Summary:
During the wangle accept process and in a few pieces of application code we transform one type of `AsyncSocket` to another, potentially *after* a write has occurred.

Since we do not currently carry `appBytesWritten` and `rawBytesWritten` during transformations, those values may not represent all bytes written. Likewise, if we transform from a `AsyncSSLSocket`, we lose count of the number of raw bytes written.

It's very difficult to reason about whether these problems will actually manifest, so I'd prefer to just guard against it.

With this change, we explicitly track the number of bytes written to the socket by incrementing a counter in `sendSocketMessage`, which is used by both `AsyncSocket` and `AsyncSSLSocket`. In addition, we copy the appBytesWritten and rawBytesWritten during socket moves.

Reviewed By: yfeldblum

Differential Revision: D24551958

fbshipit-source-id: 88416114b52931ff3ceef847401d556ccf0ab664

Summary: Both `AsyncSocket` and `AsyncSSLSocket` currently have code to generate a socket message and control messages with ancillary data. Merge this code into a new function in `AsyncSocket`.

Differential Revision: D24096351

fbshipit-source-id: 87d90648c10c87832f868e322acf59c97b8ac8b7

Summary:
Move `ready_awaitable`, `variant_awaitable` types to `folly/experimental/coro/Coroutine.h`, which reexports the foundational vocabulary coroutine helper types and is a suitable place for these vocabulary coroutine helper types.

`ready_awaitable` is an awaitable which is ready and has a value or, if of void, which is just ready. `variant_awaitable` is an awaitable composed of one of several possible backing awaitables.

Reviewed By: aary

Differential Revision: D26270528

fbshipit-source-id: e98f64b3d3ffaf5bbd322397a41bb5fe85a6bb55

Summary:
`folly::format` is a problematic API because it returns a `Formatter` object that may store references to arguments as its comment warns:

```
 * Formatter class.
 *
 * Note that this class is tricky, as it keeps *references* to its lvalue
 * arguments (while it takes ownership of the temporaries), and it doesn't
 * copy the passed-in format string. Thankfully, you can't use this
 * directly, you have to use format(...) below.
```

This has negative safety and performance (encourages reuse of the same formatter) implications because contrary to what the comment says you can use the object directly since it's returned from `folly::format`. For example
```
auto f = folly::format(std::string("{}"), 42);
f.str();
```
is a UB with no compile-time diagnostic (only caught by ASAN).

It's also unnecessary because the `Formatter` object is usually converted to string straight away via `str()` or written to an output stream. Reusing the formatter doesn't make much sense either because the expensive part is formatting, not capturing arguments.

This diff deprecates `folly::format` suggesting `fmt::format` as a potential replacement. `fmt::format` doesn't have the above problem because arguments are always in scope. It also has the following advantages:

* Better compile times.
* Compile-time format string checks.
* Compatibility with C++20 `std::format`.
* Better performance, particularly with format string compilation which eliminates format string processing overhead altogether.
* Smaller binary footprint.

Also remove `folly::writeTo` which is no longer used and the `format_nested_fbstrings` benchmark which is identical to `format_nested_strings` since there is no `fbstr()` any more.

Reviewed By: yfeldblum

Differential Revision: D26391489

fbshipit-source-id: f0309e78db0eb6d8c22b426d4cc333a17c53f73e

Summary: Follow a convention that function object types with corresponding function object instances be named with a `_fn` suffix.

Reviewed By: ericniebler

Differential Revision: D26674781

fbshipit-source-id: f8a3b8f18677c905897da8bae38cc76693146073

Summary: Use of `std::coroutine_traits` and `std::experimental::coroutine_traits` can get awkward and we do not actually need the flexibility. Just define member type aliases `promise_type`.

Reviewed By: andriigrynenko

Differential Revision: D26706363

fbshipit-source-id: 0cdb59d542a64ff85d8a126003a014b7b6be3134

Summary: Invokers for `begin` and `end` with `std::begin` and `std::end` in scope.

Reviewed By: ericniebler

Differential Revision: D26683890

fbshipit-source-id: 79e57b235c847b5bea29e2e6aac767bdfcef72e8

Summary: Namely, let the backports of `std::size`, `std::empty`, and `std::data` be function objects in folly to eliminate possibility of ADL overloading.

Reviewed By: ericniebler

Differential Revision: D26681127

fbshipit-source-id: 0c2868f25818afca7efd6b2337cb398daa9bb7f3

Summary: Add FOLLY_PORT_WIN32_OPEN_BINARY define

Reviewed By: yfeldblum

Differential Revision: D26693403

fbshipit-source-id: 51fb9ceef31cffdeff691ad0eb49939725cc047b

Summary: Reexport remaining names, including `noop_coroutine`, from `folly/experimental/coro/Coroutine.h`, which wraps inclusion of `experimental/coroutine`.

