rust: bssl-tls: parse_all_from_pem should recover from BIO failure

Signed-off-by: Xiangfei Ding <xfding@google.com>
Change-Id: I7cf2f800ad74f3624f840066f43c931f6a6a6964
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/101411
Presubmit-BoringSSL-Verified: boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Benjamin <davidben@google.com>

rust/bssl-tls/src/credentials.rs

diff --git a/rust/bssl-tls/src/credentials.rs b/rust/bssl-tls/src/credentials.rs
index 106df17..61fb5a6 100644
--- a/rust/bssl-tls/src/credentials.rs
+++ b/rust/bssl-tls/src/credentials.rs
@@ -476,7 +476,7 @@
         cert: &[u8],
         cache: Option<&CertificateCache>,
     ) -> Result<Vec<Self>, Error> {
-        let mut bio = Bio::from_bytes(cert).unwrap();
+        let mut bio = Bio::from_bytes(cert);
         let mut res = vec![];
         loop {
             match Self::parse_one(&mut bio, cache) {
@@ -497,7 +497,7 @@
         cert: &[u8],
         cache: Option<&CertificateCache>,
     ) -> Result<Self, Error> {
-        let mut bio = Bio::from_bytes(cert)?;
+        let mut bio = Bio::from_bytes(cert);
         let (cert, _) = Self::parse_one(&mut bio, cache)?;
         Ok(cert)
     }

rust/bssl-tls/src/ffi.rs

diff --git a/rust/bssl-tls/src/ffi.rs b/rust/bssl-tls/src/ffi.rs
index ae6397a..5ca3bd0 100644
--- a/rust/bssl-tls/src/ffi.rs
+++ b/rust/bssl-tls/src/ffi.rs
@@ -33,10 +33,7 @@
 
 use crate::{
     context::CertificateCache,
-    errors::{
-        Error,
-        IoError, //
-    }, //
+    errors::Error, //
 };
 
 pub(crate) fn slice_into_ffi_raw_parts<T>(slice: &[T]) -> (*const T, usize) {
@@ -97,21 +94,18 @@
         Bio(bio, PhantomData)
     }
 
-    pub fn from_bytes(buf: &'a [u8]) -> Result<Self, Error> {
-        let len = if let Ok(len) = buf.len().try_into() {
-            len
-        } else {
-            return Err(Error::Io(IoError::TooLong));
-        };
+    pub fn from_bytes(buf: &'a [u8]) -> Self {
+        #[allow(clippy::expect_used, reason = "breach of fundamental invariant")]
+        let len = buf.len().try_into().expect("impossible allocation size");
         let mem_buf = unsafe {
             // Safety: buf is still valid
             bssl_sys::BIO_new_mem_buf(buf.as_ffi_void_ptr(), len)
         };
         let mem_buf = NonNull::new(mem_buf).expect("allocation failure");
-        Ok(unsafe {
+        unsafe {
             // Safety: our returned object is outlived by the input buffer.
             Self::new(mem_buf)
-        })
+        }
     }
 
     pub fn ptr(&mut self) -> *mut bssl_sys::BIO {