TOML - Go Lang

This tutorial explains reading and writing to toml file in Golang

go-toml is a Go language parser for reading and writing toml files.

First, Install the go-toml library.

Open the terminal, install the module

$ go get github.com/pelletier/go-toml
go: downloading github.com/pelletier/go-toml v1.9.5
go: added github.com/pelletier/go-toml v1.9.5

Let’s c

How to read toml files content in Golang

We can read TOML files in Golang in multiple ways.

Let’s have a config.toml file

[mysql]
host = "localhost:31016"
username = "root"
password = "password"
database = "students"

• First way, read individual values from toml file

  • import go-toml from the github repository
  • toml.LoadFile() loads the toml file and reads into a variable, It throws an error if any IO exception
  • You can access the individual values using Get with the given key. Nested values can be get using key.nestedkey.

Here is an example

package main

import (
    "fmt"
    "github.com/pelletier/go-toml"
)

func main() {
    // Reading from a TOML file
    data, err := toml.LoadFile("config.toml")
    if err != nil {
        fmt.Println("Error reading TOML file:", err)
        return
    }

    // Accessing values from the TOML tree
    value := data.Get("mysql")
    fmt.Println("data : ", value)
    // Access individual values
    host := data.Get("mysql.host")
    fmt.Println("host : ", host)
    password := data.Get("mysql.password")
    fmt.Println("password : ", password)
    username := data.Get("mysql.username")
    fmt.Println("username : ", username)
}

Output:

data :  database = "students"
host = "localhost:31016"
password = "password"
username = "root"

host :  localhost:31016
password :  password
username :  root

• Second Way, Parse toml content into Struct.

  • Define struct in golang similar to the structure of some content
  • First, read the toml file using the os.ReadFile() function, it throws an error if the IO exception
  • It reads into a variable
  • Pass the variable and struct reference to toml.Unmarshal() function.
  • toml content is converted to Struct type and access the keys using dot notation.

Here is an example

package main

import (
    "fmt"
    "os"
    "github.com/pelletier/go-toml"
)
type Database struct {
    host string
    username string
    password string
    database string
}
func main() {
    // Reading from a TOML file
    var db Database
    // Read the toml file content
    doc, err := os.ReadFile("config.toml")
    if err != nil {
        fmt.Println("Error reading TOML file:", err)
        return
    }


    err1 := toml.Unmarshal(doc, &db)

    if err1 != nil {
        fmt.Println("Error convert TOML to Struct:", err1)
        return
    }

    // Accessing values from the TOML tree
    fmt.Println("Host:", db.host)
    fmt.Println("Username:", db.username)
    fmt.Println("Password:", db.password)
    fmt.Println("Database:", db.database)

}

How to write to toml file in Golang

Multiple ways we can write to the TOML file, you can use inline data creation with toml.tree() function, another using struct type and create a file.

• Toml provides Tree function to take data
• Create data using the Tree() constructor
• call the WriteFile() function on the tree data
• It creates a toml file with the content.

package main

import (
    "fmt"
    "github.com/pelletier/go-toml"
)

func main() {
    // Creating a TOML tree
    data := toml.Tree{
        "mysql": toml.Tree{
            "host": "localhost",
            "password":  "root",
            "username": "root",
            "database": "students"
        },
    }

    // Writing the TOML tree to a file
    err := data.WriteFile("result.toml")
    if err != nil {
        fmt.Println("Error create TOML file:", err)
    }
}

you can also use Struct to write a toml file