[tor-announce] Tor is released! (Also,, and

Nick Mathewson nickm at torproject.org
Mon Sep 10 20:36:01 UTC 2018

Hello, everyone!

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After months of work, Tor is now available! This is the first
stable release in the 0.3.4 series, and we hope you find it useful.

You can download the source code from the usual place on the website's
download page, under "source code". Packages should be available
within the next several weeks, with a new Tor Browser by some time
next week.

Also today we are releasing updates for our other supported stable
series: Tor, Tor, and Tor  You can
download the source code for older supported releases from
https://dist.torproject.org/. Their changelogs are available at:


Below is the list of changes in Tor since  For a list
of only those changes made since, see the

Changes in version - 2018-09-10
  Tor is the first stable release in its series; it includes
  compilation and portability fixes.

  The Tor 0.3.4 series includes improvements for running Tor in
  low-power and embedded environments, which should help performance in
  general. We've begun work on better modularity, and included preliminary
  changes on the directory authority side to accommodate a new bandwidth
  measurement system.  We've also integrated more continuous-integration
  systems into our development process, and made corresponding changes to
  Tor's testing infrastructure.  Finally, we've continued to refine
  our anti-denial-of-service code.

  Below are the changes since For a list of only the changes
  since, see the ChangeLog file.

  o New system requirements:
    - Tor no longer tries to support old operating systems without
      mmap() or some local equivalent. Apparently, compilation on such
      systems has been broken for some time, without anybody noticing or
      complaining. Closes ticket 25398.

  o Major features (directory authority, modularization):
    - The directory authority subsystem has been modularized. The code
      is now located in src/or/dirauth/, and is compiled in by default.
      To disable the module, the configure option
      --disable-module-dirauth has been added. This module may be
      disabled by default in some future release. Closes ticket 25610.

  o Major features (main loop, CPU usage):
    - When Tor is disabled (via DisableNetwork or via hibernation), it
      no longer needs to run any per-second events. This change should
      make it easier for mobile applications to disable Tor while the
      device is sleeping, or Tor is not running. Closes ticket 26063.
    - Tor no longer enables all of its periodic events by default.
      Previously, Tor would enable all possible main loop events,
      regardless of whether it needed them. Furthermore, many of these
      events are now disabled when Tor is hibernating or DisableNetwork
      is set. This is a big step towards reducing client CPU usage by
      reducing the amount of wake-ups the daemon does. Closes tickets
      25376 and 25762.
    - The bandwidth-limitation logic has been refactored so that
      bandwidth calculations are performed on-demand, rather than every
      TokenBucketRefillInterval milliseconds. This change should improve
      the granularity of our bandwidth calculations, and limit the
      number of times that the Tor process needs to wake up when it is
      idle. Closes ticket 25373.
    - Move responsibility for many operations from a once-per-second
      callback to a callback that is only scheduled as needed. Moving
      this functionality has allowed us to disable the callback when
      Tor's network is disabled. Once enough items are removed from our
      once-per-second callback, we can eliminate it entirely to conserve
      CPU when idle. The functionality removed includes: closing
      connections, circuits, and channels (ticket 25932); consensus
      voting (25937); flushing log callbacks (25951); honoring delayed
      SIGNEWNYM requests (25949); rescanning the consensus cache
      (25931); saving the state file to disk (25948); warning relay
      operators about unreachable ports (25952); and keeping track of
      Tor's uptime (26009).

  o Minor features (accounting):
    - When Tor becomes dormant, it now uses a scheduled event to wake up
      at the right time. Previously, we would use the per-second timer
      to check whether to wake up, but we no longer have any per-second
      timers enabled when the network is disabled. Closes ticket 26064.

  o Minor features (bug workaround):
    - Compile correctly on systems that provide the C11 stdatomic.h
      header, but where C11 atomic functions don't actually compile.
      Closes ticket 26779; workaround for Debian issue 903709.

  o Minor features (code quality):
    - Add optional spell-checking for the Tor codebase, using the
      "misspell" program. To use this feature, run "make check-typos".
      Closes ticket 25024.

  o Minor features (compatibility):
    - Tell OpenSSL to maintain backward compatibility with previous
      RSA1024/DH1024 users in Tor. With OpenSSL 1.1.1-pre6, these
      ciphers are disabled by default. Closes ticket 27344.
    - Tor now detects versions of OpenSSL 1.1.0 and later compiled with
      the no-deprecated option, and builds correctly with them. Closes
      tickets 19429, 19981, and 25353.

