# echo — CBOR-free (`abi = c`) C bindings

Generated by `nimble genbindings_c_abi_echo`, this is the **pure C ABI**
rendering of the echo library, meant to be read side-by-side with the CBOR
rendering in [`../c_bindings/`](../c_bindings/) (issue #105). Both come from the
single `c` target (`-d:targetLang=c`); the library's `defaultABIFormat` picks
the shape.

| | `../c_bindings/` (`abi = cbor`) | this dir (`abi = c`) |
|---|---|---|
| Wire format on the C side | CBOR | native C structs (no serialization) |
| Third-party dependency | vendored TinyCBOR | none |
| Files | `echo.h` + `nim_ffi_cbor.h` + `nim_ffi_prelude.h` | one self-contained `echo.h` |
| String type | `NimFfiStr` (owned) | `const char*` (borrowed for the call) |

Both talk to the *same* unmodified Nim dylib API shape (`echo_ctx_create`,
`echo_ctx_shout`, …) and share the async, binding-owned callback contract. The
difference is only the ABI at the boundary: here the macro-generated `_CWire`
structs (`ShoutRequest { const char* text; }`, …) are passed as native C structs
and the Nim side converts them to/from Nim objects. CBOR is still used, but only
as an internal transport between the exported wrapper and the FFI worker thread —
it never appears in this header.

The library is built with `-d:ffiEchoAbiC`, which flips the shared
`examples/echo/echo.nim` source to `declareLibrary(..., defaultABIFormat = "c")`.
A library that always wants the C ABI would set that in its own `declareLibrary`
call and need no extra flag.

Run the end-to-end test with `nimble test_c_abi_e2e`.