Hmbown/CodeWhale · error

MCP command cannot be empty

Error message

MCP command cannot be empty

What it means

parse_mcp_command rejects input that is empty after trimming. The parser accepts either a local command line or an http(s) URL for an MCP server; before any parsing it requires non-whitespace input, so an empty string fails here rather than producing a server with no command and no URL.

Source

Thrown at crates/tui/src/tools/runtime_mcp.rs:34

    ApprovalRequirement, ToolCapability, ToolContext, ToolError, ToolResult, ToolSpec,
};

// === Parsing Functions ===

#[derive(Debug, Clone)]
pub struct ParsedMcpServer {
    pub name: String,
    pub config: McpServerConfig,
}

/// Parse a command string or URL into an MCP server configuration.
///
/// - Local command: `npx @modelcontextprotocol/server-filesystem /tmp`
/// - Remote URL: `https://huggingface.co/mcp`
pub fn parse_mcp_command(input: &str) -> Result<ParsedMcpServer> {
    let input = input.trim();
    if input.is_empty() {
        anyhow::bail!("MCP command cannot be empty");
    }

    if input.starts_with("http://") || input.starts_with("https://") {
        let name = extract_name_from_url(input)?;
        return Ok(ParsedMcpServer {
            name,
            config: McpServerConfig {
                command: None,
                args: Vec::new(),
                env: HashMap::new(),
                cwd: None,
                url: Some(input.to_string()),
                transport: None,
                connect_timeout: None,
                execute_timeout: None,
                read_timeout: None,
                disabled: false,
                enabled: true,

View on GitHub (pinned to 0c42157ee5)

Solutions

1. Treat blank input as 'no server configured' at the call site: check trimmed emptiness before parsing.
2. Require the field in your config schema validation so empty commands fail at load time with a path to the offending key.
3. Pass either a full command line (e.g. 'npx @modelcontextprotocol/server-filesystem /tmp') or an http(s) URL.

Example fix

// before
let parsed = parse_mcp_command(&cfg.mcp_command)?; // panics path on ""

// after
let cmd = cfg.mcp_command.trim();
if cmd.is_empty() {
    return Ok(None); // no MCP server configured
}
let parsed = parse_mcp_command(cmd)?;

fn parse_optional_mcp_command(input: &str) -> Result<Option<ParsedMcpServer>> {
    let input = input.trim();
    if input.is_empty() {
        return Ok(None);
    }
    parse_mcp_command(input).map(Some)
}

When it happens

Trigger: Calling parse_mcp_command("") or with a whitespace-only string; forwarding an unvalidated config field, CLI argument, or chat input that can be blank.

Common situations: Optional MCP command fields in config or prompts where empty means 'unset'; form inputs submitted blank; template-substituted command strings that resolve to nothing.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

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AI-assisted analysis of Hmbown/CodeWhale@0c42157ee5 (2026-08-20). Data as JSON: /api/errors/41d8cde973be01da. Report an issue: GitHub.