cleanup and simplify middleware implementations, refactor some other code

internal/net/http/middleware/middleware_chain.go

@@ -0,0 +1,58 @@
+package middleware
+
+import (
+	"net/http"
+
+	"github.com/yusing/go-proxy/internal/common"
+	E "github.com/yusing/go-proxy/internal/error"
+)
+
+type middlewareChain struct {
+	befores  []RequestModifier
+	modResps []ResponseModifier
+}
+
+// TODO: check conflict or duplicates.
+func NewMiddlewareChain(name string, chain []*Middleware) *Middleware {
+	chainMid := &middlewareChain{befores: []RequestModifier{}, modResps: []ResponseModifier{}}
+	m := &Middleware{name: name, impl: chainMid}
+
+	for _, comp := range chain {
+		if before, ok := comp.impl.(RequestModifier); ok {
+			chainMid.befores = append(chainMid.befores, before)
+		}
+		if mr, ok := comp.impl.(ResponseModifier); ok {
+			chainMid.modResps = append(chainMid.modResps, mr)
+		}
+		comp.setParent(m)
+	}
+
+	if common.IsDebug {
+		m.enableTrace()
+	}
+	return m
+}
+
+// before implements RequestModifier.
+func (m *middlewareChain) before(w http.ResponseWriter, r *http.Request) (proceedNext bool) {
+	for _, b := range m.befores {
+		if proceedNext = b.before(w, r); !proceedNext {
+			return false
+		}
+	}
+	return true
+}
+
+// modifyResponse implements ResponseModifier.
+func (m *middlewareChain) modifyResponse(resp *http.Response) error {
+	if len(m.modResps) == 0 {
+		return nil
+	}
+	errs := E.NewBuilder("modify response errors")
+	for i, mr := range m.modResps {
+		if err := mr.modifyResponse(resp); err != nil {
+			errs.Add(E.From(err).Subjectf("%d", i))
+		}
+	}
+	return errs.Error()
+}