fix: string slice decoding (#1483)

decoding string slices now reports correct amount of bytes read

packages/fuels-core/src/codec.rs

@@ -29,7 +29,7 @@ mod tests {
     use super::*;
     use crate::{
         constants::WORD_SIZE,
-        types::{Address, AssetId, ContractId},
+        types::{Address, AsciiString, AssetId, ContractId},
     };
 
     #[test]
@@ -80,4 +80,36 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn string_slice_is_read_in_total() {
+        // This was a bug where the decoder read more bytes than it reported, causing the next
+        // element to be read incorrectly.
+
+        // given
+        #[derive(
+            fuels_macros::Tokenizable, fuels_macros::Parameterize, Clone, PartialEq, Debug,
+        )]
+        #[FuelsCorePath = "crate"]
+        #[FuelsTypesPath = "crate::types"]
+        struct Test {
+            name: AsciiString,
+            age: u64,
+        }
+
+        let input = Test {
+            name: AsciiString::new("Alice".to_owned()).unwrap(),
+            age: 42,
+        };
+
+        let encoded = ABIEncoder::default()
+            .encode(&[input.clone().into_token()])
+            .unwrap();
+
+        // when
+        let decoded = try_from_bytes::<Test>(&encoded, DecoderConfig::default()).unwrap();
+
+        // then
+        assert_eq!(decoded, input);
+    }
 }

packages/fuels-core/src/codec/abi_decoder/bounded_decoder.rs

@@ -210,12 +210,14 @@ impl BoundedDecoder {
 
     fn decode_string_slice(bytes: &[u8]) -> Result<Decoded> {
         let length = peek_length(bytes)?;
-        let bytes = peek(skip(bytes, LENGTH_BYTES_SIZE)?, length)?;
-        let decoded = str::from_utf8(bytes)?.to_string();
+        // skipping over the previously read length
+        let content_bytes = skip(bytes, LENGTH_BYTES_SIZE)?;
+        let string_bytes = peek(content_bytes, length)?;
+        let decoded = str::from_utf8(string_bytes)?.to_string();
 
         Ok(Decoded {
             token: Token::StringSlice(StaticStringToken::new(decoded, None)),
-            bytes_read: bytes.len(),
+            bytes_read: string_bytes.len() + LENGTH_BYTES_SIZE,
         })
     }