util/eventbus: add a debug HTTP handler for the bus

Updates #15160

Signed-off-by: David Anderson <dave@tailscale.com>

util/eventbus/fetch-htmx.go

@@ -0,0 +1,93 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ignore
+
+// Program fetch-htmx fetches and installs local copies of the HTMX
+// library and its dependencies, used by the debug UI. It is meant to
+// be run via go generate.
+package main
+
+import (
+	"compress/gzip"
+	"crypto/sha512"
+	"encoding/base64"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+)
+
+func main() {
+	// Hash from https://htmx.org/docs/#installing
+	htmx, err := fetchHashed("https://unpkg.com/htmx.org@2.0.4", "HGfztofotfshcF7+8n44JQL2oJmowVChPTg48S+jvZoztPfvwD79OC/LTtG6dMp+")
+	if err != nil {
+		log.Fatalf("fetching htmx: %v", err)
+	}
+
+	// Hash SHOULD be from https://htmx.org/extensions/ws/ , but the
+	// hash is currently incorrect, see
+	// https://github.com/bigskysoftware/htmx-extensions/issues/153
+	//
+	// Until that bug is resolved, hash was obtained by rebuilding the
+	// extension from git source, and verifying that the hash matches
+	// what unpkg is serving.
+	ws, err := fetchHashed("https://unpkg.com/htmx-ext-ws@2.0.2", "932iIqjARv+Gy0+r6RTGrfCkCKS5MsF539Iqf6Vt8L4YmbnnWI2DSFoMD90bvXd0")
+	if err != nil {
+		log.Fatalf("fetching htmx-websockets: %v", err)
+	}
+
+	if err := writeGz("assets/htmx.min.js.gz", htmx); err != nil {
+		log.Fatalf("writing htmx.min.js.gz: %v", err)
+	}
+	if err := writeGz("assets/htmx-websocket.min.js.gz", ws); err != nil {
+		log.Fatalf("writing htmx-websocket.min.js.gz: %v", err)
+	}
+}
+
+func writeGz(path string, bs []byte) error {
+	f, err := os.Create(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	g, err := gzip.NewWriterLevel(f, gzip.BestCompression)
+	if err != nil {
+		return err
+	}
+
+	if _, err := g.Write(bs); err != nil {
+		return err
+	}
+
+	if err := g.Flush(); err != nil {
+		return err
+	}
+	if err := f.Close(); err != nil {
+		return err
+	}
+	return nil
+}
+
+func fetchHashed(url, wantHash string) ([]byte, error) {
+	resp, err := http.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("fetching %q returned error status: %s", url, resp.Status)
+	}
+	ret, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("reading file from %q: %v", url, err)
+	}
+	h := sha512.Sum384(ret)
+	got := base64.StdEncoding.EncodeToString(h[:])
+	if got != wantHash {
+		return nil, fmt.Errorf("wrong hash for %q: got %q, want %q", url, got, wantHash)
+	}
+	return ret, nil
+}