add some UUID support

lib/src/lib.rs

@@ -1 +1,2 @@
 pub mod replica;
+pub mod uuid;

lib/src/uuid.rs

@@ -0,0 +1,63 @@
+use libc;
+use taskchampion::Uuid as TcUuid;
+
+/// Uuid is used as a task identifier.  Uuids do not contain any pointers and need not be freed.
+#[repr(C)]
+pub struct Uuid([u8; 16]);
+
+impl From<TcUuid> for Uuid {
+    fn from(uuid: TcUuid) -> Uuid {
+        // TODO: can we avoid clone here?
+        Uuid(uuid.as_bytes().clone())
+    }
+}
+
+impl From<Uuid> for TcUuid {
+    fn from(uuid: Uuid) -> TcUuid {
+        TcUuid::from_bytes(uuid.0)
+    }
+}
+
+/// Create a new, randomly-generated UUID.
+#[no_mangle]
+pub extern "C" fn tc_uuid_new_v4() -> Uuid {
+    TcUuid::new_v4().into()
+}
+
+/// Create a new UUID with the nil value.
+#[no_mangle]
+pub extern "C" fn tc_uuid_nil() -> Uuid {
+    TcUuid::nil().into()
+}
+
+/// Length, in bytes, of a C string containing a Uuid.
+#[no_mangle]
+pub static TC_UUID_STRING_BYTES: usize = ::uuid::adapter::Hyphenated::LENGTH;
+
+/// Write the string representation of a Uuid into the given buffer, which must be
+/// at least TC_UUID_STRING_BYTES long.  No NUL terminator is added.
+#[no_mangle]
+pub extern "C" fn tc_uuid_to_str<'a>(uuid: Uuid, out: *mut libc::c_char) {
+    debug_assert!(!out.is_null());
+    let buf: &'a mut [u8] = unsafe {
+        std::slice::from_raw_parts_mut(out as *mut u8, ::uuid::adapter::Hyphenated::LENGTH)
+    };
+    let uuid: TcUuid = uuid.into();
+    uuid.to_hyphenated().encode_lower(buf);
+}
+
+/// Parse the given value as a UUID.  The value must be exactly TC_UUID_STRING_BYTES long.  Returns
+/// false on failure.
+#[no_mangle]
+pub extern "C" fn tc_uuid_from_str<'a>(val: *const libc::c_char, out: *mut Uuid) -> bool {
+    debug_assert!(!val.is_null());
+    debug_assert!(!out.is_null());
+    let slice = unsafe { std::slice::from_raw_parts(val as *const u8, TC_UUID_STRING_BYTES) };
+    if let Ok(s) = std::str::from_utf8(slice) {
+        if let Ok(u) = TcUuid::parse_str(s) {
+            unsafe { *out = u.into() };
+            return true;
+        }
+    }
+    false
+}