The Nim core

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143

# The Nim core

The portable half of frq, as a native library the Dart side calls through FFI.

## Why this exists

`common/` is ClojureDart, compiled into every target. That works, and the
reason to move any of it is not that it is broken: it is that the logic under
the screens — the IRC wire format, the atproto flows, the message signatures —
is the part with the most rules per line and the least to do with Flutter, and
it is the part worth having in a language with a type checker and a test runner
that does not need a Flutter toolchain to run.

So the plan is a seam, not a rewrite-in-place. Each module moves one at a time:
the Nim implementation lands here with tests, the Dart binding lands in
`flutter/src/frq/core/`, and the ClojureDart original stays until the binding
is proven against it. Nothing is deleted on faith.

## What is here

```
src/frq_core.nim        the C ABI: every exported symbol, and nothing else
src/frq/ircparse.nim    the IRC wire format
tests/                  one per module, run by `just nim-test`
```

`src/frq_core.nim` is the only file that knows about C. Everything under
`src/frq/` is ordinary Nim with ordinary Nim types, so the tests test the logic
rather than the marshalling.

## The ABI

Strings in, strings out, and JSON where the answer is not a single string.

That is a deliberate choice against a struct-based ABI. A struct means the Dart
side and the Nim side have to agree on a memory layout, and every field added
later is a version skew that segfaults instead of failing. JSON costs a parse
per call, which is nothing against a network round trip, and it lets one side
gain a field without the other crashing.

Every function that returns a string returns memory the **caller must free**
with `frq_free`. Nim's allocator is not Dart's; a `free()` from the Dart side
on a Nim pointer is undefined. The bindings in `flutter/src/frq/core/` wrap
that in a `try/finally` so no call site has to remember.

`frq_init` must be called once before anything else, and calls `NimMain` to set
up Nim's runtime. The bindings do it on first use.

## The web

A native library does not load in a browser, so the web target cannot call this
through `dart:ffi`. Nim compiles through C, so the route is emscripten to wasm
and a JS binding rather than a second implementation — but that is not built
yet, and until it is, **the web build must keep using the ClojureDart
originals**. This is why the originals stay in `common/` rather than being
deleted as each module lands: they are the web's implementation, not dead code.

## What is wired up

`just nim-app run` is the real client with the Nim core as its transport. Every
screen, cell and action is the one that was already there; `frq.main-nim` is
`frq.main` with one line changed.

```
src/frq/conn.nim      the socket, the TLS, the line framing — on its own thread
src/frq/ircparse.nim  the IRC wire format
src/frq/trace.nim     FRQ_TRACE=1, the same switch the rest of frq uses
```

The seam is `frq.net`, which already existed with two implementations;
`flutter/src/frq/net/nim.cljd` is a third beside `frq.net.dart` and
`frq.net.web`. Nim owns the socket and nothing above it — the line goes to the
existing `frq.irc.parse`, so `on-msg` receives the same map from the same
parser and nothing upstairs can tell which transport it is on.

Two things to know before changing `conn.nim`:

* **Nothing is shared with the socket thread.** Nim's ORC is thread-local for
  ref types, so sharing state would mean a lock per field and a heap two
  threads both collect. It speaks only in channels.
* **Writes drain before reads.** IRC has the client speak first, and reading
  first deadlocked completely: CAP/NICK/USER sat queued while the loop waited
  for a server that had nothing to say until we registered.

There was an experiment where Nim owned the state and the screens too. It is
gone. It meant a 43-line chat screen standing in for 1,518 — no reactions, no
replies, no images — and the path forward from it was rewriting every screen
in Nim and losing all of that. It is at 1d62d1a if it is ever wanted.

```bash
just nim-app run     # the real client, Nim transport
just nim-test        # the Nim suite
just dart-test       # the Dart side of the boundary
just nim-lib         # libfrqcore.so into build/nim

FRQ_TRACE=1 just nim-app run    # every line in and out, both languages
```

The GUI needs OpenSSL on its loader path, which the `flutter-desktop` shell
provides as `FRQ_OPENSSL_LIB` and the `nim-app` recipe prepends for the app
alone. Not set as `LD_LIBRARY_PATH` in the shell itself: that shell also runs
Flutter through nixGL, which does its own careful things to the loader path.

## Status

`frq/ircparse.nim` is ported and tested — 29 cases, `just nim-test` — and the
ABI is exercised from C through `dlopen`, including the allocation contract
under a hundred thousand parse/free cycles. That half is real.

The Dart binding is real too, and is `dart/frq_core` — **plain Dart, not
ClojureDart**. It calls the library over `dart:ffi` and is covered by 20 tests
on the Dart VM, including the UTF-8 round trip and ten thousand calls against
the ownership rules. `just dart-test` runs the pair of them in about a second.

The binding was ClojureDart for one commit and should not have been: the Nim
core exists to have less Clojure in the tree, and `lookupFunction` takes two
type arguments, so it meant fighting generic interop to write more of the
thing being removed. In Dart it is a typedef. See `dart/README.md`.

The transport is wired up and runs. What is **not** done is replacing
anything else: `frq.main` is untouched and still installs `frq.net.dart`, so
the shipping app is unchanged and `frq.main-nim` is a second entry point
beside it. `common/frq/irc/parse.cljc` is still what does the parsing on every
target, including this one. That step is its
own piece of work — the Flutter app takes the package as a path dependency
(which means a `pubspec.lock` regeneration and widening the nix build's source
root), the library has to reach each target (`jniLibs` for the APK, beside the
executable for the desktop bundle), and only then can a call site choose Nim
on native and the ClojureDart original on the web.

Modules still in `common/` and not yet here: `rooms`, `msgsig`, `crypto`,
`atproto/core`, `oauth/core`, `store`, `irc/handshake`, `irc/mutate`,
`profile`, `members`, `reactions`, `replies`, `edits`, `clock`.

## Building

```bash
just nim-test     # the Nim test suite
just nim-lib      # libfrqcore.so into build/nim
```

Both want `nix develop .#nim`, and re-enter it themselves if they are not
already inside.