.TH SNOOPY 8
.SH NAME
snoopy \- spy on network packets
.SH SYNOPSIS
.B snoopy
[
.B -?stdCp
] [
.B -f
.I filter-expression
] [
.B -N
.I n
] [
.B -h first-header
] [
packet-file
]
.SH DESCRIPTION
.PP
.I Snoopy
reads packets from a packet source (default
.BR /net/ether0 ),
matches them to a filter (by default anything matches), and writes
matching packets to standard output either in human readable form (default)
or in a binary trace format that can be reinput to
.IR snoopy .
.PP
The human readable format consists of multiple lines per packet.
The first line contains the milliseconds since the
trace was started.  Subsequent ones are indented with a tab
and each contains the dump of a single protocol header.  The last line
contains the dump of any contained data.  For example, a
.SM BOOTP
packet would look like:
.sp
.EX
324389 ms
	ether(s=0000929b1b54 d=ffffffffffff pr=0800 ln=342)
	ip(s=135.104.9.62 d=255.255.255.255 id=5099 frag=0000...
	udp(s=68 d=67 ck=d151 ln= 308)
	bootp(t=Req ht=1 hl=16 hp=0 xid=217e5f27 sec=0 fl=800...
	dhcp(t=Request clientid=0152415320704e7266238ebf01030...
.EE
.PP
The binary format consists of:
.IP
2 bytes of packet length, msb first
.IP
8 bytes of nanosecond time, msb first
.IP
the packet
.PP
Filters are expressions specifying protocols to be traced
and specific values for fields in the protocol headers.
The grammar is:
.sp
.EX
expr	: protocol
	| field '=' value
	| protocol '(' expr ')'
	| '(' expr ')'
	| expr '||' expr
	| expr '&&' expr
	| '!' expr
.EE
.PP
The values for <protocol> and <field> can
be obtained using the
.B -?
option.  It will list each known protocol,
which subprotocols it can multiplex to,
and which fields can be used for filtering.
For example, the listing for ethernet is currently:
.sp
.EX
ether's filter attr:
	s	- source address
	d	- destination address
	a	- source|destination address
	t	- type
ether's subprotos:
	ip
	arp
	rarp
	ip6
	pppoe_disc
	pppoe_sess
.EE
.PP
The format of <value> depends on context.  In general,
ethernet addresses are entered as a string of hex
digits; IP numbers in the canonical `.' format for v4 and `:' format
for v6; and ports in decimal.
.PP
.IR Snoopy 's
options are:
.TP
.B -t
input is a binary trace file.  The default assumes
a packet device, one packet per read.
.TP
.B -d
output will be a binary trace file.  The default is
human readable.
.TP
.B -s
force one output line per packet.  The
default is multiline.
.TP
.B -C
compute correct checksums and if doesn't match
the contained one, add a field
.B !ck=\fIxxxx\fP
where
.I xxxx
is the correct checksum.
.TP
.B -p
do not enter promiscuous mode.  Only packets to
this interface will be seen.
.TP
.B -N
dump
.I n
data bytes per packet.  The default is 32.
.TP
.B -f
use
.I filter-expression
to filter the packet stream.  The default is
to match all packets.
.TP
.B -h
assume the first header per packet to be
.IR first-header .
The default is
.IR ether .
.SH EXAMPLES
the following would display only
.SM BOOTP
and
.SM ARP
packets:
.sp
.EX
% snoopy -f 'arp || bootp'
after optimize: ether( arp || ip( udp( bootp ) ) )
.EE
.PP
The first line of output shows the completed filter
expression.
.I Snoopy
will fill in other protocols as necessary to complete
the filter and then optimize to remove redundant
comparisons.
.PP
To save all packets between 135.104.9.2 to 135.104.9.6 and
later display those to/from TCP port 80:
.sp
.EX
% ramfs
% snoopy -df 'ip(s=135.104.9.2&d=135.104.9.6)||\\
	ip(s=135.104.9.6&d=135.104.9.2)' > /tmp/quux
<interrupt from the keyboard>
% snoopy -tf 'tcp(sd=80)' /tmp/quux
.EE
.SH FILES
.TP
.B /net/ether
Ethernet device
.SH SOURCE
.B /sys/src/cmd/ip/snoopy
.SH BUGS
At the moment it only dumps ethernet packets because there's
no device to get IP packets without the media header.  This will
be corrected soon.