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Some Information for Contributors
---------------------------------
You want to contribute to Tcpdump, Thanks!
Please, read these lines.
1) Fork the Tcpdump repository on GitHub from
https://github.com/the-tcpdump-group/tcpdump
(See https://help.github.com/articles/fork-a-repo/)
2) Setup an optional Travis-CI build
You can setup a travis build for your fork. So, you can test your changes
on Linux and OSX before sending pull requests.
(See http://docs.travis-ci.com/user/getting-started/)
3) Clone your repository
git clone https://github.com/<username>/tcpdump.git
4) Do a 'touch .devel' in your working directory.
Currently, the effect is
a) add (via configure, in Makefile) some warnings options ( -Wall
-Wmissing-prototypes -Wstrict-prototypes, ...) to the compiler if it
supports these options,
b) have the Makefile support "make depend" and the configure script run it.
5) Configure and build
./configure && make -s && make check
6) Add/update sample.pcap files
We use tests directory to do regression tests on the dissection of captured
packets, by running tcpdump against a savefile sample.pcap, created with -w
option and comparing the results with a text file sample.out giving the
expected results.
Any new/updated fields in a dissector must be present in a sample.pcap file
and the corresponding output file.
Configuration is set in tests/TESTLIST.
Each line in this file has the following format:
test-name sample.pcap sample.out tcpdump-options
the sample.out file can be build by:
(cd tests && ../tcpdump -n -r sample.pcap tcpdump-options > sample.out)
It is often useful to have test outputs with different verbosity levels
(none, -v, -vv, -vvv, etc.) depending on the code.
7) Test with 'make check'
Don't send a pull request if 'make check' gives failed tests.
8) Rebase your commits against upstream/master
(To keep linearity)
9) Initiate and send a pull request
(See https://help.github.com/articles/using-pull-requests/)
Some remarks
------------
a) A thorough reading of some other printers code is useful.
b) Put the normative reference if any as comments (RFC, etc.).
c) Put the format of packets/headers/options as comments.
d) The printer may receive incomplete packet in the buffer, truncated at any
random position, for example by capturing with '-s size' option.
Thus use ND_TTEST, ND_TTEST2, ND_TCHECK or ND_TCHECK2 for bound checking.
For ND_TCHECK2:
Define : static const char tstr[] = " [|protocol]";
Define a label: trunc
Print with: ND_PRINT((ndo, "%s", tstr));
You can test the code via:
sudo ./tcpdump -s snaplen [-v][v][...] -i lo # in a terminal
sudo tcpreplay -i lo sample.pcap # in another terminal
You should try several values for snaplen to do various truncation.
e) Do invalid packet checks in code: Think that your code can receive in input
not only a valid packet but any arbitrary random sequence of octets (packet
- built malformed originally by the sender or by a fuzz tester,
- became corrupted in transit).
Print with: ND_PRINT((ndo, "%s", istr)); /* to print " (invalid)" */
f) Use 'struct tok' for indexed strings and print them with
tok2str() or bittok2str() (for flags).
g) Avoid empty lines in output of printers.
h) A commit message must have:
First line: Capitalized short summary in the imperative (70 chars or less)
Body: Detailed explanatory text, if necessary. Fold it to approximately
72 characters. There must be an empty line separating the summary from
the body.
i) Avoid non-ASCII characters in code and commit messages.
j) Use the style of the modified sources.
k) Don't mix declarations and code
l) Don't use // for comments
Not all C compilers accept C++/C99 comments by default.
m) Avoid trailing tabs/spaces
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