Added the 'AsAny' trait to allow casting from 'FapiCallback' to the concrete type, even in older Rust versions.

Author: danieltrick

.github/workflows/cargo-workflow.yaml

@@ -5,7 +5,7 @@ on:
       TOOLCHAIN_MIN:
         required: false
         type: string
-        default: "1.86.0"
+        default: "1.85.0"
       TOOLCHAIN_MAX:
         required: false
         type: string

Cargo.toml

@@ -2,7 +2,7 @@
 name = "tss2-fapi-rs"
 version = "0.9.0"
 edition = "2024"
-rust-version = "1.86"
+rust-version = "1.85"
 description = "Provides a Rust interface to the TSS2.0 Feature API (FAPI)"
 license = "BSD-3-Clause"
 authors = ["Daniel Trick <daniel.trick@sit.fraunhofer.de>"]

src/callback.rs

@@ -100,16 +100,41 @@ impl<'a> PolicyActionCbParam<'a> {
     }
 }
 
+// ==========================================================================
+// AsAny trait
+// ==========================================================================
+
+/// Helper trait that provides the [`as_any()`](AsAny::as_any) and [`as_mut_any()`](AsAny::as_mut_any) functions.
+pub trait AsAny {
+    /// A helper function that returns the implementation as a [`&dyn Any`](std::any::Any) reference.
+    fn as_any(&self) -> &dyn Any;
+
+    /// A helper function that returns the implementation as a [`&mut dyn Any`](std::any::Any) reference.
+    fn as_mut_any(&mut self) -> &mut dyn Any;
+}
+
+impl<T: Any> AsAny for T {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn as_mut_any(&mut self) -> &mut dyn Any {
+        self
+    }
+}
+
 // ==========================================================================
 // Callbacks trait
 // ==========================================================================
 
 /// Represents the set of application-defined callback functions that the FAPI invokes.
 ///
-/// Implementations of this trait can be registered with a FAPI context via the [`FapiContext::set_callbacks()`](crate::FapiContext::set_callbacks) function.
+/// Implementations of this trait are registered with a FAPI context via the [**`FapiContext::set_callbacks()`**](crate::FapiContext::set_callbacks) function.
 ///
 /// ### Example
 ///
+/// Applications shall implement this trait as follows:
+///
 /// ```
 /// #[derive(Debug)]
 /// pub struct MyCallbacks;
@@ -132,10 +157,10 @@ impl<'a> PolicyActionCbParam<'a> {
 ///     }
 /// }
 /// ```
-pub trait FapiCallbacks: Any + Send + Debug {
+pub trait FapiCallbacks: AsAny + Send + Debug + 'static {
     /// A callback function that allows the FAPI to request authorization values.
     ///
-    /// The default implementation of this function returns `None`. Please override as needed!
+    /// The default implementation of this function returns `None`. Please override the function as needed!
     ///
     /// *See also:* [`Fapi_SetAuthCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_auth_c_b.html)
     fn auth_cb(&self, _param: AuthCbParam) -> Option<Cow<'static, str>> {
@@ -146,7 +171,7 @@ pub trait FapiCallbacks: Any + Send + Debug {
     ///
     /// Signatures are requested for authorizing TPM objects.
     ///
-    /// The default implementation of this function returns `None`. Please override as needed!
+    /// The default implementation of this function returns `None`. Please override the function as needed!
     ///
     /// *See also:* [`Fapi_SetSignCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_sign_c_b.html)
     fn sign_cb(&self, _param: SignCbParam) -> Option<Vec<u8>> {
@@ -157,7 +182,7 @@ pub trait FapiCallbacks: Any + Send + Debug {
     ///
     /// It is usually called during policy evaluation.
     ///
-    /// The default implementation of this function returns `None`. Please override as needed!
+    /// The default implementation of this function returns `None`. Please override the function as needed!
     ///
     /// *See also:* [`Fapi_SetBranchCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_sign_c_b.html)
     fn branch_cb(&self, _param: BranchCbParam) -> Option<usize> {
@@ -168,7 +193,7 @@ pub trait FapiCallbacks: Any + Send + Debug {
     ///
     /// It is usually called to announce policy actions.
     ///
-    /// The default implementation of this function returns `false`. Please override as needed!
+    /// The default implementation of this function returns `false`. Please override the function as needed!
     ///
     /// *See also:* [`Fapi_SetPolicyActionCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_sign_c_b.html)
     fn policy_action_cb(&self, _param: PolicyActionCbParam) -> bool {

src/context.rs

@@ -148,18 +148,18 @@ impl FapiContext {
     // Callback setters
     // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-    /// This function registers application-defined callback functions with the FAPI context, replacing any previously registered callbacks.
+    /// Registers application-defined callback functions with the FAPI context, replacing the previously registered callbacks.
     ///
-    /// The callback functions are implemented via the [`FapiCallbacks`](crate::FapiCallbacks) trait.
+    /// Please see the [**`FapiCallbacks`**](crate::FapiCallbacks) trait for details!
     ///
-    /// If successful, the function retruns the previously registered callback functions, which may be `None`.
+    /// If successful, the function retruns an option containing the previously registered `FapiCallbacks`, which may be `None`.
     ///
     /// *See also:*
     /// - [`Fapi_SetAuthCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_auth_c_b.html)
     /// - [`Fapi_SetSignCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_sign_c_b.html)
     /// - [`Fapi_SetBranchCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_sign_c_b.html)
     /// - [`Fapi_SetPolicyActionCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_sign_c_b.html)
-    pub fn set_callbacks(&mut self, callbacks: impl FapiCallbacks + 'static) -> Result<Option<Box<dyn FapiCallbacks>>, ErrorCode> {
+    pub fn set_callbacks(&mut self, callbacks: impl FapiCallbacks) -> Result<Option<Box<dyn FapiCallbacks + 'static>>, ErrorCode> {
         let previous = self.callbacks.replace(CallbackManager::new(callbacks));
         let callbacks_ptr = self.callbacks.as_mut().unwrap() as *mut CallbackManager as *mut c_void;
         let results = [
@@ -171,10 +171,16 @@ impl FapiContext {
         results.iter().try_fold(previous.map(|cb| cb.into_inner()), |acc, ret| ret.map(|_| acc))
     }
 
