make a reference cycle that will keep this
+                # Python object alive, which will keep the upstream iterator
+                # Babeltrace object alive.
+                self._self = self
+
+                # Finally, raise an exception to make __init__ fail.
+                raise ValueError('woops')
+
+        class MyFilter(bt2._UserFilterComponent, message_iterator_class=MyFilterIter):
+            def __init__(self, config, params, obj):
+                self._in = self._add_input_port('in')
+                self._out = self._add_output_port('out')
+
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._input_port = self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._upstream_iter = self._create_message_iterator(self._input_port)
+
+            def _user_consume(self):
+                # We should not reach this.
+                assert False
+
+        g = bt2.Graph()
+        src = g.add_component(MySource, 'src')
+        flt = g.add_component(MyFilter, 'flt')
+        snk = g.add_component(MySink, 'snk')
+        g.connect_ports(src.output_ports['out'], flt.input_ports['in'])
+        g.connect_ports(flt.output_ports['out'], snk.input_ports['in'])
+
+        with self.assertRaisesRegex(bt2._Error, 'ValueError: woops'):
+            g.run()
+
+
+def _setup_seek_test(
+    sink_cls,
+    user_seek_beginning=None,
+    user_can_seek_beginning=None,
+    user_seek_ns_from_origin=None,
+    user_can_seek_ns_from_origin=None,
+    can_seek_forward=False,
+):
+    class MySourceIter(bt2._UserMessageIterator):
+        def __init__(self, config, port):
+            tc, sc, ec = port.user_data
+            trace = tc()
+            stream = trace.create_stream(sc)
+            packet = stream.create_packet()
+
+            self._msgs = [
+                self._create_stream_beginning_message(stream),
+                self._create_packet_beginning_message(packet),
+                self._create_event_message(ec, packet),
+                self._create_event_message(ec, packet),
+                self._create_packet_end_message(packet),
+                self._create_stream_end_message(stream),
+            ]
+            self._at = 0
+            config.can_seek_forward = can_seek_forward
+
+        def __next__(self):
+            if self._at < len(self._msgs):
+                msg = self._msgs[self._at]
+                self._at += 1
+                return msg
             else:
-                self.assertIsInstance(msg, bt2.message._EventMessage)
-                self.assertEqual(msg.event.event_class.name, 'salut')
-                field = msg.event.payload_field['my_int']
-                self.assertEqual(field, at * 3)
+                raise StopIteration
+
+    if user_seek_beginning is not None:
+        MySourceIter._user_seek_beginning = user_seek_beginning
+
+    if user_can_seek_beginning is not None:
+        MySourceIter._user_can_seek_beginning = user_can_seek_beginning
+
+    if user_seek_ns_from_origin is not None:
+        MySourceIter._user_seek_ns_from_origin = user_seek_ns_from_origin
+
+    if user_can_seek_ns_from_origin is not None:
+        MySourceIter._user_can_seek_ns_from_origin = user_can_seek_ns_from_origin
+
+    class MySource(bt2._UserSourceComponent, message_iterator_class=MySourceIter):
+        def __init__(self, config, params, obj):
+            tc = self._create_trace_class()
+            sc = tc.create_stream_class(supports_packets=True)
+            ec = sc.create_event_class()
+
+            self._add_output_port('out', (tc, sc, ec))
+
+    class MyFilterIter(bt2._UserMessageIterator):
+        def __init__(self, config, port):
+            self._upstream_iter = self._create_message_iterator(
+                self._component._input_ports['in']
+            )
+            config.can_seek_forward = self._upstream_iter.can_seek_forward
+
+        def __next__(self):
+            return next(self._upstream_iter)
+
+        def _user_can_seek_beginning(self):
+            return self._upstream_iter.can_seek_beginning()
+
+        def _user_seek_beginning(self):
+            self._upstream_iter.seek_beginning()
+
+        def _user_can_seek_ns_from_origin(self, ns_from_origin):
+            return self._upstream_iter.can_seek_ns_from_origin(ns_from_origin)
+
+        def _user_seek_ns_from_origin(self, ns_from_origin):
+            self._upstream_iter.seek_ns_from_origin(ns_from_origin)
+
+    class MyFilter(bt2._UserFilterComponent, message_iterator_class=MyFilterIter):
+        def __init__(self, config, params, obj):
+            self._add_input_port('in')
+            self._add_output_port('out')
+
