gnucobol-rs-ffi

A cob_field C-ABI shim that exposes the native-Rust libcob algorithms of gnucobol-rs with extern "C" linkage, so a C program can link gnucobol-rs as a drop-in libcob replacement. The cob_field / cob_field_attr struct layouts match GnuCOBOL 3.2's libcob (common.h), so existing field buffers work unchanged.

This is the only crate in the workspace that uses unsafe — confined to the raw-pointer C boundary. The gnucobol-rs core stays #![forbid(unsafe_code)]; every function here just reads the C struct, calls the safe-Rust algorithm, and writes the result back.

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Use it

#include "gnucobol-rs-ffi.h"

cob_field_attr da  = { 0x12 /*PACKED*/, 4, 0, 0, 0 };
cob_field      dst = { 3, buf, &da };

cob_move(&src, &dst);            /* native-Rust MOVE, byte-identical to libcob */
int n = cob_get_int(&dst);

Build a cdylib (libgnucobol_rs_ffi.so) or staticlib and link it where you would link libcob. Exports: cob_move, cob_get_int, cob_get_llint, cob_set_int, and cobrs_version(). The header include/gnucobol-rs-ffi.h mirrors libcob common.h (cob_field_attr @1097, cob_field @1107).

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Verified byte-identical to libcob

tests/verify_vs_libcob.sh compiles the same C program against both libgnucobol_rs_ffi and the real libcob and requires identical output. Correctness is judged against the admitted GnuCOBOL 3.2 oracle, not self-asserted.

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Crate types & license

• Crate types: cdylib / staticlib / rlib.
• License: LGPL-3.0-or-later — this shim exposes the LGPL gnucobol-rs runtime, which is a faithful copyleft derivative of libcob, not clean-room. A distributed binary that statically links it is a Combined Work under LGPL-3.0 §4.

This is an independent effort that reproduces GnuCOBOL 3.2; it is not GnuCOBOL and not affiliated with or endorsed by the GNU project. See the docs/derivation-and-license.md and docs/license-boundaries.md in the repository for the full derivation boundary.