  o Minor features (compilation):
    - When compiling with --enable-openbsd-malloc or --enable-tcmalloc,
      tell the compiler not to include the system malloc implementation.
      Fixes bug 20424; bugfix on
    - Don't try to use a pragma to temporarily disable the
      -Wunused-const-variable warning if the compiler doesn't support
      it. Fixes bug 26785; bugfix on
    - When building Tor, prefer to use Python 3 over Python 2, and more
      recent (contemplated) versions over older ones. Closes
      ticket 26372.

  o Minor features (compression, zstd):
    - When running with zstd, Tor now considers using advanced functions
      that the zstd maintainers have labeled as potentially unstable. To
      prevent breakage, Tor will only use this functionality when the
      runtime version of the zstd library matches the version with which
      Tor was compiled. Closes ticket 25162.

  o Minor features (configuration):
    - The "DownloadSchedule" options have been renamed to end with
      "DownloadInitialDelay". The old names are still allowed, but will
      produce a warning. Comma-separated lists are still permitted for
      these options, but all values after the first are ignored (as they
      have been since 0.2.9). Closes ticket 23354.

  o Minor features (continuous integration):
    - Log the compiler path and version during Appveyor builds.
      Implements ticket 27449.
    - Show config.log and test-suite.log after failed Appveyor builds.
      Also upload the zipped full logs as a build artifact. Implements
      ticket 27430.
    - Backport Travis rust distcheck to 0.3.3. Closes ticket 24629.
    - Enable macOS builds in our Travis CI configuration. Closes
      ticket 24629.
    - Install libcap-dev and libseccomp2-dev so these optional
      dependencies get tested on Travis CI. Closes ticket 26560.
    - Only post Appveyor IRC notifications when the build fails.
      Implements ticket 27275.
    - Run asciidoc during Travis CI. Implements ticket 27087.
    - Use ccache in our Travis CI configuration. Closes ticket 26952.
    - Add the necessary configuration files for continuous integration
      testing on Windows, via the Appveyor platform. Closes ticket
      25549. Patches from Marcin Cieślak and Isis Lovecruft.

  o Minor features (continuous integration, rust):
    - Use cargo cache in our Travis CI configuration. Closes
      ticket 26952.

  o Minor features (control port):
    - Introduce GETINFO "current-time/{local,utc}" to return the local
      and UTC times respectively in ISO format. This helps a controller
      like Tor Browser detect a time-related error. Closes ticket 25511.
      Patch by Neel Chauhan.
    - Introduce new fields to the CIRC_BW event. There are two new
      fields in each of the read and written directions. The DELIVERED
      fields report the total valid data on the circuit, as measured by
      the payload sizes of verified and error-checked relay command
      cells. The OVERHEAD fields report the total unused bytes in each
      of these cells. Closes ticket 25903.

  o Minor features (controller):
    - The control port now exposes the list of HTTPTunnelPorts and
      ExtOrPorts via GETINFO net/listeners/httptunnel and
      net/listeners/extor respectively. Closes ticket 26647.

  o Minor features (directory authorities):
    - Stop warning about incomplete bw lines before the first complete
      bw line has been found, so that additional header lines can be
      ignored. Fixes bug 25960; bugfix on
    - Authorities no longer vote to make the subprotocol version
      "LinkAuth=1" a requirement: it is unsupportable with NSS, and
      hasn't been needed since Tor Closes ticket 27286.

  o Minor features (directory authority):
    - Directory authorities now open their key-pinning files as O_SYNC,
      to limit their chances of accidentally writing partial lines.
      Closes ticket 23909.

  o Minor features (directory authority, forward compatibility):
    - Make the lines of the measured bandwidth file able to contain
      their entries in any order. Previously, the node_id entry needed
      to come first. Closes ticket 26004.

  o Minor features (entry guards):
    - Introduce a new torrc option NumPrimaryGuards for controlling the
      number of primary guards. Closes ticket 25843.

  o Minor features (geoip):
    - Update geoip and geoip6 to the August 7 2018 Maxmind GeoLite2
      Country database. Closes ticket 27089.

  o Minor features (performance):
    - Avoid a needless call to malloc() when processing an incoming
      relay cell. Closes ticket 24914.
    - Make our timing-wheel code run a tiny bit faster on 32-bit
      platforms, by preferring 32-bit math to 64-bit. Closes
      ticket 24688.
    - Avoid a needless malloc()/free() pair every time we handle an ntor
      handshake. Closes ticket 25150.