+    return _create_graph(MySource, sink_cls, flt_comp_cls=MyFilter)
+
+
+class UserMessageIteratorSeekBeginningTestCase(unittest.TestCase):
+    def test_can_seek_beginning_without_seek_beginning(self):
+        with self.assertRaisesRegex(
+            bt2._IncompleteUserClass,
+            "cannot create component class 'MySource': message iterator class implements _user_can_seek_beginning but not _user_seek_beginning",
+        ):
+            _setup_seek_test(SimpleSink, user_can_seek_beginning=lambda: None)
+
+    def test_can_seek_beginning(self):
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                nonlocal can_seek_beginning
+                can_seek_beginning = self._msg_iter.can_seek_beginning()
+
+        def _user_can_seek_beginning(self):
+            nonlocal input_port_iter_can_seek_beginning
+            return input_port_iter_can_seek_beginning
+
+        graph = _setup_seek_test(
+            MySink,
+            user_can_seek_beginning=_user_can_seek_beginning,
+            user_seek_beginning=lambda: None,
+        )
+
+        input_port_iter_can_seek_beginning = True
+        can_seek_beginning = None
+        graph.run_once()
+        self.assertIs(can_seek_beginning, True)
+
+        input_port_iter_can_seek_beginning = False
+        can_seek_beginning = None
+        graph.run_once()
+        self.assertIs(can_seek_beginning, False)
+
+    def test_no_can_seek_beginning_with_seek_beginning(self):
+        # Test an iterator without a _user_can_seek_beginning method, but with
+        # a _user_seek_beginning method.
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                nonlocal can_seek_beginning
+                can_seek_beginning = self._msg_iter.can_seek_beginning()
+
+        def _user_seek_beginning(self):
+            pass
+
+        graph = _setup_seek_test(MySink, user_seek_beginning=_user_seek_beginning)
+        can_seek_beginning = None
+        graph.run_once()
+        self.assertIs(can_seek_beginning, True)
+
+    def test_no_can_seek_beginning(self):
+        # Test an iterator without a _user_can_seek_beginning method, without
+        # a _user_seek_beginning method.
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                nonlocal can_seek_beginning
+                can_seek_beginning = self._msg_iter.can_seek_beginning()
+
+        graph = _setup_seek_test(MySink)
+        can_seek_beginning = None
+        graph.run_once()
+        self.assertIs(can_seek_beginning, False)
+
+    def test_can_seek_beginning_user_error(self):
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                # This is expected to raise.
+                self._msg_iter.can_seek_beginning()
+
+        def _user_can_seek_beginning(self):
+            raise ValueError('moustiquaire')
+
+        graph = _setup_seek_test(
+            MySink,
+            user_can_seek_beginning=_user_can_seek_beginning,
+            user_seek_beginning=lambda: None,
+        )
+
+        with self.assertRaises(bt2._Error) as ctx:
+            graph.run_once()
+
+        cause = ctx.exception[0]
+        self.assertIn('ValueError: moustiquaire', cause.message)
+
+    def test_can_seek_beginning_wrong_return_value(self):
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                # This is expected to raise.
+                self._msg_iter.can_seek_beginning()
+
+        def _user_can_seek_beginning(self):
+            return 'Amqui'
+
+        graph = _setup_seek_test(
+            MySink,
+            user_can_seek_beginning=_user_can_seek_beginning,
+            user_seek_beginning=lambda: None,
+        )
+
+        with self.assertRaises(bt2._Error) as ctx:
+            graph.run_once()
+
+        cause = ctx.exception[0]
+        self.assertIn("TypeError: 'str' is not a 'bool' object", cause.message)
+
+    def test_seek_beginning(self):
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                nonlocal do_seek_beginning
+                nonlocal msg
+
+                if do_seek_beginning:
+                    self._msg_iter.seek_beginning()
+                    return
+
+                msg = next(self._msg_iter)
+
+        def _user_seek_beginning(self):
+            self._at = 0
+
+        msg = None
+        graph = _setup_seek_test(MySink, user_seek_beginning=_user_seek_beginning)
+
+        # Consume message.
+        do_seek_beginning = False
+        graph.run_once()
+        self.assertIs(type(msg), bt2._StreamBeginningMessageConst)
+
+        # Consume message.
+        graph.run_once()
+        self.assertIs(type(msg), bt2._PacketBeginningMessageConst)
+
+        # Seek beginning.
