Add FFI wrappers for constructing and deleting MessagePact (#43)

Fixes #35, #36

rust/pact_matching_ffi/src/models/message_pact.rs

@@ -0,0 +1,62 @@
+//! FFI wrapper for `MessagePact` from pact_matching.
+
+use anyhow::{anyhow, Context};
+use libc::{c_char, c_int, EXIT_FAILURE, EXIT_SUCCESS};
+
+// Necessary to make 'cbindgen' generate an opaque struct on the C side.
+pub use pact_matching::models::message_pact::MessagePact;
+
+use crate::util::*;
+use crate::{cstr, ffi, safe_str};
+
+/// Construct a new `MessagePact` from the JSON string.
+/// The provided file name is used when generating error messages.
+#[no_mangle]
+#[allow(clippy::missing_safety_doc)]
+pub unsafe extern "C" fn message_pact_new_from_json(
+    file_name: *const c_char,
+    json_str: *const c_char,
+) -> *mut MessagePact {
+    ffi! {
+        name: "message_pact_new_from_json",
+        params: [file_name, json_str],
+        op: {
+            let file_name = safe_str!(file_name);
+            let json_str = safe_str!(json_str);
+
+            let json_value: serde_json::Value =
+                serde_json::from_str(json_str)
+                .context("error parsing json_str as JSON")?;
+
+            let message_pact = MessagePact::from_json(
+                &file_name.to_string(),
+                &json_value,
+            ).map_err(|e| anyhow!("{}", e))?;
+
+            Ok(ptr::raw_to(message_pact))
+        },
+        fail: {
+            ptr::null_mut_to::<MessagePact>()
+        }
+    }
+}
+
+/// Delete the `MessagePact` being pointed to.
+#[no_mangle]
+#[allow(clippy::missing_safety_doc)]
+pub unsafe extern "C" fn message_pact_delete(
+    message_pact: *mut MessagePact,
+) -> c_int {
+    ffi! {
+        name: "message_pact_delete",
+        params: [message_pact],
+        op: {
+            ptr::drop_raw(message_pact);
+            Ok(EXIT_SUCCESS)
+        },
+        fail: {
+            EXIT_FAILURE
+        }
+    }
+}
+

rust/pact_matching_ffi/src/models/mod.rs

@@ -1,5 +1,6 @@
 //! Represents messages in `pact_matching`.
 
 pub mod message;
+pub mod message_pact;
 pub mod pact_specification;
 pub mod provider_state;