Validate string max length

protocol-derive/src/lib.rs

@@ -37,6 +37,13 @@ fn impl_encoder_trait(name: &Ident, fields: &Fields) -> TokenStream2 {
         let unparsed_meta = get_packet_field_meta(field);
         let parsed_meta = parse_packet_field_meta(&unparsed_meta);
 
+        // This is special case because max length are used only for strings.
+        if let Some(max_length) = parsed_meta.max_length {
+            return quote! {
+                crate::EncoderWriteExt::write_string(writer, &self.#name, #max_length)?;
+            };
+        }
+
         let module = parsed_meta.module.as_deref().unwrap_or("Encoder");
         let module_ident = Ident::new(&module, Span::call_site());
 
@@ -65,6 +72,13 @@ fn impl_decoder_trait(name: &Ident, fields: &Fields) -> TokenStream2 {
         let unparsed_meta = get_packet_field_meta(field);
         let parsed_meta = parse_packet_field_meta(&unparsed_meta);
 
+        // This is special case because max length are used only for strings.
+        if let Some(max_length) = parsed_meta.max_length {
+            return quote! {
+                let #name = crate::DecoderReadExt::read_string(reader, #max_length)?;
+            };
+        }
+
         match parsed_meta.module {
             Some(module) => {
                 let module_ident = Ident::new(&module, Span::call_site());

protocol/src/game.rs

@@ -236,8 +236,8 @@ mod tests {
         ChunkData, ClientBoundChatMessage, ClientBoundKeepAlive, GameMode, JoinGame,
         MessagePosition, ServerBoundChatMessage, ServerBoundKeepAlive,
     };
-    use crate::Decoder;
+    use crate::{DecodeError, Encoder, EncoderWriteExt, STRING_MAX_LENGTH};
-    use crate::Encoder;
+    use crate::{Decoder, EncodeError};
     use nbt::CompoundTag;
     use std::io::Cursor;
 
@@ -266,6 +266,50 @@ mod tests {
         assert_eq!(chat_message.message, "hello server!");
     }
 
+    #[test]
+    fn test_server_bound_chat_message_encode_invalid_length() {
+        let chat_message = ServerBoundChatMessage {
+            message: "abc".repeat(100),
+        };
+
+        let mut vec = Vec::new();
+
+        let encode_error = chat_message
+            .encode(&mut vec)
+            .err()
+            .expect("Expected error `StringTooLong` because message has invalid length");
+
+        match encode_error {
+            EncodeError::StringTooLong { length, max_length } => {
+                assert_eq!(length, 300);
+                assert_eq!(max_length, 256);
+            }
+            _ => panic!("Expected `StringTooLong` but got `{:?}`", encode_error),
+        }
+    }
+
+    #[test]
+    fn test_server_bound_chat_message_decode_invalid_length() {
+        let message = "abc".repeat(100);
+
+        let mut vec = Vec::new();
+        vec.write_string(&message, STRING_MAX_LENGTH).unwrap();
+
+        let mut cursor = Cursor::new(vec);
+
+        let decode_error = ServerBoundChatMessage::decode(&mut cursor)
+            .err()
+            .expect("Expected error `StringTooLong` because message has invalid length");
+
+        match decode_error {
+            DecodeError::StringTooLong { length, max_length } => {
+                assert_eq!(length, 300);
+                assert_eq!(max_length, 256);
+            }
+            _ => panic!("Expected `StringTooLong` but got `{:?}`", decode_error),
+        }
+    }
+
     #[test]
     fn test_client_bound_chat_message_encode() {
         let chat_message = ClientBoundChatMessage {

protocol/src/lib.rs

@@ -25,8 +25,8 @@ pub mod status;
 /// Current supported protocol version.
 pub const PROTOCOL_VERSION: u32 = 498;
 /// Protocol limits maximum string length.
-const STRING_MAX_LENGTH: u32 = 32_768;
+const STRING_MAX_LENGTH: u16 = 32_768;
-const HYPHENATED_UUID_LENGTH: u32 = 36;
+const HYPHENATED_UUID_LENGTH: u16 = 36;
 
 /// Possible errors while encoding packet.
 #[derive(Debug)]
@@ -36,7 +36,7 @@ pub enum EncodeError {
         /// String length.
         length: usize,
         /// Max string length.
-        max_length: u32,
+        max_length: u16,
     },
     IOError {
         io_error: IoError,
@@ -68,9 +68,9 @@ pub enum DecodeError {
     /// String length can't be more than provided value.
     StringTooLong {
         /// String length.
-        length: u32,
+        length: usize,
         /// Max string length.
-        max_length: u32,
+        max_length: u16,
     },
     IOError {
         io_error: IoError,
@@ -140,7 +140,7 @@ trait Decoder {
 trait EncoderWriteExt {
     fn write_bool(&mut self, value: bool) -> Result<(), EncodeError>;
 
-    fn write_string(&mut self, value: &str, max_length: u32) -> Result<(), EncodeError>;
+    fn write_string(&mut self, value: &str, max_length: u16) -> Result<(), EncodeError>;
 
     fn write_byte_array(&mut self, value: &[u8]) -> Result<(), EncodeError>;
 
@@ -155,7 +155,7 @@ trait EncoderWriteExt {
 trait DecoderReadExt {
     fn read_bool(&mut self) -> Result<bool, DecodeError>;
 
-    fn read_string(&mut self, max_length: u32) -> Result<String, DecodeError>;
+    fn read_string(&mut self, max_length: u16) -> Result<String, DecodeError>;
 
     fn read_byte_array(&mut self) -> Result<Vec<u8>, DecodeError>;
 
@@ -177,7 +177,7 @@ impl<W: Write> EncoderWriteExt for W {
         Ok(())
     }
 
-    fn write_string(&mut self, value: &str, max_length: u32) -> Result<(), EncodeError> {
+    fn write_string(&mut self, value: &str, max_length: u16) -> Result<(), EncodeError> {
         let length = value.len();
 
         if length > max_length as usize {
@@ -224,10 +224,10 @@ impl<R: Read> DecoderReadExt for R {
         }
     }
 
-    fn read_string(&mut self, max_length: u32) -> Result<String, DecodeError> {
+    fn read_string(&mut self, max_length: u16) -> Result<String, DecodeError> {
-        let length = self.read_var_i32()? as u32;
+        let length = self.read_var_i32()? as usize;
 
-        if length > max_length as u32 {
+        if length as u16 > max_length {
             return Err(DecodeError::StringTooLong { length, max_length });
         }