Source code analysis of etcd database -- peer RT of inter cluster network layer client

peerRt（RoundTripper type ） Mainly responsible for the realization of etcdserver Network request and other functions , Used to send version or lease The service request . We know it is in ETCD Database source code analysis ——etcdserver bootstrap The second step in initialization is to initialize . How to use it ？
Such as server/etcdserver/cluster_util.go Of promoteMemberHTTP Shown , Use peerRt establish http client , Then construct the request Url And specify the request method as POST, establish http Request Structure , call http Client's do Function to make a request to the server , And get its response .

func promoteMemberHTTP(ctx context.Context, url string, id uint64, peerRt http.RoundTripper) ([]*membership.Member, error) {
    
	cc := &http.Client{
    Transport: peerRt}  //  Use peerRt establish http client 
	// TODO: refactor member http handler code cannot import etcdhttp, so manually construct url
	requestUrl := url + "/members/promote/" + fmt.Sprintf("%d", id)
	req, err := http.NewRequest("POST", requestUrl, nil)
	if err != nil {
     return nil, err }
	req = req.WithContext(ctx)
	resp, err := cc.Do(req)
	if err != nil {
     return nil, err }
	defer resp.Body.Close()
	b, err := io.ReadAll(resp.Body)
	if err != nil {
     return nil, err }
 
    //  Processing request timed out 
	if resp.StatusCode == http.StatusRequestTimeout {
     return nil, errors.ErrTimeout }
	if resp.StatusCode == http.StatusPreconditionFailed {
    
		// both ErrMemberNotLearner and ErrLearnerNotReady have same http status code
		if strings.Contains(string(b), errors.ErrLearnerNotReady.Error()) {
     return nil, errors.ErrLearnerNotReady }
		if strings.Contains(string(b), membership.ErrMemberNotLearner.Error()) {
     return nil, membership.ErrMemberNotLearner }
		return nil, fmt.Errorf("member promote: unknown error(%s)", string(b))
	}
	if resp.StatusCode == http.StatusNotFound {
     return nil, membership.ErrIDNotFound }
    //  Other types of errors 
	if resp.StatusCode != http.StatusOK {
     // all other types of errors
		return nil, fmt.Errorf("member promote: unknown error(%s)", string(b))
	}

	var membs []*membership.Member
	if err := json.Unmarshal(b, &membs); err != nil {
     return nil, err } //  Deserialize request response content 
	return membs, nil
}

as follows server/etcdserver/adapters.go Medium GetMembersVersions Is also used peerRt obtain MembersVersions.

func (s *serverVersionAdapter) GetMembersVersions() map[string]*version.Versions {
    
	return getMembersVersions(s.lg, s.cluster, s.MemberId(), s.peerRt, s.Cfg.ReqTimeout())
}