MCP Memory Service (Rust Implementation)

This is a Rust implementation of the Model Context Protocol (MCP) Memory Service, using the official Rust MCP SDK.

Features

• Implements an MCP server that provides memory storage and retrieval functionality
• Communicates over stdio for easy integration with MCP clients
• Provides the following tools:
  • store_memory: Store a new memory with content, tags, and metadata
  • retrieve_memory: Retrieve memories semantically similar to a query
  • search_by_tag: Search memories by tags
  • delete_memory: Delete a memory by its hash
• Supports multiple storage backends:
  • In-memory storage (for testing and development)
  • ChromaDB storage (for production use)
• Supports multiple embedding models:
  • Dummy embedding generator (for testing and development)
  • ONNX embedding model (transformer-based embeddings using ONNX Runtime)

Prerequisites

• Rust and Cargo (1.75.0 or later)
• Node.js and npm (for testing with the MCP inspector)
• Optional: ChromaDB server (for production use)

Building

cargo build

For a release build:

cargo build --release

Running

To run the server directly:

cargo run

With environment variables for configuration:

MCP_MEMORY_STORAGE_BACKEND=chromadb \
MCP_MEMORY_CHROMA_PATH=/path/to/chroma \
MCP_MEMORY_EMBEDDING_MODEL=onnx \
cargo run

Configuration

The server can be configured using environment variables:

Variable	Description	Default
MCP_MEMORY_STORAGE_BACKEND	Storage backend (inmemory or chromadb)	inmemory
MCP_MEMORY_CHROMA_PATH	Path to ChromaDB data directory	Platform-specific data directory
MCP_MEMORY_CHROMA_URL	URL to ChromaDB server (optional)	None
MCP_MEMORY_CHROMA_COLLECTION	ChromaDB collection name	memory_collection
MCP_MEMORY_EMBEDDING_MODEL	Embedding model (dummy or onnx)	dummy
MCP_MEMORY_EMBEDDING_MODEL_PATH	Path to ONNX model file (optional)	None
MCP_MEMORY_EMBEDDING_SIZE	Embedding vector size	384
MCP_MEMORY_LOG_LEVEL	Log level	info

Testing

This project includes a simple Node.js test script for testing the server. To run the tests:

npm test

Project Structure

• src/main.rs: The main server implementation
• src/config.rs: Configuration handling
• src/models.rs: Data models
• src/storage/: Storage implementations
  • mod.rs: Storage trait and in-memory implementation
  • chroma.rs: ChromaDB storage implementation
• src/embeddings.rs: Embedding model implementations
• src/utils.rs: Utility functions
• Cargo.toml: Rust project configuration
• package.json: Node.js project configuration for testing tools
• test-mcp-server.js: A simple Node.js script to test the server programmatically

Implementation Details

The server is implemented using the rmcp crate from the Rust MCP SDK. It uses:

• The #[tool(tool_box)] attribute macro to define tools
• The ServerHandler trait to implement the MCP protocol
• The stdio() transport for CLI usage
• Asynchronous Rust with Tokio for concurrent operations
• Tracing for structured logging

Example Usage

After starting the server with cargo run, you can send JSON-RPC requests to its stdin. For example:

{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocol_version":"2024-11-05","capabilities":{"tools":true},"client_info":{"name":"test-client","version":"0.1.0"}}}
{"jsonrpc":"2.0","id":2,"method":"list_tools","params":{}}
{"jsonrpc":"2.0","id":3,"method":"call_tool","params":{"name":"store_memory","arguments":{"content":"This is a test memory","tags":["test","example"]}}}

ONNX Embedding Implementation

The ONNX embedding model implementation uses the ONNX Runtime to run transformer-based models for generating embeddings. Here's how it works:

1. Model Loading: The OnnxEmbeddingGenerator loads a pre-trained transformer model in ONNX format and a tokenizer from the specified paths.

2. Tokenization: Input text is tokenized using the HuggingFace tokenizers library, which converts text into token IDs, attention masks, and token type IDs.

3. Inference: The tokenized inputs are passed to the ONNX model, which produces the transformer's hidden states.

4. Mean Pooling: The last hidden state is processed using mean pooling (weighted by the attention mask) to create a fixed-size embedding vector.

