bug: RLP::decode() should return an empty string instead of "0" when decoding 0x80

crates/utils/src/errors.cairo

@@ -1,11 +1,13 @@
 // LENGTH
 const RLP_EMPTY_INPUT: felt252 = 'KKT: EmptyInput';
 const RLP_INPUT_TOO_SHORT: felt252 = 'KKT: InputTooShort';
+const RLP_PAYLOAD_TOO_LONG: felt252 = 'KKT: PayloadTooLong';
 
 #[derive(Drop, Copy, PartialEq)]
 enum RLPError {
     EmptyInput: felt252,
     InputTooShort: felt252,
+    PayloadTooLong: felt252,
 }
 
 
@@ -14,6 +16,7 @@ impl RLPErrorIntoU256 of Into<RLPError, u256> {
         match self {
             RLPError::EmptyInput(error_message) => error_message.into(),
             RLPError::InputTooShort(error_message) => error_message.into(),
+            RLPError::PayloadTooLong(error_message) => error_message.into(),
         }
     }
 }

crates/utils/src/rlp.cairo

@@ -1,6 +1,8 @@
 use core::byte_array::ByteArrayTrait;
 use core::result::ResultTrait;
-use utils::errors::{RLPError, RLPHelpersError, RLP_EMPTY_INPUT, RLP_INPUT_TOO_SHORT};
+use utils::errors::{
+    RLPError, RLPHelpersError, RLP_EMPTY_INPUT, RLP_INPUT_TOO_SHORT, RLP_PAYLOAD_TOO_LONG
+};
 use utils::helpers::{U32Trait, U256Impl, U128Impl, ArrayExtension};
 
 // Possible RLP types
@@ -43,6 +45,9 @@ impl RLPImpl of RLPTrait {
             Result::Ok((RLPType::String, 1, prefix_byte.into() - 0x80))
         } else if prefix_byte < 0xc0 { // Long String
             let len_bytes_count: u32 = (prefix_byte - 0xb7).into();
+            if len_bytes_count > 4 {
+                return Result::Err(RLPError::PayloadTooLong(RLP_PAYLOAD_TOO_LONG));
+            }
             if input_len <= len_bytes_count {
                 return Result::Err(RLPError::InputTooShort(RLP_INPUT_TOO_SHORT));
             }
@@ -54,6 +59,9 @@ impl RLPImpl of RLPTrait {
             Result::Ok((RLPType::List, 1, prefix_byte.into() - 0xc0))
         } else { // Long List
             let len_bytes_count = prefix_byte.into() - 0xf7;
+            if len_bytes_count > 4 {
+                return Result::Err(RLPError::PayloadTooLong(RLP_PAYLOAD_TOO_LONG));
+            }
             if input.len() <= len_bytes_count {
                 return Result::Err(RLPError::InputTooShort(RLP_INPUT_TOO_SHORT));
             }
@@ -158,9 +166,9 @@ impl RLPImpl of RLPTrait {
 
         match rlp_type {
             RLPType::String => {
-                // checking for default value `0`
                 if (len == 0) {
-                    output.append(RLPItem::String(array![0].span()));
+                    // Empty strings are parsed as 0 for an integer
+                    output.append(RLPItem::String(array![].span()));
                 } else {
                     output.append(RLPItem::String(input.slice(offset, len)));
                 }
@@ -192,6 +200,10 @@ impl RLPHelpersImpl of RLPHelpersTrait {
     fn parse_u128_from_string(self: RLPItem) -> Result<u128, RLPHelpersError> {
         match self {
             RLPItem::String(bytes) => {
+                // Empty strings means 0
+                if bytes.len() == 0 {
+                    return Result::Ok(0);
+                }
                 let value = U128Impl::from_bytes(bytes).ok_or(RLPHelpersError::FailedParsingU128)?;
                 Result::Ok(value)
             },
@@ -202,6 +214,10 @@ impl RLPHelpersImpl of RLPHelpersTrait {
     fn parse_u256_from_string(self: RLPItem) -> Result<u256, RLPHelpersError> {
         match self {
             RLPItem::String(bytes) => {
+                // Empty strings means 0
+                if bytes.len() == 0 {
+                    return Result::Ok(0);
+                }
                 let value = U256Impl::from_bytes(bytes).ok_or(RLPHelpersError::FailedParsingU256)?;
                 Result::Ok(value)
             },

crates/utils/src/tests/test_data.cairo

@@ -51,7 +51,7 @@ fn legacy_rlp_encoded_tx() -> Span<u8> {
         239,
         1,
         128,
-        128
+        128,
     ]
         .span()
 }
@@ -110,7 +110,7 @@ fn eip_2930_encoded_tx() -> Span<u8> {
         171,
         205,
         239,
-        192
+        192,
     ]
         .span()
 }
@@ -169,7 +169,7 @@ fn eip_1559_encoded_tx() -> Span<u8> {
         171,
         205,
         239,
-        192
+        192,
     ]
         .span()
 }

crates/utils/src/tests/test_rlp.cairo

@@ -3,7 +3,7 @@ use core::option::OptionTrait;
 use core::traits::Into;
 
 use result::ResultTrait;
-use utils::errors::{RLPError, RLP_EMPTY_INPUT, RLP_INPUT_TOO_SHORT};
+use utils::errors::{RLPError, RLP_EMPTY_INPUT, RLP_INPUT_TOO_SHORT, RLP_PAYLOAD_TOO_LONG};
 use utils::rlp::{RLPType, RLPTrait, RLPItem};
 
 // Tests source : https://github.com/HerodotusDev/cairo-lib/blob/main/src/encoding/tests/test_rlp.cairo
@@ -82,6 +82,32 @@ fn test_rlp_decode_type_long_list_len_too_short() {
     );
 }
 
+#[test]
+#[available_gas(99999999)]
+fn test_rlp_decode_type_long_string_payload_too_long() {
+    let mut arr = array![0xbf, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02];
+
+    let res = RLPTrait::decode_type(arr.span());
+
+    assert(res.is_err(), 'Should have failed');
+    assert(
+        res.unwrap_err() == RLPError::PayloadTooLong(RLP_PAYLOAD_TOO_LONG), 'err != PayloadTooLong'
+    );
+}
+
+#[test]
+#[available_gas(99999999)]
+fn test_rlp_decode_type_long_list_payload_too_long() {
+    let mut arr = array![0xfc, 0x01, 0x02, 0x02, 0x02, 0x02];
+
+    let res = RLPTrait::decode_type(arr.span());
+
+    assert(res.is_err(), 'Should have failed');
+    assert(
+        res.unwrap_err() == RLPError::PayloadTooLong(RLP_PAYLOAD_TOO_LONG), 'err != PayloadTooLong'
+    );
+}
+
 #[test]
 #[available_gas(9999999)]
 fn test_rlp_empty() {
@@ -381,7 +407,7 @@ fn test_rlp_decode_string_default_value() {
     let mut arr = array![0x80];
 
     let rlp_item = RLPTrait::decode(arr.span()).unwrap();
-    let expected = RLPItem::String(array![0].span());
+    let expected = RLPItem::String(array![].span());
 
     assert(rlp_item.len() == 1, 'item length not 1');
     assert(*rlp_item[0] == expected, 'default value not 0');
@@ -2121,7 +2147,7 @@ fn test_rlp_decode_long_list() {
             .span()
     );
 
-    let mut expected_16 = RLPItem::String(array![0].span());
+    let mut expected_16 = RLPItem::String(array![].span());
 
     let mut expected = array![
         expected_0,