You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: connect_tcp.go
    path of file: ./repos/golang-samples/cloudsql/sqlserver/database-sql
    
    the code of the file until where you have to start completion: // Copyright 2022 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// [START cloud_sql_sqlserver_databasesql_connect_tcp]
// [START cloud_sql_sqlserver_databasesql_connect_tcp_sslcerts]
// [START cloud_sql_sqlserver_databasesql_sslcerts]
package cloudsql

import (
	"database/sql"
	"fmt"
	"log"
	"os"
	"strings"

	_ "github.com/denisenkom/go-mssqldb"
)

// connectTCPSocket initializes a TCP connection pool for a Cloud SQL
// instance of SQL Server.
func connectTCPSocket() (*sql.DB, error) {
	mustGetenv := func(k string) string {
		v := os.Getenv(k)
		if v == "" {
			log.Fatalf("Fatal Error in connect_tcp.go: %s environment variable not set.\n", k)
		}
		return v
	}
	// Note: Saving credentials in environment variables is convenient, but not
	// secure - consider a more secur
    
func connectTCPSocket() (*sql.DB, error) {
	mustGetenv := func(k string) string {
		v := os.Getenv(k)
		if v == "" {
			log.Fatalf("Fatal Error in connect_tcp.go: %s environment variable not set.\n", k)
		}
		return v
	}
	// Note: Saving credentials in environment variables is convenient, but not
	// secure - consider a more secure solution such as
	// Cloud Secret Manager (https://cloud.google.com/secret-manager) to help
	// keep secrets safe.
	var (
		dbUser    = mustGetenv("DB_USER")       // e.g. 'my-db-user'
		dbPwd     = mustGetenv("DB_PASS")       // e.g. 'my-db-password'
		dbTCPHost = mustGetenv("INSTANCE_HOST") // e.g. '127.0.0.1' ('172.17.0.1' if deployed to GAE Flex)
		dbPort    = mustGetenv("DB_PORT")       // e.g. '1433'
		dbName    = mustGetenv("DB_NAME")       // e.g. 'my-database'
	)

	dbURI := fmt.Sprintf("server=%s;user id=%s;password=%s;port=%s;database=%s;",
		dbTCPHost, dbUser, dbPwd, dbPort, dbName)

	// [END cloud_sql_sqlserver_databasesql_connect_tcp]
	// (OPTIONAL) Configure SSL certificates
	// For deployments that connect directly to a Cloud SQL instance without
	// using the Cloud SQL Proxy, configuring SSL certificates will ensure the
	// connection is encrypted.
	if dbRootCert, ok := os.LookupEnv("DB_ROOT_CERT"); ok { // e.g., '/path/to/my/server-ca.pem'
		// Get connection host name to be matched with host name in SSL certificate.
		var instanceConnectionName = mustGetenv("INSTANCE_CONNECTION_NAME")
		// Expected format of INSTANCE_CONNECTION_NAME is project_id:region:instance_name
		hostNameParts := strings.Split(instanceConnectionName, ":")
		if len(hostNameParts) != 3 {
			log.Fatalf("Invalid format for INSTANCE_CONNECTION_NAME environment variable, got = %q", instanceConnectionName)
		}
		// Specify encrypted connection, host name and certificate.
		dbURI += fmt.Sprintf("encrypt=true;hostnameincertificate=%s:%s;certificate=%s;",
			hostNameParts[0], hostNameParts[2], dbRootCert)
	}
	// [START cloud_sql_sqlserver_databasesql_connect_tcp]

	// dbPool is the pool of database connections.
	dbPool, err := sql.Open("sqlserver", dbURI)
	if err != nil {
		return nil, fmt.Errorf("sql.Open: %w", err)
	}

	// [START_EXCLUDE]
	configureConnectionPool(dbPool)
	// [END_EXCLUDE]

	return dbPool, nil
}