Implement pre allocation context creation

src/context.rs

@@ -0,0 +1,223 @@
+use core::marker::PhantomData;
+use {ffi, types::{c_uint, c_void}, Error, Secp256k1};
+
+#[cfg(feature = "std")]
+pub use self::std_only::*;
+
+/// A trait for all kinds of Context's that let's you define the exact flags and a function to deallocate memory.
+/// * DO NOT * implement it for your own types.
+pub unsafe trait Context {
+    /// Flags for the ffi.
+    const FLAGS: c_uint;
+    /// A constant description of the context.
+    const DESCRIPTION: &'static str;
+    /// A function to deallocate the memory when the context is dropped.
+    fn deallocate(ptr: *mut [u8]);
+}
+
+/// Marker trait for indicating that an instance of `Secp256k1` can be used for signing.
+pub trait Signing: Context {}
+
+/// Marker trait for indicating that an instance of `Secp256k1` can be used for verification.
+pub trait Verification: Context {}
+
+/// Represents the set of capabilities needed for signing with a user preallocated memory.
+pub struct SignOnlyPreallocated<'buf> {
+    phantom: PhantomData<&'buf ()>,
+}
+
+/// Represents the set of capabilities needed for verification with a user preallocated memory.
+pub struct VerifyOnlyPreallocated<'buf> {
+    phantom: PhantomData<&'buf ()>,
+}
+
+/// Represents the set of all capabilities with a user preallocated memory.
+pub struct AllPreallocated<'buf> {
+    phantom: PhantomData<&'buf ()>,
+}
+
+#[cfg(feature = "std")]
+mod std_only {
+    use super::*;
+
+    /// Represents the set of capabilities needed for signing.
+    pub enum SignOnly {}
+
+    /// Represents the set of capabilities needed for verification.
+    pub enum VerifyOnly {}
+
+    /// Represents the set of all capabilities.
+    pub enum All {}
+
+    impl Signing for SignOnly {}
+    impl Signing for All {}
+
+    impl Verification for VerifyOnly {}
+    impl Verification for All {}
+
+    unsafe impl Context for SignOnly {
+        const FLAGS: c_uint = ffi::SECP256K1_START_SIGN;
+        const DESCRIPTION: &'static str = "signing only";
+
+        fn deallocate(ptr: *mut [u8]) {
+            let _ = unsafe { Box::from_raw(ptr) };
+        }
+    }
+
+    unsafe impl Context for VerifyOnly {
+        const FLAGS: c_uint = ffi::SECP256K1_START_VERIFY;
+        const DESCRIPTION: &'static str = "verification only";
+
+        fn deallocate(ptr: *mut [u8]) {
+            let _ = unsafe { Box::from_raw(ptr) };
+        }
+    }
+
+    unsafe impl Context for All {
+        const FLAGS: c_uint = VerifyOnly::FLAGS | SignOnly::FLAGS;
+        const DESCRIPTION: &'static str = "all capabilities";
+
+        fn deallocate(ptr: *mut [u8]) {
+            let _ = unsafe { Box::from_raw(ptr) };
+        }
+    }
+
+    impl<C: Context> Secp256k1<C> {
+        fn gen_new() -> Secp256k1<C> {
+            let buf = vec![0u8; Self::preallocate_size_gen()].into_boxed_slice();
+            let ptr = Box::into_raw(buf);
+            Secp256k1 {
+                ctx: unsafe { ffi::secp256k1_context_preallocated_create(ptr as *mut c_void, C::FLAGS) },
+                phantom: PhantomData,
+                buf: ptr,
+            }
+        }
+    }
+
+    impl Secp256k1<All> {
+        /// Creates a new Secp256k1 context with all capabilities
+        pub fn new() -> Secp256k1<All> {
+            Secp256k1::gen_new()
+        }
+    }
+
+    impl Secp256k1<SignOnly> {
+        /// Creates a new Secp256k1 context that can only be used for signing
+        pub fn signing_only() -> Secp256k1<SignOnly> {
+            Secp256k1::gen_new()
+        }
+    }
+
+    impl Secp256k1<VerifyOnly> {
+        /// Creates a new Secp256k1 context that can only be used for verification
+        pub fn verification_only() -> Secp256k1<VerifyOnly> {
+            Secp256k1::gen_new()
+        }
+    }
+
+    impl Default for Secp256k1<All> {
+        fn default() -> Self {
+            Self::new()
+        }
+    }
+
+    impl<C: Context> Clone for Secp256k1<C> {
+        fn clone(&self) -> Secp256k1<C> {
+            let buf = vec![0u8; unsafe { (&*self.buf).len() }].into_boxed_slice();
