feat(opax-web): add secure MCP agent client

opax-web/backend/agentClient.js

@@ -0,0 +1,145 @@
+import { randomUUID } from 'node:crypto';
+
+const TIMEOUT_MS = 10000;
+const MAX_REQUEST_SIZE = 16384;
+const MAX_RESPONSE_SIZE = 1024 * 1024;
+const GENERIC_ERROR_MESSAGE = 'Agent request failed.';
+
+const READ_ONLY_TOOLS = new Set([
+  'get_health',
+  'get_build_status',
+  'get_state',
+  'get_telemetry',
+  'get_git_status',
+  'get_git_branch',
+  'get_git_log',
+  'get_git_diff',
+  'list_repo_files',
+  'read_repo_file',
+]);
+
+export class AgentNotConfiguredError extends Error {
+  constructor() {
+    super('Agent integration is not configured.');
+    this.name = 'AgentNotConfiguredError';
+  }
+}
+
+function validateMcpUrl(urlString, allowedOrigin) {
+  const url = new URL(urlString);
+
+  if (url.username || url.password || url.hash) {
+    throw new Error(GENERIC_ERROR_MESSAGE);
+  }
+
+  if (url.protocol === 'http:') {
+    const isLoopback =
+      url.hostname === 'localhost' ||
+      url.hostname === '127.0.0.1' ||
+      url.hostname === '[::1]';
+
+    if (!isLoopback) {
+      throw new Error(GENERIC_ERROR_MESSAGE);
+    }
+
+    return url;
+  }
+
+  if (url.protocol !== 'https:' || !allowedOrigin) {
+    throw new Error(GENERIC_ERROR_MESSAGE);
+  }
+
+  const configuredOrigin = new URL(allowedOrigin);
+
+  if (url.origin !== configuredOrigin.origin) {
+    throw new Error(GENERIC_ERROR_MESSAGE);
+  }
+
+  return url;
+}
+
+export async function callAgent(tool, args) {
+  const mcpUrl = process.env.OPAX_MCP_URL?.trim();
+  const mcpSecret = process.env.MCP_SECRET?.trim();
+
+  if (!mcpUrl || !mcpSecret) {
+    throw new AgentNotConfiguredError();
+  }
+
+  try {
+    const allowedOrigin = process.env.OPAX_MCP_ALLOWED_ORIGIN?.trim();
+
+    if (!READ_ONLY_TOOLS.has(tool)) {
+      throw new Error(GENERIC_ERROR_MESSAGE);
+    }
+
+    const validatedUrl = validateMcpUrl(mcpUrl, allowedOrigin);
+
+    const requestBody = JSON.stringify({
+      jsonrpc: '2.0',
+      id: randomUUID(),
+      method: 'tools/call',
+      params: {
+        name: tool,
+        arguments: args,
+      },
+    });
+
+    if (requestBody.length > MAX_REQUEST_SIZE) {
+      throw new Error(GENERIC_ERROR_MESSAGE);
+    }
+
+    const controller = new AbortController();
+    const timeoutId = setTimeout(() => controller.abort(), TIMEOUT_MS);
+
+    try {
+      const response = await fetch(validatedUrl, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          Authorization: `Bearer ${mcpSecret}`,
+        },
+        body: requestBody,
+        signal: controller.signal,
+      });
+
+      if (!response.ok) {
+        throw new Error(GENERIC_ERROR_MESSAGE);
+      }
+
+      const responseText = await response.text();
+
+      if (responseText.length > MAX_RESPONSE_SIZE) {
+        throw new Error(GENERIC_ERROR_MESSAGE);
+      }
+
+      const rpcResponse = JSON.parse(responseText);
+
+      if (rpcResponse.error) {
+        throw new Error(GENERIC_ERROR_MESSAGE);
+      }
+
+      const content = rpcResponse.result?.content;
+
+      if (!Array.isArray(content) || content.length === 0) {
+        throw new Error(GENERIC_ERROR_MESSAGE);
+      }
+
+      const firstContent = content[0];
+
+      if (
+        firstContent?.type !== 'text' ||
+        typeof firstContent.text !== 'string' ||
+        firstContent.text.length > MAX_RESPONSE_SIZE
+      ) {
+        throw new Error(GENERIC_ERROR_MESSAGE);
+      }
+
+      return JSON.parse(firstContent.text);
+    } finally {
+      clearTimeout(timeoutId);
+    }
+  } catch {
+    throw new Error(GENERIC_ERROR_MESSAGE);
+  }
+}