Added load balancer (wip)

+ Added support for multiple upstreams
+ Added load balancer
+ Added upstream abstraction in endpoint
+ Added load balancer structure
+ Added breaking change auto-updater
+ Added uptime monitor proxy type definitions
+ Added upstream editor UI
+ Fixed charset bug in many snippets HTML files

src/mod/dynamicproxy/loadbalance/upstream.go

@@ -0,0 +1,75 @@
+package loadbalance
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"imuslab.com/zoraxy/mod/dynamicproxy/dpcore"
+)
+
+// StartProxy create and start a HTTP proxy using dpcore
+// Example of webProxyEndpoint: https://example.com:443 or http://192.168.1.100:8080
+func (u *Upstream) StartProxy() error {
+	//Filter the tailing slash if any
+	domain := u.OriginIpOrDomain
+	if len(domain) == 0 {
+		return errors.New("invalid endpoint config")
+	}
+	if domain[len(domain)-1:] == "/" {
+		domain = domain[:len(domain)-1]
+	}
+
+	if !strings.HasPrefix("http://", domain) && !strings.HasPrefix("https://", domain) {
+		//TLS is not hardcoded in proxy target domain
+		if u.RequireTLS {
+			domain = "https://" + domain
+		} else {
+			domain = "http://" + domain
+		}
+	}
+
+	//Create a new proxy agent for this upstream
+	path, err := url.Parse(domain)
+	if err != nil {
+		return err
+	}
+
+	proxy := dpcore.NewDynamicProxyCore(path, "", &dpcore.DpcoreOptions{
+		IgnoreTLSVerification: u.SkipCertValidations,
+	})
+
+	u.proxy = proxy
+	return nil
+}
+
+// IsReady return the proxy ready state of the upstream server
+// Return false if StartProxy() is not called on this upstream before
+func (u *Upstream) IsReady() bool {
+	return u.proxy != nil
+}
+
+// Clone return a new deep copy object of the identical upstream
+func (u *Upstream) Clone() *Upstream {
+	newUpstream := Upstream{}
+	js, _ := json.Marshal(u)
+	json.Unmarshal(js, &newUpstream)
+	return &newUpstream
+}
+
+// ServeHTTP uses this upstream proxy router to route the current request
+func (u *Upstream) ServeHTTP(w http.ResponseWriter, r *http.Request, rrr *dpcore.ResponseRewriteRuleSet) error {
+	//Auto rewrite to upstream origin if not set
+	if rrr.ProxyDomain == "" {
+		rrr.ProxyDomain = u.OriginIpOrDomain
+	}
+
+	return u.proxy.ServeHTTP(w, r, rrr)
+}
+
+// String return the string representations of endpoints in this upstream
+func (u *Upstream) String() string {
+	return u.OriginIpOrDomain
+}