From c2dbf2c3040d05b8dfe888e305f4b691e774b952 Mon Sep 17 00:00:00 2001
From: Emily Toop <etoop@mozilla.com>
Date: Fri, 11 May 2018 12:23:32 +0100
Subject: [PATCH] Return `&str` from `c_char_to_string` rather than `String` to
 avoid unnecessary allocations.

---
 ffi/src/lib.rs   | 6 +++---
 ffi/src/utils.rs | 9 ++++-----
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/ffi/src/lib.rs b/ffi/src/lib.rs
index 037c9771..3b77ad33 100644
--- a/ffi/src/lib.rs
+++ b/ffi/src/lib.rs
@@ -296,7 +296,7 @@ pub unsafe extern "C" fn tx_report_get_tx_instant(tx_report: *mut TxReport) -> c
 pub unsafe extern "C" fn tx_report_entity_for_temp_id(tx_report: *mut TxReport, tempid: *const c_char) -> *mut c_longlong {
     let tx_report = &*tx_report;
     let key = c_char_to_string(tempid);
-    if let Some(entid) = tx_report.tempids.get(&key) {
+    if let Some(entid) = tx_report.tempids.get(key) {
         Box::into_raw(Box::new(entid.clone() as c_longlong))
     } else {
         std::ptr::null_mut()
@@ -853,14 +853,14 @@ pub unsafe extern "C" fn store_register_observer(store: *mut Store,
         };
         callback(string_to_c_char(obs_key), &reports);
     }));
-    store.register_observer(key, tx_observer);
+    store.register_observer(key.to_string(), tx_observer);
 }
 
 /// Unregisters a [TxObserver](mentat::TxObserver)  with the `key` to observe changes on this `store`.
 #[no_mangle]
 pub unsafe extern "C" fn store_unregister_observer(store: *mut Store, key: *const c_char) {
     let store = &mut*store;
-    let key = c_char_to_string(key);
+    let key = c_char_to_string(key).to_string();
     store.unregister_observer(&key);
 }
 
diff --git a/ffi/src/utils.rs b/ffi/src/utils.rs
index 76aeee47..1a4abbf5 100644
--- a/ffi/src/utils.rs
+++ b/ffi/src/utils.rs
@@ -19,19 +19,18 @@ pub mod strings {
         Keyword,
     };
 
-    pub fn c_char_to_string(cchar: *const c_char) -> String {
+    pub fn c_char_to_string(cchar: *const c_char) -> &'static str {
         let c_str = unsafe { CStr::from_ptr(cchar) };
-        let r_str = c_str.to_str().unwrap_or("");
-        r_str.to_string()
+        c_str.to_str().unwrap_or("")
     }
 
     pub fn string_to_c_char<T>(r_string: T) -> *mut c_char where T: Into<String> {
         CString::new(r_string.into()).unwrap().into_raw()
     }
 
+    pub fn kw_from_string(keyword_string: &'static str) -> NamespacedKeyword {
     // TODO: validate. The input might not be a keyword!
-    pub fn kw_from_string(mut keyword_string: String) -> Keyword {
-        let attr_name = keyword_string.split_off(1);
+        let attr_name = keyword_string.trim_left_matches(":");
         let parts: Vec<&str> = attr_name.split("/").collect();
         Keyword::namespaced(parts[0], parts[1])
     }