Make BlobReader a slice newtype

recapn/src/data.rs

@@ -59,16 +59,7 @@ impl<'a> Reader<'a> {
     /// If the slice is too large to be in a message, this function panics.
     #[inline]
     pub const fn from_slice(slice: &'a [u8]) -> Self {
-        let len = slice.len();
-        if len > ElementCount::MAX_VALUE as usize {
-            panic!("slice is too large to be contained within a cap'n proto message")
-        }
-
-        let count = ElementCount::new(len as u32).unwrap();
-        unsafe {
-            let ptr = NonNull::new_unchecked(slice.as_ptr().cast_mut());
-            Self(ptr::Reader::new(ptr, count))
-        }
+        Self(ptr::Reader::new(slice).expect("slice is too large to be contained within a cap'n proto message"))
     }
 
     #[inline]
@@ -83,9 +74,7 @@ impl<'a> Reader<'a> {
 
     #[inline]
     pub const fn as_slice(&self) -> &'a [u8] {
-        let data = self.0.data().as_ptr().cast_const();
-        let len = self.len() as usize;
-        unsafe { core::slice::from_raw_parts(data, len) }
+        self.0.as_slice()
     }
 }
 
@@ -164,7 +153,9 @@ impl<'a> Builder<'a> {
 
     #[inline]
     pub fn as_reader<'b>(&'b self) -> Reader<'b> {
-        Data(ptr::Reader::new(self.0.data(), self.0.len()))
+        Data(unsafe {
+            ptr::Reader::new_unchecked(self.0.data(), self.0.len())
+        })
     }
 
     #[inline]

recapn/src/ptr.rs

@@ -2256,7 +2256,9 @@ impl<'a, T: Table> PtrReader<'a, T> {
             }
         }?;
 
-        Ok(BlobReader::new(ptr.as_inner().cast(), element_count))
+        Ok(unsafe {
+            BlobReader::new_unchecked(ptr.as_inner().cast(), element_count)
+        })
     }
 
     #[inline]
@@ -2915,32 +2917,43 @@ impl<'a, T: Table> Capable for ListReader<'a, T> {
 
 #[derive(Clone, Copy)]
 pub struct BlobReader<'a> {
-    a: PhantomData<&'a [u8]>,
-    ptr: NonNull<u8>,
-    len: ElementCount,
+    slice: &'a [u8],
 }
 
 impl<'a> BlobReader<'a> {
-    pub(crate) const fn new(ptr: NonNull<u8>, len: ElementCount) -> Self {
-        Self { a: PhantomData, ptr, len }
+    #[inline]
+    pub(crate) const fn new(slice: &'a [u8]) -> Option<Self> {
+        if slice.len() < ElementCount::MAX_VALUE as usize {
+            Some(Self { slice })
+        } else {
+            None
+        }
+    }
+
+    pub(crate) const unsafe fn new_unchecked(ptr: NonNull<u8>, len: ElementCount) -> Self {
+        Self {
+            slice: std::slice::from_raw_parts(ptr.as_ptr(), len.get() as usize),
+        }
     }
 
     pub const fn empty() -> Self {
-        Self::new(NonNull::dangling(), ElementCount::ZERO)
+        Self { slice: &[] }
     }
 
     pub const fn data(&self) -> NonNull<u8> {
-        self.ptr
+        unsafe {
+            NonNull::new_unchecked(self.slice.as_ptr().cast_mut())
+        }
     }
 
     pub const fn len(&self) -> ElementCount {
-        self.len
+        unsafe {
+            ElementCount::new_unchecked(self.slice.len() as _)
+        }
     }
 
     pub const fn as_slice(&self) -> &'a [u8] {
-        unsafe {
-            core::slice::from_raw_parts(self.ptr.as_ptr().cast_const(), self.len.get() as usize)
-        }
+        self.slice
     }
 }
 
@@ -5268,18 +5281,19 @@ impl BlobBuilder<'_> {
 
     #[inline]
     pub const fn as_reader(&self) -> BlobReader {
-        BlobReader::new(self.ptr, self.len)
+        unsafe {
+            BlobReader::new_unchecked(self.ptr, self.len)
+        }
     }
 
     #[inline]
     pub(crate) fn copy_from(&mut self, other: BlobReader) {
-        assert_eq!(self.len, other.len);
+        assert_eq!(self.len, other.len());
 
         let dst = self.ptr.as_ptr();
-        let src = other.ptr.as_ptr().cast_const();
-        let len = other.len.get() as usize;
+        let src = other.as_slice();
         unsafe {
-            ptr::copy_nonoverlapping(src, dst, len)
+            ptr::copy_nonoverlapping(src.as_ptr(), dst, src.len())
         }
     }
 

recapn/src/text.rs

@@ -72,13 +72,15 @@ impl<'a> Reader<'a> {
     #[inline]
     pub const fn from_slice(s: &'a [u8]) -> Self {
         match s {
-            [.., 0] if s.len() <= ByteCount::MAX_VALUE as usize => {
-                let ptr = unsafe { NonNull::new_unchecked(s.as_ptr().cast_mut()) };
-                let len = ElementCount::new(s.len() as u32).unwrap();
-                Self(ptr::Reader::new(ptr, len))
+            [.., 0] => {
+                match ptr::Reader::new(s) {
+                    Some(r) => Some(Self(r)),
+                    None => None,
+                }
             },
-            _ => panic!("attempted to make invalid text blob from slice"),
+            _ => None,
         }
+        .expect("attempted to make invalid text blob from slice")
     }
 
     pub const fn byte_count(&self) -> ByteCount {
@@ -99,14 +101,19 @@ impl<'a> Reader<'a> {
     /// Returns the bytes of the text field without the null terminator
     #[inline]
     pub const fn as_bytes(&self) -> &'a [u8] {
-        let (_, remainder) = self.as_bytes_with_nul().split_last().unwrap();
-        remainder
+        match self.as_bytes_with_nul().split_last() {
+            Some((_, remainder)) => remainder,
+            _ => {
+                debug_assert!(false, "this shouldn't happen, it's to avoid panic code in release");
+                EMPTY_SLICE
+            },
+        }
     }
 
     /// Returns the bytes of the text field with the null terminator
     #[inline]
     pub const fn as_bytes_with_nul(&self) -> &'a [u8] {
-        unsafe { slice::from_raw_parts(self.0.data().as_ptr().cast_const(), self.len() as usize) }
+        self.0.as_slice()
     }
 
     #[inline]
@@ -254,4 +261,4 @@ impl PartialEq<Builder<'_>> for str {
     fn eq(&self, other: &Builder<'_>) -> bool {
         self.as_bytes() == other.as_bytes()
     }
-}
+}