Merge #535: call the alloc error handle if we get NULL from the alloc…

…ator

8b17fc0 call the alloc error handle if we get NULL from the allocator (Elichai Turkel)

Pull request description:

  Found that this was missing in this discussion: #529 (comment)

  It is documented here that it returns a NULL on memory exhaustion: https://doc.rust-lang.org/alloc/alloc/trait.GlobalAlloc.html#tymethod.alloc
  And you can see that this is called in this example: https://doc.rust-lang.org/alloc/alloc/fn.alloc.html
  Docs for the handle itself: https://doc.rust-lang.org/alloc/alloc/fn.handle_alloc_error.html

ACKs for top commit:
  apoelstra:
    ACK 8b17fc0
  Kixunil:
    Good argument, ACK 8b17fc0

Tree-SHA512: 4b8f79ab5f691cb92621a314ceb8556c26fa7e159de359697b766043a0269e1ecf9746e6d4bfd5b45f18bccaff435c1fff491168b8bb77459ae849c38664d563

secp256k1-sys/src/lib.rs

@@ -811,6 +811,9 @@ pub unsafe extern "C" fn rustsecp256k1_v0_6_1_context_create(flags: c_uint) -> *
     let bytes = secp256k1_context_preallocated_size(flags) + ALIGN_TO;
     let layout = alloc::Layout::from_size_align(bytes, ALIGN_TO).unwrap();
     let ptr = alloc::alloc(layout);
+    if ptr.is_null() {
+        alloc::handle_alloc_error(layout);
+    }
     (ptr as *mut usize).write(bytes);
     // We must offset a whole ALIGN_TO in order to preserve the same alignment
     // this means we "lose" ALIGN_TO-size_of(usize) for padding.

src/context.rs

@@ -202,6 +202,9 @@ mod alloc_only {
             let size = unsafe { ffi::secp256k1_context_preallocated_size(C::FLAGS) };
             let layout = alloc::Layout::from_size_align(size, ALIGN_TO).unwrap();
             let ptr = unsafe { alloc::alloc(layout) };
+            if ptr.is_null() {
+                alloc::handle_alloc_error(layout);
+            }
 
             #[allow(unused_mut)] // ctx is not mutated under some feature combinations.
             let mut ctx = Secp256k1 {
@@ -262,6 +265,9 @@ mod alloc_only {
             let size = unsafe { ffi::secp256k1_context_preallocated_clone_size(self.ctx as _) };
             let layout = alloc::Layout::from_size_align(size, ALIGN_TO).unwrap();
             let ptr = unsafe { alloc::alloc(layout) };
+            if ptr.is_null() {
+                alloc::handle_alloc_error(layout);
+            }
             Secp256k1 {
                 ctx: unsafe {
                     ffi::secp256k1_context_preallocated_clone(self.ctx, ptr as *mut c_void)