Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:  closed
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:  fixed
 Keywords:  rust, rust-pilot, review-group-29,   |  Actual Points:
  review-group-34|
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-

Comment (by isis):

 Cool, thanks Nick!

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:  closed
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:  fixed
 Keywords:  rust, rust-pilot, review-group-29,   |  Actual Points:
  review-group-34|
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-
Changes (by nickm):

 * status:  needs_review => closed
 * resolution:   => fixed


Comment:

 It seems to fix the problem, so I'm merging it to master.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:
 |  needs_review
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:
 Keywords:  rust, rust-pilot, review-group-29,   |  Actual Points:
  review-group-34|
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-
Changes (by nickm):

 * status:  reopened => needs_review


Comment:

 I think that my branch `move_torlog_rust_declarations` shoudl fix this, if
 I have it diagnosed properly.  Currently trying it with Travis on github.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:
 |  reopened
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:
 Keywords:  rust, rust-pilot, review-group-29,   |  Actual Points:
  review-group-34|
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-
Changes (by isis):

 * status:  closed => reopened
 * resolution:  implemented =>


Comment:

 Clang builds are [https://travis-
 ci.org/isislovecruft/tor/jobs/355600626#L1373 failing] on Travis because
 of `-Wmissing-variable-definitions`:

 {{{
 src/common/log.c:57:11: error: no previous extern declaration for non-
 static
   variable 'LOG_WARN_' [-Werror,-Wmissing-variable-declarations]
 const int LOG_WARN_ = LOG_WARN;
 }}}

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:
 |  needs_revision
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:
 Keywords:  rust, rust-pilot, review-group-29,   |  Actual Points:
  review-group-34|
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-

Comment (by nickm):

 Great!  Merged that one to master, with minor conflict resolution, in
 d8893bc93c52e1edd0a76b81f5d65bb10d790474

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:  closed
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:
 Keywords:  rust, rust-pilot, review-group-29,   |  implemented
  review-group-34|  Actual Points:
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-
Changes (by nickm):

 * status:  needs_revision => closed
 * resolution:   => implemented


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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:
 |  needs_revision
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:
 Keywords:  rust, rust-pilot, review-group-29,   |  Actual Points:
  review-group-34|
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-

Comment (by isis):

 Replying to [comment:44 nickm]:
 > When I try to build this, I get some wide-line warnings in torlog.h from
 your d560384fd948ad24625312ee07e04f0cb60ac5b5 .
 >
 > Also, I think that d560384fd948ad24625312ee07e04f0cb60ac5b5 is breaking
 the compilation, since I see a bunch of these linker warnings:
 > {{{
 > src/common/libor-
 event.a(procmon.o):/home/nickm/src/tor/src/common/torlog.h:146: multiple
 definition of `LOG_WARN_'
 > src/or/libtor.a(main.o):/home/nickm/src/tor/./src/common/torlog.h:146:
 first defined here
 > }}}
 >
 > Maybe we should just remove d560384fd948ad24625312ee07e04f0cb60ac5b5 and
 merge the rest?

 Sounds good to me. I've made `bug23881_r1` which is exactly the same
 branch, just without d560384f.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:
 |  needs_revision
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:
 Keywords:  rust, rust-pilot, review-group-29,   |  Actual Points:
  review-group-34|
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-

Comment (by nickm):

 Other than that, I'm pretty satisfied that my review issues were all
 addressed.  If I find anything else, it can be a post-merge followup
 ticket.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:
 |  needs_revision
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:
 Keywords:  rust, rust-pilot, review-group-29,   |  Actual Points:
  review-group-34|
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-
Changes (by nickm):

 * status:  needs_review => needs_revision


Comment:

 When I try to build this, I get some wide-line warnings in torlog.h from
 your d560384fd948ad24625312ee07e04f0cb60ac5b5 .

