greentic-mcp-client

Client for MCP servers over JSON-RPC 2.0 (protocol 2025-06-18), via two native transports:

• HTTP — remote servers over Streamable HTTP / SSE (McpHttpClient).
• stdio — local subprocess servers over newline-delimited JSON-RPC on the child's stdin/stdout (McpStdioClient).

Not to be confused with greentic-mcp (greentic-mcp-exec), which loads and executes wasix:mcp WASM components locally. This crate is the network-client side.

Layout

• proto — sans-io protocol core: request builders, SSE-aware response parsing, tool mapping. Compiles for wasm32-wasip2 (default-features = false).
• client — native transports (feature native, default), both exposing the shared McpClient shape (initialize / list_tools / call_tool):
  • McpHttpClient — reqwest transport, Mcp-Session-Id threading, configurable auth header.
  • McpStdioClient — tokio-process transport; spawns a local MCP server and frames messages as line-delimited JSON. The child is killed on drop.

Usage (native, HTTP)

use greentic_mcp_client::{McpAuth, McpClientOptions, McpHttpClient};
use url::Url;

let mut client = McpHttpClient::new(
    Url::parse("https://example.com/mcp")?,
    Some(McpAuth::bearer("token")),
    McpClientOptions::default(),
)?;
let info = client.initialize().await?;
let tools = client.list_tools().await?;
let out = client.call_tool("echo", &serde_json::json!({ "msg": "hi" })).await?;

Usage (native, stdio)

use greentic_mcp_client::{McpClientOptions, McpStdioClient};

let mut client = McpStdioClient::spawn(
    "npx",
    &["-y".into(), "@modelcontextprotocol/server-everything".into()],
    &[], // extra env pairs, on top of the inherited environment
    McpClientOptions::default(),
)?;
let info = client.initialize().await?;
let tools = client.list_tools().await?;
let out = client.call_tool("echo", &serde_json::json!({ "msg": "hi" })).await?;

Usage (wasm extension)

greentic-mcp-client = { version = "1.2", default-features = false }

Use the proto builders/parsers with your host's HTTP imports.

Consumers

• greentic-designer-admin — tenant MCP-server test-connection endpoint
• greentic-designer — flow-prompt MCP tool source (planned)
• greentic-aw-runtime — agentic-worker MCP tool dispatch (planned)
• component-github-mcp-ext — proto layer inside the WASM extension (planned refactor)