binding

binding

Reflectionless data binding for Go's net/http

Features

• HTTP request data binding
• Data validation (custom and built-in)
• Error handling

Benefits

• Moves data binding, validation, and error handling out of your application's handler
• Reads Content-Type to deserialize form, multipart form, and JSON data from requests
• No middleware: just a function call
• Usable in any setting where net/http is present (Negroni, gocraft/web, std lib, etc.)
• No reflection

Usage example

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Multipart/form-data usage example

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You can test from CLI using the excellent httpie client

http -f POST localhost:3000/upload data@myupload

Custom data validation

You may optionally have your type implement the binding.Validator interface to perform your own data validation. The .Validate() method is called after the struct is populated.

func (cf ContactForm) Validate(req *http.Request) error {
	if cf.Message == "Go needs generics" {
		return binding.Errors{
			binding.NewError([]string{"message"}, "ComplaintError", "Go has generics. They're called interfaces.")
		}
	}
	return nil
}

Binding custom types

For types you've defined, you can bind form data to it by implementing the Binder interface. Here's a contrived example:

type MyBinder map[string]string

func (t MyBinder) Bind(fieldName string, strVals []string) error {
	t["formData"] = strVals[0]
	return nil
}

If you can't add a method to the type, you can still specify a Binder func in the field spec. Here's a contrived example that binds an integer (not necessary, but you get the idea):

func (t *MyType) FieldMap(req *http.Request) binding.FieldMap {
	return binding.FieldMap{
		"a-key": binding.Field{
			Form: "number",
			Binder: func(fieldName string, formVals []string) error {
				val, err := strconv.Atoi(formVals[0])
				if err != nil {
					return binding.Errors{binding.NewError([]string{fieldName}, binding.DeserializationError, err.Error())}
				}
				t.SomeNumber = val
				return nil
			},
		},
	}
}

The Errors type has a convenience method, Add, which you can use to append to the slice if you prefer.

Supported types (forms)

The following types are supported in form deserialization by default. (JSON requests are delegated to encoding/json.)

• uint, *uint, []uint, uint8, *uint8, []uint8, uint16, *uint16, []uint16, uint32, *uint32, []uint32, uint64, *uint64, []uint64
• int, *int, []int, int8, *int8, []int8, int16, *int16, []int16, int32, *int32, []int32, int64, *int64, []int64
• float32, *float32, []float32, float64, *float64, []float64
• bool, *bool, []bool
• string, *string, []string
• time.Time, *time.Time, []time.Time
• *multipart.FileHeader, []*multipart.FileHeader