rework CastPtr, CastConstPtr, BoxCastPtr, ArcCastPtr

This commit reworks the existing `CastPtr`, `CastConstPtr`,
`BoxCastPtr`, and `ArcCastPtr` traits into a new `Castable` trait with
an associated `CastType`, constrained to be a type implementing the new
`CastTypeMarker` trait. Two implementations of this `CastTypeMarker`
trait are offered: `BoxCastTypeMarker` and `ArcCastTypeMarker`.

The net result is that the type system is now able to enforce our
invariant that a single type can't be cast as both an immutable `Arc`
over the underlying Rust type and a mutable `Box` over the underlying
Rust type.

Along the way crate-internal documentation for the traits and associated
free-standing helper `fs`s were reworked for clarity/consistency.

src/acceptor.rs

@@ -11,8 +11,8 @@ use crate::io::{rustls_read_callback, CallbackReader, ReadCallback};
 use crate::rslice::{rustls_slice_bytes, rustls_str};
 use crate::server::rustls_server_config;
 use crate::{
-    ffi_panic_boundary, rustls_result, try_arc_from_ptr, try_callback, try_mut_from_ptr,
-    try_ref_from_ptr, BoxCastPtr, CastPtr,
+    ffi_panic_boundary, free_box, rustls_result, set_boxed_mut_ptr, to_box, to_boxed_mut_ptr,
+    try_arc_from_ptr, try_callback, try_mut_from_ptr, try_ref_from_ptr, Castable, OwnershipBox,
 };
 use rustls_result::NullParameter;
 
@@ -42,12 +42,11 @@ pub struct rustls_acceptor {
     _private: [u8; 0],
 }
 
-impl CastPtr for rustls_acceptor {
+impl Castable for rustls_acceptor {
+    type Ownership = OwnershipBox;
     type RustType = Acceptor;
 }
 
-impl BoxCastPtr for rustls_acceptor {}
-
 /// A parsed ClientHello produced by a rustls_acceptor. It is used to check
 /// server name indication (SNI), ALPN protocols, signature schemes, and
 /// cipher suites. It can be combined with a rustls_server_config to build a
@@ -56,12 +55,11 @@ pub struct rustls_accepted {
     _private: [u8; 0],
 }
 
-impl CastPtr for rustls_accepted {
+impl Castable for rustls_accepted {
+    type Ownership = OwnershipBox;
     type RustType = Option<Accepted>;
 }
 
-impl BoxCastPtr for rustls_accepted {}
-
 impl rustls_acceptor {
     /// Create and return a new rustls_acceptor.
     ///
@@ -70,7 +68,7 @@ impl rustls_acceptor {
     #[no_mangle]
     pub extern "C" fn rustls_acceptor_new() -> *mut rustls_acceptor {
         ffi_panic_boundary! {
-            BoxCastPtr::to_mut_ptr(Acceptor::default())
+            to_boxed_mut_ptr(Acceptor::default())
         }
     }
 
@@ -84,7 +82,7 @@ impl rustls_acceptor {
     #[no_mangle]
     pub extern "C" fn rustls_acceptor_free(acceptor: *mut rustls_acceptor) {
         ffi_panic_boundary! {
-            BoxCastPtr::to_box(acceptor);
+            to_box(acceptor);
         }
     }
 
@@ -185,7 +183,7 @@ impl rustls_acceptor {
                 Ok(None) => rustls_result::AcceptorNotReady,
                 Err(e) => map_error(e),
                 Ok(Some(accepted)) => {
-                    BoxCastPtr::set_mut_ptr(out_accepted, Some(accepted));
+                    set_boxed_mut_ptr(out_accepted, Some(accepted));
                     rustls_result::Ok
                 }
             }
@@ -408,7 +406,7 @@ impl rustls_accepted {
             match accepted.into_connection(config) {
                 Ok(built) => {
                     let wrapped = crate::connection::Connection::from_server(built);
-                    BoxCastPtr::set_mut_ptr(out_conn, wrapped);
+                    set_boxed_mut_ptr(out_conn, wrapped);
                     rustls_result::Ok
                 },
                 Err(e) => map_error(e),
@@ -426,7 +424,7 @@ impl rustls_accepted {
     #[no_mangle]
     pub extern "C" fn rustls_accepted_free(accepted: *mut rustls_accepted) {
         ffi_panic_boundary! {
-            BoxCastPtr::to_box(accepted);
+            free_box(accepted);
         }
     }
 }

