<p>ERF记录可以包含附加到16字节ERF记录头的可选扩展头。“type”字段的高位表示存在扩展头。我在strix的例子中添加了一个扩展头的测试,以及扩展头本身的解码。注意,如果存在扩展头,以太网帧的测试也需要稍微改变。在</p>
<p><strong>注意:</strong>我认为ERF记录可以包含多个扩展头,但我不知道要测试这些头。扩展头结构并没有特别好地记录,我所掌握的唯一记录只包含一个扩展名。在</p>
<pre><code>import struct
import scapy.layers.all as sl
def erf_records( f ):
"""
Generator which parses ERF records from file-like ``f``
"""
while True:
# The ERF header is fixed length 16 bytes
hdr = f.read( 16 )
if hdr:
rec = {}
# The timestamp is in Intel byte-order
rec['ts'] = struct.unpack( '<Q', hdr[:8] )[0]
# The rest is in network byte-order
rec.update( zip( ('type', # ERF record type
'flags', # Raw flags bit field
'rlen', # Length of entire record
'lctr', # Interstitial loss counter
'wlen'), # Length of packet on wire
struct.unpack( '>BBHHH', hdr[8:] ) ) )
rec['iface'] = rec['flags'] & 0x03
rec['rx_err'] = rec['flags'] & 0x10 != 0
#- Check if ERF Extension Header present.
# Each Extension Header is 8 bytes.
if rec['type'] & 0x80:
ext_hdr = f.read( 8 )
rec.update( zip( (
'ext_hdr_signature', # 1 byte
'ext_hdr_payload_hash', # 3 bytes
'ext_hdr_filter_color', # 1 bye
'ext_hdr_flow_hash'), # 3 bytes
struct.unpack( '>B3sB3s', ext_hdr ) ) )
#- get remaining payload, less ext_hdr
rec['pkt'] = f.read( rec['rlen'] - 24 )
else:
rec['pkt'] = f.read( rec['rlen'] - 16 )
if rec['type'] & 0x02:
# ERF Ethernet has an extra two bytes of pad between ERF header
# and beginning of MAC header so that IP-layer data are DWORD
# aligned. From memory, none of the other types have pad.
rec['pkt'] = rec['pkt'][2:]
rec['pkt'] = sl.Ether( rec['pkt'] )
yield rec
else:
return
</code></pre>