  o Minor features (Rust, portability):
    - Rust cross-compilation is now supported. Closes ticket 25895.

  o Minor features (testing):
    - Add a unit test for voting_schedule_get_start_of_next_interval().
      Closes ticket 26014, and helps make unit test coverage
      more deterministic.
    - A new unittests module specifically for testing the functions in
      the (new-ish) bridges.c module has been created with new
      unittests, raising the code coverage percentages. Closes 25425.
    - We now have improved testing for addressmap_get_virtual_address()
      function. This should improve our test coverage, and make our test
      coverage more deterministic. Closes ticket 25993.

  o Minor features (timekeeping, circuit scheduling):
    - When keeping track of how busy each circuit have been recently on
      a given connection, use coarse-grained monotonic timers rather
      than gettimeofday(). This change should marginally increase
      accuracy and performance. Implements part of ticket 25927.

  o Minor features (unit tests):
    - Test complete bandwidth measurements files, and test that
      incomplete bandwidth lines only give warnings when the end of the
      header has not been detected. Fixes bug 25947; bugfix

  o Minor bugfixes (bandwidth management):
    - Consider ourselves "low on write bandwidth" if we have exhausted
      our write bandwidth some time in the last second. This was the
      documented behavior before, but the actual behavior was to change
      this value every TokenBucketRefillInterval. Fixes bug 25828;
      bugfix on

  o Minor bugfixes (C correctness):
    - Add a missing lock acquisition in the shutdown code of the control
      subsystem. Fixes bug 25675; bugfix on Found by
      Coverity; this is CID 1433643.

  o Minor bugfixes (code style):
    - Fixed multiple includes of transports.h in src/or/connection.c
      Fixes bug 25261; bugfix on
    - Remove the unused variable n_possible from the function
      channel_get_for_extend(). Fixes bug 25645; bugfix on

  o Minor bugfixes (compilation):
    - Silence a spurious compiler warning on the GetAdaptersAddresses
      function pointer cast. This issue is already fixed by 26481 in
      0.3.5 and later, by removing the lookup and cast. Fixes bug 27465;
      bugfix on
    - Stop calling SetProcessDEPPolicy() on 64-bit Windows. It is not
      supported, and always fails. Some compilers warn about the
      function pointer cast on 64-bit Windows. Fixes bug 27461; bugfix
    - Fix a compilation warning on some versions of GCC when building
      code that calls routerinfo_get_my_routerinfo() twice, assuming
      that the second call will succeed if the first one did. Fixes bug
      26269; bugfix on
    - Refrain from compiling unit testing related object files when
      --disable-unittests is set to configure script. Fixes bug 24891;
      bugfix on
    - The --enable-fatal-warnings flag now affects Rust code as well.
      Closes ticket 26245.
    - Avoid a compiler warning when casting the return value of
      smartlist_len() to double with DEBUG_SMARTLIST enabled. Fixes bug
      26283; bugfix on

  o Minor bugfixes (compilation, windows):
    - Don't link or search for pthreads when building for Windows, even
      if we are using build environment (like mingw) that provides a
      pthreads library. Fixes bug 27081; bugfix on

  o Minor bugfixes (continuous integration):
    - Build with zstd on macOS. Fixes bug 27090; bugfix on
    - Skip a pair of unreliable key generation tests on Windows, until
      the underlying issue in bug 26076 is resolved. Fixes bug 26830 and
      bug 26853; bugfix on and respectively.

  o Minor bugfixes (control port):
    - Respond with more human-readable error messages to GETINFO exit-
      policy/* requests. Also, let controller know if an error is
      transient (response code 551) or not (response code 552). Fixes
      bug 25852; bugfix on
    - Parse the "HSADDRESS=" parameter in HSPOST commands properly.
      Previously, it was misparsed and ignored. Fixes bug 26523; bugfix
      on Patch by "akwizgran".
    - Make CIRC_BW event reflect the total of all data sent on a
      circuit, including padding and dropped cells. Also fix a mis-
      counting bug when STREAM_BW events were enabled. Fixes bug 25400;
      bugfix on

  o Minor bugfixes (correctness, flow control):
    - Upon receiving a stream-level SENDME cell, verify that our window
      has not grown too large. Fixes bug 26214; bugfix on svn
      r54 (pre-0.0.1)