Differential Revision: D26227580

fbshipit-source-id: b7ea0bb0bb7447bf4327b2f178c51db544f70f46

Summary: TSIA

Differential Revision: D26697902

fbshipit-source-id: bd0a552959474c0efa6167e8da1ed31916c77346

Summary: The static cast and forward were backwards. Previously it happily converted an rvalue to a const lvalue. Now it causes the exact same static_assert failure as std::forward in every rvalue->lvalue case.

Reviewed By: yfeldblum

Differential Revision: D26680263

fbshipit-source-id: f1ca4c4bfdd6333d24fe3c406d5373a2f72dea31

Summary: There are no correct uses of the catch-all overload of `folly::exceptionStr`. Every use is a bug of some kind, leading to the impression that this overload ought to be removed.

Differential Revision: D26539622

fbshipit-source-id: dc2ca0781ea02f1327a334bb1fe2e533fa46d1b3

Summary: Prevent a race condition where a session's reference count can be decremented to 0 (causing the session to be freed) by one thread before another thread can increment the reference count.

Reviewed By: mingtaoy

Differential Revision: D26614966

fbshipit-source-id: 6c55321becfc1a3467f57c692065680a32ac21f3

Summary:
BoundedAsyncPipe::write() accepts arguments by-reference, so even
these constants may be out-of-scope by the time the coroutine actually runs,
causing use-after-scope problems which are detected by ASAN.

Wrapping in co_invoke allows us to scope the parameter so that it
lives long enough.

Reviewed By: lxfind

Differential Revision: D26649913

fbshipit-source-id: 5bc6b7f64a5e75c9386b245fa3fd1484efaf1d13

Summary:
This is needed if we have an AsyncStackRoot pointer, and we
want to call both `getTopFrame()` and `getNextRoot()`
(e.g. walking async stacks) without const-casting the pointer.

Reviewed By: yfeldblum

Differential Revision: D26675131

fbshipit-source-id: 84de25c67d563e118483d67d0fedb4ea7aef2604

Summary: Currently there is an extension point `folly_co_invoke` for providing customizations for `co_invoke`. But `tag_invoke` is intended as a generic mechanism for providing namespaced customizations. So let us use that.

Reviewed By: ericniebler

Differential Revision: D26674580

fbshipit-source-id: b1baea04996f162699510c3aba8d2c330fcf34bb

Reviewed By: zertosh

Differential Revision: D26660179

fbshipit-source-id: bc0ae7deeb3a3097bfb77cbf0bc471157f586326

Summary: As per title, stub it out in a way that will just trigger exceptions for everything not yet implemented.

Reviewed By: yfeldblum

Differential Revision: D26579892

fbshipit-source-id: 5bfc20b1f6737bbda80616ea1407a5cf108be3c3

Summary: Choose a single strategy for guarding coro files. Namely, all includes are unconditional, but otherwise the bodies of all headers, sources, and tests are conditional.

Reviewed By: ericniebler

Differential Revision: D26647625

fbshipit-source-id: 33eeb12fb231bd7ae7fe5cb97ead16ab017b15f5

Summary:
There is a Most Vexing Parse problem in `folly/MapUtil.h`:

```
xplat/folly/MapUtil.h:44:75: error: expected expression
  return (pos != map.end()) ? (pos->second) : M(std::forward<Value>(dflt));
                                                                          ^
```

Fix the issue by replacing paren-init with `static_cast`.

Reviewed By: yfeldblum, ispeters, ot

Differential Revision: D26610359

fbshipit-source-id: 89842b9b68cebaaab43ea5f82abe7e500f98ff2c

Summary:
Newer libiberty has limits that over constrain
the size of symbols that can be demangled.
This applies the same adjustment in the default
platform009 demangler, done in D26380825

Differential Revision: D26617797

fbshipit-source-id: 8d3e72a0807aa9ecff18d26f38c1acb83f9c051b

Summary:
Right now we have a single option verifyPeer_(SSLVerifyPeerEnum) that
controls how verification is done regardless of how the ssl context is
inevitably used (client or server). This is confusing for our users since it
is 1. unclear of what the current values mean 2. It is unclear that setting an
option such as VERIFY_REQ_CLIENT_CERT also sets your verification mode when
running as a client.In order to make this api more clear for
our users we separate out this enum to two separate enums for client and
server. When this is passed to openSSL we still pass the same single mode int.

Reviewed By: mingtaoy

Differential Revision: D18308192

fbshipit-source-id: 5d49d3dc5117075a55681cf67b5f8e72b5e62c89

Summary:
Original commit changeset: b48fe4683165

Our application can't terminate since this change was committed. 100% reproducible.

