Vlang tutorials — logs

Hi guys It’s been a looooong time since my last blog post, I decided to make my comeback with one more tutorial on how to use a feature in Vlang, today’s feature is a feature I noticed a few weeks ago and immediately applied to one of my projects, you probably already guessed we are talking about the log module.

The log module is a module to add logs to your application, and I will showcase how to use it by adding logs into a url shortener app that I wrote in V.

The first log I added was to print in the terminal when the server has started:
shortener.v

module main

import vweb
import server
import log

fn main() {
    log.info('server running')
    vweb.run_at(server.new_shortener(), vweb.RunParams{
        port: 8081
    }) or { panic(err) }
}

To make it work I just imported the module log:

import log

And called the info function with the info message that the server has started:

log.info('server running')

After informing the server status I started to add logs in controllers and services:
controllers.v

module controllers

import structs as s
import requests as r
import httperrors as he
import services
import log

pub fn create_link(req_body r.CreateLinkRequest) s.ResponseObject<s.Response> {
    log.info('[CONTROLLER] - create_link function')
    if req_body.is_empty() {
        log.warn('request without body')
        return he.create_response_error(
            'fields link_name(string) or link_url(string) should not be empty',
            400)
    }

    return services.create_link(req_body)
}

pub fn get_link(link_name string) s.ResponseObject<s.Response> {
    log.info('[CONTROLLER] - get_link function')
    return services.get_link_url(link_name)
}

As usual in controllers.v I added two info in both functions create_link, get_link informing that I reached that respective function in the controllers file.

But notice that in the create_link I added a warning if the request body is empty, because if it is It’s not an error on the server, but on the client, so it’s a warning.

Soon we will see how to deal with errors that occur in the server, but first, let´s take a look at the services file:
services.v

module services

import structs as s
import requests as r
import repository as repo
import httperrors as he
import time
import log

pub fn create_link(req_body r.CreateLinkRequest) s.ResponseObject<s.Response> {
    log.info('[SERVICE] - create_link function')
    db := repo.setup()
    if !db.save(req_body.link_name, req_body.link_url) {
        log.error('lost connection with database')
        return he.create_response_error('unable to reach database', 500)
    }
    
    created_link := s.Response(s.CreatedLink{
        link_name: req_body.link_name
        creation_date: time.now().hhmmss()
    })

    return s.ResponseObject<s.Response>{
            code: 201
            body: created_link
            format: s.FileFormats.json
        }
}

pub fn get_link_url(link_name string) s.ResponseObject<s.Response> {
    log.info('[SERVICE] - get_link_url function')
    db := repo.setup()
    result := db.get(link_name)
    if !result.success {
        log.warn('${link_name} not found')
        return he.create_response_error('url not found', 404)
    }

    page_link := result.data
    script := '<script>window.location.href = "${page_link}"</script>'
    response := s.Response(script)

    return s.ResponseObject<s.Response>{
            code: 200
            body: response
            format: s.FileFormats.html
        }
}

In services, I also added infos informing that we reached the respective functions in the services module, and also added a warning in the get_link_url function when a link URL is not found, but if we take a look at the create_link function we can notice that in this case an error log is emitted because if we can’t communicate with Redis to save a link it means that is a server error, and to inform a server error I used:

log.error('lost connection with database')

I found logs a useful tool to have in the standard library that worked very well with my web server, in case you want to learn more about it I recommend reading the documentation about it here!

Hope you liked it, see ya ;)