 Also, I think that d560384fd948ad24625312ee07e04f0cb60ac5b5 is breaking
 the compilation, since I see a bunch of these linker warnings:
 {{{
 src/common/libor-
 event.a(procmon.o):/home/nickm/src/tor/src/common/torlog.h:146: multiple
 definition of `LOG_WARN_'
 src/or/libtor.a(main.o):/home/nickm/src/tor/./src/common/torlog.h:146:
 first defined here
 }}}

 Maybe we should just remove d560384fd948ad24625312ee07e04f0cb60ac5b5 and
 merge the rest?

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
-+-
 Reporter:  isis |  Owner:  isis
 Type:  enhancement  | Status:
 |  needs_review
 Priority:  High |  Milestone:  Tor:
 |  0.3.3.x-final
Component:  Core Tor/Tor |Version:
 Severity:  Normal   | Resolution:
 Keywords:  rust, rust-pilot, review-group-29,   |  Actual Points:
  review-group-34|
Parent ID:   | Points:  3
 Reviewer:  nickm|Sponsor:
 |  SponsorM-can
-+-

Comment (by nickm):

 Replying to [comment:40 isis]:
 > Yesterday I tried to find a way to get the name of the current function
 we're being called from, so that we wouldn't have to manually type it out
 everytime we log something. It seems like there [https://github.com/rust-
 lang/rfcs/pull/1719 was a proposed RFC] to make this info available, but
 it unfortunately stalled out.

 Hm.  Yeah, if this isn't available, it isn't available.  Let's put it on
 the wishlist (assuming we have one?)

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:  isis
 Type:  enhancement| Status:
   |  needs_review
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:  SponsorM-
   |  can
---+---
Changes (by isis):

 * status:  accepted => needs_review
 * sponsor:   => SponsorM-can


Comment:

 There's a couple tiny fixes for typos and to address Nick's concerns in my
 `bug23881`
 [https://gitweb.torproject.org/user/isis/tor.git/log/?h=bug23881 branch].
 I reviewed Chelsea's code. If someone wants to review my fixups then we
 could maybe merge?

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:  isis
 Type:  enhancement| Status:  accepted
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by isis):

 Yesterday I tried to find a way to get the name of the current function
 we're being called from, so that we wouldn't have to manually type it out
 everytime we log something. It seems like there [https://github.com/rust-
 lang/rfcs/pull/1719 was a proposed RFC] to make this info available, but
 it unfortunately stalled out. One of the major logger implementation in
 Rust, slog, also [https://github.com/slog-
 rs/slog/blob/9ec2bc5286c273fe7c0df7dd29c4f23f1ef9c705/src/lib.rs#L307
 doesn't/can't log function names currently] but instead stubs it out with
 `function: ""` and logs lines/columns/filenames instead. We could maybe do
 something like what this `nameof`
 [https://github.com/SilentByte/nameof/blob/master/src/lib.rs#L37 crate is
 doing], but then we'd have to find some way to call the macro outside of
 the function that is calling the logger somehow, and I still don't really
 see a way to make it automatic. Perhaps this could be something for the
 Rust wishlist?

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:  isis
 Type:  enhancement| Status:  accepted
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by manish.earth):

 >  Aha, I missed that part, thanks! So it'll be copied even if the
 originally borrowed thing is &'static?

 Currently, yes. In the future there may be an optimization that allows
 `&'static` strings to be treated as `String`s, though that may not affect
 this because it gets converted to a `Vec` anyway.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:  isis
 Type:  enhancement| Status:  accepted
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by isis):

 Replying to [comment:37 manish.earth]:
 > Yeah, I'd missed the "not" in the second half.
 >
 >
 > You're right that `CString::_new` does no copies or allocations; the
 sneaky bit is the `t.into()` -- the `From<>` impl for `Vec`. That
 itself calls the `From<&[u8]> for Vec` impl (https://github.com/rust-
 
lang/rust/blob/29f5c699b11a6a148f097f82eaa05202f8799bbc/src/liballoc/vec.rs#L2161-L2171)
 :
 >
 > {{{#!rust
 > impl<'a, T: Clone> From<&'a [T]> for Vec {
 > #[cfg(not(test))]
 > fn from(s: &'a [T]) -> Vec {
 > s.to_vec()
 > }
 > #[cfg(test)]
 > fn from(s: &'a [T]) -> Vec {
 > ::slice::to_vec(s)
 > }
 > }
 > }}}
 >
 > which calls `alloc::slice::to_vec` (https://github.com/rust-
 
