From 7c00e0c8bf148ba1abcbd7a9ed390bdaab27832b Mon Sep 17 00:00:00 2001
From: William Petit <wpetit@cadoles.com>
Date: Fri, 28 Dec 2018 11:45:30 +0100
Subject: [PATCH] Add 'api' package to ease basic JSON API development

---
 api/api.go  | 47 ++++++++++++++++++++++++++++++++
 api/bind.go | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 124 insertions(+)
 create mode 100644 api/api.go
 create mode 100644 api/bind.go

diff --git a/api/api.go b/api/api.go
new file mode 100644
index 0000000..7f8f5cd
--- /dev/null
+++ b/api/api.go
@@ -0,0 +1,47 @@
+package api
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+)
+
+// Response is a JSON encoded HTTP response body
+type Response struct {
+	Error *Error      `json:",omitempty"`
+	Data  interface{} `json:",omitempty"`
+}
+
+type ErrorCode string
+
+// Error is a JSON encoded error
+type Error struct {
+	Code ErrorCode
+	Data interface{} `json:",omitempty"`
+}
+
+func (e *Error) Error() string {
+	return fmt.Sprintf("%s: %v", e.Code, e.Data)
+}
+
+func DataResponse(w http.ResponseWriter, status int, data interface{}) {
+	response(w, status, &Response{
+		Data: data,
+	})
+}
+
+func ErrorResponse(w http.ResponseWriter, status int, code ErrorCode, data interface{}) {
+	response(w, status, &Response{
+		Error: &Error{code, data},
+	})
+}
+
+func response(w http.ResponseWriter, status int, res *Response) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	encoder := json.NewEncoder(w)
+	encoder.SetIndent("", "  ")
+	if err := encoder.Encode(res); err != nil {
+		panic(err)
+	}
+}
diff --git a/api/bind.go b/api/bind.go
new file mode 100644
index 0000000..520aaf7
--- /dev/null
+++ b/api/bind.go
@@ -0,0 +1,77 @@
+package api
+
+import (
+	"encoding/json"
+	"net/http"
+
+	validator "gopkg.in/go-playground/validator.v9"
+)
+
+const (
+	ErrCodeMalformedRequest  ErrorCode = "malformed-request"
+	ErrCodeInvalidRequest    ErrorCode = "invalid-request"
+	ErrCodeInvalidFieldValue ErrorCode = "invalid-field-value"
+)
+
+// Bind parses and bind the request body to the given target
+// Bind wil also validates the received data with a validator instance.
+// If the data does not match the target constraints, an ErrorResponse will be
+// sent back.
+// See gopkg.in/go-playground/validator.v9 for more informations about data
+// validation.
+func Bind(w http.ResponseWriter, r *http.Request, target interface{}) (ok bool) {
+	if err := parseBody(r, target); err != nil {
+		ErrorResponse(
+			w, http.StatusBadRequest,
+			ErrCodeMalformedRequest,
+			nil,
+		)
+		return false
+	}
+	validate := validator.New()
+	if err := validate.Struct(target); err != nil {
+		handleValidateError(w, err)
+		return false
+	}
+	return true
+}
+
+func parseBody(r *http.Request, target interface{}) error {
+	decoder := json.NewDecoder(r.Body)
+	if err := decoder.Decode(target); err != nil {
+		return err
+	}
+	return nil
+}
+
+type fieldError struct {
+	Field string
+	Tag   string
+	Param string
+}
+
+func handleValidateError(w http.ResponseWriter, err error) {
+	if validationErrors, ok := err.(validator.ValidationErrors); ok {
+		fields := make([]fieldError, 0)
+		for _, e := range validationErrors {
+			fields = append(fields, fieldError{
+				Field: e.Field(),
+				Tag:   e.Tag(),
+				Param: e.Param(),
+			})
+		}
+		ErrorResponse(
+			w, http.StatusBadRequest,
+			ErrCodeInvalidFieldValue,
+			map[string]interface{}{
+				"Fields": fields,
+			},
+		)
+		return
+	}
+	ErrorResponse(
+		w, http.StatusBadRequest,
+		ErrCodeInvalidRequest,
+		nil,
+	)
+}