+        do_seek_beginning = True
+        graph.run_once()
+
+        # Consume message.
+        do_seek_beginning = False
+        graph.run_once()
+        self.assertIs(type(msg), bt2._StreamBeginningMessageConst)
+
+    def test_seek_beginning_user_error(self):
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                self._msg_iter.seek_beginning()
+
+        def _user_seek_beginning(self):
+            raise ValueError('ouch')
+
+        graph = _setup_seek_test(MySink, user_seek_beginning=_user_seek_beginning)
+
+        with self.assertRaises(bt2._Error):
+            graph.run_once()
+
+
+class UserMessageIteratorSeekNsFromOriginTestCase(unittest.TestCase):
+    def test_can_seek_ns_from_origin_without_seek_ns_from_origin(self):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: Returns True (don't really care, as long
+        #     as it's provided)
+        #   - seek_ns_from_origin provided: No
+        #   - can the iterator seek beginning: Don't care
+        #   - can the iterator seek forward: Don't care
+        for can_seek_ns_from_origin in (False, True):
+            for iter_can_seek_beginning in (False, True):
+                for iter_can_seek_forward in (False, True):
+                    with self.assertRaisesRegex(
+                        bt2._IncompleteUserClass,
+                        "cannot create component class 'MySource': message iterator class implements _user_can_seek_ns_from_origin but not _user_seek_ns_from_origin",
+                    ):
+                        self._can_seek_ns_from_origin_test(
+                            None,
+                            user_can_seek_ns_from_origin_ret_val=True,
+                            user_seek_ns_from_origin_provided=False,
+                            iter_can_seek_beginning=iter_can_seek_beginning,
+                            iter_can_seek_forward=iter_can_seek_forward,
+                        )
+
+    def test_can_seek_ns_from_origin_returns_true(self):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: returns True
+        #   - seek_ns_from_origin provided: Yes
+        #   - can the iterator seek beginning: Don't care
+        #   - can the iterator seek forward: Don't care
+        #
+        # We expect iter.can_seek_ns_from_origin to return True.
+        for iter_can_seek_beginning in (False, True):
+            for iter_can_seek_forward in (False, True):
+                self._can_seek_ns_from_origin_test(
+                    expected_outcome=True,
+                    user_can_seek_ns_from_origin_ret_val=True,
+                    user_seek_ns_from_origin_provided=True,
+                    iter_can_seek_beginning=iter_can_seek_beginning,
+                    iter_can_seek_forward=iter_can_seek_forward,
+                )
+
+    def test_can_seek_ns_from_origin_returns_false_can_seek_beginning_forward_seekable(
+        self,
+    ):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: returns False
+        #   - seek_ns_from_origin provided: Yes
+        #   - can the iterator seek beginning: Yes
+        #   - can the iterator seek forward: Yes
+        #
+        # We expect iter.can_seek_ns_from_origin to return True.
+        self._can_seek_ns_from_origin_test(
+            expected_outcome=True,
+            user_can_seek_ns_from_origin_ret_val=False,
+            user_seek_ns_from_origin_provided=True,
+            iter_can_seek_beginning=True,
+            iter_can_seek_forward=True,
+        )
+
+    def test_can_seek_ns_from_origin_returns_false_can_seek_beginning_not_forward_seekable(
+        self,
+    ):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: returns False
+        #   - seek_ns_from_origin provided: Yes
+        #   - can the iterator seek beginning: Yes
+        #   - can the iterator seek forward: No
+        #
+        # We expect iter.can_seek_ns_from_origin to return False.
+        self._can_seek_ns_from_origin_test(
+            expected_outcome=False,
+            user_can_seek_ns_from_origin_ret_val=False,
+            user_seek_ns_from_origin_provided=True,
+            iter_can_seek_beginning=True,
+            iter_can_seek_forward=False,
+        )
+
+    def test_can_seek_ns_from_origin_returns_false_cant_seek_beginning_forward_seekable(
+        self,
+    ):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: returns False
+        #   - seek_ns_from_origin provided: Yes
+        #   - can the iterator seek beginning: No
+        #   - can the iterator seek forward: Yes
+        #
+        # We expect iter.can_seek_ns_from_origin to return False.
