deku-derive: deku_read: Use checked slice for remaining data (sharksforarms#581)

Author: amboar

deku-derive/src/macros/deku_read.rs

@@ -137,7 +137,10 @@ fn emit_struct(input: &DekuData) -> Result<TokenStream, syn::Error> {
             } else {
                 (__deku_reader.bits_read - (__deku_reader.bits_read % 8)) / 8
             };
-            Ok(((&__deku_input.0[idx..], __deku_reader.bits_read % 8), __deku_value))
+            let Some(rest) = __deku_input.0.get(idx..) else {
+                return Err(deku::DekuError::Incomplete(deku::prelude::NeedSize::new(8 * (idx - __deku_input.0.len()))));
+            };
+            Ok(((rest, __deku_reader.bits_read % 8), __deku_value))
         };
 
         tokens.extend(emit_try_from(&imp, &lifetime, &ident, wher));
@@ -436,7 +439,10 @@ fn emit_enum(input: &DekuData) -> Result<TokenStream, syn::Error> {
             } else {
                 (__deku_reader.bits_read - (__deku_reader.bits_read % 8)) / 8
             };
-            Ok(((&__deku_input.0[idx..], __deku_reader.bits_read % 8), __deku_value))
+            let Some(rest) = __deku_input.0.get(idx..) else {
+                return Err(deku::DekuError::Incomplete(deku::prelude::NeedSize::new(8 * (idx - __deku_input.0.len()))));
+            };
+            Ok(((rest, __deku_reader.bits_read % 8), __deku_value))
         };
 
         tokens.extend(emit_try_from(&imp, &lifetime, &ident, wher));

tests/test_from_bytes.rs

@@ -81,3 +81,30 @@ fn test_from_bytes_long() {
     assert_eq!(6, i);
     assert_eq!(0b0101_1010u8, rest[0]);
 }
+
+#[test]
+fn test_from_bytes_short_with_seek() {
+    #[derive(Debug, DekuRead, Eq, PartialEq)]
+    #[deku(ctx = "mid: u8", id = "mid")]
+    enum Sneaky {
+        #[deku(id = 0)]
+        Zero,
+        #[deku(id = 1)]
+        One,
+    }
+
+    #[derive(Debug, DekuRead, Eq, PartialEq)]
+    struct Seeky {
+        id: u8,
+        // Use seek to force an out-of-bounds slice for remaining data
+        #[deku(seek_from_current = "1")]
+        #[deku(ctx = "*id")]
+        body: Sneaky,
+    }
+
+    let bytes: [u8; 1] = [0x01];
+    assert_eq!(
+        Err(DekuError::Incomplete(NeedSize::new(8))),
+        Seeky::from_bytes((&bytes, 0))
+    );
+}