Pass the endianness to all writing locations

Issue: rshk#41

Author: gmacon

CHANGELOG.rst

@@ -1,6 +1,11 @@
 History
 #######
 
+Unreleased
+==========
+
+- Use the explicit endianness everywhere when writing.
+
 v0.1
 ====
 

pcapng/blocks.py

@@ -54,7 +54,9 @@ def __init__(self, **kwargs):
             for key, packed_type, default in self.schema:
                 if key == "options":
                     self._decoded[key] = Options(
-                        schema=packed_type.options_schema, data={}, endianness="="
+                        schema=packed_type.options_schema,
+                        data={},
+                        endianness=kwargs["endianness"],
                     )
                     if "options" in kwargs:
                         for oky, ovl in kwargs["options"].items():
@@ -83,10 +85,10 @@ def _write(self, outstream):
         block_length = 12 + subblock_length
         if subblock_length % 4 != 0:
             block_length += 4 - (subblock_length % 4)
-        write_int(self.magic_number, outstream, 32)
-        write_int(block_length, outstream, 32)
+        write_int(self.magic_number, outstream, 32, endianness=self.section.endianness)
+        write_int(block_length, outstream, 32, endianness=self.section.endianness)
         write_bytes_padded(outstream, encoded_block)
-        write_int(block_length, outstream, 32)
+        write_int(block_length, outstream, 32, endianness=self.section.endianness)
 
     def _encode(self, outstream):
         """Encodes the fields of this block into raw data"""

tests/test_write_support.py

@@ -17,17 +17,19 @@ def compare_blocklists(list1, list2):
         assert list1[i] == list2[i], "block #{} mismatch".format(i)
 
 
-def test_write_read_all_blocks():
+@pytest.mark.parametrize("endianness", ["<", ">"])
+def test_write_read_all_blocks(endianness):
     # Track the blocks we're writing
     out_blocks = []
 
     # Build our original/output session
     o_shb = blocks.SectionHeader(
+        endianness=endianness,
         options={
             "shb_hardware": "pytest",
             "shb_os": "python",
             "shb_userappl": "python-pcapng",
-        }
+        },
     )
     out_blocks.append(o_shb)
 
@@ -129,7 +131,8 @@ def test_write_read_all_blocks():
     compare_blocklists(in_blocks, out_blocks)
 
 
-def test_spb_snap_lengths():
+@pytest.mark.parametrize("endianness", ["<", ">"])
+def test_spb_snap_lengths(endianness):
     """
     Simple Packet Blocks present a unique challenge in parsing. The packet does not
     contain an explicit "captured length" indicator, only the original observed
@@ -147,7 +150,7 @@ def test_spb_snap_lengths():
     data = bytes(range(0, 256))
 
     # First session: no snap length
-    o_shb = blocks.SectionHeader()
+    o_shb = blocks.SectionHeader(endianness=endianness)
     o_idb = o_shb.new_member(blocks.InterfaceDescription)  # noqa: F841
     o_blk1 = o_shb.new_member(blocks.SimplePacket, packet_data=data)
 
@@ -162,7 +165,7 @@ def test_spb_snap_lengths():
     assert i_blk1.packet_data == data
 
     # Second session: with snap length
-    o_shb = blocks.SectionHeader()
+    o_shb = blocks.SectionHeader(endianness=endianness)
     o_idb = o_shb.new_member(blocks.InterfaceDescription, snaplen=32)  # noqa: F841
     o_blk1 = o_shb.new_member(blocks.SimplePacket, packet_data=data[:16])
     o_blk2 = o_shb.new_member(blocks.SimplePacket, packet_data=data[:32])