tests: Add tests for Datagram{,Iterator,InputFile,OutputFile}

This also includes a test for my previous commit which changes
DatagramInputFile::get_datagram().

tests/putil/test_datagram.py

@@ -0,0 +1,149 @@
+import pytest
+from panda3d import core
+
+# Fixtures for generating interesting datagrams (and verification functions) on
+# the fly...
+
+@pytest.fixture(scope='module',
+                params=[False, True],
+                ids=['stdfloat_float', 'stdfloat_double'])
+def datagram_small(request):
+    """Returns a small datagram, along with a verification function."""
+    dg = core.Datagram()
+
+    dg.set_stdfloat_double(request.param)
+
+    dg.add_uint8(3)
+    dg.add_uint16(14159)
+    dg.add_uint32(0xDEADBEEF)
+    dg.add_uint64(0x0123456789ABCDEF)
+
+    dg.add_int8(-77)
+    dg.add_int16(-1)
+    dg.add_int32(-972965890)
+    dg.add_int64(-1001001001001001)
+
+    dg.add_string('this is a string')
+    dg.add_string32('this is another string')
+    dg.add_string('this is yet a third string')
+
+    dg.add_stdfloat(800.2)
+    dg.add_stdfloat(3.1415926)
+    dg.add_stdfloat(2.7182818)
+
+    def readback_function(dgi):
+        assert dgi.get_remaining_size() > 0
+
+        assert dgi.get_uint8() == 3
+        assert dgi.get_uint16() == 14159
+        assert dgi.get_uint32() == 0xDEADBEEF
+        assert dgi.get_uint64() == 0x0123456789ABCDEF
+
+        assert dgi.get_int8() == -77
+        assert dgi.get_int16() == -1
+        assert dgi.get_int32() == -972965890
+        assert dgi.get_int64() == -1001001001001001
+
+        assert dgi.get_string() == 'this is a string'
+        assert dgi.get_string32() == 'this is another string'
+        assert dgi.get_string() == 'this is yet a third string'
+
+        assert dgi.get_stdfloat() == pytest.approx(800.2)
+        assert dgi.get_stdfloat() == pytest.approx(3.1415926)
+        assert dgi.get_stdfloat() == pytest.approx(2.7182818)
+
+        assert dgi.get_remaining_size() == 0
+
+    return dg, readback_function
+
+@pytest.fixture(scope='module')
+def datagram_large():
+    """Returns a big datagram, along with a verification function."""
+
+    dg = core.Datagram()
+    for x in range(2000000):
+        dg.add_uint32(x)
+        dg.add_string('the magic words are squeamish ossifrage')
+
+    def readback_function(dgi):
+        assert dgi.get_remaining_size() > 0
+
+        for x in range(2000000):
+            assert dgi.get_uint32() == x
+            assert dgi.get_string() == 'the magic words are squeamish ossifrage'
+
+        assert dgi.get_remaining_size() == 0
+
+    return dg, readback_function
+
+def test_iterator(datagram_small):
+    """This tests Datagram/DatagramIterator, and sort of serves as a self-check
+    of the test fixtures too."""
+    dg, verify = datagram_small
+
+    dgi = core.DatagramIterator(dg)
+    verify(dgi)
+
+
+# These test DatagramInputFile/DatagramOutputFile:
+
+def do_file_test(dg, verify, filename):
+    dof = core.DatagramOutputFile()
+    dof.open(filename)
+    dof.put_datagram(dg)
+    dof.close()
+
+    dg2 = core.Datagram()
+    dif = core.DatagramInputFile()
+    dif.open(filename)
+    assert dif.get_datagram(dg2)
+    dif.close()
+
+    # This is normally saved by the DatagramOutputFile header. We cheat here.
+    dg2.set_stdfloat_double(dg.get_stdfloat_double())
+
+    dgi = core.DatagramIterator(dg2)
+    verify(dgi)
+
+def test_file_small(datagram_small, tmpdir):
+    """This tests DatagramOutputFile/DatagramInputFile on small datagrams."""
+    dg, verify = datagram_small
+
+    p = tmpdir.join('datagram.bin')
+    filename = core.Filename.from_os_specific(str(p))
+
+    do_file_test(dg, verify, filename)
+
+def test_file_large(datagram_large, tmpdir):
+    """This tests DatagramOutputFile/DatagramInputFile on very large datagrams."""
+    dg, verify = datagram_large
+
+    p = tmpdir.join('datagram.bin')
+    filename = core.Filename.from_os_specific(str(p))
+
+    do_file_test(dg, verify, filename)
+
+def test_file_corrupt(datagram_small, tmpdir):
+    """This tests DatagramInputFile's handling of a corrupt size header."""
+    dg, verify = datagram_small
+
+    p = tmpdir.join('datagram.bin')
+    filename = core.Filename.from_os_specific(str(p))
+
+    dof = core.DatagramOutputFile()
+    dof.open(filename)
+    dof.put_datagram(dg)
+    dof.close()
+
+    # Corrupt the size header to 4GB
+    with p.open(mode='wb') as f:
+        f.seek(0)
+        f.write(b'\xFF\xFF\xFF\xFF')
+
+    dg2 = core.Datagram()
+    dif = core.DatagramInputFile()
+    dif.open(filename)
+    assert not dif.get_datagram(dg2)
+    dif.close()
+
+    # Should we test that dg2 is unmodified?