lang/rust/blob/29f5c699b11a6a148f097f82eaa05202f8799bbc/src/liballoc/slice.rs#L164-L170),
 which creates a new vector and copies stuff into it via
 `extend_from_slice`
 >
 > {{{#!rust
 > pub fn to_vec(s: &[T]) -> Vec
 > where T: Clone
 > {
 > let mut vector = Vec::with_capacity(s.len());
 > vector.extend_from_slice(s);
 > vector
 > }
 > }}}
 >
 > If `T` is a `String` or `Vec`, it won't be copied, because the
 `From for Vec` impl is basically a no-op move. But if it's a
 borrow (e.g. `` or `&[u8]` or something), it will be copied into a new
 allocation. It has to be -- you can't guarantee that borrow will live
 forever.

 Aha, I missed that part, thanks! So it'll be copied even if the originally
 borrowed thing is `&'static`?

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:  isis
 Type:  enhancement| Status:  accepted
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by manish.earth):

 Yeah, I'd missed the "not" in the second half.


 You're right that `CString::_new` does no copies or allocations; the
 sneaky bit is the `t.into()` -- the `From<>` impl for `Vec`. That
 itself calls the `From<&[u8]> for Vec` impl (https://github.com/rust-
 
lang/rust/blob/29f5c699b11a6a148f097f82eaa05202f8799bbc/src/liballoc/vec.rs#L2161-L2171)
 :

 {{{#!rust
 impl<'a, T: Clone> From<&'a [T]> for Vec {
 #[cfg(not(test))]
 fn from(s: &'a [T]) -> Vec {
 s.to_vec()
 }
 #[cfg(test)]
 fn from(s: &'a [T]) -> Vec {
 ::slice::to_vec(s)
 }
 }
 }}}

 which calls `alloc::slice::to_vec` (https://github.com/rust-
 
lang/rust/blob/29f5c699b11a6a148f097f82eaa05202f8799bbc/src/liballoc/slice.rs#L164-L170),
 which creates a new vector and copies stuff into it via
 `extend_from_slice`

 {{{#!rust
 pub fn to_vec(s: &[T]) -> Vec
 where T: Clone
 {
 let mut vector = Vec::with_capacity(s.len());
 vector.extend_from_slice(s);
 vector
 }
 }}}

 If `T` is a `String` or `Vec`, it won't be copied, because the
 `From for Vec` impl is basically a no-op move. But if it's a
 borrow (e.g. `` or `&[u8]` or something), it will be copied into a new
 allocation. It has to be -- you can't guarantee that borrow will live
 forever.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:  isis
 Type:  enhancement| Status:  accepted
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by isis):

 Okay, to answer the question of "Does `CString::new` perform a copy?"

 Manish answered above, but I ''think'' there was a typo in the answer? (It
 seems to be missing the word "not" in the latter clause?) I had assumed it
 always copied, so I went and dug through the stdlib to figure it out.

 So [https://doc.rust-lang.org/src/std/ffi/c_str.rs.html#330-332 looking at
 the source of `CString::new`]:

 {{{#!rust
 pub fn new>>(t: T) -> Result {
 Self::_new(t.into())
 }

 fn _new(bytes: Vec) -> Result {
 match memchr::memchr(0, ) {
 Some(i) => Err(NulError(i, bytes)),
 None => Ok(unsafe { CString::from_vec_unchecked(bytes) }),
 }
 }
 }}}

 [wow!!! check out that ↑↑ frickin syntax highlighting! zomg, my
 life is changed!!]

 it takes a any `T` which has implemented a way (`Into`) to transmute it
 into a `Vec` and calls [https://doc.rust-
 lang.org/src/std/ffi/c_str.rs.html#334-339 `Cstring::_new()`] on it. There
 [https://doc.rust-lang.org/src/alloc/vec.rs.html#2226-2230 exists]
 `impl<'a> From<&'a str> for Vec`:

 {{{#!rust
 impl<'a> From<&'a str> for Vec {
 fn from(s: &'a str) -> Vec {
 From::from(s.as_bytes())
 }
 }
 }}}

 The `_new()` function checks that is has no NUL bytes, and errors if it
 does, then calls [https://doc.rust-
 lang.org/src/std/ffi/c_str.rs.html#361-365
 `CString::from_vec_unchecked()`]:

 {{{#!rust
 pub unsafe fn from_vec_unchecked(mut v: Vec) -> CString {
 v.reserve_exact(1);
 v.push(0);
 CString { inner: v.into_boxed_slice() }
 }
 }}}

 And then [https://doc.rust-
 lang.org/alloc/vec/struct.Vec.html#method.into_boxed_slice
 `Vec::into_boxed_slice()`]:

 {{{#!rust
 pub fn into_boxed_slice(mut self) -> Box<[T]> {
 unsafe {
 self.shrink_to_fit();
 let buf = ptr::read();
 mem::forget(self);
 buf.into_box()
 }
 }
 }}}

 which is doing some olympic level gymnastics where [https://doc.rust-
 lang.org/std/ptr/fn.read.html `std::ptr::read`] is returning a `Rawvec`,
 then it `mem::forget()`s itself so that the deallocator never runs, and
 finally it `Box`es the memory it forgot about by calling
 `RawVec::into_box()`:

 {{{#!rust
 impl RawVec {
 /// Converts the entire buffer into `Box<[T]>`.
 ///
 /// While it is not *strictly* Undefined Behavior to call
 /// this procedure while some of the RawVec is uninitialized,
 /// it certainly makes it trivial to trigger it.
 ///
 /// Note that this will correctly reconstitute any `cap` changes
 /// that may have been performed. (see description of type for
 details)
 pub unsafe fn into_box(self) -> Box<[T]> {
 // NOTE: not calling `cap()` here, actually using the real `cap`
 field!
 let slice = slice::from_raw_parts_mut(self.ptr(), self.cap);
 let output: Box<[T]> = Box::from_raw(slice);
 mem::forget(self);
 output
 }
 }
 }}}

 which is doing even more olympic level gymnastics with [https://doc.rust-
 lang.org/std/slice/fn.from_raw_parts.html `slice::from_raw_parts`], which
 is like the King of Capital-U Unsafety, because it just says "N bytes from
 this pointer forward are now a slice, with an lifetime that I decided by
 royal proclamation, and which is not necessarily the correct lifetime
 given that I was handed a raw pointer that I know nothing about". But it
 doesn't copy. Then it does a similar pirouette as the trick we saw before
 with `std::ptr::read` and then `Box`ing the `RawVec`, but even more
 complicated and dangerous, like if the last one was a pirouette, this is
 like a pirouette while juggling machetes. `Box::from_raw` is only
 ''really'' supposed to be called on pointers produced via `Box::into_raw`,
 but whatever, so many crazy things have already been done with these
 pointers to this memory. So `Box::from_raw` creates a [https://doc.rust-
 lang.org/std/ptr/struct.Unique.html `Unique`], which just says, "I own
 this raw pointer to a `T` (`*mut T`), and I'm just going to pretend it
 

Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:  isis
 Type:  enhancement| Status:  accepted
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---
Changes (by isis):

 * status:  needs_revision => accepted
 * owner:  chelseakomlo => isis


Comment:

 I had a call with Chelsea last weekend, and we went over this patch.
 Chelsea has been super busy, so I offered to make whatever little tweaks
 are necessary to address the comments on this ticket.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_revision
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by isis):

 [non sequitur] Wow! Today I learned, after like eight years of using Trac,
 from Manish, that you can do `{{{#!rust` and get syntax highlighting on
 Trac. I literally had no idea. Amazing.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_revision
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by chelseakomlo):

 Sounds good! I got a late start on this but about 3/4 of the way through,
 hoping to have everything up soon.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_revision
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-29  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by nickm):

 (I'm still okay with taking this in 0.3.3 postfreeze if it remains pretty
 much rust-only.)