-    /// This function un-registers the application-defined callback functions that have been registers via [`set_callbacks()`](FapiContext::set_callbacks).
+    /// Un-registers the application-defined callback functions that have been registers via [`set_callbacks()`](FapiContext::set_callbacks).
     ///
-    /// If successful, the function retruns the previously registered callback functions, which may be `None`.
-    pub fn clear_callbacks(&mut self) -> Result<Option<Box<dyn FapiCallbacks>>, ErrorCode> {
+    /// If successful, the function retruns an option containing the previously registered `FapiCallbacks`, which may be `None`.
+    ///
+    /// *See also:*
+    /// - [`Fapi_SetAuthCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_auth_c_b.html)
+    /// - [`Fapi_SetSignCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_sign_c_b.html)
+    /// - [`Fapi_SetBranchCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_sign_c_b.html)
+    /// - [`Fapi_SetPolicyActionCB()`](https://tpm2-tss.readthedocs.io/en/stable/group___fapi___set_sign_c_b.html)
+    pub fn clear_callbacks(&mut self) -> Result<Option<Box<dyn FapiCallbacks + 'static>>, ErrorCode> {
         let previous = self.callbacks.take();
         let results = [
             self.fapi_call(false, |context| unsafe { fapi_sys::Fapi_SetAuthCB(context, None, ptr::null_mut()) }),

src/lib.rs

@@ -451,7 +451,7 @@ mod types;
 mod version;
 
 pub use algorithm_id::HashAlgorithm;
-pub use callback::{AuthCbParam, BranchCbParam, FapiCallbacks, PolicyActionCbParam, SignCbParam};
+pub use callback::{AsAny, AuthCbParam, BranchCbParam, FapiCallbacks, PolicyActionCbParam, SignCbParam};
 pub use context::FapiContext;
 pub use error::{BaseErrorCode, ErrorCode, InternalError, Tpm2ErrFmt0, Tpm2ErrFmt1, Tpm2ErrorCode, Tpm2Warning};
 pub use flags::{BlobType, KeyFlags, NvFlags, PaddingFlags, QuoteFlags, SealFlags};

tests/09_policy_test.rs

@@ -20,8 +20,8 @@ use rand::SeedableRng;
 use rand_chacha::ChaChaRng;
 use serial_test::serial;
 use sha2::{Digest, Sha256};
-use std::{any::Any, fs, path::Path};
-use tss2_fapi_rs::{FapiContext, ImportData, KeyFlags, json::JsonValue};
+use std::{fs, path::Path};
+use tss2_fapi_rs::{FapiCallbacks, FapiContext, ImportData, KeyFlags, json::JsonValue};
 
 const KEY_FLAGS_SIGN: &[KeyFlags] = &[KeyFlags::NoDA, KeyFlags::Sign];
 
@@ -188,7 +188,8 @@ fn test_policy_or() {
         };
 
         // Check retrieved branches
-        let callbacks: Box<MyCallbacks> = downcast(context.clear_callbacks().expect("Failed to clear!").expect("No callbacks!")).expect("Downcast has failed!");
+        let callbacks: Box<dyn FapiCallbacks> = context.clear_callbacks().expect("Failed to clear callbacks!").expect("No callbacks!");
+        let callbacks: &MyCallbacks = callbacks.as_any().downcast_ref().expect("Downcast has failed!");
         let branches = callbacks.get_branches();
         assert_eq!(branches.len(), 2);
         assert!(branches[0].eq_ignore_ascii_case("#0,PolicySignedRSA"));
@@ -245,7 +246,8 @@ fn test_policy_action() {
         };
 
         // Check retrieved actions
-        let callbacks: Box<MyCallbacks> = downcast(context.clear_callbacks().expect("Failed to clear!").expect("No callbacks!")).expect("Downcast has failed!");
+        let callbacks: Box<dyn FapiCallbacks> = context.clear_callbacks().expect("Failed to clear callbacks!").expect("No callbacks!");
+        let callbacks: &MyCallbacks = callbacks.as_any().downcast_ref().expect("Downcast has failed!");
         let actions = callbacks.get_actions();
         assert!(!actions.is_empty());
         assert!(actions[0].eq_ignore_ascii_case("myaction"));
@@ -267,8 +269,3 @@ fn read_private_key(data_path: &Path, key_type: KeyType, key_name: &str) -> Opti
     let pem_file = data_path.join("keys").join(format!("{}.pem", key_name));
     fs::read_to_string(pem_file).ok().and_then(|pem_data| load_private_key(&pem_data[..], key_type))
 }
-
-/// Downcast helper
-fn downcast<T: 'static>(boxed: Box<dyn Any>) -> Option<Box<T>> {
-    boxed.downcast().ok()
-}