Porta

A secure MCP bridge for Almide-compiled WASM agents.
The gate between the sandbox and the world.

Written in Almide with a built-in WASM interpreter. No external runtime dependency.

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What is Porta?

Porta loads an Almide-compiled .wasm binary and exposes it as an MCP server over JSON-RPC 2.0 / stdio. It includes a built-in WASM interpreter — no wasmtime, wasmer, or other external runtime needed.

Install

# From source (requires Almide >= 0.12.0)
almide build
cp porta ~/.local/bin/

Quick Start

# Run a WASM agent
porta run agent.wasm

# Start as MCP server (for Claude Code, Cursor, etc.)
porta serve agent.wasm

# Generate manifest from WASM binary
porta build agent.wasm

# Inspect module info
porta inspect agent.wasm

Architecture

MCP Client (Claude Code / Cursor / etc.)
    | JSON-RPC 2.0 / stdio
Porta
    |-- jsonrpc.almd       JSON-RPC 2.0 protocol
    |-- mcp.almd           MCP state machine (tools, resources, prompts)
    |-- manifest.almd      manifest.json parser
    |-- dispatch.almd      Instance lifecycle, restart policies
    |-- sandbox.almd       Capability enforcement (deny-by-default)
    |-- observability.almd Metrics and diagnostic logging
    |-- util.almd          CLI utilities
    +-- wasm/
        |-- binary.almd    .wasm binary parser
        |-- interp.almd    Stack machine interpreter + WASI
        +-- memory.almd    Linear memory management

CLI Reference

porta run <agent.wasm> [options]     Execute WASM binary
porta serve <agent.wasm> [options]   Start MCP server on stdio
porta build <agent.wasm>             Generate manifest.json
porta inspect <agent.wasm>           Show module info
porta validate <agent.wasm>          Validate WASI imports against profile
porta help [command]                 Show help
porta version                        Show version

Common Options

Flag	Description	Default
--entry <name>	Entry point function	_start
--step-limit <n>	Max WASM instructions (0 = unlimited)	0
--max-memory <pages>	Max WASM memory pages (0 = unlimited)	0
--restart <policy>	no, on-failure, always	no
--profile <name>	ai-agent, worker, full	varies
--env <KEY=VALUE>	Set environment variable (repeatable)
--env-file <path>	Load env vars from file
--secret <KEY=VALUE>	Inject secret (repeatable, redacted in inspect)
--manifest <path>	Path to manifest.json

MCP Integration

Claude Code

// .claude/.mcp.json
{
  "mcpServers": {
    "agent": {
      "type": "stdio",
      "command": "porta",
      "args": ["serve", "agent.wasm"]
    }
  }
}

Supported MCP Methods

• initialize / notifications/initialized
• tools/list, tools/call
• resources/list, resources/read
• prompts/list, prompts/get
• ping

Security Model

Porta uses a capability-based, deny-by-default security model. All WASI access requires explicit capability grants.

Capability Profiles

Profile	Grants
ai-agent	IO, Process (minimal for MCP tool dispatch)
worker	IO, Process, Clock, Random
full	All capabilities

8 Capability Types

io, fs, fs.write, process, env, clock, random, net

Enforcement

1. Import validation — WASI imports checked against capabilities at module load
2. Runtime check — Every WASI call verified before execution

Three-Layer Defense

1. Compiler (Layer 1) — Almide rejects capability violations at compile time
2. Binary (Layer 2) — Disallowed WASI imports are absent from .wasm
3. Porta (Layer 3) — Runtime enforcement: fd table, preopen dirs, env filtering, memory limits, step limits

Manifest Format

{
  "schema_version": "1.0",
  "name": "my-agent",
  "version": "0.1.0",
  "description": "An example agent",
  "entry": "_start",
  "capabilities": ["io", "fs"],
  "tools": [
    {
      "name": "greet",
      "description": "Say hello",
      "inputSchema": { "type": "object", "properties": { "name": { "type": "string" } } }
    }
  ],
  "resources": [
    {
      "uri": "file:///config",
      "name": "Config",
      "description": "Agent configuration",
      "mimeType": "application/json"
    }
  ],
  "prompts": [
    {
      "name": "summarize",
      "description": "Summarize a document",
      "arguments": [{ "name": "text", "description": "Text to summarize", "required": true }]
    }
  ],
  "wasi_imports": ["fd_write", "fd_read", "proc_exit"]
}

Observability

• Run mode: Metrics summary printed to stderr after execution (steps, memory, restarts)
• Serve mode: Diagnostic log per tool call to stderr: [porta] tool=name steps=N memory=M ok

License

MIT