+        self._can_seek_ns_from_origin_test(
+            expected_outcome=False,
+            user_can_seek_ns_from_origin_ret_val=False,
+            user_seek_ns_from_origin_provided=True,
+            iter_can_seek_beginning=False,
+            iter_can_seek_forward=True,
+        )
+
+    def test_can_seek_ns_from_origin_returns_false_cant_seek_beginning_not_forward_seekable(
+        self,
+    ):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: returns False
+        #   - seek_ns_from_origin provided: Yes
+        #   - can the iterator seek beginning: No
+        #   - can the iterator seek forward: No
+        #
+        # We expect iter.can_seek_ns_from_origin to return False.
+        self._can_seek_ns_from_origin_test(
+            expected_outcome=False,
+            user_can_seek_ns_from_origin_ret_val=False,
+            user_seek_ns_from_origin_provided=True,
+            iter_can_seek_beginning=False,
+            iter_can_seek_forward=False,
+        )
+
+    def test_no_can_seek_ns_from_origin_seek_ns_from_origin(self):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: Not provided
+        #   - seek_ns_from_origin provided: Yes
+        #   - can the iterator seek beginning: Don't care
+        #   - can the iterator seek forward: Don't care
+        #
+        # We expect iter.can_seek_ns_from_origin to return True.
+        for iter_can_seek_beginning in (False, True):
+            for iter_can_seek_forward in (False, True):
+                self._can_seek_ns_from_origin_test(
+                    expected_outcome=True,
+                    user_can_seek_ns_from_origin_ret_val=None,
+                    user_seek_ns_from_origin_provided=True,
+                    iter_can_seek_beginning=iter_can_seek_beginning,
+                    iter_can_seek_forward=iter_can_seek_forward,
+                )
+
+    def test_no_can_seek_ns_from_origin_no_seek_ns_from_origin_can_seek_beginning_forward_seekable(
+        self,
+    ):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: Not provided
+        #   - seek_ns_from_origin provided: Not provided
+        #   - can the iterator seek beginning: Yes
+        #   - can the iterator seek forward: Yes
+        #
+        # We expect iter.can_seek_ns_from_origin to return True.
+        self._can_seek_ns_from_origin_test(
+            expected_outcome=True,
+            user_can_seek_ns_from_origin_ret_val=None,
+            user_seek_ns_from_origin_provided=False,
+            iter_can_seek_beginning=True,
+            iter_can_seek_forward=True,
+        )
+
+    def test_no_can_seek_ns_from_origin_no_seek_ns_from_origin_can_seek_beginning_not_forward_seekable(
+        self,
+    ):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: Not provided
+        #   - seek_ns_from_origin provided: Not provided
+        #   - can the iterator seek beginning: Yes
+        #   - can the iterator seek forward: No
+        #
+        # We expect iter.can_seek_ns_from_origin to return False.
+        self._can_seek_ns_from_origin_test(
+            expected_outcome=False,
+            user_can_seek_ns_from_origin_ret_val=None,
+            user_seek_ns_from_origin_provided=False,
+            iter_can_seek_beginning=True,
+            iter_can_seek_forward=False,
+        )
+
+    def test_no_can_seek_ns_from_origin_no_seek_ns_from_origin_cant_seek_beginning_forward_seekable(
+        self,
+    ):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: Not provided
+        #   - seek_ns_from_origin provided: Not provided
+        #   - can the iterator seek beginning: No
+        #   - can the iterator seek forward: Yes
+        #
+        # We expect iter.can_seek_ns_from_origin to return False.
+        self._can_seek_ns_from_origin_test(
+            expected_outcome=False,
+            user_can_seek_ns_from_origin_ret_val=None,
+            user_seek_ns_from_origin_provided=False,
+            iter_can_seek_beginning=False,
+            iter_can_seek_forward=True,
+        )
+
+    def test_no_can_seek_ns_from_origin_no_seek_ns_from_origin_cant_seek_beginning_not_forward_seekable(
+        self,
+    ):
+        # Test the case where:
+        #
+        #   - can_seek_ns_from_origin: Not provided
+        #   - seek_ns_from_origin provided: Not provided
+        #   - can the iterator seek beginning: No
+        #   - can the iterator seek forward: No
+        #
+        # We expect iter.can_seek_ns_from_origin to return False.