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_revision
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-28  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by nickm):

 It looks like the merge request on oniongit is back up! Please let me know
 if you'd like me to copy my comments from here there, or from there here.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_revision
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-28  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by manish.earth):

 > Does CString::new() do a complete copy on the message?

 It depends what you give it. If you give it borrowed data, it will copy.
 If you give it a String or a Vec, it will copy.

 (I'll have a look at the code soon, missed that it was updated)

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_revision
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-28  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---
Changes (by nickm):

 * status:  needs_review => needs_revision


Comment:

 Newbie questions from oniongit that I can remember:
   * Does CString::new() do a complete copy on the message?
   * What part of the Rust code removes the indentation on the log strings?

 Change requests I can remember from oniongit:
   * The `tor_log_msg!()` macro documentation should document its support
 for `format!` syntax.
   * In C, all identifiers that start with an underscore are reserved: we
 can create constants like `LOG_WARN_`, but using `_LOG_WARN` is risky and
 we try not to do that.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_review
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-28  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by nickm):

 I added some comments to the merge request, but then apparently
 oniongit.eu decided to start giving me 500 errors.

 Here are the other questionsissues that I didn't enter into oniongit -- I
 hope that it comes back up again soon, and we can find the other
 questions/issues too.

 1) I'd recommend a rename on `rust_welcome_string()` to
 `rust_log_welcome_string()`: by convention, a function whose primary
 purpose is to _do_ something should have a verb name.

 2) Will the translate_* functions get inlined and compiled down to
 constants?  Logging is pretty critical-path.

 3) The C log functions exit fast, without formatting the message, if the
 log message isn't "interesting" because its severity is too low.  I think
 that if possible the Rust log macro should do the same, and avoid
 formatting messages when the function `log_message_is_interesting()`
 returns false.  That could be a separate commit, though.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_review
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-28  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---

Comment (by nickm):

 I'd be fine with the change in log level and/or domain macros.  Reviewing
 the branch now...

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_review
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-28  |  Actual Points:
Parent ID: | Points:  3
 Reviewer:  nickm  |Sponsor:
---+---
Changes (by nickm):

 * reviewer:   => nickm


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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
---+---
 Reporter:  isis   |  Owner:
   |  chelseakomlo
 Type:  enhancement| Status:
   |  needs_review
 Priority:  High   |  Milestone:  Tor:
   |  0.3.3.x-final
Component:  Core Tor/Tor   |Version:
 Severity:  Normal | Resolution:
 Keywords:  rust, rust-pilot, review-group-28  |  Actual Points:
Parent ID: | Points:  3
 Reviewer: |Sponsor:
---+---

Comment (by chelseakomlo):

 It would also be great to hear recommendations (Nick might be the best
 person) on whether refactoring the C side should be in scope for this
 ticket. See this comment regarding log level macros
 https://trac.torproject.org/projects/tor/ticket/23881#comment:14

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by chelseakomlo):

 Replying to [comment:21 manish.earth]:
 > (that commit doesn't seem to be on your oniongit repo -- got a link?)

 Apologies! Multiple remotes- it should be updated now. Thanks for taking a
 look.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by manish.earth):

 (that commit doesn't seem to be on your oniongit repo -- got a link?)

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by chelseakomlo):

 Replying to [comment:18 manish.earth]:
 > Alternatively, have a `static FOO: *const YourType = 0 as *const _;` and
 allocate it at the beginning of the test program. That's basically what
 lazy_static does, except lazily.

 Good suggestion- I took a stab at implementing something similar to what
 lazy_static does (declare a static mutable pointer and allocate data on
 the heap during assignment). As this code is purely for testing, I don't
 have as many safety checks, but open to feedback.

