func()

in garbage/nethttp.go [6874:6983]
104 lines of code
24 McCabe index (conditional complexity)

func (t *Transport) dialConn(cm connectMethod) (*persistConn, error) {
	pconn := &persistConn{
		t:          t,
		cacheKey:   cm.key(),
		reqch:      make(chan requestAndChan, 1),
		writech:    make(chan writeRequest, 1),
		closech:    make(chan struct{}),
		writeErrCh: make(chan error, 1),
	}
	tlsDial := t.DialTLS != nil && cm.targetScheme == "https" && cm.proxyURL == nil
	if tlsDial {
		var err error
		pconn.conn, err = t.DialTLS("tcp", cm.addr())
		if err != nil {
			return nil, err
		}
		if tc, ok := pconn.conn.(*tls.Conn); ok {
			cs := tc.ConnectionState()
			pconn.tlsState = &cs
		}
	} else {
		conn, err := t.dial("tcp", cm.addr())
		if err != nil {
			if cm.proxyURL != nil {
				err = fmt.Errorf("http: error connecting to proxy %s: %v", cm.proxyURL, err)
			}
			return nil, err
		}
		pconn.conn = conn
	}

	switch {
	case cm.proxyURL == nil:

	case cm.targetScheme == "http":
		pconn.isProxy = true
		if pa := cm.proxyAuth(); pa != "" {
			pconn.mutateHeaderFunc = func(h Header) {
				h.Set("Proxy-Authorization", pa)
			}
		}
	case cm.targetScheme == "https":
		conn := pconn.conn
		connectReq := &Request{
			Method: "CONNECT",
			URL:    &url.URL{Opaque: cm.targetAddr},
			Host:   cm.targetAddr,
			Header: make(Header),
		}
		if pa := cm.proxyAuth(); pa != "" {
			connectReq.Header.Set("Proxy-Authorization", pa)
		}
		connectReq.Write(conn)

		br := bufio.NewReader(conn)
		resp, err := ReadResponse(br, connectReq)
		if err != nil {
			conn.Close()
			return nil, err
		}
		if resp.StatusCode != 200 {
			f := strings.SplitN(resp.Status, " ", 2)
			conn.Close()
			return nil, errors.New(f[1])
		}
	}

	if cm.targetScheme == "https" && !tlsDial {

		cfg := cloneTLSClientConfig(t.TLSClientConfig)
		if cfg.ServerName == "" {
			cfg.ServerName = cm.tlsHost()
		}
		plainConn := pconn.conn
		tlsConn := tls.Client(plainConn, cfg)
		errc := make(chan error, 2)
		var timer *time.Timer // for canceling TLS handshake
		if d := t.TLSHandshakeTimeout; d != 0 {
			timer = time.AfterFunc(d, func() {
				errc <- tlsHandshakeTimeoutError{}
			})
		}
		go func() {
			err := tlsConn.Handshake()
			if timer != nil {
				timer.Stop()
			}
			errc <- err
		}()
		if err := <-errc; err != nil {
			plainConn.Close()
			return nil, err
		}
		if !cfg.InsecureSkipVerify {
			if err := tlsConn.VerifyHostname(cfg.ServerName); err != nil {
				plainConn.Close()
				return nil, err
			}
		}
		cs := tlsConn.ConnectionState()
		pconn.tlsState = &cs
		pconn.conn = tlsConn
	}

	pconn.br = bufio.NewReader(noteEOFReader{pconn.conn, &pconn.sawEOF})
	pconn.bw = bufio.NewWriter(pconn.conn)
	go pconn.readLoop()
	go pconn.writeLoop()
	return pconn, nil
}