Reviewed By: WillerZ

Differential Revision: D26621716

fbshipit-source-id: 571ecd9a6f5286469877bf510f1f55b036df9217

Summary: This is the second attempt, the first one was D22958650. Decided to do a different diff as some affected files were moved from experimental/afrind/coro/h2proxy to proxygen/facebook/lib/experimental/coro/ which created some confusion while arc pulling

Reviewed By: yfeldblum

Differential Revision: D25432869

fbshipit-source-id: a183898302a79084d890548b9b7ecc4409f501d2

Summary:
`/proc/self/exe` doesn't exist on apple platforms, so provide an
implementation that does.

Reviewed By: yfeldblum

Differential Revision: D26599826

fbshipit-source-id: e00dde59d639063e59cb97feb75caf0a49a01954

Summary: Move `order_preserving_reinsertion_view` to a new header `folly/container/View.h` and revise its customization facility in terms of `folly::tag_invoke`.

Reviewed By: iahs

Differential Revision: D25787117

fbshipit-source-id: b7ccd3b6a1413a2639ef1beb1f1ee23bbed045e3

Summary:
This'll move getdeps dependency for katran to 0.3 (which is already the case
for travis build)

Reviewed By: avasylev

Differential Revision: D26129525

fbshipit-source-id: ec9d0615a3e02d75454a3f9dd974ac5c7589e40a

Summary: IoUringBackend benchmarks

Reviewed By: kevin-vigor

Differential Revision: D26594012

fbshipit-source-id: c6a08e6ec13b736c32619958713706118e2f1a49

Summary: No need to overload coroutine `promise_type::return_value` to handle initializer list expressions - just template and default the parameter.

Reviewed By: Orvid

Differential Revision: D26508901

fbshipit-source-id: 61c4a2225355b0044638cd89b9153d599317a453

Summary: When EventBase is destructed, the underlying local storage should be destructed prior to event loop being destroyed.

Reviewed By: andriigrynenko

Differential Revision: D26583298

fbshipit-source-id: 9bfb8442b2a827aa2b3564b27ea765ec1e7b26a2

Summary: Owing to a set of bugs, it is not currently possible to actually declare ranges::enable_view without actually defining it, so we have to include the actual definition when we're in compilation units with it available. If the definition is not available, then the `const` form is sufficient to keep things compiling.

Reviewed By: yfeldblum

Differential Revision: D26337214

fbshipit-source-id: fb042b62967e3e6f536e8268e1b6dd6ccd20b810

Summary: Some compilers fail when `friend` declarations have mismatched `constexpr`-specifiers.

Reviewed By: Mizuchi

Differential Revision: D26601032

fbshipit-source-id: a49e327ff9353ddb21eac96776f97d4089c85374

Summary: Use `std::filesystem` or `std::experimental::filesystem`, via `folly/portability/Filesystem.h`, in `folly/test/FileTest.cpp`. Replaces the use of `boost::filesystem`.

Reviewed By: Orvid

Differential Revision: D26572916

fbshipit-source-id: f769e00b2772f3bfaed899f5694d89db87089e35

Summary:
Make the implementation of `folly::fs::lexically_normal` match C++17 `std::filesystem::path::lexically_normal`. The implementation from `boost::filesystem::path::lexically_normal` is easy to fall back on but has some differences.

The implementation is copied mutatis mutandis from https://github.com/gulrak/filesystem/ at tag v1.5.0, in which `ghc::filesystem` is a complete portable standalone implementation of the `std::filesystem` spec and released under the MIT license.

Reviewed By: Orvid

Differential Revision: D26572520

fbshipit-source-id: 5ce03f37c078ee4f62e3480d4abc259199867c8e

Summary: [Folly] Prefer to nest helper functions in coro tests within the specific tests which use them.

Reviewed By: ispeters, Orvid

Differential Revision: D20324066

fbshipit-source-id: 4134145c406f2d1fdeaddf9a7d244c1bd25ec60b

Summary: Some versions of gcc miscompile the code in the parallel-map exception test. Work around the miscompile by adding an extra log line.

Reviewed By: Orvid

Differential Revision: D26509079

fbshipit-source-id: 1474437d96aeabad0294bcb395b7baec229eb9ba

Summary: The CMake function `check_cxx_compiler_flag` is snake-case rather than uppercase.

Reviewed By: vitaut

Differential Revision: D26573998

fbshipit-source-id: 91d5e2cea933d35967d013b2344e50f52fb6ba77

Summary: Tweak a test that relies on hardcoding the expected result of `std::exception().what()` instead to call that and use the result without hardcoding it.

Differential Revision: D26573226

fbshipit-source-id: 3802d12186c96b864e2680d99f5cfca185235f8d

Reviewed By: andriigrynenko

Differential Revision: D26572552

fbshipit-source-id: 035e1313cd4dec070555b5cd41efc58a0b4a948a