posline

The posline package aims to provide easy serialization of Go structs into positional fixed-width strings. These kind of structures are useful when integrating with old system which depends on positional flat files

Installation

import "github.com/noverde/posline"

Usage

Consider the following fixed-width string line:

JOHN      DOE       23São Paulo      BR

Looking at this file, we can see the following structure:

firstname with 10 fixed columns;
surname with 10 fixed columns;
age with 2 fixed columns;
city with 15 fixed columns;
country with 2 fixed columns.

Let's map it into a Go Struct:

type Person struct {
    FirstName string `posline:"10"`
    SurName   string `posline:"10"`
    Age       int    `posline:"2"`
    City      string `posline:"15"`
    Country   string `posline:"2"
}

Now, to generate the previous flat line, we just need to marshal it:

  john := Person{
      FirstName: "JOHN",
      SurName:   "DOE",
      Age:       23,
      City:      "São Paulo",
      Country:   "BR",
  }

  flat, err := posline.Marshal(john)

  if err != nil {
      // handle error
  }

  fmt.Println(flat) // => JOHN      DOE       23São Paulo      BR

Modifiers

To help with common tasks when dealing with positional flat files, this lib includes some modifiers.

The modifiers should be passed as tag options.

leftpad

This modifier pads the text to the left to fill the blank space.

type Person struct {
    FirstName string `posline:"10,leftpad"`
    Country   string `posline:"2"`
}

This will pad blank spaces to the left of string JOHN:

      JOHNBR

zerofill

This modifier fills the empty space with 0 instead of blank space(" ")

type Person struct {
    Age       string `posline:"10,zerofill"`
    Country   string `posline:"2"`
}

Will produce:

2300000000BR

nofp

The nofp (No Floating Point) modifier removes the "." when dealing with float32 or float64 values. Example:

type Bank struct {
    Owner   string   `posline:"10"`
    Balance float32  `posline:"10,nofp"`
}

func main() {
	bank := Bank{
		Owner:   "JOHN",
		Balance: 123.45,
	}

	flat, err := posline.Marshal(bank)

	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}

    fmt.Println(flat)
}

This example will produce:

JOHN      12345

Note: The nofp modifier will round the float number to 2 decimal places.

Multiple Modifiers

You can use multiple modifier as the following example:

type Bank struct {
    Owner   string   `posline:"10"`
    Balance float32  `posline:"10,leftpad,zerofill,nofp"`
}

Using the previous example, will output:

JOHN      0000012345