5. Normalization: The resulting embedding is L2-normalized to ensure consistent vector magnitudes.

To use the ONNX embedding model:

1. Export a transformer model (like BERT, RoBERTa, etc.) to ONNX format using a tool like HuggingFace's transformers.onnx.
2. Save the tokenizer as a tokenizer.json file in the same directory as the model or specify a separate path.
3. Set the environment variables:

   MCP_MEMORY_EMBEDDING_MODEL=onnx
   MCP_MEMORY_EMBEDDING_MODEL_PATH=/path/to/model.onnx
   MCP_MEMORY_EMBEDDING_SIZE=768  # Adjust based on your model's output size
   

Registering with an MCP Client

To register this server with an MCP client (like Claude), you need to add it to the client's MCP configuration. Here's an example JSON configuration:

{
  "mcpServers": {
    "memory-service": {
      "command": "/path/to/mcp-rust-server",
      "args": [],
      "env": {
        "MCP_MEMORY_STORAGE_BACKEND": "inmemory",
        "MCP_MEMORY_EMBEDDING_MODEL": "onnx",
        "MCP_MEMORY_EMBEDDING_MODEL_PATH": "/path/to/model.onnx",
        "MCP_MEMORY_EMBEDDING_SIZE": "768",
        "MCP_MEMORY_LOG_LEVEL": "info"
      },
      "disabled": false,
      "autoApprove": []
    }
  }
}

For Claude Desktop, this configuration would be added to:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json
• Linux: ~/.config/Claude/claude_desktop_config.json

For Claude VSCode extension, the configuration would be added to:

• ~/Library/Application Support/Code/User/globalStorage/saoudrizwan.claude-dev/settings/cline_mcp_settings.json

Future Improvements

• Add support for more transformer architectures
• Add more storage backends
• Add more embedding models
• Add more tools for memory management
• Add authentication and authorization
• Add support for more transports (HTTP, WebSocket, etc.)

Architecture

graph TD
    subgraph "External Interactions"
        direction LR
        Client([MCP Client]) -. JSON-RPC .-> StdioTransport[Stdio Transport]
        EnvVars[(Environment Variables)] -.-> Config
        ChromaDBServer[(ChromaDB Server)] <-. HTTP API .-> ChromaStorage
        OnnxModel[("ONNX Model File (.onnx)")] <-. Loads .-> OnnxEmbed
        TokenizerFile[("Tokenizer File (tokenizer.json)")] <-. Loads .-> OnnxEmbed
    end

    subgraph "MCP Memory Service (Rust Application)"
        direction TB
        StdioTransport -- Forwards Requests --> ServerCore{MCP Server Core} 

        ServerCore -- Reads --> Config(Configuration) 
        ServerCore -- Instantiates --> EmbeddingImpl{{Selected Embedding Generator}}
        ServerCore -- Instantiates --> StorageImpl{{Selected Storage Backend}}
        ServerCore -- Uses Tool Impls --> ToolLogic(Tool Logic: store, retrieve, search, delete)

        ToolLogic -- Uses --> StorageImpl
        ToolLogic -- Uses --> EmbeddingImpl
        ToolLogic -- Uses --> Models(Data Models) 
        ToolLogic -- Uses --> Utils(Utilities) 

        %% FIX: Added IDs EL and SL to subgraphs below
        subgraph EL [Embedding Layer]
            direction TB
            EmbeddingImpl -- Is an instance of --> EmbeddingTrait(EmbeddingGenerator Trait)
            DummyEmbed(DummyEmbeddingGenerator) -- Implements --> EmbeddingTrait
            OnnxEmbed(OnnxEmbeddingGenerator) -- Implements --> EmbeddingTrait
            OnnxEmbed -- Uses Lib --> OrtLib[ort crate]
            OnnxEmbed -- Uses Lib --> TokenizersLib[tokenizers crate]
        end

        subgraph SL [Storage Layer]
            direction TB
            StorageImpl -- Is an instance of --> StorageTrait(MemoryStorage Trait)
            InMemoryStorage(InMemoryStorage) -- Implements --> StorageTrait
            ChromaStorage(ChromaMemoryStorage) -- Implements --> StorageTrait
            StorageImpl -- Uses --> EmbeddingImpl
            StorageImpl -- Uses --> Models
            ChromaStorage -- Uses Lib --> ReqwestLib[reqwest crate]
        end

    end

    %% Styling
    classDef external fill:#f9f,stroke:#333,stroke-width:1px;
    classDef rust_app fill:#e6ffed,stroke:#333,stroke-width:1px;
    classDef trait fill:#lightblue,stroke:#333,stroke-width:1px;
    classDef impl fill:#lightgrey,stroke:#333,stroke-width:1px;
    classDef module fill:#whitesmoke,stroke:#333,stroke-width:1px;
    classDef lib fill:#cornsilk,stroke:#333,stroke-width:1px;


    class Client,EnvVars,ChromaDBServer,OnnxModel,TokenizerFile external;
    class StdioTransport,ServerCore,ToolLogic,Config,Models,Utils rust_app;
    class EmbeddingTrait,StorageTrait trait;
    class EmbeddingImpl,StorageImpl,DummyEmbed,OnnxEmbed,InMemoryStorage,ChromaStorage impl;
    class OrtLib,TokenizersLib,ReqwestLib lib;
    %% FIX: Used subgraph IDs EL and SL below
    class EL,SL module

License

This project is licensed under the MIT License - see the LICENSE file for details.