 See commit 4cdf0c8899796582b058d289bcd21b95dd1bd452.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by manish.earth):

 If you give me code that works using lazy_static I can de-lazy-static it,
 if you want

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by manish.earth):

 >  I don't think we should import this crate just for this test case- I
 did see that come up as an option though.

 you can use a dev-dependency so it only gets used in testing

 Alternatively, have a `static FOO: *const YourType = 0 as *const _;` and
 allocate it at the beginning of the test program. That's basically what
 lazy_static does, except lazily.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by chelseakomlo):

 Replying to [comment:16 manish.earth]:
 > > However, I ran into issues due to the limitation of creating non-
 struct static types in stable Rust.
 >
 > The `lazy_static` crate helps here, `static mut` is something you rarely
 use.

 I don't think we should import this crate just for this test case- I did
 see that come up as an option though.


 > > I am unable to run cargo test with a specific flag. For example, I
 wanted to be able to run cargo test --feature "testing",
 >
 >
 > You'll want to make the feature depend on features from other crates.

 Thanks! I didn't see that that was a possibility, that is super helpful, I
 added this in the last commit in this branch. We can now run tests via
 `cargo test --features "testing"` where the code has a dependency to C
 with a no-op (such as in the protover module), and still unit test the
 Rust code. I'm pretty happy about that.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by manish.earth):

 > However, I ran into issues due to the limitation of creating non-struct
 static types in stable Rust.

 The `lazy_static` crate helps here, `static mut` is something you rarely
 use.

 > I am unable to run cargo test with a specific flag. For example, I
 wanted to be able to run cargo test --feature "testing",


 You'll want to make the feature depend on features from other crates.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+
Changes (by chelseakomlo):

 * status:  needs_revision => needs_review


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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_revision
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by chelseakomlo):

 See fixes from Manish's review on the same branch:
 `https://oniongit.eu/network/tor/merge_requests/7`

 A couple thoughts:

 1. Testing

 I wasn't able to test the inline logging function, as I wasn't sure the
 best way how to. I think I could properly test this with a global variable
 that was only defined for unit tests (such as a Cursor, and "log" to
 it in the no-op implementation. However, I ran into issues due to the
 limitation of creating non-struct static types in stable Rust.

 For example, for the following declaration:

 `pub static mut log_cursor: Cursor =
 Cursor::new(Vec::new());`

 I received this error:
 `calls in statics are limited to struct and enum constructors`

 And for this declaration:

 {{{
   struct LastLogged {
 function: Option
 message: Option
   }
 }}}

 I received this error:
 `destructors in statics are an unstable feature`

 Maybe we just need to wait for this feature to land in stable, but it
 would be nice to have the flexibility for functions that are inherently
 hard to test, without having to change the code itself.

 2. Feature flags for `cargo test`

 I am unable to run `cargo test` with a specific flag. For example, I
 wanted to be able to run `cargo test --feature "testing"`, but this flag
 is not applied to other modules as well (i.e, running tests in protover
 will not result in tor_log being compiled with the "testing" flag). I'm
 able to run `cargo test --all-features` but being able to turn on features
 at a fine-grained level for tests would be nice.

 3. Binding compile-time constants to log level macros

 Nick- as for the declaration of log levels in src/common/torlog.h, if we
 can refactor these into compile-time constants (instead of macros) that
 would remove the need to declare _constant for each. Let me know what you
 think, I can help do this refactor.

 For example, instead of binding _LD_NET to LD_NET, we could declare LD_NET
 as a constant directly.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_revision
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by manish.earth):

 > Would you recommend using the #[inline] tag for that function then?

 yep.

 To give an exact description of #[inline]:

 For the *same* crate it acts as a small hint for inlining. This is also
 true for generics that get instantiated in a different crate.

 For non-generic functions from a different crate, it is impossible for
 rustc to inline without this, because by the time you get to the current
 crate it's already been codegenned. #[inline] forces rustc to include
 extra metadata that lets the next crate re-codegen it if it wishes to. (It
 also contains the small hint for inlining)

 #[inline(always)] is a *strong* hint, and will force inlining unless it's
 impossible (e.g. in the presence of a lot of recursion). #[inline(never)]
 does what it says on the tin.