  o Minor bugfixes (directory authority):
    - When voting for recommended versions, make sure that all of the
      versions are well-formed and parsable. Fixes bug 26485; bugfix

  o Minor bugfixes (directory client):
    - When unverified-consensus is verified, rename it to cached-
      consenus. Fixes bug 4187; bugfix on
    - Fixed launching a certificate fetch always during the scheduled
      periodic consensus fetch by fetching only in those cases when
      consensus are waiting for certs. Fixes bug 24740; bugfix

  o Minor bugfixes (error reporting):
    - Improve tolerance for directory authorities with skewed clocks.
      Previously, an authority with a clock more than 60 seconds ahead
      could cause a client with a correct clock to warn that the
      client's clock was behind. Now the clocks of a majority of
      directory authorities have to be ahead of the client before this
      warning will occur. Fixes bug 25756; bugfix on

  o Minor bugfixes (in-process restart):
    - Always call tor_free_all() when leaving tor_run_main(). When we
      did not, restarting tor in-process would cause an assertion
      failure. Fixes bug 26948; bugfix on

  o Minor bugfixes (Linux seccomp2 sandbox):
    - Fix a bug in our sandboxing rules for the openat() syscall.
      Previously, no openat() call would be permitted, which would break
      filesystem operations on recent glibc versions. Fixes bug 25440;
      bugfix on Diagnosis and patch from Daniel Pinto.

  o Minor bugfixes (logging):
    - Improve the log message when connection initiators fail to
      authenticate direct connections to relays. Fixes bug 26927; bugfix

  o Minor bugfixes (onion services):
    - Silence a spurious compiler warning in
      rend_client_send_introduction(). Fixes bug 27463; bugfix
    - Fix bug that causes services to not ever rotate their descriptors
      if they were getting SIGHUPed often. Fixes bug 26932; bugfix
    - Recompute some consensus information after detecting a clock jump,
      or after transitioning from a non-live consensus to a live
      consensus. We do this to avoid having an outdated state, and
      miscalculating the index for next-generation onion services. Fixes
      bug 24977; bugfix on

  o Minor bugfixes (portability):
    - Fix compilation of the unit tests on GNU/Hurd, which does not
      define PATH_MAX. Fixes bug 26873; bugfix on Patch
      from "paulusASol".
    - Work around two different bugs in the OS X 10.10 and later SDKs
      that would prevent us from successfully targeting earlier versions
      of OS X. Fixes bug 26876; bugfix on
    - Do not align mmap length, as it is not required by POSIX, and the
      getpagesize function is deprecated. Fixes bug 25399; bugfix

  o Minor bugfixes (portability, FreeBSD):
    - In have_enough_mem_for_dircache(), the variable DIRCACHE_MIN_MEM_MB
      does not stringify on FreeBSD, so we switch to tor_asprintf().
      Fixes bug 20887; bugfix on Patch by Neel Chauhan.

  o Minor bugfixes (relay statistics):
    - When a relay is collecting internal statistics about how many
      create cell requests it has seen of each type, accurately count
      the requests from relays that temporarily fall out of the
      consensus. (To be extra conservative, we were already ignoring
      requests from clients in our counts, and we continue ignoring them
      here.) Fixes bug 24910; bugfix on

  o Minor bugfixes (rust):
    - Backport test_rust.sh from master. Fixes bug 26497; bugfix
    - Protover parsing was accepting the presence of whitespace in
      version strings, which the C implementation would choke on, e.g.
      "Desc=1\t,2". Fixes bug 27177; bugfix on
    - Protover parsing was ignoring a 2nd hyphen and everything after
      it, accepting entries like "Link=1-5-foo". Fixes bug 27164; bugfix
    - Stop setting $CARGO_HOME. cargo will use the user's $CARGO_HOME, or
      $HOME/.cargo by default. Fixes bug 26497; bugfix on
    - cd to ${abs_top_builddir}/src/rust before running cargo in
      src/test/test_rust.sh. This makes the working directory consistent
      between builds and tests. Fixes bug 26497; bugfix on

  o Minor bugfixes (single onion services, Tor2web):
    - Log a protocol warning when single onion services or Tor2web
      clients fail to authenticate direct connections to relays. Fixes
      bug 26924; bugfix on

