0. Useful tools. 0.0 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. 0.1.1. Dmalloc dmalloc -l ~/dmalloc.log (run the commands it tells you) ./configure --with-dmalloc 0.2.2. Valgrind valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor (Note that if you get a zillion openssl warnings, you will also need to pass --undef-value-errors=no to valgrind, or rebuild your openssl with -DPURIFY.) 0.2. 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 1.0. 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 - A blank line at the end of each file - Never more than one blank line in a row - Always spaces, never tabs - No more than 79-columns per line. - Two spaces per indent. - A space between control keywords and their corresponding paren "if (x)", "while (x)", and "switch (x)", never "if(x)", "while(x)", or "switch(x)". - A space between anything and an open brace. - No space between a function name and an opening paren. "puts(x)", not "puts (x)". - Function declarations at the start of the line. We try hard to build without warnings everywhere. In particular, if you're using gcc, you should invoke the configure script with the option "--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. 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) (set-variable 'show-trailing-whitespace t) (let ((fname (expand-file-name (buffer-file-name)))) (cond ((string-match "^/home/nickm/src/libevent" fname) (set-variable 'indent-tabs-mode t) (set-variable 'c-basic-offset 4) (set-variable 'tab-width 4)) ((string-match "^/home/nickm/src/tor" fname) (set-variable 'indent-tabs-mode nil) (set-variable 'c-basic-offset 2)) ((string-match "^/home/nickm/src/openssl" fname) (set-variable 'indent-tabs-mode t) (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. 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 Use tor_malloc, tor_free, tor_strdup, and tor_gettimeofday instead of their generic equivalents. (They always succeed or exit.) 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. Use 'INLINE' instead of 'inline', so that we work properly on Windows. 1.2. Calling and naming conventions Whenever possible, functions should return -1 on error and 0 on success. For multi-word identifiers, use lowercase words combined with underscores. (e.g., "multi_word_identifier"). Use ALL_CAPS for macros and constants. 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.) Functions that do things should have imperative-verb names (e.g. buffer_clear, buffer_resize); functions that return booleans should have predicate names (e.g. buffer_is_empty, buffer_needs_resizing). 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. 1.3. 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. 1.4. 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. [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] 1.5. Doxygen We use the 'doxygen' utility to generate documentation from our source code. Here's how to use it: 1. Begin every file that should be documented with /** * \file filename.c * \brief Short description of the file. **/ (Doxygen will recognize any comment beginning with /** as special.) 2. Before any function, structure, #define, or variable you want to document, add a comment of the form: /** Describe the function's actions in imperative sentences. * * Use blank lines for paragraph breaks * - and * - hyphens * - for * - lists. * * Write argument_names in boldface. * * \code * place_example_code(); * between_code_and_endcode_commands(); * \endcode */ 3. Make sure to escape the characters "<", ">", "\", "%" and "#" as "\<", "\>", "\\", "\%", and "\#". 4. To document structure members, you can use two forms: struct foo { /** You can put the comment before an element; */ int a; int b; /**< Or use the less-than symbol to put the comment * after the element. */ }; 5. To generate documentation from the Tor source code, type: $ doxygen -g To generate a file called 'Doxyfile'. Edit that file and run 'doxygen' to generate the API documentation. 6. See the Doxygen manual for more information; this summary just scratches the surface. 1.5.1. 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: /** The strtol function parses a number. * * nptr -- the string to parse. It can include whitespace. * endptr -- a string pointer to hold the first thing that is not part * of the number, if present. * base -- the numeric base. * returns: the resulting number. */ long strtol(const char *nptr, char **nptr, int base); Instead, please DO say: /** Parse a number in radix base from the string nptr, * and return the result. Skip all leading whitespace. If * endptr is not NULL, set *endptr to the first character * after the number parsed. **/ long strtol(const char *nptr, char **nptr, int base); 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. 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().