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====== OMNeT++/INET Packetdrill ======

Packetdrill in INET consists of
  - Node (src/inet/node/packetdrill/PacketDrillQuicHost.ned)
  - Tests (tests/packetdrill)
  - Application (src/inet/applications/packetdrill)

With a Packetdrill test script, it is possible to check the content and the time of packets a host sends.   The expected behavior is described in the script (in a line with ">"). To trigger outgoing packets, a test script can contain system calls and inject a packet described in the script (in a line with "<"). 

===== Node =====

The PacketDrillQuicHost node uses a tun interface to capture outgoing packets and to
be able to inject generated packets. A tun interface has a direct connection to the App. The green arrows in the following figure show the packet flow.

{{:public:packetdrillhost.png?400|}}

===== Tests =====

The packetdrill directory under tests has a subdirectory for each protocol to test (e. g.
quic). Inside one of these subdirectorys, There are .test files that are similar to a
omnet.ini file, a runtest script to run packetdrill tests from a terminal, and a subfolder 
(e. g. quictests) containing the packetdrill tests scripts. Before the runtest script is able to run a test, INET needs to be built in debug mode. In INET root directory, run

    $ make MODE=debug -j3

After that change to the packetdrill protocol test folder (e. g. tests/packetdrill/quic)
and execute all tests with

    $ ./runtest

or a specific test with

    $ ./runtest quicOpenClose.test

The runtest script links against the debug version of the INET library (libINET_dbg). The output of this command shows the result. For more detailed logs, see 
work/quicOpenClose/test.out for stdout or work/quicOpenClose/test.err for stderr output.

===== Application =====

The packetdrill app parses the packetdrill test script file, generates events for each
line (like run system call or inject packet) and executes these events.

Packetdrill uses bison as parser. The syntax is specified in parser.y and constants are
specified in lexer.l. parser.y uses functions from PacketDrill.h to generate the described
packets in the packetdrill test script, while parsing it. Each line results in an object
of the class PacketDrillEvent. Thus, parsing a packetdrill test script results in a list 
of PacketDrillEvent objects. A PacketDrillEvent is either a packet event (inject packet
"<", expect outbound packet ">"), a syscall event (socket, connect, etc.), or a command
event. Run

    $ ./generate_parser

to generate C++ code (parser.cc, parser.h, and lexer.cc) from parser.y and lexer.l.

The PacketDrillApp uses the list of events generated by the parser and execute these
events.
* syscall event (e. g. connect) - Runs the equivalent of the described syscall (e. g. calls 
the connect method on the socket).
* inbound packet event ("<") - Uses the generated packet by the parser and sends it
via tunOut interface.
* outbound packet event (">") - Uses the generated packet by the parser and compares it
to a real outbound packet captured from tunIn interface. If no real packet was sent or
if the real packet differs from the generated packet, the packetdrill test fails.