README.md
1# dbus-pcap: A tool to analyse D-Bus traffic captures
2
3`dbus-pcap` is a tool to slice, dice and display captures of D-Bus traffic
4captured into a the standard `pcap` packet container.
5
6D-Bus traffic on OpenBMC can be captured using `busctl`:
7
8```sh
9busctl capture > /tmp/dbus.pcap
10```
11
12## Use
13
14```sh
15$ ./dbus-pcap --help
16usage: dbus-pcap [-h] [--json] [--no-track-calls] file [expressions [expressions ...]]
17
18positional arguments:
19 file The pcap file
20 expressions DBus message match expressions
21
22optional arguments:
23 -h, --help show this help message and exit
24 --json Emit a JSON representation of the messages
25 --no-track-calls Make a call response pass filters
26```
27
28## Examples of Simple Invocations and Output
29
30The default output style:
31
32```sh
33$ ./dbus-pcap dbus.pcap | head -n 3
341553600866.443112: CookedMessage(header=CookedHeader(fixed=FixedHeader(endian=108, type=4, flags=1, version=1, length=76, cookie=6919136), fields=[Field(type=<MessageFieldType.PATH: 1>, data='/xyz/openbmc_project/sensors/fan_tach/fan0_0'), Field(type=<MessageFieldType.INTERFACE: 2>, data='org.freedesktop.DBus.Properties'), Field(type=<MessageFieldType.MEMBER: 3>, data='PropertiesChanged'), Field(type=<MessageFieldType.SIGNATURE: 8>, data='sa{sv}as'), Field(type=<MessageFieldType.SENDER: 7>, data=':1.95')]), body=['xyz.openbmc_project.Sensor.Value', [['Value', 3210]], []])
35
361553600866.456774: CookedMessage(header=CookedHeader(fixed=FixedHeader(endian=108, type=4, flags=1, version=1, length=76, cookie=6919137), fields=[Field(type=<MessageFieldType.PATH: 1>, data='/xyz/openbmc_project/sensors/fan_tach/fan1_0'), Field(type=<MessageFieldType.INTERFACE: 2>, data='org.freedesktop.DBus.Properties'), Field(type=<MessageFieldType.MEMBER: 3>, data='PropertiesChanged'), Field(type=<MessageFieldType.SIGNATURE: 8>, data='sa{sv}as'), Field(type=<MessageFieldType.SENDER: 7>, data=':1.95')]), body=['xyz.openbmc_project.Sensor.Value', [['Value', 3081]], []])
37
38...
39```
40
41With JSON output, useful for piping through
42[`jq`](https://stedolan.github.io/jq/):
43
44```sh
45$ ./dbus-pcap --json | head -n 2
46$ dbus-pcap --json dbus.pcap | head
47[[[108, 4, 1, 1, 76, 6919136], [[1, "/xyz/openbmc_project/sensors/fan_tach/fan0_0"], [2, "org.freedesktop.DBus.Properties"], [3, "PropertiesChanged"], [8, "sa{sv}as"], [7, ":1.95"]]], ["xyz.openbmc_project.Sensor.Value", [["Value", 3210]], []]]
48[[[108, 4, 1, 1, 76, 6919137], [[1, "/xyz/openbmc_project/sensors/fan_tach/fan1_0"], [2, "org.freedesktop.DBus.Properties"], [3, "PropertiesChanged"], [8, "sa{sv}as"], [7, ":1.95"]]], ["xyz.openbmc_project.Sensor.Value", [["Value", 3081]], []]]
49...
50```
51
52## Discussion
53
54While [Wireshark](https://www.wireshark.org/) has the ability to inspect D-Bus
55captures it falls down in terms of scriptability and the filters exposed by the
56dissector.
57
58In addition to parsing and displaying packet contents `dbus-pcap` can filter the
59capture based on
60[standard D-Bus match expressions](https://dbus.freedesktop.org/doc/dbus-specification.html#message-bus-routing-match-rules)
61(though does not yet support argument matching).
62