ssl: Use Box instead of Arc for SSL

It seems that we can be more strict here - CassSSL type do not
require shared ownership.

scylla-rust-wrapper/src/cluster.rs

@@ -818,7 +818,7 @@ pub unsafe extern "C" fn cass_cluster_set_retry_policy(
 #[no_mangle]
 pub unsafe extern "C" fn cass_cluster_set_ssl(cluster: *mut CassCluster, ssl: *mut CassSsl) {
     let cluster_from_raw = BoxFFI::as_mut_ref(cluster);
-    let cass_ssl = ArcFFI::cloned_from_ptr(ssl);
+    let cass_ssl = BoxFFI::as_ref(ssl);
 
     let ssl_context_builder = SslContextBuilder::from_ptr(cass_ssl.ssl_context);
     // Reference count is increased as tokio_openssl will try to free `ssl_context` when calling `SSL_free`.

scylla-rust-wrapper/src/ssl.rs

@@ -1,4 +1,4 @@
-use crate::argconv::ArcFFI;
+use crate::argconv::BoxFFI;
 use crate::cass_error::CassError;
 use crate::types::size_t;
 use libc::{c_int, strlen};
@@ -12,14 +12,13 @@ use openssl_sys::{
 use std::convert::TryInto;
 use std::os::raw::c_char;
 use std::os::raw::c_void;
-use std::sync::Arc;
 
 pub struct CassSsl {
     pub(crate) ssl_context: *mut SSL_CTX,
     pub(crate) trusted_store: *mut X509_STORE,
 }
 
-impl ArcFFI for CassSsl {}
+impl BoxFFI for CassSsl {}
 
 pub const CASS_SSL_VERIFY_NONE: i32 = 0x00;
 pub const CASS_SSL_VERIFY_PEER_CERT: i32 = 0x01;
@@ -45,16 +44,9 @@ pub unsafe extern "C" fn cass_ssl_new_no_lib_init() -> *const CassSsl {
         trusted_store,
     };
 
-    ArcFFI::into_ptr(Arc::new(ssl))
+    BoxFFI::into_ptr(Box::new(ssl))
 }
 
-// This is required for the type system to impl Send + Sync for Arc<CassSsl>.
-// Otherwise, clippy complains about using Arc where Rc would do.
-// In our case, though, we need to use Arc because we potentially do share
-// the Arc between threads, so employing Rc here would lead to races.
-unsafe impl Send for CassSsl {}
-unsafe impl Sync for CassSsl {}
-
 impl Drop for CassSsl {
     fn drop(&mut self) {
         unsafe {
@@ -65,7 +57,7 @@ impl Drop for CassSsl {
 
 #[no_mangle]
 pub unsafe extern "C" fn cass_ssl_free(ssl: *mut CassSsl) {
-    ArcFFI::free(ssl);
+    BoxFFI::free(ssl);
 }
 
 unsafe extern "C" fn pem_password_callback(
@@ -112,7 +104,7 @@ pub unsafe extern "C" fn cass_ssl_add_trusted_cert_n(
     cert: *const c_char,
     cert_length: size_t,
 ) -> CassError {
-    let ssl = ArcFFI::cloned_from_ptr(ssl);
+    let ssl = BoxFFI::as_mut_ref(ssl);
     let bio = BIO_new_mem_buf(cert as *const c_void, cert_length.try_into().unwrap());
 
     if bio.is_null() {
@@ -140,7 +132,7 @@ pub unsafe extern "C" fn cass_ssl_add_trusted_cert_n(
 
 #[no_mangle]
 pub unsafe extern "C" fn cass_ssl_set_verify_flags(ssl: *mut CassSsl, flags: i32) {
-    let ssl = ArcFFI::cloned_from_ptr(ssl);
+    let ssl = BoxFFI::as_mut_ref(ssl);
 
     match flags {
         CASS_SSL_VERIFY_NONE => {
@@ -178,7 +170,7 @@ pub unsafe extern "C" fn cass_ssl_set_cert_n(
     cert: *const c_char,
     cert_length: size_t,
 ) -> CassError {
-    let ssl = ArcFFI::cloned_from_ptr(ssl);
+    let ssl = BoxFFI::as_mut_ref(ssl);
     let bio = BIO_new_mem_buf(cert as *const c_void, cert_length.try_into().unwrap());
 
     if bio.is_null() {
@@ -271,7 +263,7 @@ pub unsafe extern "C" fn cass_ssl_set_private_key_n(
     password: *mut c_char,
     _password_length: size_t,
 ) -> CassError {
-    let ssl = ArcFFI::cloned_from_ptr(ssl);
+    let ssl = BoxFFI::as_mut_ref(ssl);
     let bio = BIO_new_mem_buf(key as *const c_void, key_length.try_into().unwrap());
 
     if bio.is_null() {