zeroclaw-labs/zeroclaw · error · anyhow::Error

MCP server returned no response

Error message

MCP server returned no response

What it means

Error "MCP server returned no response" thrown in zeroclaw-labs/zeroclaw.

Source

Thrown at crates/zeroclaw-tools/src/mcp_transport.rs:1653

        last_event_data_lines = current_data_lines;
    }

    if last_event_data_lines.is_empty() {
        return Cow::Borrowed(text.trim());
    }

    if last_event_data_lines.len() == 1 {
        return Cow::Borrowed(last_event_data_lines[0].trim());
    }

    let joined = last_event_data_lines.join("\n");
    Cow::Owned(joined.trim().to_string())
}

fn parse_jsonrpc_response_text(resp_text: &str) -> Result<JsonRpcResponse> {
    let trimmed = resp_text.trim();
    if trimmed.is_empty() {
        bail!("MCP server returned no response");
    }

    let json_text = if looks_like_sse_text(trimmed) {
        extract_json_from_sse_text(trimmed)
    } else {
        Cow::Borrowed(trimmed)
    };

    let mcp_resp: JsonRpcResponse = serde_json::from_str(json_text.as_ref())
        .with_context(|| format!("invalid JSON-RPC response: {}", resp_text))?;
    Ok(mcp_resp)
}

fn looks_like_sse_text(text: &str) -> bool {
    text.starts_with("data:")
        || text.starts_with("event:")
        || text.contains("\ndata:")
        || text.contains("\nevent:")

View on GitHub (pinned to 88bb9c8533)

Solutions

1. Check the MCP server is responding; verify transport health and retry.

When it happens

Trigger: Thrown at crates/zeroclaw-tools/src/mcp_transport.rs:1653 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of zeroclaw-labs/zeroclaw@88bb9c8533 (2026-08-23). Data as JSON: /api/errors/34f325109c6728f2. Report an issue: GitHub.