Implement CFDP directory listing

oresat_c3/protocols/cachestore.py

@@ -42,6 +42,20 @@ def file_exists(self, path: Path) -> bool:
         with self._lock:
             return any(path.name == f.name for f in self._data)
 
+    def stat(self, file: Path) -> os.stat_result:
+        """Implements os.stat() but for a filestore
+
+        I needed to find the size of a file but there's nothing that I can see in the spec that
+        would do it. That said it only gives a minimum recommended set of operations, so maybe
+        they just expect you to do it yourself?
+        """
+
+        with self._lock:
+            for f in self._data:
+                if file.name == f.name:
+                    return Path(self._dir, f.name).stat()
+            raise FileNotFoundError(file)
+
     def truncate_file(self, file: Path) -> None:
         with self._lock:
             for f in self._data:

oresat_c3/protocols/cfdp.py

@@ -0,0 +1,100 @@
+"""This module contains bugfixes to cfdp-py implementations.
+
+Most or all of these changes should eventually be submitted upstream.
+"""
+
+import struct
+from pathlib import Path
+
+from cfdppy.exceptions import SourceFileDoesNotExist
+from cfdppy.handler.crc import CrcHelper
+from cfdppy.handler.source import SourceHandler
+from spacepackets.cfdp import NULL_CHECKSUM_U32, ChecksumType
+from spacepackets.cfdp.pdu import FileDataPdu
+from spacepackets.cfdp.pdu.file_data import FileDataParams
+
+
+class VfsSourceHandler(SourceHandler):
+    """A SourceHandler but modified to always and only use Filestore operations"""
+
+    def _prepare_file_params(self):
+        """Fixes the parent implementation not using vfs operations for file ops
+
+        in particular file_exists() and stat()
+        """
+        assert self._put_req is not None
+        if self._put_req.metadata_only:
+            self._params.fp.metadata_only = True
+            self._params.fp.no_eof = True
+        else:
+            assert self._put_req.source_file is not None
+            if not self.user.vfs.file_exists(self._put_req.source_file):
+                raise SourceFileDoesNotExist(self._put_req.source_file)
+            file_size = self.user.vfs.stat(self._put_req.source_file).st_size
+            if file_size == 0:
+                self._params.fp.metadata_only = True
+            else:
+                self._params.fp.file_size = file_size
+
+    def _prepare_file_data_pdu(self, offset: int, read_len: int):
+        """Fixes the parent not using vfs operations
+
+        They opened source_file manually and then used read_from_open_file(), but read_data()
+        will do all that for you but properly.
+        """
+        assert self._put_req is not None
+        assert self._put_req.source_file is not None
+        file_data = self.user.vfs.read_data(self._put_req.source_file, offset, read_len)
+        fd_params = FileDataParams(file_data=file_data, offset=offset, segment_metadata=None)
+        file_data_pdu = FileDataPdu(pdu_conf=self._params.pdu_conf, params=fd_params)
+        self._add_packet_to_be_sent(file_data_pdu)
+
+
+class VfsCrcHelper(CrcHelper):
+    """CrcHelper but modified to only use Filestore operations.
+
+    It previously would attempt to open the paths passed to it directly instead of asking the
+    filestore, which failed when using the above PrefixFilestore.
+    """
+
+    def calc_modular_checksum(self, file_path: Path) -> bytes:
+        """Calculates the modular checksum of the file in file_path.
+
+        This was a module level function in cfdppy but it accessed the filesystem directly
+        instead of going through a filestore. It needs to become a CrcHelper method to use the
+        provided filestore.
+        """
+        checksum = 0
+        offset = 0
+        while True:
+            data = self.vfs.read_data(file_path, offset, 4)
+            offset += 4
+            if not data:
+                break
+            checksum += int.from_bytes(data.ljust(4, b"\0"), byteorder="big", signed=False)
+
+        checksum %= 2**32
+        return struct.pack("!I", checksum)
+
+    def calc_for_file(self, file_path: Path, file_sz: int, segment_len: int = 4096) -> bytes:
+        if self.checksum_type == ChecksumType.NULL_CHECKSUM:
+            return NULL_CHECKSUM_U32
+        if self.checksum_type == ChecksumType.MODULAR:
+            return self.calc_modular_checksum(file_path)
+        crc_obj = self.generate_crc_calculator()
+        if segment_len == 0:
+            raise ValueError("Segment length can not be 0")
+        if not self.vfs.file_exists(file_path):
+            raise SourceFileDoesNotExist(file_path)
+        current_offset = 0
+
+        # Calculate the file CRC
+        while current_offset < file_sz:
+            if current_offset + segment_len > file_sz:
+                read_len = file_sz - current_offset
+            else:
+                read_len = segment_len
+            if read_len > 0:
+                crc_obj.update(self.vfs.read_data(file_path, current_offset, read_len))
+            current_offset += read_len
+        return crc_obj.digest()