src/cipher.rs

@@ -18,8 +18,9 @@ use rustls_pemfile::{certs, crls, pkcs8_private_keys, rsa_private_keys};
 use crate::error::{map_error, rustls_result};
 use crate::rslice::{rustls_slice_bytes, rustls_str};
 use crate::{
-    ffi_panic_boundary, try_box_from_ptr, try_mut_from_ptr, try_ref_from_ptr, try_slice,
-    ArcCastPtr, BoxCastPtr, CastConstPtr, CastPtr,
+    ffi_panic_boundary, free_arc, to_arc_const_ptr, to_boxed_mut_ptr, try_box_from_ptr,
+    try_mut_from_ptr, try_ref_from_ptr, try_slice, Castable, OwnershipArc, OwnershipBox,
+    OwnershipRef,
 };
 use rustls_result::{AlreadyUsed, NullParameter};
 
@@ -33,7 +34,8 @@ pub struct rustls_certificate {
     _private: [u8; 0],
 }
 
-impl CastPtr for rustls_certificate {
+impl Castable for rustls_certificate {
+    type Ownership = OwnershipRef;
     type RustType = Certificate;
 }
 
@@ -66,7 +68,8 @@ pub struct rustls_supported_ciphersuite {
     _private: [u8; 0],
 }
 
-impl CastPtr for rustls_supported_ciphersuite {
+impl Castable for rustls_supported_ciphersuite {
+    type Ownership = OwnershipRef;
     type RustType = SupportedCipherSuite;
 }
 
@@ -262,12 +265,11 @@ pub struct rustls_certified_key {
     _private: [u8; 0],
 }
 
-impl CastPtr for rustls_certified_key {
+impl Castable for rustls_certified_key {
+    type Ownership = OwnershipArc;
     type RustType = CertifiedKey;
 }
 
-impl ArcCastPtr for rustls_certified_key {}
-
 impl rustls_certified_key {
     /// Build a `rustls_certified_key` from a certificate chain and a private key.
     /// `cert_chain` must point to a buffer of `cert_chain_len` bytes, containing
@@ -366,7 +368,7 @@ impl rustls_certified_key {
             } else {
                 new_key.ocsp = None;
             }
-            *cloned_key_out = ArcCastPtr::to_const_ptr(new_key);
+            *cloned_key_out = to_arc_const_ptr(new_key);
             rustls_result::Ok
         }
     }
@@ -380,7 +382,7 @@ impl rustls_certified_key {
     #[no_mangle]
     pub extern "C" fn rustls_certified_key_free(key: *const rustls_certified_key) {
         ffi_panic_boundary! {
-            rustls_certified_key::free(key);
+            free_arc(key);
         }
     }
 
@@ -443,12 +445,11 @@ pub struct rustls_root_cert_store {
     _private: [u8; 0],
 }
 
-impl CastPtr for rustls_root_cert_store {
+impl Castable for rustls_root_cert_store {
+    type Ownership = OwnershipBox;
     type RustType = RootCertStore;
 }
 
-impl BoxCastPtr for rustls_root_cert_store {}
-
 impl rustls_root_cert_store {
     /// Create a rustls_root_cert_store. Caller owns the memory and must
     /// eventually call rustls_root_cert_store_free. The store starts out empty.
@@ -458,7 +459,7 @@ impl rustls_root_cert_store {
     pub extern "C" fn rustls_root_cert_store_new() -> *mut rustls_root_cert_store {
         ffi_panic_boundary! {
             let store = rustls::RootCertStore::empty();
-            BoxCastPtr::to_mut_ptr(store)
+            to_boxed_mut_ptr(store)
         }
     }
 
@@ -517,14 +518,13 @@ pub struct rustls_allow_any_authenticated_client_builder {
     _private: [u8; 0],
 }
 
