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28 lines
1.5 KiB
Markdown
28 lines
1.5 KiB
Markdown
# echo — CBOR-free `abi = c` C bindings
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Generated by `nimble genbindings_c_abi_echo` (`-d:targetLang=c_abi`), this is the
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**pure C ABI** rendering of the echo library, meant to be read side-by-side with
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the CBOR rendering in [`../c_bindings/`](../c_bindings/) (issue #105).
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| | `../c_bindings/` (`-d:targetLang=c`) | this dir (`-d:targetLang=c_abi`) |
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|---|---|---|
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| Wire format on the C side | CBOR | flat C structs (no serialization) |
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| Third-party dependency | vendored TinyCBOR | none |
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| Files | `echo.h` + `nim_ffi_cbor.h` + `nim_ffi_prelude.h` | one self-contained `echo.h` |
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| String type | `NimFfiStr` (owned) | `const char*` (borrowed for the call) |
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Both talk to the *same* unmodified Nim dylib API shape (`echo_ctx_create`,
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`echo_ctx_shout`, …) and share the async, binding-owned callback contract. The
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difference is only the ABI at the boundary: here the macro-generated `_CWire`
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structs (`ShoutRequest { const char* text; }`, …) are passed as native C structs
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and the Nim side converts them to/from Nim objects. CBOR is still used, but only
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as an internal transport between the exported wrapper and the FFI worker thread —
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it never appears in this header.
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The library is built with `-d:ffiEchoAbiC`, which flips the shared
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`examples/echo/echo.nim` source to `declareLibrary(..., defaultABIFormat = "c")`.
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A library that always wants the C ABI would set that in its own `declareLibrary`
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call and need no extra flag.
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Run the end-to-end test with `nimble test_c_abi_e2e`.
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