writer: roll back buffer after exceptions

If an exception was caught on the Python side, then the item that
caused the exception would remain in the buffer and be written out
with the next valid item.

Fixes #212.

Author: lonvia

lib/simple_writer.cc

@@ -30,6 +30,12 @@ class SimpleWriter
 
     void add_osmium_object(const osmium::OSMObject& o)
     {
+        if (!buffer) {
+            throw std::runtime_error{"Writer already closed."};
+        }
+
+        buffer.rollback();
+
         buffer.add_item(o);
         flush_buffer();
     }
@@ -40,6 +46,8 @@ class SimpleWriter
             throw std::runtime_error{"Writer already closed."};
         }
 
+        buffer.rollback();
+
         if (py::isinstance<osmium::Node>(o)) {
             buffer.add_item(o.cast<osmium::Node &>());
         } else {
@@ -65,6 +73,8 @@ class SimpleWriter
             throw std::runtime_error{"Writer already closed."};
         }
 
+        buffer.rollback();
+
         if (py::isinstance<osmium::Way>(o)) {
             buffer.add_item(o.cast<osmium::Way &>());
         } else {
@@ -88,6 +98,8 @@ class SimpleWriter
             throw std::runtime_error{"Writer already closed."};
         }
 
+        buffer.rollback();
+
         if (py::isinstance<osmium::Relation>(o)) {
             buffer.add_item(o.cast<osmium::Relation &>());
         } else {

test/test_writer.py

@@ -246,3 +246,75 @@ def test_add_relation_after_close(tmp_path, simple_handler):
 
     with pytest.raises(RuntimeError, match='closed'):
         simple_handler(node_opl, relation=lambda o: writer.add_relation(o))
+
+
+@pytest.mark.parametrize("final_item", (True, False))
+def test_catch_errors_in_add_node(tmp_path, final_item):
+    test_file = tmp_path / 'test.opl'
+
+    writer = o.SimpleWriter(str(test_file), 4000)
+
+    try:
+        writer.add_node(o.osm.mutable.Node(id=123))
+        with pytest.raises(TypeError):
+            writer.add_node(o.osm.mutable.Node(id=124, tags=34))
+        if not final_item:
+            writer.add_node(o.osm.mutable.Node(id=125))
+    finally:
+        writer.close()
+
+    output = test_file.read_text()
+
+    expected = 'n123 v0 dV c0 t i0 u T x y\n'
+    if not final_item:
+        expected += 'n125 v0 dV c0 t i0 u T x y\n'
+
+    assert output == expected
+
+
+@pytest.mark.parametrize("final_item", (True, False))
+def test_catch_errors_in_add_way(tmp_path, final_item):
+    test_file = tmp_path / 'test.opl'
+
+    writer = o.SimpleWriter(str(test_file), 4000)
+
+    try:
+        writer.add_way(o.osm.mutable.Way(id=123, nodes=[1, 2, 3]))
+        with pytest.raises(TypeError):
+            writer.add_way(o.osm.mutable.Way(id=124, nodes=34))
+        if not final_item:
+            writer.add_way(o.osm.mutable.Way(id=125, nodes=[11, 12]))
+    finally:
+        writer.close()
+
+    output = test_file.read_text()
+
+    expected = 'w123 v0 dV c0 t i0 u T Nn1,n2,n3\n'
+    if not final_item:
+        expected += 'w125 v0 dV c0 t i0 u T Nn11,n12\n'
+
+    assert output == expected
+
+
+@pytest.mark.parametrize("final_item", (True, False))
+def test_catch_errors_in_add_relation(tmp_path, final_item):
+    test_file = tmp_path / 'test.opl'
+
+    writer = o.SimpleWriter(str(test_file), 4000)
+
+    try:
+        writer.add_relation(o.osm.mutable.Relation(id=123))
+        with pytest.raises(TypeError):
+            writer.add_relation(o.osm.mutable.Relation(id=124, members=34))
+        if not final_item:
+            writer.add_relation(o.osm.mutable.Relation(id=125))
+    finally:
+        writer.close()
+
+    output = test_file.read_text()
+
+    expected = 'r123 v0 dV c0 t i0 u T M\n'
+    if not final_item:
+        expected += 'r125 v0 dV c0 t i0 u T M\n'
+
+    assert output == expected