Add problem library

README.md

@@ -1,4 +1,5 @@
 # PlayNet Libs
+
 [![Go Report Card](https://goreportcard.com/badge/github.com/playnet-public/libs)](https://goreportcard.com/report/github.com/playnet-public/libs)
 [![License: GPL v3](https://img.shields.io/badge/License-GPL%20v3-blue.svg)](https://www.gnu.org/licenses/gpl-3.0)
 [![Build Status](https://travis-ci.org/playnet-public/libs.svg?branch=master)](https://travis-ci.org/playnet-public/libs)
@@ -9,7 +10,8 @@ The repository containing various shared libs for the entire playnet project.
 ## Libs
 
 ### Logging
-Our logging setup using go.uber.org/zap.
+
+Our logging setup using `go.uber.org/zap`.
 Sentry and Jaeger are being added for production environments.
 
 ```go
@@ -27,6 +29,46 @@ If you provide a zap.Error tag, the related stacktrace will also be attached.
 
 Additionally there is a tracer(opentracing/jaeger) available in the logger which should be closed before exiting main.
 
+### Problems
+
+`problems` is a small library which implements the RFC7807 error response format standard for e.g. HTTP API's.
+
+The `problems` lib provides a struct called `Problem` and an interface called `ProblemInfo`.
+`Problem` implements the `error` interface, so you can simply return the problem as an error in your application.
+
+```go
+func returnError() error {
+    return problems.New()
+}
+```
+
+You can marshal the `Problem` struct to JSON:
+
+```go
+func makeJSON(problem *Problem) ([]byte, error) {
+    return json.Marshal(&problem)
+}
+```
+
+If you want to define a HTTP problem, you can do it like this:
+
+```go
+var problemNotFound = problems.New().SetTitle("NotFound").SetDetail("The requested url was not found.").SetStatus(404).SetType("https://example.com/problem/description")
+```
+
+For custom fields for more detailed problem information, you can implement `Problem` in your custom struct:
+
+```go
+type customInfo struct {
+    AdditionalField1 bool `json:"additional_field_1"`
+}
+
+type customProblem struct {
+    *problems.Problem
+    *customInfo
+}
+```
+
 ## Contributions
 
 Pull Requests and Issue Reports are welcome.

problems/problems.go

@@ -0,0 +1,74 @@
+package errors
+
+import (
+	"fmt"
+)
+
+//Problem implements the RFC7807 "problem"/error standard
+//Additional error field can be defined in custom struct implementing the Problem struct
+type Problem struct {
+	Title    string `json:"title"`
+	Detail   string `json:"detail,omitempty"`
+	Type     string `json:"type,omitempty"`
+	Instance string `json:"instance,omitempty"`
+	Status   int    `json:"status,omitempty"`
+}
+
+//Error implements the error interface
+func (p *Problem) Error() string {
+	return fmt.Sprintf("Title: %s; Detail: %s", p.Title, p.Detail)
+}
+
+//DefaultType implements the default type content described in RFC7807
+const DefaultType = "about:blank"
+
+//SetTitle sets the title of the problem object
+func (p *Problem) SetTitle(title string) *Problem {
+	p.Title = title
+	return p
+}
+
+//SetDetail sets the detail info of the problem object
+func (p *Problem) SetDetail(detail string) *Problem {
+	p.Detail = detail
+	return p
+}
+
+//SetType sets the type of the problem object
+func (p *Problem) SetType(typ string) *Problem {
+	if typ == "" {
+		p.Type = DefaultType
+	} else {
+		p.Type = typ
+	}
+
+	return p
+}
+
+//SetInstance sets the instance of the problem object
+func (p *Problem) SetInstance(instance string) *Problem {
+	p.Instance = instance
+	return p
+}
+
+//SetStatus sets the HTTP status of the problem object HTTP request
+func (p *Problem) SetStatus(status int) *Problem {
+	p.Status = status
+	return p
+}
+
+//New creates a new Problem with all object details described in RFC7807
+func New() *Problem {
+	return &Problem{
+		Type: DefaultType,
+	}
+}
+
+//NewFromError returns a new Problem object from an error interface
+//The error message is replaced with the detail field
+func NewFromError(err error) *Problem {
+	return &Problem{
+		Type:   DefaultType,
+		Detail: err.Error(),
+	}
+}