zed-industries/zed · error

cannot read LSP message headers

Error message

cannot read LSP message headers

What it means

Raised when read_headers hits EOF on the language server's stdout before a complete LSP Content-Length header block was received: the server exited or closed its output without sending a message. Not a header syntax error — the stream ended prematurely.

Source

Thrown at crates/lsp/src/input_handler.rs:47

/// Handler for stdout of language server.
pub struct LspStdoutHandler {
    pub(super) loop_handle: Task<Result<()>>,
    pub(super) incoming_messages: Receiver<NotificationOrRequest>,
}

async fn read_headers<Stdout>(reader: &mut BufReader<Stdout>, buffer: &mut Vec<u8>) -> Result<()>
where
    Stdout: AsyncRead + Unpin + Send + 'static,
{
    loop {
        if buffer.len() >= HEADER_DELIMITER.len()
            && buffer[(buffer.len() - HEADER_DELIMITER.len())..] == HEADER_DELIMITER[..]
        {
            return Ok(());
        }

        if reader.read_until(b'\n', buffer).await? == 0 {
            anyhow::bail!("cannot read LSP message headers");
        }
    }
}

impl LspStdoutHandler {
    pub fn new<Input>(
        stdout: Input,
        response_handlers: Arc<Mutex<Option<HashMap<RequestId, ResponseHandler>>>>,
        io_handlers: Arc<Mutex<HashMap<i32, IoHandler>>>,
        cx: BackgroundExecutor,
    ) -> Self
    where
        Input: AsyncRead + Unpin + Send + 'static,
    {
        let (tx, notifications_channel) = channel(INCOMING_MESSAGE_QUEUE_CAPACITY);
        let loop_handle = cx.spawn(Self::handler(stdout, tx, response_handlers, io_handlers));
        Self {
            loop_handle,

View on GitHub (pinned to f4178619ac)

Solutions

1. Check the language server logs for a crash or startup failure
2. Verify the server binary is compatible with the platform and not missing libraries
3. Restart the language server / Zed and retry

When it happens

Trigger: Thrown at crates/lsp/src/input_handler.rs:47 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of zed-industries/zed@f4178619ac (2026-08-20). Data as JSON: /api/errors/ceda830d14fe7e49. Report an issue: GitHub.