 In this case it's a macro and going to be used from a different crate, so
 we _need_ `#[inline]` so that the other crate can inline it if the
 optimizer thinks it is a good idea. We don't need inline(always) -- the
 optimizer is smart.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_revision
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by chelseakomlo):

 Thanks for the really helpful review! All of these suggestions make sense-
 I wasn't sure about the best way to import dependencies for a macro in
 other modules.

 It is interesting to hear your recommendation to use a function for the
 macro body. Would you recommend using the #[inline] tag for that function
 then?

 I'll make these fixes over the weekend, thanks again for the help.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_revision
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+
Changes (by chelseakomlo):

 * status:  needs_review => needs_revision


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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by manish.earth):

 This looks pretty good! I like how you've set up the testing code.

 Some review comments

 > `const int _LOG_WARN = LOG_WARN;`

 This is interesting. Usually I'd just mirror the constants and leave
 comments, and bindgen is useful for automirroring (but y'all aren't using
 bindgen and that's ok).

 I guess this works. I've never seen constants mirrored this way but I do
 feel it is more resilient to code changing.

 {{{#!rust
 /// Allow for default cases in case Rust and C log types get out of
 sync
 #[allow(unreachable_patterns)]
 pub unsafe fn translate_severity(severity: LogSeverity) -> c_int {
 match severity {
 LogSeverity::Warn => _LOG_WARN,
 LogSeverity::Notice => _LOG_NOTICE,
 _ => _LOG_NOTICE,
 }
 }
 }}}



 There's no need for that `unreachable_patterns`. The only way stuff will
 go out of sync is if `LogSeverity` gets a variant added, however that will
 trigger a compiler error in this match (if you leave off the `_` branch).
 It's nice to be able to modify enums and immediately have the compiler
 tell you where you need to update things


 {{{#!rust
 unsafe {
 tor_log_string(translate_severity($severity),
 translate_domain($domain),
 func_ptr, msg_ptr
 )
 }
 }}}

 These will fail to resolve if called outside of the correct module with
 the right imports.

 The best thing to do is to use `$crate::tor_log_string(..)` (see the docs
 on `$crate`, https://doc.rust-lang.org/1.7.0/book/macros.html#the-
 variable-crate) which will ensure these will resolve wherever you use
 them.


 > `const ERR_LOG_MSG: &'static str`

 Rust lets you omit the `'static` now (this is recent, so it works on the
 latest stable but may not work on the compiler you're using)

 -

 One concern of mine is that the `tor_log_msg` macro contains unsafe code,
 and more problematically, it contains macro variables in that unsafe code.

 Now this is firmly in "why would anyone even _do_ that" territory, but for
 example someone could call `tor_log_msg!({some code}, )`, and that
 code would be expanded to be inside an unsafe block without the caller
 ever having to use unsafe.

 You should probably have severity/domain get bound to variables outside of
 the unsafe block.

 Ideally the entire macro body would be moved to a function, making the
 body just handle the `format!` stuff and calling the function. However,
 this means you can no longer do the testing trick where the test function
 itself returns what was printed.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  assigned
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by chelseakomlo):

 Ok, see the merge request on gitlab here:
 https://oniongit.eu/network/tor/merge_requests/7

 This PR creates a minimal implementation for Rust modules to log using
 tor's existing logger.

 One issue that I ran into is that log levels/domains are defined as macros
 in C. I redeclared a small subset of these as constants- if this is the
 approach that we want to take, I can fill out the remainder of necessary
 constants. Another alternative is to define log level/log domain macros as
 constants in C.

 In order to run module-level Rust tests without linking to C, it is
 necessary to "stub" out direct calls to C functions. This PR adds a
 "testing" feature in order to optionally compile no-op implementations for
 testing. (The approach of "write C integration tests and test Rust in
 isolation" is an approach taken by Servo, although it would be great to
 get Rust people's eyes on this to double check how I've done this).

 Looking forward to feedback and suggestions how to improve!