-impl CastPtr for rustls_allow_any_authenticated_client_builder {
-    // NOTE: contained value is consumed even on error, so this can contain None. but the caller
+impl Castable for rustls_allow_any_authenticated_client_builder {
+    type Ownership = OwnershipBox;
+    // NOTE: contained value is consumed even on error, so this can contain None, but the caller
     // still needs to free it
     type RustType = Option<AllowAnyAuthenticatedClient>;
 }
 
-impl BoxCastPtr for rustls_allow_any_authenticated_client_builder {}
-
 impl rustls_allow_any_authenticated_client_builder {
     /// Create a new allow any authenticated client certificate verifier builder using the root store.
     ///
@@ -542,7 +542,7 @@ impl rustls_allow_any_authenticated_client_builder {
         ffi_panic_boundary! {
             let store: &RootCertStore = try_ref_from_ptr!(store);
             let client_cert_verifier = Some(AllowAnyAuthenticatedClient::new(store.clone()));
-            BoxCastPtr::to_mut_ptr(client_cert_verifier)
+            to_boxed_mut_ptr(client_cert_verifier)
         }
     }
 
@@ -604,12 +604,11 @@ pub struct rustls_allow_any_authenticated_client_verifier {
     _private: [u8; 0],
 }
 
-impl CastConstPtr for rustls_allow_any_authenticated_client_verifier {
+impl Castable for rustls_allow_any_authenticated_client_verifier {
+    type Ownership = OwnershipArc;
     type RustType = AllowAnyAuthenticatedClient;
 }
 
-impl ArcCastPtr for rustls_allow_any_authenticated_client_verifier {}
-
 impl rustls_allow_any_authenticated_client_verifier {
     /// Create a new allow any authenticated client certificate verifier from a builder.
     ///
@@ -649,7 +648,7 @@ impl rustls_allow_any_authenticated_client_verifier {
         verifier: *const rustls_allow_any_authenticated_client_verifier,
     ) {
         ffi_panic_boundary! {
-            rustls_allow_any_authenticated_client_verifier::free(verifier);
+            free_arc(verifier);
         }
     }
 }
@@ -661,14 +660,13 @@ pub struct rustls_allow_any_anonymous_or_authenticated_client_builder {
     _private: [u8; 0],
 }
 
-impl CastPtr for rustls_allow_any_anonymous_or_authenticated_client_builder {
-    // NOTE: contained value is consumed even on error, so this can contain None. but the caller
+impl Castable for rustls_allow_any_anonymous_or_authenticated_client_builder {
+    type Ownership = OwnershipBox;
+    // NOTE: contained value is consumed even on error, so this can contain None, but the caller
     // still needs to free it
     type RustType = Option<AllowAnyAnonymousOrAuthenticatedClient>;
 }
 
-impl BoxCastPtr for rustls_allow_any_anonymous_or_authenticated_client_builder {}
-
 impl rustls_allow_any_anonymous_or_authenticated_client_builder {
     /// Create a new allow any anonymous or authenticated client certificate verifier builder
     /// using the root store.
@@ -688,7 +686,7 @@ impl rustls_allow_any_anonymous_or_authenticated_client_builder {
         ffi_panic_boundary! {
             let store: &RootCertStore = try_ref_from_ptr!(store);
             let client_cert_verifier = Some(AllowAnyAnonymousOrAuthenticatedClient::new(store.clone()));
-            BoxCastPtr::to_mut_ptr(client_cert_verifier)
+            to_boxed_mut_ptr(client_cert_verifier)
         }
     }
 
@@ -753,12 +751,11 @@ pub struct rustls_allow_any_anonymous_or_authenticated_client_verifier {
     _private: [u8; 0],
 }
 
-impl CastConstPtr for rustls_allow_any_anonymous_or_authenticated_client_verifier {
+impl Castable for rustls_allow_any_anonymous_or_authenticated_client_verifier {
+    type Ownership = OwnershipArc;
     type RustType = AllowAnyAnonymousOrAuthenticatedClient;
 }
 
