Write a PCAP header when no packets are provided

Author: guedou

scapy/utils.py

@@ -24,7 +24,7 @@
 
 from scapy.config import conf
 from scapy.consts import DARWIN, WINDOWS
-from scapy.data import MTU
+from scapy.data import MTU, DLT_EN10MB
 from scapy.compat import *
 from scapy.error import log_runtime, log_loading, log_interactive, Scapy_Exception, warning
 from scapy.base_classes import BasePacketList
@@ -1155,6 +1155,7 @@ def write(self, pkt):
                 try:
                     p = next(pkt)
                 except StopIteration:
+                    self._write_header(None)
                     return
                 self._write_header(p)
                 self._write_packet(p)
@@ -1208,7 +1209,7 @@ def _write_header(self, pkt):
                 self.linktype = conf.l2types[pkt.__class__]
             except KeyError:
                 warning("PcapWriter: unknown LL type for %s. Using type 1 (Ethernet)", pkt.__class__.__name__)
-                self.linktype = 1
+                self.linktype = DLT_EN10MB
         RawPcapWriter._write_header(self, pkt)
 
     def _write_packet(self, packet):

test/regression.uts

@@ -5880,6 +5880,15 @@ wrpcap(filename, [IP()/UDP(), IPv6()/UDP()], linktype=DLT_RAW)
 packets = rdpcap(filename)
 assert(isinstance(packets[0], IP) and isinstance(packets[1], IPv6))
 
+= Check wrpcap() with no packet
+
+import tempfile
+filename = tempfile.mktemp(suffix=".pcap")
+wrpcap(filename, [])
+fstat = os.stat(filename)
+assert fstat.st_size != 0
+os.remove(filename)
+
 ############
 ############
 + LLMNR protocol