Go语言连接PostgreSQL报错求助：getaddrinfow找不到指定类

错误信息 #

panic: dial tcp: lookup tcp/5432,: getaddrinfow: The specified class was not found.

goroutine 1 [running]:
main.main()
        C:/Dev/Digitalent/scalable-web-service-with-golang/go-sql/main.go:35 +0x23a
exit status 2

原代码 #

package main

import (
    "database/sql"
    "fmt"

    _ "github.com/lib/pq"
)

const (
    host     = "localhost"
    port     = 5432
    username = "postgres"
    password = "*********"
    dbName   = "db-go-sql"
)

var (
    db  *sql.DB
    err error
)

func main() {
    psqlURL := fmt.Sprintf("host=%s port=%d, user=%s, password=%s "+"dbname=%s sslmode=disable", host, port, username, password, dbName)

    db, err = sql.Open("postgres", psqlURL)
    if err != nil {
        panic(err)
    }
    defer db.Close()

    err = db.Ping()
    if err != nil {
        panic(err)
    }

    fmt.Println("Connection to postgresql established")
}

问题根源 #

错误出在连接字符串的格式上：github.com/lib/pq驱动要求连接参数的键值对之间用空格分隔，但代码里给port、user、password后面加了逗号，导致驱动把port的值解析成了5432,，进而错误地将tcp/5432,当作主机名去做DNS解析，最终触发getaddrinfow错误。

修正后的代码 #

只需要去掉连接字符串里的逗号即可：

package main

import (
    "database/sql"
    "fmt"

    _ "github.com/lib/pq"
)

const (
    host     = "localhost"
    port     = 5432
    username = "postgres"
    password = "*********"
    dbName   = "db-go-sql"
)

var (
    db  *sql.DB
    err error
)

func main() {
    // 去掉参数之间的逗号，用空格分隔
    psqlURL := fmt.Sprintf("host=%s port=%d user=%s password=%s dbname=%s sslmode=disable", host, port, username, password, dbName)

    db, err = sql.Open("postgres", psqlURL)
    if err != nil {
        panic(err)
    }
    defer db.Close()

    err = db.Ping()
    if err != nil {
        panic(err)
    }

    fmt.Println("Connection to postgresql established")
}

补充说明 #

如果习惯用URI格式的连接字符串，也可以这样写（注意格式正确）：

psqlURL := fmt.Sprintf("postgres://%s:%s@%s:%d/%s?sslmode=disable", username, password, host, port, dbName)

内容的提问来源于stack exchange，提问作者Bayu Aji