Formatters Package

Formatters is a package which contains a useful and customizable set of formatters for your application.

1. Formatter - A generic interface to format data.

2. TextFormatter - Formats and Prints interface{} to Text String - Binded to String() method.

3. JSONFormatter - Formats and Prints interface{} to JSON String - Binded to json.Marshal() method.

Usage

type TestType struct {
   field1 string `json:"field1,omitempty"` //same json tag as required by json.Marshal
   field2 int    `json:"field2"`           //same json tag as required by json.Marshal
}

var a Formatter = TextFormatter{}
var b JSONFormatter = JSONFormatter{}

var test TestType{
    field1 : "test",
    field2 : 42,
}

var testString = a.Format(test)
fmt.Println(testString) // Prints test.String()
a.Print(test) // Does the same.

testString = b.Format(test)
fmt.Println(testString) // Prints { field1 : "test", field2 : "42" }
b.Print(test) // Does the same

The default formatter

There is a global formatter which can be used across other packages. You can set it with the formatter.setFormatter(Formatter) function.

type TestType struct {
   field1 string `json:"field1,omitempty"` //same json tag as required by json.Marshal
   field2 int    `json:"field2"`           //same json tag as required by json.Marshal
}

var test TestType{
    field1 : "test",
    field2 : 42,
}

formatter.setFormatter("text")
formatter.Print(test) // Prints string representation of the test struct, using String().
formatter.setFormatter("json")
formatter.Print(test) // Prints test struct as a JSON object.

Custom Formatters

It is possible to add custom formatters with the formatter.AddCustomFormatter(format, Formatter) function.

Let’s assume we want to add a YamlFormatter which parses to Yaml Objects.

// Solution 1 : YamlFormatter is a struct.
type YamlFormatter struct{}

func (yf YamlFormatter) Format(msg interface{}) (string, error) {
    // do something and return values.
}

//...
formatter.AddCustomFormatter("yaml", YamlFormatter{})
//...

// Solution 2 : YamlFormatter is a int8 or other primitive type, useful for formatters which does not need fields.
type YamlFormatter int8

func (yf YamlFormatter) Format(msg interface{}) (string, error) {
    // do something and return values.
}

//...
formatter.AddCustomFormatter("yaml", YamlFormatter(3)) // every int8 is valid, this is a cast.

Printing Errors

Just use formatter.PrintErrorMessage(string) or formatter.PrintError(error) function.

var errormessage string = "Some error occurred"
formatter.PrintErrorMessage(errormessage) // Prints the error formatted properly.

err := functionWhichMayReturnAnError()
if err != nil {
    formatter.PrintError(err)
}

Debug with JSON values

JSONFormatter by default does not print what it cannot parse (everything which is not a map or a struct). If you are in a debugging session you will print an error message instead. Sessions are opened by formatterInstance.StartDebug() and closed by formatterInstance.EndDebug()

formatter = JSONFormatter{}
formatter.StartDebug()
formatter.Print("Invalid String")
//Outputs "\"Invalid String\" is a non supported data, please use map or struct"
formatter.EndDebug()