Google Cloud MCP Server

Implementation Reference

• src/services/spanner/tools.ts:300-369 (handler)

  The main handler function for the 'list-spanner-databases' tool. It retrieves the project ID, creates a Spanner client, lists all databases in the specified instance, formats the results as a markdown table with state info, and includes resource URIs for further exploration (tables and schema).

  async ({ instanceId }, _extra) => {
    try {
      // First try to get the project ID from the state manager
      let projectId = stateManager.getCurrentProjectId();
      
      if (!projectId) {
        // If not in state manager, try to get it from our function
        const authProjectId = await getProjectId();
        if (authProjectId) {
          projectId = authProjectId;
          console.log(`Got project ID from getProjectId: ${projectId}`);
        }
      } else {
        console.log(`Got project ID from state manager: ${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 project ID: ${projectId} for list-spanner-databases`);
      const instance = spanner.instance(Array.isArray(instanceId) ? instanceId[0] : instanceId);
      
      const [databases] = await instance.getDatabases();
      
      if (!databases || databases.length === 0) {
        return {
          content: [{
            type: 'text',
            text: `# Spanner Databases\n\nProject: ${projectId}\nInstance: ${Array.isArray(instanceId) ? instanceId[0] : instanceId}\n\nNo databases found in the instance.`
          }]
        };
      }
      
      let markdown = `# Spanner Databases\n\nProject: ${projectId}\nInstance: ${Array.isArray(instanceId) ? instanceId[0] : instanceId}\n\n`;
      
      // Table header
      markdown += '| Database ID | State |\n';
      markdown += '|-------------|-------|\n';
      
      // Table rows
      for (const database of databases) {
        const metadata = database.metadata || {};
        markdown += `| ${database.id || 'unknown'} | ${metadata.state || 'unknown'} |\n`;
      }
      
      // Add resource links for further exploration
      markdown += '\n## Available Resources\n\n';
      
      for (const database of databases) {
        markdown += `- Tables in ${database.id}: \`gcp-spanner://${projectId}/${Array.isArray(instanceId) ? instanceId[0] : instanceId}/${database.id}/tables\`\n`;
        markdown += `- Schema for ${database.id}: \`gcp-spanner://${projectId}/${Array.isArray(instanceId) ? instanceId[0] : instanceId}/${database.id}/schema\`\n`;
      }
      
      return {
        content: [{
          type: 'text',
          text: markdown
        }]
      };
    } catch (error: any) {
      console.error('Error listing Spanner databases:', error);
      throw error;
    }
  }

• src/services/spanner/tools.ts:297-299 (schema)

  Zod input schema for the tool, requiring a single 'instanceId' parameter as string.

  {
    instanceId: z.string().describe('Spanner instance ID')
  },

• src/services/spanner/tools.ts:295-370 (registration)

  Registers the 'list-spanner-databases' tool on the MCP server within the registerSpannerTools function.

  server.tool(
    'list-spanner-databases',
    {
      instanceId: z.string().describe('Spanner instance ID')
    },
    async ({ instanceId }, _extra) => {
      try {
        // First try to get the project ID from the state manager
        let projectId = stateManager.getCurrentProjectId();
        
        if (!projectId) {
          // If not in state manager, try to get it from our function
          const authProjectId = await getProjectId();
          if (authProjectId) {
            projectId = authProjectId;
            console.log(`Got project ID from getProjectId: ${projectId}`);
          }
        } else {
          console.log(`Got project ID from state manager: ${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 project ID: ${projectId} for list-spanner-databases`);
        const instance = spanner.instance(Array.isArray(instanceId) ? instanceId[0] : instanceId);
        
        const [databases] = await instance.getDatabases();
        
        if (!databases || databases.length === 0) {
          return {
            content: [{
              type: 'text',
              text: `# Spanner Databases\n\nProject: ${projectId}\nInstance: ${Array.isArray(instanceId) ? instanceId[0] : instanceId}\n\nNo databases found in the instance.`
            }]
          };
        }
        
        let markdown = `# Spanner Databases\n\nProject: ${projectId}\nInstance: ${Array.isArray(instanceId) ? instanceId[0] : instanceId}\n\n`;
        
        // Table header
        markdown += '| Database ID | State |\n';
        markdown += '|-------------|-------|\n';
        
        // Table rows
        for (const database of databases) {
          const metadata = database.metadata || {};
          markdown += `| ${database.id || 'unknown'} | ${metadata.state || 'unknown'} |\n`;
        }
        
        // Add resource links for further exploration
        markdown += '\n## Available Resources\n\n';
        
        for (const database of databases) {
          markdown += `- Tables in ${database.id}: \`gcp-spanner://${projectId}/${Array.isArray(instanceId) ? instanceId[0] : instanceId}/${database.id}/tables\`\n`;
          markdown += `- Schema for ${database.id}: \`gcp-spanner://${projectId}/${Array.isArray(instanceId) ? instanceId[0] : instanceId}/${database.id}/schema\`\n`;
        }
        
        return {
          content: [{
            type: 'text',
            text: markdown
          }]
        };
      } catch (error: any) {
        console.error('Error listing Spanner databases:', error);
        throw error;
      }
    }
  );

• src/index.ts:139-142 (registration)

  Top-level server initialization calls registerSpannerTools(server), which includes the list-spanner-databases tool registration.

    registerSpannerResources(server);
    registerSpannerTools(server);
    registerSpannerQueryCountTool(server);
  } catch (error) {