[gapi] add pattern body validation

examples/3-params/internal/body_with_validation.go

@@ -30,7 +30,9 @@ type OrderBody struct {
 	// The required tag validates that the value is not the data types default zero value
 	// For numbers ensures value is not zero. For strings ensures value is not "".
 	// For slices, maps, pointers, interfaces, channels and functions ensures the value is not nil.
-	ProductID string `json:"product_id" required:"true"`
+	// You can add validation using the pattern tag which is a regexp condition
+	// that the value of the field product_id must follow works also for float and integer
+	ProductID string `json:"product_id" required:"true" pattern:"^product_[\\d_]+"`
 	// if you want to make a custom validation you can implement Validate() as the example bellow for quantity.
 	Quantity int `json:"quantity"`
 }

middleware/body_decoder.go

@@ -2,10 +2,12 @@ package middleware
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"mime"
 	"net/http"
 	"reflect"
+	"regexp"
 	"strings"
 
 	"github.com/mwm-io/gapi/errors"
@@ -124,6 +126,18 @@ func (m BodyDecoder) Wrap(h handler.Handler) handler.Handler {
 				typeOfParameters := val.Type()
 				typeOfFieldI := typeOfParameters.Field(i)
 
+				if pattern := typeOfFieldI.Tag.Get("pattern"); pattern != "" {
+					rex, errC := regexp.Compile(pattern)
+					if errC != nil {
+						return nil, errors.InternalServerError("pattern_must_be_regex", "pattern must contain a regular expression")
+					}
+
+					fieldValue := val.Field(i).Interface()
+					if !rex.MatchString(fmt.Sprintf("%v", fieldValue)) {
+						return nil, errors.BadRequest("body_validation_failed", "field %s does not match the required pattern", typeOfFieldI.Name)
+					}
+				}
+
 				if typeOfFieldI.Tag.Get("required") != "true" {
 					continue
 				}