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+
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+TODO: revise this to talk about how things are, rather than how things
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+have changed.
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+
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+TODO: Make this into good markdown.
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+
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+
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+
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+For quite a while now, the program "tor" has been built from source
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+code in just two directories: src/common and src/or.
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+
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+This has become more-or-less untenable, for a few reasons -- most
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+notably of which is that it has led our code to become more
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+spaghetti-ish than I can endorse with a clean conscience.
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+
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+So to fix that, we've gone and done a huge code movement in our git
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+master branch, which will land in a release once Tor 0.3.5.1-alpha is
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+out.
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+
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+Here's what we did:
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+
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+ * src/common has been turned into a set of static libraries. These
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+all live in the "src/lib/*" directories. The dependencies between
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+these libraries should have no cycles. The libraries are:
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+
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+ arch -- Headers to handle architectural differences
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+ cc -- headers to handle differences among compilers
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+ compress -- wraps zlib, zstd, lzma
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+ container -- high-level container types
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+ crypt_ops -- Cryptographic operations. Planning to split this into
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+a higher and lower level library
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+ ctime -- Operations that need to run in constant-time. (Properly,
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+data-invariant time)
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+ defs -- miscelaneous definitions needed throughout Tor.
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+ encoding -- transforming one data type into another, and various
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+data types into strings.
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+ err -- lowest-level error handling, in cases where we can't use
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+the logs because something that the logging system needs has broken.
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+ evloop -- Generic event-loop handling logic
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+ fdio -- Low-level IO wrapper functions for file descriptors.
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+ fs -- Operations on the filesystem
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+ intmath -- low-level integer math and misc bit-twiddling hacks
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+ lock -- low-level locking code
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+ log -- Tor's logging module. This library sits roughly halfway up
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+the library dependency diagram, since everything it depends on has to
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+be carefully crafted to *not* log.
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+ malloc -- Low-level wrappers for the platform memory allocation functions.
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+ math -- Higher-level mathematical functions, and floating-point math
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+ memarea -- An arena allocator
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+ meminfo -- Functions for querying the current process's memory
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+status and resources
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+ net -- Networking compatibility and convenience code
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+ osinfo -- Querying information about the operating system
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+ process -- Launching and querying the status of other processes
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+ sandbox -- Backend for the linux seccomp2 sandbox
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+ smartlist_core -- The lowest-level of the smartlist_t data type.
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+Separated from the rest of the containers library because the logging
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+subsystem depends on it.
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+ string -- Compatibility and convenience functions for manipulating
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+C strings.
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+ term -- Terminal-related functions (currently limited to a getpass
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+function).
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+ testsupport -- Macros for mocking, unit tests, etc.
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+ thread -- Higher-level thread compatibility code
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+ time -- Higher-level time management code, including format
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+conversions and monotonic time
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+ tls -- Our wrapper around our TLS library
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+ trace -- Formerly src/trace -- a generic event tracing API
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+ wallclock -- Low-level time code, used by the log module.
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+
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+ * To ensure that the dependency graph in src/common remains under
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+control, there is a tool that you can run called "make
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+check-includes". It verifies that each module in Tor only includes
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+the headers that it is permitted to include, using a per-directory
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+".may_include" file.
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+
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+ * The src/or/or.h header has been split into numerous smaller
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+headers. Notably, many important structures are now declared in a
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+header called foo_st.h, where "foo" is the name of the structure.
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+
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+ * The src/or directory, which had most of Tor's code, had been split
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+up into several directories. This is still a work in progress: This
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+code has not itself been refactored, and its dependency graph is still
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+a tangled web. I hope we'll be working on that over the coming
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+releases, but it will take a while to do.
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+
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+ The new top-level source directories are:
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+
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+ src/core -- Code necessary to actually perform or use onion routing.
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+ src/feature -- Code used only by some onion routing
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+configurations, or only for a special purpose.
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+ src/app -- Top-level code to run, invoke, and configure the
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+lower-level code
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+
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+ The new second-level source directories are:
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+ src/core/crypto -- High-level cryptographic protocols used in Tor
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+ src/core/mainloop -- Tor's event loop, connection-handling, and
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+traffic-routing code.
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+ src/core/or -- Parts related to handling onion routing itself
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+ src/core/proto -- support for encoding and decoding different
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+wire protocols
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+
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+ src/feature/api -- Support for making Tor embeddable
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+ src/feature/client -- Functionality which only Tor clients need
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+ src/feature/control -- Controller implementation
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+ src/feature/dirauth -- Directory authority
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+ src/feature/dircache -- Directory cache
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+ src/feature/dirclient -- Directory client
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+ src/feature/dircommon -- Shared code between the other directory modules
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+ src/feature/hibernate -- Hibernating when Tor is out of bandwidth
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+or shutting down
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+ src/feature/hs -- v3 onion service implementation
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+ src/feature/hs_common -- shared code between both onion service
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+implementations
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+ src/feature/nodelist -- storing and accessing the list of relays on
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+the network.
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+ src/feature/relay -- code that only relay servers and exit servers need.
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+ src/feature/rend -- v2 onion service implementation
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+ src/feature/stats -- statistics and history
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+
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+ src/app/config -- configuration and state for Tor
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+ src/app/main -- Top-level functions to invoke the rest or Tor.
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+
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+ * The "tor" executable is now built in src/app/tor rather than src/or/tor.
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+
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+ * There are more static libraries than before that you need to build
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+into your application if you want to embed Tor. Rather than
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+maintaining this list yourself, I recommend that you run "make
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+show-libs" to have Tor emit a list of what you need to link.
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Nick Mathewson