mesh-delivery/modules/mesh-delivery-view/internal/view/serve.go

package view

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"html/template"
	"io"
	"net"
	"net/http"
	"os"
	"path/filepath"
	"text/tabwriter"
	"time"
)

// ListenSocket listens on the unix socket at path, in a directory of mode 0755, with mode 0666 on the socket: the
// status it carries is no secret and the socket can change nothing.
func ListenSocket(path string) (net.Listener, error) {
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return nil, err
	}
	if err := os.Chmod(dir, 0o755); err != nil {
		return nil, err
	}
	if err := os.Remove(path); err != nil && !errors.Is(err, os.ErrNotExist) {
		return nil, err
	}
	l, err := net.Listen("unix", path)
	if err != nil {
		return nil, err
	}
	if err := os.Chmod(path, 0o666); err != nil {
		l.Close()
		return nil, err
	}
	return l, nil
}

type ask struct {
	Ask string `json:"ask"`
}

// ServeSocket answers {"ask":"rows"} on l, line-delimited JSON, until ctx ends. Any other ask is refused.
func ServeSocket(ctx context.Context, l net.Listener, m *Model) error {
	go func() { <-ctx.Done(); l.Close() }()
	for {
		c, err := l.Accept()
		if err != nil {
			if ctx.Err() != nil {
				return nil
			}
			return err
		}
		go answer(c, m)
	}
}

func answer(c net.Conn, m *Model) {
	defer c.Close()
	c.SetDeadline(time.Now().Add(10 * time.Second))
	line, err := bufio.NewReader(io.LimitReader(c, 4096)).ReadBytes('\n')
	if err != nil && len(line) == 0 {
		return
	}
	var a ask
	if json.Unmarshal(line, &a) != nil || a.Ask != "rows" {
		json.NewEncoder(c).Encode(map[string]string{"error": `refused: this socket answers {"ask":"rows"} and nothing else`})
		return
	}
	json.NewEncoder(c).Encode(m.Snapshot())
}

// Ask asks the socket at path for the rows.
func Ask(path string) (Snapshot, error) {
	c, err := net.DialTimeout("unix", path, 5*time.Second)
	if err != nil {
		return Snapshot{}, fmt.Errorf("cannot reach the view at %s: %w", path, err)
	}
	defer c.Close()
	c.SetDeadline(time.Now().Add(10 * time.Second))
	if _, err := c.Write([]byte(`{"ask":"rows"}` + "\n")); err != nil {
		return Snapshot{}, err
	}
	var reply struct {
		Snapshot
		Error string `json:"error"`
	}
	if err := json.NewDecoder(c).Decode(&reply); err != nil {
		return Snapshot{}, fmt.Errorf("the view's answer is not rows: %w", err)
	}
	if reply.Error != "" {
		return Snapshot{}, errors.New(reply.Error)
	}
	return reply.Snapshot, nil
}

func since(t time.Time) string {
	if t.IsZero() {
		return ""
	}
	return t.Local().Format("2006-01-02 15:04:05")
}

func rowText(r Row) []string {
	what := r.Waits
	if r.Error != "" {
		what = "unreadable: " + r.Error
	}
	if r.Status == StatusLeftBehind && what == "" {
		what = r.Status
	} else if r.Status == StatusLeftBehind {
		what = r.Status + "; " + what
	}
	return []string{r.Node, r.Module, r.Assigned, r.Have, r.Phase, r.Health, since(r.Since), r.Detail, what}
}

var head = []string{"NODE", "MODULE", "ASSIGNED", "HAVE", "PHASE", "HEALTH", "SINCE", "DETAIL", "WAITS"}

// Table prints the snapshot as a table.
func Table(w io.Writer, s Snapshot) {
	tw := tabwriter.NewWriter(w, 0, 4, 2, ' ', 0)
	row := func(cells []string) {
		for i, c := range cells {
			if i > 0 {
				fmt.Fprint(tw, "\t")
			}
			fmt.Fprint(tw, c)
		}
		fmt.Fprintln(tw)
	}
	row(head)
	for _, r := range s.Rows {
		row(rowText(r))
	}
	if len(s.Nodes) > 0 {
		fmt.Fprintln(tw)
		row([]string{"NODE", "WINDOWS", "BUSY", "STRAYS", "SINCE"})
		for _, n := range s.Nodes {
			row([]string{n.Node, fmt.Sprint(n.Windows), fmt.Sprint(n.Busy), fmt.Sprint(n.Strays), since(n.Since)})
		}
	}
	tw.Flush()
}

var page = template.Must(template.New("p").Parse(`<!doctype html><html><head><meta charset="utf-8"><meta http-equiv="refresh" content="5">
<title>Delivery</title><style>body{font:14px sans-serif;margin:1em}table{border-collapse:collapse}td,th{padding:2px 10px;text-align:left}</style></head>
<body><h1>What each node runs</h1><table><tr>{{range .Head}}<th>{{.}}</th>{{end}}</tr>
{{range .Rows}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table></body></html>`))

// Web is the read-only web view of the same rows, refreshed by the browser.
func Web(m *Model) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet && r.Method != http.MethodHead {
			w.Header().Set("Allow", "GET, HEAD")
			http.Error(w, "this view is read-only", http.StatusMethodNotAllowed)
			return
		}
		if r.URL.Path != "/" {
			http.NotFound(w, r)
			return
		}
		var rows [][]string
		for _, row := range m.Snapshot().Rows {
			rows = append(rows, rowText(row))
		}
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		page.Execute(w, map[string]any{"Head": head, "Rows": rows})
	})
}