stackoutputs: add deserializer and size validation

core/src/errors.rs

@@ -33,6 +33,7 @@ pub enum OutputError {
     InvalidOverflowAddress(u64),
     InvalidOverflowAddressLength(usize, usize),
     InvalidStackElement(u64),
+    OutputSizeTooBig(usize),
 }
 
 impl fmt::Display for OutputError {
@@ -48,6 +49,9 @@ impl fmt::Display for OutputError {
             InvalidStackElement(element) => {
                 write!(f, "stack contains {element} that is not a valid field element")
             }
+            OutputSizeTooBig(size) => {
+                write!(f, "too many elements for output stack, {size} elements")
+            }
         }
     }
 }

core/src/stack/outputs.rs

@@ -33,6 +33,8 @@ pub struct StackOutputs {
     overflow_addrs: Vec<u64>,
 }
 
+pub const MAX_STACK_OUTPUTS_SIZE: usize = u16::MAX as usize;
+
 impl StackOutputs {
     // CONSTRUCTOR
     // --------------------------------------------------------------------------------------------
@@ -45,6 +47,10 @@ impl StackOutputs {
     /// - If the number of stack elements is greater than `STACK_TOP_SIZE` (16) and `overflow_addrs`
     ///   does not contain exactly `stack.len() + 1 - STACK_TOP_SIZE` elements.
     pub fn new(mut stack: Vec<u64>, overflow_addrs: Vec<u64>) -> Result<Self, OutputError> {
+        if stack.len() > MAX_STACK_OUTPUTS_SIZE {
+            return Err(OutputError::OutputSizeTooBig(stack.len()));
+        }
+
         // Validate stack elements
         if let Some(element) = find_invalid_elements(&stack) {
             return Err(OutputError::InvalidStackElement(element));
@@ -212,16 +218,6 @@ impl ToElements<Felt> for StackOutputs {
 
 impl Serializable for StackOutputs {
     fn write_into<W: ByteWriter>(&self, target: &mut W) {
-        // TODO the length of the stack, by design, will not be greater than `u32::MAX`. however,
-        // we must define a common serialization format as we might diverge from the implementation
-        // here and the one provided by default from winterfell.
-
-        // stack
-        debug_assert!(self.stack.len() <= u32::MAX as usize);
-        target.write_u32(self.stack.len() as u32);
-        self.stack.write_into(target);
-
-        // overflow addrs
         debug_assert!(self.overflow_addrs.len() <= u32::MAX as usize);
         target.write_u32(self.overflow_addrs.len() as u32);
         self.overflow_addrs.write_into(target);
@@ -230,14 +226,14 @@ impl Serializable for StackOutputs {
 
 impl Deserializable for StackOutputs {
     fn read_from<R: ByteReader>(source: &mut R) -> Result<Self, DeserializationError> {
-        let count = source.read_u32()?;
-        let mut stack = Vec::with_capacity(count as usize);
+        let count = source.read_u32()?.try_into().expect("u32 must fit in a usize");
+        let mut stack = Vec::with_capacity(count);
         for _ in 0..count {
             stack.push(source.read_u64()?);
         }
 
-        let count = source.read_u32()?;
-        let mut overflow_addrs = Vec::with_capacity(count as usize);
+        let count = source.read_u32()?.try_into().expect("u32 must fit in a usize");
+        let mut overflow_addrs = Vec::with_capacity(count);
         for _ in 0..count {
             overflow_addrs.push(source.read_u64()?);
         }