Guard max size of msg

crates/oc2r-core/src/error.rs

@@ -8,6 +8,7 @@ pub enum Error {
     Json(miniserde::Error),
     Framing,
     Protocol(String),
+    MessageTooLarge(usize),
 }
 
 pub type Result<T> = std::result::Result<T, Error>;
@@ -31,6 +32,7 @@ impl std::fmt::Display for Error {
             Error::Json(e) => write!(f, "json error: {e}"),
             Error::Framing => f.write_str("invalid message framing"),
             Error::Protocol(msg) => write!(f, "protocol error: {msg}"),
+            Error::MessageTooLarge(n) => write!(f, "rpc frame too large: {n} bytes"),
         }
     }
 }

crates/oc2r-core/src/transport.rs

@@ -9,6 +9,7 @@ use std::os::fd::RawFd;
 use std::time::{Duration, Instant};
 
 const DELIM: [u8; 1] = [0];
+const MAX_MESSAGE_SIZE: usize = 4096;
 
 pub(crate) fn set_raw(fd: RawFd) -> Result<()> {
     unsafe {
@@ -74,6 +75,11 @@ pub(crate) fn flush_fd(fd: RawFd) -> Result<usize> {
 
 pub(crate) fn write_message(fd: RawFd, msg: &impl Serialize) -> Result<()> {
     let payload = json::to_string(msg);
+
+    let total_len = payload.len() + 2;
+    if total_len > MAX_MESSAGE_SIZE {
+        return Err(Error::MessageTooLarge(total_len));
+    }
     write_all_fd(fd, &DELIM)?;
     write_all_fd(fd, payload.as_bytes())?;
     write_all_fd(fd, &DELIM)?;