Google Cloud MCP Server

Implementation Reference

• src/services/spanner/tools.ts:216-291 (handler)

  The handler function that implements the core logic of listing Spanner instances. It retrieves the project ID from various sources, creates a Spanner client, fetches the list of instances, formats them into a Markdown table with metadata, and includes navigation resource URIs.

  async (_params, _extra) => {
    try {
      // First try to get the project ID from the state manager
      let projectId = stateManager.getCurrentProjectId();
      
      if (projectId) {
        console.log(`Got project ID from state manager: ${projectId}`);
      } else {
        // If not in state manager, try to get it from environment
        const envProjectId = process.env.GOOGLE_CLOUD_PROJECT;
        
        if (envProjectId) {
          projectId = envProjectId;
          console.log(`Got project ID from environment: ${projectId}`);
          // Store in state manager for future use
          await stateManager.setCurrentProjectId(projectId);
        } else {
          // If not in environment, try to get it from our function
          projectId = await getProjectId();
          console.log(`Got project ID from getProjectId: ${projectId}`);
        }
      }
      
      if (!projectId) {
        throw new Error('Project ID could not be determined. Please set a project ID using the set-project-id tool.');
      }
      
      // Create Spanner client with explicit project ID
      const spanner = new (await import('@google-cloud/spanner')).Spanner({
        projectId: projectId
      });
      
      console.log(`Using Spanner client with explicit project ID: ${projectId} for list-spanner-instances`);
      
      const [instances] = await spanner.getInstances();
      
      if (!instances || instances.length === 0) {
        return {
          content: [{
            type: 'text',
            text: `# Spanner Instances\n\nProject: ${projectId}\n\nNo instances found in the project.`
          }]
        };
      }
      
      let markdown = `# Spanner Instances\n\nProject: ${projectId}\n\n`;
      
      // Table header
      markdown += '| Instance ID | State | Config | Nodes |\n';
      markdown += '|-------------|-------|--------|-------|\n';
      
      // Table rows
      for (const instance of instances) {
        const metadata = instance.metadata || {};
        markdown += `| ${instance.id || 'unknown'} | ${metadata.state || 'unknown'} | ${metadata.config?.split('/').pop() || 'unknown'} | ${metadata.nodeCount || 'unknown'} |\n`;
      }
      
      // Add resource links for further exploration
      markdown += '\n## Available Resources\n\n';
      markdown += `- All Instances: \`gcp-spanner://${projectId}/instances\`\n`;
      
      for (const instance of instances) {
        markdown += `- Databases in ${instance.id}: \`gcp-spanner://${projectId}/${instance.id}/databases\`\n`;
      }
      
      return {
        content: [{
          type: 'text',
          text: markdown
        }]
      };
    } catch (error: any) {
      console.error('Error listing Spanner instances:', error);
      throw error;
    }
  }

• src/services/spanner/tools.ts:211-215 (schema)

  The Zod input schema for the list-spanner-instances tool. It defines an optional dummy string parameter to maintain compatibility with MCP clients that expect an input object.

  // Define an empty schema with a dummy parameter that's optional
  // This ensures compatibility with clients that expect an object parameter
  {
    _dummy: z.string().optional().describe('Not used, just to ensure parameter compatibility')
  },

• src/services/spanner/tools.ts:209-292 (registration)

  The server.tool() call that registers the 'list-spanner-instances' tool on the MCP server, specifying its name, input schema, and handler function.

  server.tool(
    'list-spanner-instances',
    // Define an empty schema with a dummy parameter that's optional
    // This ensures compatibility with clients that expect an object parameter
    {
      _dummy: z.string().optional().describe('Not used, just to ensure parameter compatibility')
    },
    async (_params, _extra) => {
      try {
        // First try to get the project ID from the state manager
        let projectId = stateManager.getCurrentProjectId();
        
        if (projectId) {
          console.log(`Got project ID from state manager: ${projectId}`);
        } else {
          // If not in state manager, try to get it from environment
          const envProjectId = process.env.GOOGLE_CLOUD_PROJECT;
          
          if (envProjectId) {
            projectId = envProjectId;
            console.log(`Got project ID from environment: ${projectId}`);
            // Store in state manager for future use
            await stateManager.setCurrentProjectId(projectId);
          } else {
            // If not in environment, try to get it from our function
            projectId = await getProjectId();
            console.log(`Got project ID from getProjectId: ${projectId}`);
          }
        }
        
        if (!projectId) {
          throw new Error('Project ID could not be determined. Please set a project ID using the set-project-id tool.');
        }
        
        // Create Spanner client with explicit project ID
        const spanner = new (await import('@google-cloud/spanner')).Spanner({
          projectId: projectId
        });
        
        console.log(`Using Spanner client with explicit project ID: ${projectId} for list-spanner-instances`);
        
        const [instances] = await spanner.getInstances();
        
        if (!instances || instances.length === 0) {
          return {
            content: [{
              type: 'text',
              text: `# Spanner Instances\n\nProject: ${projectId}\n\nNo instances found in the project.`
            }]
          };
        }
        
        let markdown = `# Spanner Instances\n\nProject: ${projectId}\n\n`;
        
        // Table header
        markdown += '| Instance ID | State | Config | Nodes |\n';
        markdown += '|-------------|-------|--------|-------|\n';
        
        // Table rows
        for (const instance of instances) {
          const metadata = instance.metadata || {};
          markdown += `| ${instance.id || 'unknown'} | ${metadata.state || 'unknown'} | ${metadata.config?.split('/').pop() || 'unknown'} | ${metadata.nodeCount || 'unknown'} |\n`;
        }
        
        // Add resource links for further exploration
        markdown += '\n## Available Resources\n\n';
        markdown += `- All Instances: \`gcp-spanner://${projectId}/instances\`\n`;
        
        for (const instance of instances) {
          markdown += `- Databases in ${instance.id}: \`gcp-spanner://${projectId}/${instance.id}/databases\`\n`;
        }
        
        return {
          content: [{
            type: 'text',
            text: markdown
          }]
        };
      } catch (error: any) {
        console.error('Error listing Spanner instances:', error);
        throw error;
      }
    }
  );

• src/index.ts:140-140 (registration)

  Invocation of registerSpannerTools in the main server initialization, which registers all Spanner tools including list-spanner-instances.

  registerSpannerTools(server);