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Convert HACKING file to asciidoc: I am tired of re-numbering the sections.

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Nick Mathewson 2010-04-16 12:58:13 -04:00
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doc/HACKING
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@ -1,20 +1,27 @@
Hacking Tor: An Incomplete Guide
================================
0. Useful tools.
0.0 The buildbot.
Useful tools
------------
The buildbot
~~~~~~~~~~~~
https://buildbot.vidalia-project.net/one_line_per_build
0.1. Useful command-lines that are non-trivial to reproduce but can
help with tracking bugs or leaks.
Useful command-lines
~~~~~~~~~~~~~~~~~~~~
0.1.1. Dmalloc
Dmalloc
^^^^^^^
dmalloc -l ~/dmalloc.log
(run the commands it tells you)
./configure --with-dmalloc
0.2.2. Valgrind
Valgrind
^^^^^^^^
valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor
@ -22,25 +29,31 @@ valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor
pass --undef-value-errors=no to valgrind, or rebuild your openssl
with -DPURIFY.)
0.2. Running gcov for unit test coverage
Running gcov for unit test coverage
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-----
make clean
make CFLAGS='-g -fprofile-arcs -ftest-coverage'
./src/test/test
cd src/common; gcov *.[ch]
cd ../or; gcov *.[ch]
-----
Then, look at the .gcov files. '-' before a line means that the
compiler generated no code for that line. '######' means that the
line was never reached. Lines with numbers were called that number
of times.
1. Coding conventions
Coding conventions
------------------
1.0. Whitespace and C conformance
Whitespace and C conformance
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Invoke "make check-spaces" from time to time, so it can tell you about
deviations from our C whitespace style. Generally, we use:
- Unix-style line endings
- K&R-style indentation
- No space before newlines
@ -62,10 +75,13 @@ valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor
"--enable-gcc-warnings". This will give a bunch of extra warning flags to
the compiler, and help us find divergences from our preferred C style.
1.0.1. Getting emacs to edit Tor source properly.
Getting emacs to edit Tor source properly
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Hi, folks! Nick here. I like to put the following snippet in my .emacs
file:
-----
(add-hook 'c-mode-hook
(lambda ()
(font-lock-mode 1)
@ -85,28 +101,32 @@ valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor
(set-variable 'c-basic-offset 8)
(set-variable 'tab-width 8))
))))
-----
You'll note that it defaults to showing all trailing whitespace. The
"cond" test detects whether the file is one of a few C free software
projects that I often edit, and sets up the indentation level and tab
preferences to match what they want.
You'll note that it defaults to showing all trailing whitespace. The "cond"
test detects whether the file is one of a few C free software projects that I
often edit, and sets up the indentation level and tab preferences to match
what they want.
If you want to try this out, you'll need to change the filename regex
patterns to match where you keep your Tor files.
If you *only* use emacs to edit Tor, you could always just say:
-----
(add-hook 'c-mode-hook
(lambda ()
(font-lock-mode 1)
(set-variable 'show-trailing-whitespace t)
(set-variable 'indent-tabs-mode nil)
(set-variable 'c-basic-offset 2)))
-----
There is probably a better way to do this. No, we are probably not going
to clutter the files with emacs stuff.
1.1. Details
Details
~~~~~~~
Use tor_malloc, tor_free, tor_strdup, and tor_gettimeofday instead of their
generic equivalents. (They always succeed or exit.)
@ -114,12 +134,13 @@ valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor
You can get a full list of the compatibility functions that Tor provides by
looking through src/common/util.h and src/common/compat.h. You can see the
available containers in src/common/containers.h. You should probably
familiarize yourself with these modules before you write too much code,
or else you'll wind up reinventing the wheel.
familiarize yourself with these modules before you write too much code, or
else you'll wind up reinventing the wheel.
Use 'INLINE' instead of 'inline', so that we work properly on Windows.
1.2. Calling and naming conventions
Calling and naming conventions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Whenever possible, functions should return -1 on error and 0 on success.
@ -130,8 +151,8 @@ valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor
Typenames should end with "_t".
Function names should be prefixed with a module name or object name. (In
general, code to manipulate an object should be a module with the same
name as the object, so it's hard to tell which convention is used.)
general, code to manipulate an object should be a module with the same name
as the object, so it's hard to tell which convention is used.)
Functions that do things should have imperative-verb names
(e.g. buffer_clear, buffer_resize); functions that return booleans should
@ -139,33 +160,35 @@ valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor
If you find that you have four or more possible return code values, it's
probably time to create an enum. If you find that you are passing three or
more flags to a function, it's probably time to create a flags argument
that takes a bitfield.
more flags to a function, it's probably time to create a flags argument that
takes a bitfield.
