Add functions to create from raw context

src/context.rs

@@ -1,4 +1,5 @@
 use core::marker::PhantomData;
+use ptr;
 use ffi::{self, CPtr};
 use types::{c_uint, c_void};
 use Error;
@@ -199,6 +200,25 @@ impl<'buf> Secp256k1<AllPreallocated<'buf>> {
     pub fn preallocate_size() -> usize {
         Self::preallocate_size_gen()
     }
+
+    /// Create a context from a raw context.
+    ///
+    /// # Safety
+    /// This is highly unsafe, due to the number of conditions that aren't checked.
+    /// * `raw_ctx` needs to be a valid Secp256k1 context pointer.
+    /// that was generated by *exactly* the same code/version of the libsecp256k1 used here.
+    /// * The capabilities (All/SignOnly/VerifyOnly) of the context *must* match the flags passed to libsecp256k1
+    /// when generating the context.
+    /// * The user must handle the freeing of the context(using the correct functions) by himself.
+    /// * Violating these may lead to Undefined Behavior.
+    ///
+    pub unsafe fn from_raw_all(raw_ctx: *mut ffi::Context) -> Secp256k1<AllPreallocated<'buf>> {
+        Secp256k1 {
+            ctx: raw_ctx,
+            phantom: PhantomData,
+            buf: ptr::null_mut::<[u8;0]>() as *mut [u8] ,
+        }
+    }
 }
 
 impl<'buf> Secp256k1<SignOnlyPreallocated<'buf>> {
@@ -212,6 +232,25 @@ impl<'buf> Secp256k1<SignOnlyPreallocated<'buf>> {
     pub fn preallocate_signing_size() -> usize {
         Self::preallocate_size_gen()
     }
+
+    /// Create a context from a raw context.
+    ///
+    /// # Safety
+    /// This is highly unsafe, due to the number of conditions that aren't checked.
+    /// * `raw_ctx` needs to be a valid Secp256k1 context pointer.
+    /// that was generated by *exactly* the same code/version of the libsecp256k1 used here.
+    /// * The capabilities (All/SignOnly/VerifyOnly) of the context *must* match the flags passed to libsecp256k1
+    /// when generating the context.
+    /// * The user must handle the freeing of the context(using the correct functions) by himself.
+    /// * This list *is not* exhaustive, and any violation may lead to Undefined Behavior.,
+    ///
+    pub unsafe fn from_raw_signining_only(raw_ctx: *mut ffi::Context) -> Secp256k1<SignOnlyPreallocated<'buf>> {
+        Secp256k1 {
+            ctx: raw_ctx,
+            phantom: PhantomData,
+            buf: ptr::null_mut::<[u8;0]>() as *mut [u8] ,
+        }
+    }
 }
 
 impl<'buf> Secp256k1<VerifyOnlyPreallocated<'buf>> {
@@ -225,4 +264,23 @@ impl<'buf> Secp256k1<VerifyOnlyPreallocated<'buf>> {
     pub fn preallocate_verification_size() -> usize {
         Self::preallocate_size_gen()
     }
+
+    /// Create a context from a raw context.
+    ///
+    /// # Safety
+    /// This is highly unsafe, due to the number of conditions that aren't checked.
+    /// * `raw_ctx` needs to be a valid Secp256k1 context pointer.
+    /// that was generated by *exactly* the same code/version of the libsecp256k1 used here.
+    /// * The capabilities (All/SignOnly/VerifyOnly) of the context *must* match the flags passed to libsecp256k1
+    /// when generating the context.
+    /// * The user must handle the freeing of the context(using the correct functions) by himself.
+    /// * This list *is not* exhaustive, and any violation may lead to Undefined Behavior.,
+    ///
+    pub unsafe fn from_raw_verification_only(raw_ctx: *mut ffi::Context) -> Secp256k1<VerifyOnlyPreallocated<'buf>> {
+        Secp256k1 {
+            ctx: raw_ctx,
+            phantom: PhantomData,
+            buf: ptr::null_mut::<[u8;0]>() as *mut [u8] ,
+        }
+    }
 }