Fix documented lifetime on connection getters (#194)

And change rustls_connection_get_peer_certificate to take a `*const rustls_connection`.

Fixes #178.

CHANGELOG.md

@@ -55,6 +55,10 @@ If you are importing this as a library from other Rust code, you should import `
   rustls_server_config_builder_set_client_verifier and
   rustls_server_config_builder_set_client_verifier_optional, which are setters
   rather than constructors.
+- The documented lifetime for pointers returned by rustls_connection_get_peer_certificate
+  and rustls_connection_get_alpn_protocol has been fixed - the pointers those
+  functions provide are valid until the next mutating function call on that
+  connection.
 
 ## Removed
 

src/connection.rs

@@ -307,15 +307,18 @@ impl rustls_connection {
     /// Index 0 is the end entity certificate. Higher indexes are certificates
     /// in the chain. Requesting an index higher than what is available returns
     /// NULL.
-    /// The returned pointer lives as long as the rustls_connection does.
+    /// The returned pointer is valid until the next mutating function call
+    /// affecting the connection. A mutating function call is one where the
+    /// first argument has type `struct rustls_connection *` (as opposed to
+    ///  `const struct rustls_connection *`).
     /// <https://docs.rs/rustls/0.20.0/rustls/enum.Connection.html#method.peer_certificates>
     #[no_mangle]
     pub extern "C" fn rustls_connection_get_peer_certificate(
-        conn: *mut rustls_connection,
+        conn: *const rustls_connection,
         i: size_t,
     ) -> *const rustls_certificate {
         ffi_panic_boundary! {
-            let conn: &mut Connection = try_mut_from_ptr!(conn);
+            let conn: &Connection = try_ref_from_ptr!(conn);
             match conn.peer_certificates().and_then(|c| c.get(i)) {
                 Some(cert) => cert as *const Certificate as *const _,
                 None => null()
@@ -328,6 +331,10 @@ impl rustls_connection {
     /// The borrow lives as long as the connection.
     /// If the connection is still handshaking, or no ALPN protocol was negotiated,
     /// stores NULL and 0 in the output parameters.
+    /// The provided pointer is valid until the next mutating function call
+    /// affecting the connection. A mutating function call is one where the
+    /// first argument has type `struct rustls_connection *` (as opposed to
+    ///  `const struct rustls_connection *`).
     /// <https://www.iana.org/assignments/tls-parameters/>
     /// <https://docs.rs/rustls/0.20.0/rustls/enum.Connection.html#method.alpn_protocol>
     #[no_mangle]
@@ -385,9 +392,13 @@ impl rustls_connection {
                 Some(cs) => cs,
                 None => return null(),
             };
-            for &cs in ALL_CIPHER_SUITES {
-                if negotiated == cs {
-                    return &cs as *const SupportedCipherSuite as *const _;
+            for cs in ALL_CIPHER_SUITES {
+                // This type annotation is here to enforce the lifetime stated
+                // in the doccomment - that the returned pointer lives as long
+                // as the program.
+                let cs: &'static SupportedCipherSuite = cs;
+                if negotiated == *cs {
+                    return cs as *const SupportedCipherSuite as *const _;
                 }
             }
             null()

src/rustls.h

@@ -904,10 +904,13 @@ void rustls_connection_send_close_notify(struct rustls_connection *conn);
  * Index 0 is the end entity certificate. Higher indexes are certificates
  * in the chain. Requesting an index higher than what is available returns
  * NULL.
- * The returned pointer lives as long as the rustls_connection does.
+ * The returned pointer is valid until the next mutating function call
+ * affecting the connection. A mutating function call is one where the
+ * first argument has type `struct rustls_connection *` (as opposed to
+ *  `const struct rustls_connection *`).
  * <https://docs.rs/rustls/0.20.0/rustls/enum.Connection.html#method.peer_certificates>
  */
-const struct rustls_certificate *rustls_connection_get_peer_certificate(struct rustls_connection *conn,
+const struct rustls_certificate *rustls_connection_get_peer_certificate(const struct rustls_connection *conn,
                                                                         size_t i);
 
 /**
@@ -916,6 +919,10 @@ const struct rustls_certificate *rustls_connection_get_peer_certificate(struct r
  * The borrow lives as long as the connection.
  * If the connection is still handshaking, or no ALPN protocol was negotiated,
  * stores NULL and 0 in the output parameters.
+ * The provided pointer is valid until the next mutating function call
+ * affecting the connection. A mutating function call is one where the
+ * first argument has type `struct rustls_connection *` (as opposed to
+ *  `const struct rustls_connection *`).
  * <https://www.iana.org/assignments/tls-parameters/>
  * <https://docs.rs/rustls/0.20.0/rustls/enum.Connection.html#method.alpn_protocol>
  */