Abstract dependencies

Projects depend on packages, internal ones or from 3rd parties. In all cases, your architecture should dictate what it needs and not evolve around a package, otherwise changing the dependency with another package and mocking it in tests could take unnecessary effort and time.

While it’s very easy to include a package in any file you need and start using it, time will show it’s painful to spread dependencies all over. Someday you’ll want to change a package because it’s not maintained anymore or you discover security issues which lead to loss of trust, or maybe you just want to experiment with another package.

This is where abstraction comes in, helping to decouple an implementation in your project, to set the rules which a dependency must follow. Each package has its own API, thus you need to wrap it by your API.

To show an example, I’ve chosen to integrate a validation package into Echo framework. The validator package requires you to tag your structs with its validation rules. Continue reading Abstract dependencies

Error handling in Echo framework

If misused, error handling and logging in Go can become too verbose and tangled. If the two are decoupled, you can just pass the error forward (maybe add some context to it if necessary, or have specific error structs) and have it logged or sent to various systems (like New Relic) somewhere else in the code, not where you receive it from a function call.

One of the features I appreciate the most in Echo framework is the HTTPErrorHandler which can be customized to any needs. And combined with the recover middleware, error management becomes an easy task.

package main

import (
   "errors"
   "fmt"
   "net/http"

   "github.com/labstack/echo/v4"
   "github.com/labstack/echo/v4/middleware"
   "github.com/labstack/gommon/log"
)

func main() {
   server := echo.New()
   server.Use(
      middleware.Recover(),   // Recover from all panics to always have your server up
      middleware.Logger(),    // Log everything to stdout
      middleware.RequestID(), // Generate a request id on the HTTP response headers for identification
   )
   server.Debug = false
   server.HideBanner = true
   server.HTTPErrorHandler = func(err error, c echo.Context) {
      // Take required information from error and context and send it to a service like New Relic
      fmt.Println(c.Path(), c.QueryParams(), err.Error())

      // Call the default handler to return the HTTP response
      server.DefaultHTTPErrorHandler(err, c)
   }

   server.GET("/users", func(c echo.Context) error {
      users, err := dbGetUsers()
      if err != nil {
         return err
      }

      return c.JSON(http.StatusOK, users)
   })

   server.GET("/posts", func(c echo.Context) error {
      posts, err := dbGetPosts()
      if err != nil {
         return err
      }

      return c.JSON(http.StatusOK, posts)
   })

   log.Fatal(server.Start(":8088"))
}

func dbGetUsers() ([]string, error) {
   return nil, errors.New("database error")
}

func dbGetPosts() ([]string, error) {
   panic("an unhandled error occurred")
   return nil, nil
}

Avoid logging in functions:

server.GET("/users", func(c echo.Context) error {
   users, err := dbGetUsers()
   if err != nil {
      log.Errorf("cannot get users: %s", err)
      return err
   }

   return c.JSON(http.StatusOK, users)
})

Keep the handler functions clean, check your errors and pass them forward.

Race condition on Echo context with GraphQL in Go

Given an API setup with GraphQL and Echo, a colleague ran into a race condition situation. There was a concurrent read/write issue on Echo’s context. GraphQL runs its resolvers in parallel if set so, and when context is shared between resolvers, things can go wrong.

I took a look into Echo’s context implementation and I saw a simple map is used for Get/Set.

For every API call, a handle functions is given an Echo context and executes the GraphQL schema with the specified context.

func handle(c echo.Context) error {
 schema, err := gqlgo.ParseSchema(
  ...
  gqlgo.MaxParallelism(10),
 )

 schema.Exec(
  c,
  ...
 )
}

My solution was to use a custom context which embeds the original one and uses a concurrent map instead of Echo’s. Continue reading Race condition on Echo context with GraphQL in Go