RSDK-4755: accept entity string for rpc dial (#75)

Author: ohEmily

examples/src/ffi/cpp/ffi_echo.cc

@@ -19,7 +19,7 @@ using proto::rpc::examples::echo::v1::EchoService;
 extern "C" void *init_rust_runtime();
 extern "C" int free_rust_runtime(void *ptr);
 extern "C" void free_string(char* s);
-extern "C" char *dial(const char *uri, const char *type, const char *payload,
+extern "C" char *dial(const char *uri, const char *entity, const char *type, const char *payload,
                              bool allow_insecure, void *ptr);
 
 class EchoServiceClient {

examples/src/ffi/cpp/ffi_robot.cc

@@ -19,7 +19,7 @@ using viam::robot::v1::ResourceNamesResponse;
 extern "C" void *init_rust_runtime();
 extern "C" int free_rust_runtime(void *ptr);
 extern "C" void free_string(char* s);
-extern "C" char *dial(const char *uri, const char *type, const char *payload,
+extern "C" char *dial(const char *uri, const char *entity, const char *type, const char *payload,
                              bool allow_insecure, void *ptr);
 
 class RobotServiceClient {

src/ffi/dial_ffi.rs

@@ -87,12 +87,13 @@ fn dial_without_cred(
 
 fn dial_with_cred(
     uri: String,
+    entity: Option<String>,
     r#type: &str,
     payload: &str,
     allow_insec: bool,
     disable_webrtc: bool,
 ) -> Result<DialBuilder<WithCredentials>> {
-    let creds = RPCCredentials::new(None, String::from(r#type), String::from(payload));
+    let creds = RPCCredentials::new(entity, String::from(r#type), String::from(payload));
     let c = DialOptions::builder().uri(&uri).with_credentials(creds);
     let c = if disable_webrtc {
         c.disable_webrtc()
@@ -117,6 +118,7 @@ fn dial_with_cred(
 #[no_mangle]
 pub unsafe extern "C" fn dial(
     c_uri: *const c_char,
+    c_entity: *const c_char,
     c_type: *const c_char,
     c_payload: *const c_char,
     c_allow_insec: bool,
@@ -184,11 +186,25 @@ pub unsafe extern "C" fn dial(
             false => Some(CStr::from_ptr(c_payload)),
         }
     };
+    let entity_opt = {
+        match c_entity.is_null() {
+            true => None,
+            false => match CStr::from_ptr(c_entity).to_str() {
+                Ok(ent) => Some(ent.to_string()),
+                Err(e) => {
+                    log::error!("Error unexpectedly received an invalid entity string {:?}", e);
+                    return ptr::null_mut();
+                }
+            }
+        }
+    };
+
     let (server, channel) = match runtime.block_on(async move {
         let channel = match (r#type, payload) {
             (Some(t), Some(p)) => {
                 dial_with_cred(
                     uri_str,
+                    entity_opt,
                     t.to_str()?,
                     p.to_str()?,
                     allow_insec,