First commit

.gitignore

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+/target
+*.h
+/main
+/Cargo.lock

Cargo.toml

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+[package]
+name = "bdk_ffi"
+version = "0.1.0"
+authors = ["Steve Myers <steve@notmandatory.org>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[lib]
+crate-type = ["staticlib"]
+
+[dependencies]
+bdk = { version = "^0.7", feature = ["all-keys"] }
+safer-ffi = { version = "*", features = ["proc_macros"]}
+
+[features]
+c-headers = ["safer-ffi/headers"]

main.c

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+#include <stdlib.h>
+
+#include "bdk_ffi.h"
+
+int main (int argc, char const * const argv[])
+{
+    Point_t * a = new_point(84,45);
+    Point_t * b = new_point(0.0,39.0);
+    Point_t * m = mid_point(a, b);
+    print_point(m);
+    print_point(NULL);
+    return EXIT_SUCCESS;
+}

src/lib.rs

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+use ::safer_ffi::prelude::*;
+
+/// A `struct` usable from both Rust and C
+#[derive_ReprC]
+#[repr(C)]
+#[derive(Debug, Clone, Copy)]
+pub struct Point {
+    x: f64,
+    y: f64,
+}
+
+/* Export a Rust function to the C world. */
+/// Returns the middle point of `[a, b]`.
+#[ffi_export]
+fn mid_point(a: Option<repr_c::Box<Point>>, b: Option<repr_c::Box<Point>>) -> repr_c::Box<Point> {
+    let a = a.unwrap();
+    let b = b.unwrap();
+    repr_c::Box::new(Point {
+        x: (a.x + b.x) / 2.,
+        y: (a.y + b.y) / 2.,
+    })
+}
+
+/// Pretty-prints a point using Rust's formatting logic.
+#[ffi_export]
+fn print_point(point: Option<repr_c::Box<Point>>) {
+    println!("{:?}", point);
+}
+
+#[ffi_export]
+fn new_point(x: f64, y: f64) -> repr_c::Box<Point> {
+    repr_c::Box::new(Point { x, y })
+}
+
+#[ffi_export]
+fn free_point(point: Option<repr_c::Box<Point>>) {
+    drop(point)
+}
+
+/// The following test function is necessary for the header generation.
+#[::safer_ffi::cfg_headers]
+#[test]
+fn generate_headers() -> ::std::io::Result<()> {
+    ::safer_ffi::headers::builder()
+        .to_file("bdk_ffi.h")?
+        .generate()
+}