Merge pull request #113 from tloubrieu-jpl/reset_file_obj

Add support for reset_file_obj

ccsdspy/packet_types.py

@@ -141,7 +141,7 @@ def __init__(self, fields):
 
         self._init(fields)
 
-    def load(self, file, include_primary_header=False):
+    def load(self, file, include_primary_header=False, reset_file_obj=False):
         """Decode a file-like object containing a sequence of these packets.
 
         Parameters
@@ -153,6 +153,10 @@ def load(self, file, include_primary_header=False):
            fields are: `CCSDS_VERSION_NUMBER`, `CCSDS_PACKET_TYPE`,
            `CCSDS_SECONDARY_FLAG`, `CCSDS_SEQUENCE_FLAG`, `CCSDS_APID`,
            `CCSDS_SEQUENCE_COUNT`, and `CCSDS_PACKET_LENGTH`
+        reset_file_obj : bool
+           If True, leave the file object, when it is file buffer, where it was before load is called.
+           Otherwise, (default), leave the file stream pos after the read packets.
+           Does not apply when file is a string.
 
         Returns
         -------
@@ -175,6 +179,7 @@ def load(self, file, include_primary_header=False):
             self._converters,
             "fixed_length",
             include_primary_header=True,
+            reset_file_obj=reset_file_obj,
         )
 
         # inspect the primary header and issue warning if appropriate
@@ -262,7 +267,7 @@ def __init__(self, fields):
 
         self._init(fields)
 
-    def load(self, file, include_primary_header=False):
+    def load(self, file, include_primary_header=False, reset_file_obj=False):
         """Decode a file-like object containing a sequence of these packets.
 
         Parameters
@@ -274,6 +279,10 @@ def load(self, file, include_primary_header=False):
            fields are: `CCSDS_VERSION_NUMBER`, `CCSDS_PACKET_TYPE`,
            `CCSDS_SECONDARY_FLAG`, `CCSDS_SEQUENCE_FLAG`, `CCSDS_APID`,
            `CCSDS_SEQUENCE_COUNT`, and `CCSDS_PACKET_LENGTH`
+        reset_file_obj : bool
+           If True, leave the file object, when it is file buffer, where it was before load is called.
+           Otherwise, (default), leave the file stream pos after the read packets.
+           Does not apply when file is a string.
 
         Returns
         -------
@@ -294,7 +303,12 @@ def load(self, file, include_primary_header=False):
         # they didn't want the primary header fields, we parse for them and then
         # remove them after.
         packet_arrays = _load(
-            file, self._fields, self._converters, "variable_length", include_primary_header=True
+            file,
+            self._fields,
+            self._converters,
+            "variable_length",
+            include_primary_header=True,
+            reset_file_obj=reset_file_obj,
         )
 
         # inspect the primary header and issue warning if appropriate
@@ -593,7 +607,9 @@ def _get_fields_csv_file(csv_file):
     return fields
 
 
-def _load(file, fields, converters, decoder_name, include_primary_header=False):
+def _load(
+    file, fields, converters, decoder_name, include_primary_header=False, reset_file_obj=False
+):
     """Decode a file-like object containing a sequence of these packets.
 
     Parameters
@@ -609,6 +625,10 @@ def _load(file, fields, converters, decoder_name, include_primary_header=False):
        String identifying which decoder to use.
     include_primary_header: bool
        If True, provides the primary header in the output
+    reset_file_obj : bool
+           If True, leave the file object, when it is a file buffer, where it was before _load is called.
+           Otherwise, (default), leave the file stream pos after the read packets.
+           Does not apply when file is a string.
 
     Returns
     -------
@@ -621,6 +641,7 @@ def _load(file, fields, converters, decoder_name, include_primary_header=False):
       the decoder_name is not one of the allowed values
     """
     if hasattr(file, "read"):
+        file_pos = file.tell()
         file_bytes = np.frombuffer(file.read(), "u1")
     else:
         file_bytes = np.fromfile(file, "u1")
@@ -646,6 +667,8 @@ def _load(file, fields, converters, decoder_name, include_primary_header=False):
     field_arrays = _apply_post_byte_reoderings(field_arrays, orig_fields)
     field_arrays = _apply_converters(field_arrays, converters)
 
+    if hasattr(file, "read") and reset_file_obj:
+        file.seek(file_pos)
     return field_arrays
 
 

ccsdspy/tests/test_byte_order.py

@@ -6,6 +6,7 @@
 See also:
   ccsdspy/tests/data/byte_order/byte_order_packets.py
 """
+
 import glob
 import itertools
 import os

ccsdspy/tests/test_packet_types.py

@@ -20,6 +20,12 @@
 csv_file_4col_with_array = os.path.join(packet_def_dir, "simple_csv_4col_with_array.csv")
 csv_file_3col_with_array = os.path.join(packet_def_dir, "simple_csv_3col_with_array.csv")
 
+hs_packet_dir = os.path.join(dir_path, "data", "hs")
+random_binary_file = os.path.join(
+    hs_packet_dir, "apid001", "SSAT1_2015-180-00-00-00_2015-180-01-59-58_1_1_sim.tlm"
+)
+random_packet_def = os.path.join(hs_packet_dir, "apid001", "defs.csv")
+
 
 def test_FixedLength_initializer_copies_field_list():
     """Tests that the FixedLengthPacket initializer stores a copy of the
@@ -229,3 +235,12 @@ def test_variable_length_rejects_bit_offset():
                 ),
             ]
         )
+
+
+def test_load_without_moving_file_buffer_pos():
+    """Tests that load(..., reset_file_obj=True) works as intended."""
+    pkts = FixedLength.from_file(random_packet_def)
+    with open(random_binary_file, "rb") as fp:
+        pos = fp.tell()
+        pkts.load(fp, reset_file_obj=True)
+        assert pos == fp.tell()