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  needs_review
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+
Changes (by chelseakomlo):

 * status:  assigned => needs_review
 * cc: isis (added)


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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  assigned
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by nickm):

 So, I did a really simple untested implementation of the backend
 functions.  It turned out not to actually need any refactoring, which is
 good, because that code is a mess. :)

 It's in a branch `rust_log_backend` in my public repository, and it should
 be a good basis to build on.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  assigned
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by chelseakomlo):

 Replying to [comment:5 nickm]:
 > So my first thought is to take this approach:
 >* Refactor the C a bit, though, so that there is a tor_log_string()
 function taking a severity, domain, and message.  It should work the same
 as `tor_log(severity, domain, message);`, but instead it should be safe to
 call it function with strings containing `%`.  (I can write this one if
 you want: it will involve refactoring `logv` a little.

 This sounds great- I was hesitant to add a bunch of functionality to Rust
 just to make it compatible with the existing C api. If you have time to do
 this, that would be great! Otherwise I can take a stab at it this week.

 >* Expose that function to rust.
 >* Write a single rust macro that takes severity, domain, message, and
 some format arguments, and uses the `format!` mechanism to generate the
 log message.

 This is approximately what I have, with the ability to optionally compile
 with a no-op implementation (for running tests at the rust module level).

 > Optionally afterwards:
 >* Expose a view of `log_global_min_severity` to rust, maybe via a
 function.
 >* Update the rust macro to compare `log_global_min_severity` to the
 declared severity, and avoid formatting the message if no logs actually
 want it.
 This sounds great- we can do this either in this ticket or an enhancement.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  assigned
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by nickm):

 So my first thought is to take this approach:
* Refactor the C a bit, though, so that there is a tor_log_string()
 function taking a severity, domain, and message.  It should work the same
 as `tor_log(severity, domain, message);`, but instead it should be safe to
 call it function with strings containing `%`.  (I can write this one if
 you want: it will involve refactoring `logv` a little.
* Expose that function to rust.
* Write a single rust macro that takes severity, domain, message, and
 some format arguments, and uses the `format!` mechanism to generate the
 log message.

 Optionally afterwards:
* Expose a view of `log_global_min_severity` to rust, maybe via a
 function.
* Update the rust macro to compare `log_global_min_severity` to the
 declared severity, and avoid formatting the message if no logs actually
 want it.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  assigned
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+

Comment (by chelseakomlo):

 I have been working on this and hopefully will have a patch within the
 week. One thing that has taken some time is deciding which logging
 function to use- on the C side, we have several macros which wrap log_fn_.
 We can implement similar functionality in Rust, or we can create helper
 functions in C- if anyone has arguments for/against either of these, let
 me know.

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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  chelseakomlo
 Type:  enhancement   | Status:  assigned
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+
Changes (by chelseakomlo):

 * owner:  (none) => chelseakomlo
 * status:  new => assigned


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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  (none)
 Type:  enhancement   | Status:  new
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+
Changes (by chelseakomlo):

 * cc: chelseakomlo (added)


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Re: [tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  (none)
 Type:  enhancement   | Status:  new
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  rust, rust-pilot  |  Actual Points:
Parent ID:| Points:  3
 Reviewer:|Sponsor:
--+
Changes (by manish.earth):

 * cc: manishearth@… (added)


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[tor-bugs] #23881 [Core Tor/Tor]: Implement a way to utilise tor's logging system from Rust code

[Tor Bug Tracker & Wiki]

#23881: Implement a way to utilise tor's logging system from Rust code
--+
 Reporter:  isis  |  Owner:  (none)
 Type:  enhancement   | Status:  new
 Priority:  High  |  Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor  |Version:
 Severity:  Normal|   Keywords:  rust, rust-pilot
Actual Points:|  Parent ID:
   Points:  3 |   Reviewer:
  Sponsor:|
--+
 We really need a way to use tor's logging subsystem from Rust code. I
 haven't ever really looked at our logging code because it always Just
 Works™, but it seems possible that we could construct/format `String`s to
 log in Rust code, choose a logging level, and throw the `String` across
 the FFI boundary, have the C code log it, then have the Rust code free it?

 I'm not sure what we'll do about logging in general moving forward, once
 (and if) more and more of tor is rewritten in Rust.

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