Get `run_key_action` to export correctly to C

Add a new wrapper function for `run_key_action` that uses C appropriate
inputs & outputs and calls into our Rusty `run_key_action`. This new
function now correctly gets a header generated for it by 'cbindgen'.

Immense thanks to Jake Goulding on the Rust FFI Omnibus for showing me
how to pass a slice argument from C:
http://jakegoulding.com/rust-ffi-omnibus/slice_arguments/

In order to pass the slice from C, we need to pass a C array and its
length to the function. Cool.

4 files changed, 21 insertions, 0 deletions

diff --git a/Cargo.toml b/Cargo.toml
index dca6231..2c2176e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,6 +5,7 @@ version = "0.0.1"
 [dependencies]
 cocoa = "0.18.0"
 combine = "3.4.0"
+libc = "0.2.43"
 
 [build-dependencies]
 cbindgen = "0.6.2"
diff --git a/dome_key_map.h b/dome_key_map.h
index 473d2f0..d128979 100644
--- a/dome_key_map.h
+++ b/dome_key_map.h
@@ -20,3 +20,5 @@ typedef struct {
   Option_CString action;
   MapKind kind;
 } KeyActionResult;
+
+const KeyActionResult *c_run_key_action(const HeadphoneButton *trigger, size_t length);
diff --git a/src/cocoa_bridge.rs b/src/cocoa_bridge.rs
index d4749f0..d98701f 100644
--- a/src/cocoa_bridge.rs
+++ b/src/cocoa_bridge.rs
@@ -1,7 +1,9 @@
 use std::ffi::CString;
+use std::slice;
 
 use cocoa::base::nil;
 use cocoa::foundation::{NSArray, NSAutoreleasePool, NSDictionary};
+use libc::size_t;
 
 use {HeadphoneButton, MapGroup, MapKind};
 
@@ -45,6 +47,21 @@ pub struct KeyActionResult {
 }
 
 #[no_mangle]
+pub extern "C" fn c_run_key_action(
+    trigger: *const HeadphoneButton,
+    length: size_t,
+) -> *const KeyActionResult {
+    let trigger = unsafe {
+        assert!(!trigger.is_null());
+
+        slice::from_raw_parts(trigger, length as usize)
+    };
+
+    let result = run_key_action(trigger).unwrap();
+    &result as *const KeyActionResult
+}
+
+#[no_mangle]
 pub extern "C" fn run_key_action(
     trigger: &[HeadphoneButton]
 ) -> Option<KeyActionResult> {
diff --git a/src/lib.rs b/src/lib.rs
index db113dc..cf7dd1e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,6 +2,7 @@ extern crate cocoa;
 
 #[macro_use]
 extern crate combine;
+extern crate libc;
 
 mod cocoa_bridge;
 mod parser;