fixed tcp/udp I/O, deadlock, nil dereference; improved docker watcher, idlewatcher, loading page

src/docker/idlewatcher/http.go

@@ -0,0 +1,93 @@
+package idlewatcher
+
+import (
+	"bytes"
+	_ "embed"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"text/template"
+)
+
+type templateData struct {
+	Title          string
+	Message        string
+	RequestHeaders http.Header
+	SpinnerClass   string
+}
+
+//go:embed html/loading_page.html
+var loadingPage []byte
+var loadingPageTmpl = func() *template.Template {
+	tmpl, err := template.New("loading").Parse(string(loadingPage))
+	if err != nil {
+		panic(err)
+	}
+	return tmpl
+}()
+
+const (
+	htmlContentType = "text/html; charset=utf-8"
+
+	errPrefix = "\u1000"
+
+	headerGoProxyTargetURL = "X-GoProxy-Target"
+	headerContentType      = "Content-Type"
+
+	spinnerClassSpinner   = "spinner"
+	spinnerClassErrorSign = "error"
+)
+
+func (w *watcher) makeSuccResp(redirectURL string, resp *http.Response) (*http.Response, error) {
+	h := make(http.Header)
+	h.Set("Location", redirectURL)
+	h.Set("Content-Length", "0")
+	h.Set(headerContentType, htmlContentType)
+	return &http.Response{
+		StatusCode: http.StatusTemporaryRedirect,
+		Header:     h,
+		Body:       http.NoBody,
+		TLS:        resp.TLS,
+	}, nil
+}
+
+func (w *watcher) makeErrResp(errFmt string, args ...any) (*http.Response, error) {
+	return w.makeResp(errPrefix+errFmt, args...)
+}
+
+func (w *watcher) makeResp(format string, args ...any) (*http.Response, error) {
+	msg := fmt.Sprintf(format, args...)
+
+	data := new(templateData)
+	data.Title = w.ContainerName
+	data.Message = strings.ReplaceAll(msg, "\n", "<br>")
+	data.Message = strings.ReplaceAll(data.Message, " ", "&ensp;")
+	data.RequestHeaders = make(http.Header)
+	data.RequestHeaders.Add(headerGoProxyTargetURL, "window.location.href")
+	if strings.HasPrefix(data.Message, errPrefix) {
+		data.Message = strings.TrimLeft(data.Message, errPrefix)
+		data.SpinnerClass = spinnerClassErrorSign
+	} else {
+		data.SpinnerClass = spinnerClassSpinner
+	}
+
+	buf := bytes.NewBuffer(make([]byte, 128)) // more than enough
+	err := loadingPageTmpl.Execute(buf, data)
+	if err != nil { // should never happen
+		panic(err)
+	}
+	return &http.Response{
+		StatusCode: http.StatusAccepted,
+		Header: http.Header{
+			headerContentType: {htmlContentType},
+			"Cache-Control": {
+				"no-cache",
+				"no-store",
+				"must-revalidate",
+			},
+		},
+		Body:          io.NopCloser(buf),
+		ContentLength: int64(buf.Len()),
+	}, nil
+}