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98e8e8829f
Update the native C example to cast each struct return's callback msg to its `const <Type>*` and read it in-callback (EchoResponse, ComplexResponse), instead of scanning opaque bytes. Regenerate the headers with the new return-shape note. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
42 lines
1.9 KiB
Markdown
42 lines
1.9 KiB
Markdown
# C bindings — native (same-process) example
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Generated C headers for the timer library plus a small driver that links the
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library directly and calls the **native** (zero-serialization) ABI.
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## Files
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| File | Description |
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|------|-------------|
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| `my_timer.h` | Native ABI: each `{.ffi.}` type is a plain C `struct`, passed by value to `int <name>(ctx, cb, ud, <args…>)`. Results arrive on the callback. Best for same-process callers — no serialization. |
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| `my_timer_cbor.h` | CBOR ABI (`<name>_cbor`): request/response as CBOR bytes. Use this when the call crosses a process or machine boundary. See [`../ipc`](../ipc). |
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| `example.c` | Native same-process driver: create → version → echo → complex → destroy. |
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| `Makefile` | Builds the Nim dylib (from the repo root) and the driver. |
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The headers are regenerated by `nimble genbindings_c` (run from the repo root)
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and overwritten each time — don't edit them by hand.
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## Build & run
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```sh
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cd examples/timer/c_bindings
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make run
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```
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This compiles `libmy_timer.{dylib,so}` and runs `./example`, which prints the
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library version and the round-tripped echo/complex responses. Every call is
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dispatched on the library's FFI thread, so the driver blocks on a condvar-backed
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callback for each result.
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## Native vs CBOR
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The native path passes `{.ffi.}` structs as flat C-POD values (`const char*` for
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strings, `{ T* ptr; size_t len }` for sequences, `{ int present; T }` for
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options). Arguments are **deep-copied** across the FFI-thread boundary, so the C
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caller's buffers can be freed immediately after the call returns. String returns
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arrive as raw bytes; **struct returns arrive as a typed `const <Type>*`** in the
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callback (cast and read it there — it is valid only for the callback's lifetime,
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and the library deep-frees it afterwards, so copy out anything you need).
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For the cross-process / cross-machine path, the same library is reached over a
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socket using the CBOR ABI — see [`../ipc`](../ipc).
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