This code tries to prevent a large number of possible errors by
enforcing different restrictions on the messages that different
modules publish and subscribe to.

Some of these rules are probably too strict, and some too lax: we
should feel free to change them as needed as we move forward and
learn more.

This "publish/subscribe" layer sits on top of lib/dispatch, and
tries to provide more type-safety and cross-checking for the
lower-level layer.

Even with this commit, we're still not done: more checking will come
in the next commit, and a set of usability/typesafety macros will
come after.

This module implements a way to send messages from one module to
another, with associated data types.  It does not yet do anything to
ensure that messages are correct, that types match, or that other
forms of consistency are preserved.

We already do this in our log_debug() macro, but there are times
when we'd like to avoid allocating or precomputing something that we
are only going to log if debugging is on.

Tests included.

You use this when you're defining a macro to be used at file scope,
and you want to require a semicolon afterwards.

We'll be using this for four kinds of identifier in dispatch.c

All remaining tasks are now part of #28632.

Kris Katterjohn authored 6 years ago and Nick Mathewson committed 6 years ago

When cleaning up after an error in process_unix_exec, the stdin
pipe was being double closed instead of closing both the stdin
and stdout pipes.  This occurred in two places.

Signed-off-by: Kris Katterjohn <katterjohn@gmail.com>

NOTE: This commit breaks the build, because there was a mistake in an
earlier change of exactly the sort that this is meant to detect!  I'm
leaving it broken for illustration.

Test exactly what the geometric sampler returns, because that's what
the downstream callers of it are going to use.

While here, also assert that the geometric sampler returns a positive
integer.  (Our geometric distribution is the one suported on {1, 2,
3, ...} that returns the number of trials before the first success,
not the one supported on {0, 1, 2, ...} that returns the number of
failures before the first success.)

In file included from ./src/core/or/or_circuit_st.h:12:0,
                 from src/core/or/circuitlist.c:112:
./src/core/or/circuit_st.h:15:39: error: redefinition of typedef ‘circpad_machine_spec_t’
./src/core/or/circuitpadding.h:572:3: note: previous declaration of ‘circpad_machine_spec_t’ was here
./src/core/or/circuit_st.h:16:40: error: redefinition of typedef ‘circpad_machine_state_t’
./src/core/or/circuitpadding.h:517:3: note: previous declaration of ‘circpad_machine_state_t’ was here

In file included from src/core/or/connection_edge.c:70:0:
./src/core/or/circuitpadding.h:16:26: error: redefinition of typedef ‘circuit_t’
./src/core/or/or.h:930:26: note: previous declaration of ‘circuit_t’ was here
./src/core/or/circuitpadding.h:17:33: error: redefinition of typedef ‘origin_circuit_t’
./src/core/or/or.h:931:33: note: previous declaration of ‘origin_circuit_t’ was here
./src/core/or/circuitpadding.h:18:23: error: redefinition of typedef ‘cell_t’
./src/core/or/or.h:628:23: note: previous declaration of ‘cell_t’ was here

typedef doesn't work for forward declarations, but plain struct
without a typedef wrapper does (and unlike the _t type aliases makes
it clearer for everyone whether you're talking about the struct or
the pointer).

See https://github.com/torproject/tor/pull/624#discussion_r246453777