  o Minor bugfixes (test coverage tools):
    - Update our "cov-diff" script to handle output from the latest
      version of gcov, and to remove extraneous timestamp information
      from its output. Fixes bugs 26101 and 26102; bugfix

  o Minor bugfixes (testing):
    - Disable core dumps in test_bt.sh, to avoid failures in "make
      distcheck". Fixes bug 26787; bugfix on
    - When testing workqueue event-cancellation, make sure that we
      actually cancel an event, and that cancel each event with equal
      probability. (It was previously possible, though extremely
      unlikely, for our event-canceling test not to cancel any events.)
      Fixes bug 26008; bugfix on
    - Repeat part of the test in test_client_pick_intro() a number of
      times, to give it consistent coverage. Fixes bug 25996; bugfix
    - Remove randomness from the hs_common/responsible_hsdirs test, so
      that it always takes the same path through the function it tests.
      Fixes bug 25997; bugfix on
    - Change the behavior of the "channel/outbound" test so that it
      never causes a 10-second rollover for the EWMA circuitmux code.
      Previously, this behavior would happen randomly, and result in
      fluctuating test coverage. Fixes bug 25994; bugfix
    - Use X509_new() to allocate certificates that will be freed later
      with X509_free(). Previously, some parts of the unit tests had
      used tor_malloc_zero(), which is incorrect, and which caused test
      failures on Windows when they were built with extra hardening.
      Fixes bugs 25943 and 25944; bugfix on Patch by
      Marcin Cieślak.
    - While running the circuit_timeout test, fix the PRNG to a
      deterministic AES stream, so that the test coverage from this test
      will itself be deterministic. Fixes bug 25995; bugfix

  o Minor bugfixes (testing, bootstrap):
    - When calculating bootstrap progress, check exit policies and the
      exit flag. Previously, Tor would only check the exit flag, which
      caused race conditions in small and fast networks like chutney.
      Fixes bug 27236; bugfix on

  o Minor bugfixes (testing, chutney):
    - When running make test-network-all, use the mixed+hs-v2 network.
      (A previous fix to chutney removed v3 onion services from the
      mixed+hs-v23 network, so seeing "mixed+hs-v23" in tests is
      confusing.) Fixes bug 27345; bugfix on
    - Before running make test-network-all, delete old logs and test
      result files, to avoid spurious failures. Fixes bug 27295; bugfix

  o Minor bugfixes (testing, openssl compatibility):
    - Our "tortls/cert_matches_key" unit test no longer relies on
      OpenSSL internals. Previously, it relied on unsupported OpenSSL
      behavior in a way that caused it to crash with OpenSSL 1.0.2p.
      Fixes bug 27226; bugfix on

  o Minor bugfixes (v3 onion services):
    - Stop sending ed25519 link specifiers in v3 onion service introduce
      cells and descriptors, when the rendezvous or introduction point
      doesn't support ed25519 link authentication. Fixes bug 26627;
      bugfix on

  o Minor bugfixes (vanguards):
    - Allow the last hop in a vanguard circuit to be the same as our
      first, to prevent the adversary from influencing guard node choice
      by choice of last hop. Also prevent the creation of A - B - A
      paths, or A - A paths, which are forbidden by relays. Fixes bug
      25870; bugfix on

  o Minor bugfixes (Windows, compilation):
    - Silence a compilation warning on MSVC 2017 and clang-cl. Fixes bug
      27185; bugfix on