-impl ArcCastPtr for rustls_allow_any_anonymous_or_authenticated_client_verifier {}
-
 impl rustls_allow_any_anonymous_or_authenticated_client_verifier {
     /// Create a new allow any anonymous or authenticated client certificate verifier builder
     /// from the builder.
@@ -799,7 +796,7 @@ impl rustls_allow_any_anonymous_or_authenticated_client_verifier {
         verifier: *const rustls_allow_any_anonymous_or_authenticated_client_verifier,
     ) {
         ffi_panic_boundary! {
-            rustls_allow_any_anonymous_or_authenticated_client_verifier::free(verifier);
+            free_arc(verifier);
         }
     }
 }

src/client.rs

@@ -21,8 +21,9 @@ use crate::error::{self, rustls_result};
 use crate::rslice::NulByte;
 use crate::rslice::{rustls_slice_bytes, rustls_slice_slice_bytes, rustls_str};
 use crate::{
-    ffi_panic_boundary, try_arc_from_ptr, try_box_from_ptr, try_mut_from_ptr, try_ref_from_ptr,
-    try_slice, userdata_get, ArcCastPtr, BoxCastPtr, CastConstPtr, CastPtr,
+    ffi_panic_boundary, free_arc, free_box, set_boxed_mut_ptr, to_arc_const_ptr, to_boxed_mut_ptr,
+    try_arc_from_ptr, try_box_from_ptr, try_mut_from_ptr, try_ref_from_ptr, try_slice,
+    userdata_get, Castable, OwnershipArc, OwnershipBox,
 };
 
 /// A client config being constructed. A builder can be modified by,
@@ -47,12 +48,11 @@ pub(crate) struct ClientConfigBuilder {
     cert_resolver: Option<Arc<dyn rustls::client::ResolvesClientCert>>,
 }
 
-impl CastPtr for rustls_client_config_builder {
+impl Castable for rustls_client_config_builder {
+    type Ownership = OwnershipBox;
     type RustType = ClientConfigBuilder;
 }
 
-impl BoxCastPtr for rustls_client_config_builder {}
-
 /// A client config that is done being constructed and is now read-only.
 /// Under the hood, this object corresponds to an `Arc<ClientConfig>`.
 /// <https://docs.rs/rustls/latest/rustls/struct.ClientConfig.html>
@@ -63,12 +63,11 @@ pub struct rustls_client_config {
     _private: [u8; 0],
 }
 
-impl CastConstPtr for rustls_client_config {
+impl Castable for rustls_client_config {
+    type Ownership = OwnershipArc;
     type RustType = ClientConfig;
 }
 
-impl ArcCastPtr for rustls_client_config {}
-
 struct NoneVerifier;
 
 impl ServerCertVerifier for NoneVerifier {
@@ -106,7 +105,7 @@ impl rustls_client_config_builder {
                 alpn_protocols: vec![],
                 enable_sni: true,
             };
-            BoxCastPtr::to_mut_ptr(builder)
+            to_boxed_mut_ptr(builder)
         }
     }
 
@@ -169,7 +168,7 @@ impl rustls_client_config_builder {
                 enable_sni: true,
             };
 
-            BoxCastPtr::set_mut_ptr(builder_out, config_builder);
+            set_boxed_mut_ptr(builder_out, config_builder);
             rustls_result::Ok
         }
     }
@@ -492,7 +491,7 @@ impl rustls_client_config_builder {
             };
             config.alpn_protocols = builder.alpn_protocols;
             config.enable_sni = builder.enable_sni;
-            ArcCastPtr::to_const_ptr(config)
+            to_arc_const_ptr(config)
         }
     }
 
@@ -504,7 +503,7 @@ impl rustls_client_config_builder {
     #[no_mangle]
     pub extern "C" fn rustls_client_config_builder_free(config: *mut rustls_client_config_builder) {
         ffi_panic_boundary! {
-            BoxCastPtr::to_box(config);
+            free_box(config);
         }
     }
 }
@@ -519,7 +518,7 @@ impl rustls_client_config {
     #[no_mangle]
     pub extern "C" fn rustls_client_config_free(config: *const rustls_client_config) {
         ffi_panic_boundary! {
-            rustls_client_config::free(config);
+            free_arc(config);
         }
     }
 
@@ -561,7 +560,7 @@ impl rustls_client_config {
         // to the caller. After this point, we must return rustls_result::Ok so the
         // caller knows it is responsible for this memory.
         let c = Connection::from_client(client);
-        BoxCastPtr::set_mut_ptr(conn_out, c);
+        set_boxed_mut_ptr(conn_out, c);
         rustls_result::Ok
         }
     }