1.3. What To Optimize
What To Optimize
~~~~~~~~~~~~~~~~
Don't optimize anything if it's not in the critical path. Right now,
the critical path seems to be AES, logging, and the network itself.
Feel free to do your own profiling to determine otherwise.
Don't optimize anything if it's not in the critical path. Right now, the
critical path seems to be AES, logging, and the network itself. Feel free to
do your own profiling to determine otherwise.
1.4. Log conventions
Log conventions
~~~~~~~~~~~~~~~
https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#LogLevels
No error or warning messages should be expected during normal OR or OP
operation.
If a library function is currently called such that failure always
means ERR, then the library function should log WARN and let the caller
log ERR.
If a library function is currently called such that failure always means ERR,
then the library function should log WARN and let the caller log ERR.
[XXX Proposed convention: every message of severity INFO or higher should
either (A) be intelligible to end-users who don't know the Tor source; or
(B) somehow inform the end-users that they aren't expected to understand
the message (perhaps with a string like "internal error"). Option (A) is
to be preferred to option (B). -NM]
either (A) be intelligible to end-users who don't know the Tor source; or (B)
somehow inform the end-users that they aren't expected to understand the
message (perhaps with a string like "internal error"). Option (A) is to be
preferred to option (B). -NM]
1.5. Doxygen
Doxygen
~~~~~~~~
We use the 'doxygen' utility to generate documentation from our
source code. Here's how to use it:
@ -219,11 +242,12 @@ valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor
6. See the Doxygen manual for more information; this summary just
scratches the surface.
1.5.1. Doxygen comment conventions
Doxygen comment conventions
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Say what functions do as a series of one or more imperative sentences, as
though you were telling somebody how to be the function. In other words,
DO NOT say:
though you were telling somebody how to be the function. In other words, DO
NOT say:
/** The strtol function parses a number.
*
@ -246,64 +270,8 @@ valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor
Doxygen comments are the contract in our abstraction-by-contract world: if
the functions that call your function rely on it doing something, then your
function should mention that it does that something in the documentation.
If you rely on a function doing something beyond what is in its
documentation, then you should watch out, or it might do something else
later.
2. Code notes
2.1. Dataflows
2.1.1. How Incoming data is handled
There are two paths for data arriving at Tor over the network: regular
TCP data, and DNS.
2.1.1.1. TCP.
When Tor takes information over the network, it uses the functions
read_to_buf() and read_to_buf_tls() in buffers.c. These read from a
socket or an SSL* into a buffer_t, which is an mbuf-style linkedlist
of memory chunks.
read_to_buf() and read_to_buf_tls() are called only from
connection_read_to_buf() in connection.c. It takes a connection_t
pointer, and reads data into it over the network, up to the
connection's current bandwidth limits. It places that data into the
"inbuf" field of the connection, and then:
- Adjusts the connection's want-to-read/want-to-write status as
appropriate.
- Increments the read and written counts for the connection as
appropriate.
- Adjusts bandwidth buckets as appropriate.
connection_read_to_buf() is called only from connection_handle_read().
The connection_handle_read() function is called whenever libevent
decides (based on select, poll, epoll, kqueue, etc) that there is data
to read from a connection. If any data is read,
connection_handle_read() calls connection_process_inbuf() to see if
any of the data can be processed. If the connection was closed,
connection_handle_read() calls connection_reached_eof().
Connection_process_inbuf() and connection_reached_eof() both dispatch
based on the connection type to determine what to do with the data
that's just arrived on the connection's inbuf field. Each type of
connection has its own version of these functions. For example,
directory connections process incoming data in
connection_dir_process_inbuf(), while OR connections process incoming
data in connection_or_process_inbuf(). These
connection_*_process_inbuf() functions extract data from the
connection's inbuf field (a buffer_t), using functions from buffers.c.
Some of these accessor functions are straightforward data extractors
(like fetch_from_buf()); others do protocol-specific parsing.
function should mention that it does that something in the documentation. If
you rely on a function doing something beyond what is in its documentation,
then you should watch out, or it might do something else later.
2.1.1.2. DNS
Tor launches (and optionally accepts) DNS requests using the code in
eventdns.c, which is a copy of libevent's evdns.c. (We don't use
libevent's version because it is not yet in the versions of libevent
all our users have.) DNS replies are read in nameserver_read();
DNS queries are read in server_port_read().