+            let ptr = Box::into_raw(buf);
+            Secp256k1 {
+                ctx: unsafe { ffi::secp256k1_context_preallocated_create(ptr as *mut c_void, C::FLAGS) },
+                phantom: PhantomData,
+                buf: ptr,
+            }
+        }
+    }
+
+}
+
+impl<'buf> Signing for SignOnlyPreallocated<'buf> {}
+impl<'buf> Signing for AllPreallocated<'buf> {}
+
+impl<'buf> Verification for VerifyOnlyPreallocated<'buf> {}
+impl<'buf> Verification for AllPreallocated<'buf> {}
+
+unsafe impl<'buf> Context for SignOnlyPreallocated<'buf> {
+    const FLAGS: c_uint = ffi::SECP256K1_START_SIGN;
+    const DESCRIPTION: &'static str = "signing only";
+
+    fn deallocate(ptr: *mut [u8]) {
+        let _ = ptr;
+    }
+}
+
+unsafe impl<'buf> Context for VerifyOnlyPreallocated<'buf> {
+    const FLAGS: c_uint = ffi::SECP256K1_START_VERIFY;
+    const DESCRIPTION: &'static str = "verification only";
+
+    fn deallocate(ptr: *mut [u8]) {
+        let _ = ptr;
+    }
+}
+
+unsafe impl<'buf> Context for AllPreallocated<'buf> {
+    const FLAGS: c_uint = SignOnlyPreallocated::FLAGS | VerifyOnlyPreallocated::FLAGS;
+    const DESCRIPTION: &'static str = "all capabilities";
+
+    fn deallocate(ptr: *mut [u8]) {
+        let _ = ptr;
+    }
+}
+
+impl<'buf, C: Context + 'buf> Secp256k1<C> {
+    fn preallocated_gen_new(buf: &'buf mut [u8]) -> Result<Secp256k1<C>, Error> {
+        if buf.len() < Self::preallocate_size_gen() {
+            return Err(Error::NotEnoughMemory);
+        }
+        Ok(Secp256k1 {
+            ctx: unsafe {
+                ffi::secp256k1_context_preallocated_create(
+                    buf.as_mut_ptr() as *mut c_void,
+                    C::FLAGS)
+            },
+            phantom: PhantomData,
+            buf: buf as *mut [u8],
+        })
+    }
+}
+
+impl<'buf> Secp256k1<AllPreallocated<'buf>> {
+    /// Creates a new Secp256k1 context with all capabilities
+    pub fn preallocated_new(buf: &'buf mut [u8]) -> Result<Secp256k1<AllPreallocated<'buf>>, Error> {
+        Secp256k1::preallocated_gen_new(buf)
+    }
+    /// Uses the ffi `secp256k1_context_preallocated_size` to check the memory size needed for a context
+    pub fn preallocate_size() -> usize {
+        Self::preallocate_size_gen()
+    }
+}
+
+impl<'buf> Secp256k1<SignOnlyPreallocated<'buf>> {
+    /// Creates a new Secp256k1 context that can only be used for signing
+    pub fn preallocated_signing_only(buf: &'buf mut [u8]) -> Result<Secp256k1<SignOnlyPreallocated<'buf>>, Error> {
+        Secp256k1::preallocated_gen_new(buf)
+    }
+
+    /// Uses the ffi `secp256k1_context_preallocated_size` to check the memory size needed for the context
+    #[inline]
+    pub fn preallocate_signing_size() -> usize {
+        Self::preallocate_size_gen()
+    }
+}
+
+impl<'buf> Secp256k1<VerifyOnlyPreallocated<'buf>> {
+    /// Creates a new Secp256k1 context that can only be used for verification
+    pub fn preallocated_verification_only(buf: &'buf mut [u8]) -> Result<Secp256k1<VerifyOnlyPreallocated<'buf>>, Error> {
+        Secp256k1::preallocated_gen_new(buf)
+    }
+
+    /// Uses the ffi `secp256k1_context_preallocated_size` to check the memory size needed for the context
+    #[inline]
+    pub fn preallocate_verification_size() -> usize {
+        Self::preallocate_size_gen()
+    }
+}

src/ffi.rs

@@ -144,6 +144,16 @@ extern "C" {
     // Contexts
     pub fn secp256k1_context_create(flags: c_uint) -> *mut Context;
 
+    pub fn secp256k1_context_preallocated_size(flags: c_uint) -> usize;
+
+    pub fn secp256k1_context_preallocated_create(prealloc: *mut c_void, flags: c_uint) -> *mut Context;
+
+    pub fn secp256k1_context_preallocated_destroy(cx: *mut Context);
+
+    pub fn secp256k1_context_preallocated_clone_size(cx: *const Context) -> usize;
+
+    pub fn secp256k1_context_preallocated_clone(cx: *const Context, prealloc: *mut c_void) -> *mut Context;
+
     pub fn secp256k1_context_clone(cx: *mut Context) -> *mut Context;
 
     pub fn secp256k1_context_destroy(cx: *mut Context);