net/http/httptrace: compose ClientTrace without reflect

This is to enable use of package httptrace on TinyGo, which does not have an implementation of reflect.MakeFunc.

Author: ydnar

src/net/http/httptrace/trace.go

@@ -12,7 +12,6 @@ import (
 "internal/nettrace"
 "net"
 "net/textproto"
-"reflect"
 "time"
 )
 
@@ -176,34 +175,86 @@ func (t *ClientTrace) compose(old *ClientTrace) {
 if old == nil {
 return
 }
-tv := reflect.ValueOf(t).Elem()
-ov := reflect.ValueOf(old).Elem()
-structType := tv.Type()
-for i := 0; i < structType.NumField(); i++ {
-tf := tv.Field(i)
-hookType := tf.Type()
-if hookType.Kind() != reflect.Func {
-continue
-}
-of := ov.Field(i)
-if of.IsNil() {
-continue
-}
-if tf.IsNil() {
-tf.Set(of)
-continue
-}
+t.GetConn = compose1to0(t.GetConn, old.GetConn)
+t.GotConn = compose1to0(t.GotConn, old.GotConn)
+t.PutIdleConn = compose1to0(t.PutIdleConn, old.PutIdleConn)
+t.GotFirstResponseByte = compose0to0(t.GotFirstResponseByte, old.GotFirstResponseByte)
+t.Got100Continue = compose0to0(t.Got100Continue, old.Got100Continue)
+t.Got1xxResponse = compose2to1(t.Got1xxResponse, old.Got1xxResponse)
+t.DNSStart = compose1to0(t.DNSStart, old.DNSStart)
+t.DNSDone = compose1to0(t.DNSDone, old.DNSDone)
+t.ConnectStart = compose2to0(t.ConnectStart, old.ConnectStart)
+t.ConnectDone = compose3to0(t.ConnectDone, old.ConnectDone)
+t.TLSHandshakeStart = compose0to0(t.TLSHandshakeStart, old.TLSHandshakeStart)
+t.TLSHandshakeDone = compose2to0(t.TLSHandshakeDone, old.TLSHandshakeDone)
+t.WroteHeaderField = compose2to0(t.WroteHeaderField, old.WroteHeaderField)
+t.WroteHeaders = compose0to0(t.WroteHeaders, old.WroteHeaders)
+t.Wait100Continue = compose0to0(t.Wait100Continue, old.Wait100Continue)
+t.WroteRequest = compose1to0(t.WroteRequest, old.WroteRequest)
+}
 
-// Make a copy of tf for tf to call. (Otherwise it
-// creates a recursive call cycle and stack overflows)
-tfCopy := reflect.ValueOf(tf.Interface())
+func compose0to0[F func()](f1, f2 F) F {
+if f1 == nil {
+return f2
+}
+if f2 == nil {
+return f1
+}
+return func() {
+f1()
+f2()
+}
+}
+
+func compose1to0[F func(A), A any](f1, f2 F) F {
+if f1 == nil {
+return f2
+}
+if f2 == nil {
+return f1
+}
+return func(a A) {
+f1(a)
+f2(a)
+}
+}
 
-// We need to call both tf and of in some order.
-newFunc := reflect.MakeFunc(hookType, func(args []reflect.Value) []reflect.Value {
-tfCopy.Call(args)
-return of.Call(args)
-})
-tv.Field(i).Set(newFunc)
+func compose2to0[F func(A, B), A, B any](f1, f2 F) F {
+if f1 == nil {
+return f2
+}
+if f2 == nil {
+return f1
+}
+return func(a A, b B) {
+f1(a, b)
+f2(a, b)
+}
+}
+
+func compose2to1[F func(A, B) R, A, B, R any](f1, f2 F) F {
+if f1 == nil {
+return f2
+}
+if f2 == nil {
+return f1
+}
+return func(a A, b B) R {
+f1(a, b)
+return f2(a, b)
+}
+}
+
+func compose3to0[F func(A, B, C), A, B, C any](f1, f2 F) F {
+if f1 == nil {
+return f2
+}
+if f2 == nil {
+return f1
+}
+return func(a A, b B, c C) {
+f1(a, b, c)
+f2(a, b, c)
 }
 }