+        self._can_seek_ns_from_origin_test(
+            expected_outcome=False,
+            user_can_seek_ns_from_origin_ret_val=None,
+            user_seek_ns_from_origin_provided=False,
+            iter_can_seek_beginning=False,
+            iter_can_seek_forward=False,
+        )
+
+    def _can_seek_ns_from_origin_test(
+        self,
+        expected_outcome,
+        user_can_seek_ns_from_origin_ret_val,
+        user_seek_ns_from_origin_provided,
+        iter_can_seek_beginning,
+        iter_can_seek_forward,
+    ):
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                nonlocal can_seek_ns_from_origin
+                can_seek_ns_from_origin = self._msg_iter.can_seek_ns_from_origin(
+                    passed_ns_from_origin
+                )
+
+        if user_can_seek_ns_from_origin_ret_val is not None:
+
+            def user_can_seek_ns_from_origin(self, ns_from_origin):
+                nonlocal received_ns_from_origin
+                received_ns_from_origin = ns_from_origin
+                return user_can_seek_ns_from_origin_ret_val
+
+        else:
+            user_can_seek_ns_from_origin = None
+
+        if user_seek_ns_from_origin_provided:
+
+            def user_seek_ns_from_origin(self, ns_from_origin):
+                pass
+
+        else:
+            user_seek_ns_from_origin = None
+
+        if iter_can_seek_beginning:
+
+            def user_seek_beginning(self):
+                pass
+
+        else:
+            user_seek_beginning = None
+
+        graph = _setup_seek_test(
+            MySink,
+            user_can_seek_ns_from_origin=user_can_seek_ns_from_origin,
+            user_seek_ns_from_origin=user_seek_ns_from_origin,
+            user_seek_beginning=user_seek_beginning,
+            can_seek_forward=iter_can_seek_forward,
+        )
+
+        passed_ns_from_origin = 77
+        received_ns_from_origin = None
+        can_seek_ns_from_origin = None
+        graph.run_once()
+        self.assertIs(can_seek_ns_from_origin, expected_outcome)
+
+        if user_can_seek_ns_from_origin_ret_val is not None:
+            self.assertEqual(received_ns_from_origin, passed_ns_from_origin)
+
+    def test_can_seek_ns_from_origin_user_error(self):
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                # This is expected to raise.
+                self._msg_iter.can_seek_ns_from_origin(2)
+
+        def _user_can_seek_ns_from_origin(self, ns_from_origin):
+            raise ValueError('Joutel')
+
+        graph = _setup_seek_test(
+            MySink,
+            user_can_seek_ns_from_origin=_user_can_seek_ns_from_origin,
+            user_seek_ns_from_origin=lambda: None,
+        )
+
+        with self.assertRaises(bt2._Error) as ctx:
+            graph.run_once()
+
+        cause = ctx.exception[0]
+        self.assertIn('ValueError: Joutel', cause.message)
+
+    def test_can_seek_ns_from_origin_wrong_return_value(self):
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                # This is expected to raise.
+                self._msg_iter.can_seek_ns_from_origin(2)
+
+        def _user_can_seek_ns_from_origin(self, ns_from_origin):
+            return 'Nitchequon'
+
+        graph = _setup_seek_test(
+            MySink,
+            user_can_seek_ns_from_origin=_user_can_seek_ns_from_origin,
+            user_seek_ns_from_origin=lambda: None,
+        )
+
+        with self.assertRaises(bt2._Error) as ctx:
+            graph.run_once()
+
+        cause = ctx.exception[0]
+        self.assertIn("TypeError: 'str' is not a 'bool' object", cause.message)
+
+    def test_seek_ns_from_origin(self):
+        class MySink(bt2._UserSinkComponent):
+            def __init__(self, config, params, obj):
+                self._add_input_port('in')
+
+            def _user_graph_is_configured(self):
+                self._msg_iter = self._create_message_iterator(self._input_ports['in'])
+
+            def _user_consume(self):
+                self._msg_iter.seek_ns_from_origin(17)
+
+        def _user_seek_ns_from_origin(self, ns_from_origin):
+            nonlocal actual_ns_from_origin
+            actual_ns_from_origin = ns_from_origin
+
+        graph = _setup_seek_test(
+            MySink, user_seek_ns_from_origin=_user_seek_ns_from_origin
+        )
+
+        actual_ns_from_origin = None
+        graph.run_once()
+        self.assertEqual(actual_ns_from_origin, 17)
+
+
+if __name__ == '__main__':
+    unittest.main()
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