Add a simple and pure .Regex middleware for routers that don't support regex route path validations out-of-the-box

Former-commit-id: 84cf1fb267e54543ad6d419b2ca39658b2773b58

router.go

@@ -4,6 +4,7 @@ import (
 	"net/http"
 	"os"
 	"path"
+	"regexp"
 	"strings"
 	"time"
 
@@ -130,6 +131,66 @@ type Router struct {
 	relativePath string
 }
 
+// Regex takes pairs with the named path (without symbols) following by its expression
+// and returns a middleware which will do a pure but effective validation using the regexp package.
+//
+// Note: '/adaptors/gorillamux' already supports regex path validation.
+// It's useful while the developer uses the '/adaptors/httprouter' instead.
+func (s *Framework) Regex(pairParamExpr ...string) HandlerFunc {
+	srvErr := func(ctx *Context) {
+		ctx.EmitError(StatusInternalServerError)
+	}
+
+	wp := s.policies.RouterReversionPolicy.WildcardPath
+	if wp == nil {
+		s.Log(ProdMode, "expr cannot be used when a router policy is missing\n"+errRouterIsMissing.Format(s.Config.VHost).Error())
+		return srvErr
+	}
+
+	if len(pairParamExpr)%2 != 0 {
+		s.Log(ProdMode,
+			"regexp expr pre-compile error: the correct format is paramName, expression"+
+				"paramName2, expression2. The len should be %2==0")
+		return srvErr
+	}
+	pairs := make(map[string]*regexp.Regexp, len(pairParamExpr)/2)
+
+	for i := 0; i < len(pairParamExpr)-1; i++ {
+		expr := pairParamExpr[i+1]
+		r, err := regexp.Compile(expr)
+		if err != nil {
+			s.Log(ProdMode, "expr: regexp failed on: "+expr+". Trace:"+err.Error())
+			return srvErr
+		}
+
+		pairs[pairParamExpr[i]] = r
+		i++
+	}
+
+	// return the middleware
+	return func(ctx *Context) {
+		for k, v := range pairs {
+			pathPart := ctx.Param(k)
+			if pathPart == "" {
+				// take care, the router already
+				// does the param validations
+				// so if it's empty here it means that
+				// the router has label it as optional.
+				// so we skip it, and continue to the next.
+				continue
+			}
+			// the improtant thing:
+			// if the path part didn't match with the relative exp, then fire status not found.
+			if !v.MatchString(pathPart) {
+				ctx.EmitError(StatusNotFound)
+				return
+			}
+		}
+		// otherwise continue to the next handler...
+		ctx.Next()
+	}
+}
+
 var (
 	// errDirectoryFileNotFound returns an error with message: 'Directory or file %s couldn't found. Trace: +error trace'
 	errDirectoryFileNotFound = errors.New("Directory or file %s couldn't found. Trace: %s")