Extract a CBB helper
This was nagging at me, so I thought I'd see what I could do. I'm not
worried about pinning now - the CBB by inspection is definitely
movable, and it would need to be altered in fairly weird ways.
But I am worried about the lifetime issues - that seems like an
accident waiting to happen, but can be exposed to the borrow checker
fairly easily.
(This is similar to commit 3194c466151c7d1c06b226f13d3c03298a27d40a.)
Bug: 299055662
Test: TH
Change-Id: Iada56f51800cd2af99e86b557805e65823a141da
diff --git a/rialto/src/requests/cbb.rs b/rialto/src/requests/cbb.rs
new file mode 100644
index 0000000..93cebe4
--- /dev/null
+++ b/rialto/src/requests/cbb.rs
@@ -0,0 +1,52 @@
+// Copyright 2023, The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Helpers for using BoringSSL CBB (crypto byte builder) objects.
+use bssl_ffi::{CBB_init_fixed, CBB};
+use core::marker::PhantomData;
+use core::mem::MaybeUninit;
+
+/// Wraps a CBB that references a existing fixed-sized buffer; no memory is allocated, but the
+/// buffer cannot grow.
+pub struct CbbFixed<'a> {
+ cbb: CBB,
+ // The CBB contains a mutable reference to the buffer, disguised as a pointer.
+ // Make sure the borrow checker knows that.
+ _buffer: PhantomData<&'a mut [u8]>,
+}
+
+impl CbbFixed<'_> {
+ // Create a new CBB that writes to the given buffer.
+ pub fn new(buffer: &mut [u8]) -> Self {
+ let mut cbb = MaybeUninit::uninit();
+ // SAFETY: `CBB_init_fixed()` is infallible and always returns one.
+ // The buffer remains valid during the lifetime of `cbb`.
+ unsafe { CBB_init_fixed(cbb.as_mut_ptr(), buffer.as_mut_ptr(), buffer.len()) };
+ // SAFETY: `cbb` has just been initialized by `CBB_init_fixed()`.
+ let cbb = unsafe { cbb.assume_init() };
+ Self { cbb, _buffer: PhantomData }
+ }
+}
+
+impl AsRef<CBB> for CbbFixed<'_> {
+ fn as_ref(&self) -> &CBB {
+ &self.cbb
+ }
+}
+
+impl AsMut<CBB> for CbbFixed<'_> {
+ fn as_mut(&mut self) -> &mut CBB {
+ &mut self.cbb
+ }
+}