Fix offset issue in packet pruner

scripts/prune_packets.py

+#!/usr/bin/env python
+"""
+Prune all the non-header data out of a PDS file. Usefull for geenerating test
+data for CCSDS tools.
+"""
+import ctypes as c
+import argparse
+
+from edosl0util import stream
+
+parser = argparse.ArgumentParser(description=__doc__)
+parser.add_argument('pdsfile')
+parser.add_argument('outfile')
+
+args = parser.parse_args()
+
+
+def pack_hdr_bytes(hdr):
+    return c.string_at(c.byref(hdr), c.sizeof(hdr))
+
+
+with open(args.outfile, 'wb') as fptr:
+    idx = 0
+    for pkt in stream.PacketStream(open(args.pdsfile)):
+        h1 = pkt._primary_header
+        h2 = pkt._secondary_header
+        if h2:
+            h1.data_length_minus1 = c.sizeof(h2) - 1
+            fptr.write(h1)
+            if pkt.stamp:
+                h2.packet_count = 0
+            fptr.write(h2)
+        else:
+            h1.data_length_minus1 = 0
+            fptr.write(h1)
+            fptr.write('x')
+
+        idx += 1