initialize support for versioning as requested, per route -- not finished yet

Former-commit-id: ade66610125f06a0b5ce3e90bcafe349f216a616

versioning/version.go

@@ -0,0 +1,72 @@
+package versioning
+
+import (
+	"strings"
+
+	"github.com/kataras/iris/context"
+)
+
+const (
+	AcceptVersionHeaderKey   = "Accept-Version"
+	AcceptHeaderKey          = "Accept"
+	AcceptHeaderVersionValue = "version"
+
+	Key      = "iris.api.version" // for use inside the ctx.Values(), not visible by the user.
+	NotFound = Key + ".notfound"
+)
+
+var NotFoundHandler = func(ctx context.Context) {
+	// 303 is an option too,
+	// end-dev has the chance to change that behavior by using the NotFound in the map:
+	//
+	// https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
+	/*
+		10.5.2 501 Not Implemented
+
+		The server does not support the functionality required to fulfill the request.
+		This is the appropriate response when the server does not
+		recognize the request method and is not capable of supporting it for any resource.
+	*/
+	ctx.WriteString("version not found")
+	ctx.StatusCode(501)
+}
+
+func GetVersion(ctx context.Context) string {
+	// firstly by context store, if manually set-ed by a middleware.
+	if version := ctx.Values().GetString(Key); version != "" {
+		return version
+	}
+
+	// secondly by the "Accept-Version" header.
+	if version := ctx.GetHeader(AcceptVersionHeaderKey); version != "" {
+		return version
+	}
+
+	// thirdly by the "Accept" header which is like"...; version=1.0"
+	acceptValue := ctx.GetHeader(AcceptHeaderKey)
+	if acceptValue != "" {
+		if idx := strings.Index(acceptValue, AcceptHeaderVersionValue); idx != -1 {
+			rem := acceptValue[idx:]
+			startVersion := strings.Index(rem, "=")
+			if startVersion == -1 || len(rem) < startVersion+1 {
+				return NotFound
+			}
+
+			rem = rem[startVersion+1:]
+
+			end := strings.Index(rem, " ")
+			if end == -1 {
+				end = strings.Index(rem, ";")
+			}
+			if end == -1 {
+				end = len(rem)
+			}
+
+			if version := rem[:end]; version != "" {
+				return version
+			}
+		}
+	}
+
+	return NotFound
+}