  o Code simplification and refactoring:
    - Remove duplicate code in parse_{c,s}method_line and bootstrap
      their functionalities into a single function. Fixes bug 6236;
      bugfix on
    - We remove the PortForwsrding and PortForwardingHelper options,
      related functions, and the port_forwarding tests. These options
      were used by the now-deprecated Vidalia to help ordinary users
      become Tor relays or bridges. Closes ticket 25409. Patch by
      Neel Chauhan.
    - In order to make the OR and dir checking function in router.c less
      confusing we renamed some functions and
      consider_testing_reachability() has been split into
      router_should_check_reachability() and
      router_do_reachability_checks(). Also we improved the documentation
      in some functions. Closes ticket 18918.
    - Initial work to isolate Libevent usage to a handful of modules in
      our codebase, to simplify our call structure, and so that we can
      more easily change event loops in the future if needed. Closes
      ticket 23750.
    - Introduce a function to call getsockname() and return tor_addr_t,
      to save a little complexity throughout the codebase. Closes
      ticket 18105.
    - Make hsdir_index in node_t a hsdir_index_t rather than a pointer
      as hsdir_index is always present. Also, we move hsdir_index_t into
      or.h. Closes ticket 23094. Patch by Neel Chauhan.
    - Merge functions used for describing nodes and suppress the
      functions that do not allocate memory for the output buffer
      string. NODE_DESC_BUF_LEN constant and format_node_description()
      function cannot be used externally from router.c module anymore.
      Closes ticket 25432. Patch by valentecaio.
    - Our main loop has been simplified so that all important operations
      happen inside events. Previously, some operations had to happen
      outside the event loop, to prevent infinite sequences of event
      activations. Closes ticket 25374.
    - Put a SHA1 public key digest in hs_service_intro_point_t, and use
      it in register_intro_circ() and service_intro_point_new(). This
      prevents the digest from being re-calculated each time. Closes
      ticket 23107. Patch by Neel Chauhan.
    - Refactor token-bucket implementations to use a common backend.
      Closes ticket 25766.
    - Remove extern declaration of stats_n_seconds_working variable from
      main, protecting its accesses with get_uptime() and reset_uptime()
      functions. Closes ticket 25081, patch by “valentecaio”.
    - Remove our previous logic for "cached gettimeofday()" -- our
      coarse monotonic timers are fast enough for this purpose, and far
      less error-prone. Implements part of ticket 25927.
    - Remove the return value for fascist_firewall_choose_address_base(),
      and sister functions such as fascist_firewall_choose_address_node()
      and fascist_firewall_choose_address_rs(). Also, while we're here,
      initialize the ap argument as leaving it uninitialized can pose a
      security hazard. Closes ticket 24734. Patch by Neel Chauhan.
    - Rename two fields of connection_t struct. timestamp_lastwritten is
      renamed to timestamp_last_write_allowed and timestamp_lastread is
      renamed to timestamp_last_read_allowed. Closes ticket 24714, patch
      by "valentecaio".
    - Since Tor requires C99, remove our old workaround code for libc
      implementations where free(NULL) doesn't work. Closes ticket 24484.
    - Use our standard rate-limiting code to deal with excessive
      libevent failures, rather than the hand-rolled logic we had
      before. Closes ticket 26016.
    - We remove the return value of node_get_prim_orport() and
      node_get_prim_dirport(), and introduce node_get_prim_orport() in
      node_ipv6_or_preferred() and node_ipv6_dir_preferred() in order to
      check for a null address. Closes ticket 23873. Patch by
      Neel Chauhan.
    - We switch to should_record_bridge_info() in
      geoip_note_client_seen() and options_need_geoip_info() instead of
      accessing the configuration values directly. Fixes bug 25290;
      bugfix on Patch by Neel Chauhan.

  o Deprecated features:
    - As we are not recommending 0.2.5 anymore, we require relays that
      once had an ed25519 key associated with their RSA key to always
      have that key, instead of allowing them to drop back to a version
      that didn't support ed25519. This means they need to use a new RSA
      key if the want to downgrade to an older version of tor without
      ed25519. Closes ticket 20522.

  o Removed features:
    - Directory authorities will no longer support voting according to
      any consensus method before consensus method 25. This keeps
      authorities compatible with all authorities running and
      later, and does not break any clients or relays. Implements ticket
      24378 and proposal 290.
    - The PortForwarding and PortForwardingHelper features have been
      removed. The reasoning is, given that implementations of NAT
      traversal protocols within common consumer grade routers are
      frequently buggy, and that the target audience for a NAT punching
      feature is a perhaps less-technically-inclined relay operator,
      when the helper fails to setup traversal the problems are usually
      deep, ugly, and very router specific, making them horrendously
      impossible for technical support to reliable assist with, and thus
      resulting in frustration all around. Unfortunately, relay
      operators who would like to run relays behind NATs will need to
      become more familiar with the port forwarding configurations on
      their local router. Closes 25409.
    - The TestingEnableTbEmptyEvent option has been removed. It was used
      in testing simulations to measure how often connection buckets
      were emptied, in order to improve our scheduling, but it has not
      been actively used in years. Closes ticket 25760.
    - The old "round-robin" circuit multiplexer (circuitmux)
      implementation has been removed, along with a fairly large set of
      code that existed to support it. It has not been the default
      circuitmux since we introduced the "EWMA" circuitmux in 0.2.4.x,
      but it still required an unreasonable amount of memory and CPU.
      Closes ticket 25268.

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