github.com/moogar0880/problems

Problems

Problems is an RFC-7807 and RFC-9457 compliant library for describing HTTP errors. For more information see RFC-9457, and it's predecessor RFC-7807.

Usage

The problems library exposes an assortment of types to aid HTTP service authors in defining and using HTTP Problem detail resources.

Predefined Errors

You can define basic Problem details up front by using the NewStatusProblem function

package main

import "github.com/moogar0880/problems"

var (
  // The NotFound problem will be built with an appropriate status code and
  // informative title set. Additional information can be provided in the Detail
  // field of the generated struct
  NotFound = problems.NewStatusProblem(404)
)

Which, when served over HTTP as JSON will look like the following:

{
   "type": "about:blank",
   "title": "Not Found",
   "status": 404
}

Detailed Errors

New errors can also be created a head of time, or on the fly like so:

package main

import "github.com/moogar0880/problems"

func NoSuchUser() *problems.Problem {
    nosuch := problems.NewStatusProblem(404)
    nosuch.Detail = "Sorry, that user does not exist."
    return nosuch
}

Which, when served over HTTP as JSON will look like the following:

{
   "type": "about:blank",
   "title": "Not Found",
   "status": 404,
   "detail": "Sorry, that user does not exist."
}

Extended Errors

The specification for these HTTP problems was designed to allow for arbitrary expansion of the problem resources. This can be accomplished through this library by either embedding the Problem struct in your extension type:

package main

import "github.com/moogar0880/problems"

type CreditProblem struct {
    problems.Problem

    Balance  float64  `json:"balance"`
    Accounts []string `json:"accounts"`
}

Which, when served over HTTP as JSON will look like the following:

{
   "type": "about:blank",
   "title": "Unauthorized",
   "status": 401,
   "balance": 30,
   "accounts": ["/account/12345", "/account/67890"]
}

Or by using the problems.ExtendedProblem type:

package main

import (
    "net/http"

    "github.com/moogar0880/problems"
)

type CreditProblemExt struct {
    Balance  float64  `json:"balance"`
    Accounts []string `json:"accounts"`
}

func main() {
    problems.NewExt[CreditProblemExt]().
        WithStatus(http.StatusForbidden).
        WithDetail("Your account does not have sufficient funds to complete this transaction").
        WithExtension(CreditProblemExt{
            Balance:  30,
            Accounts: []string{"/account/12345", "/account/67890"},
        })
}

Which, when served over HTTP as JSON will look like the following:

{
   "type": "about:blank",
   "title": "Unauthorized",
   "status": 401, 
   "extensions": {
       "balance": 30,
       "accounts": ["/account/12345", "/account/67890"]    
   }
}

Serving Problems

Additionally, RFC-7807 defines two new media types for problem resources, application/problem+json" and application/problem+xml. This library defines those media types as the constants ProblemMediaType and ProblemMediaTypeXML.

In order to facilitate serving problem definitions, this library exposes two http.HandlerFunc implementations which accept a problem, and return a functioning HandlerFunc that will server that error.

package main

import (
    "net/http"

    "github.com/moogar0880/problems"
)

var Unauthorized = problems.NewStatusProblem(401)

func main() {
    mux := http.NewServeMux()
    mux.HandleFunc("/secrets", problems.ProblemHandler(Unauthorized))

    server := http.Server{Handler: mux, Addr: ":8080"}
    server.ListenAndServe()
}