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cmd_serve.go
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cmd_serve.go
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package internal
import (
"bytes"
"fmt"
"net/http"
"os"
"text/template"
"time"
"github.com/fsnotify/fsnotify"
"github.com/spf13/cobra"
"github.com/lonnblad/gopuml/internal/generator"
)
const (
defaultPort = "8080"
flagPort, flagShortPort = "port", "p"
)
type serveOptions struct {
Port string
}
const flagUsagePort = `the port to use to serve the HTML page
`
// CreateServeCmd creates the serve subcommand.
// The command will run a webserver which renders the supplied Plant UML files as a static HTML page.
// The command uses a file watcher to keep track of any modifications to the supplied files.
// The HTML page execute HEAD requests to check for new updates using long-polling and the If-Modified-Since header.
// When modifications are found, the server will answer the HEAD request with a 200 OK.
func CreateServeCmd() cobra.Command {
opts := serveOptions{
Port: defaultPort,
}
serveCmd := cobra.Command{
Use: "serve",
Short: "Starts a web server which serves compiled UML files on a static HTML page.",
Long: `Starts a web server which serves compiled UML files.
On modifications to the files, the HTML page will reload.`,
RunE: serveCmdRunFunc(&opts),
}
serveCmd.Flags().StringVarP(&opts.Port, flagPort, flagShortPort, opts.Port, flagUsagePort)
return serveCmd
}
func serveCmdRunFunc(opts *serveOptions) func(cmd *cobra.Command, args []string) error {
return func(cmd *cobra.Command, args []string) error {
generator := generator.New()
fileWatcher, err := fsnotify.NewWatcher()
if err != nil {
return err
}
defer fileWatcher.Close()
go eventHandler(cmd, fileWatcher, generator)
if err = readAllFiles(fileWatcher, generator, args); err != nil {
return err
}
if err = runServer(cmd, opts.Port, generator); err != nil {
return err
}
return nil
}
}
func eventHandler(cmd *cobra.Command, watcher *fsnotify.Watcher, gen *generator.Generator) {
for {
select {
case event, ok := <-watcher.Events:
if !ok {
return
}
if event.Op&fsnotify.Write == fsnotify.Write {
path := event.Name
fmt.Fprintln(cmd.OutOrStdout(), "modified file:", path)
content, err := os.ReadFile(path)
if err != nil {
cmd.PrintErrln(err)
return
}
if err = gen.PutFile(path, content); err != nil {
cmd.PrintErrln(err)
return
}
}
case err, ok := <-watcher.Errors:
if !ok {
return
}
cmd.PrintErrln(err)
}
}
}
func readAllFiles(fileWatcher *fsnotify.Watcher, gen *generator.Generator, args []string) error {
filepaths, err := findAbsolutePaths(args)
if err != nil {
return err
}
for _, path := range filepaths {
if err = fileWatcher.Add(path); err != nil {
return err
}
content, err := os.ReadFile(path)
if err != nil {
return err
}
if err = gen.PutFile(path, content); err != nil {
return err
}
}
return nil
}
func runServer(cmd *cobra.Command, port string, gen *generator.Generator) error {
server := &http.Server{Addr: ":" + port, Handler: handler(gen)}
fmt.Fprintln(cmd.OutOrStdout(), "Server started")
fmt.Fprintf(cmd.OutOrStdout(), " http://localhost:%s\n\n", port)
if err := server.ListenAndServe(); err != http.ErrServerClosed {
return err
}
return nil
}
const (
contentType = "Content-Type"
mimeHTML = "text/html"
)
func handler(gen *generator.Generator) http.Handler {
mux := http.NewServeMux()
mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
if req.Method == "HEAD" {
handleHEAD(gen, w, req)
return
}
w.Header().Set(contentType, mimeHTML)
content, err := buildHTML(gen.GetFiles())
if err != nil {
w.WriteHeader(http.StatusInternalServerError)
w.Write([]byte("")) // nolint: errcheck
return
}
w.Write(content) // nolint: errcheck
})
return mux
}
func handleHEAD(gen *generator.Generator, w http.ResponseWriter, req *http.Request) {
content := []byte("")
etag := req.Header.Get("If-Modified-Since")
if etag == "" {
w.Write(content) // nolint: errcheck
return
}
since, err := time.Parse(time.RFC1123, etag)
if err != nil {
w.Write(content) // nolint: errcheck
return
}
id, contentChan := gen.RegisterSub()
defer gen.DeregisterSub(id)
for _, file := range gen.GetFiles() {
if file.UpdatedAt.After(since) {
w.Write(content) // nolint: errcheck
return
}
}
const longPollingTimeout = 60 * time.Second
select {
case <-contentChan:
case <-time.After(longPollingTimeout):
w.WriteHeader(http.StatusNotModified)
}
w.Write(content) // nolint: errcheck
}
func buildHTML(files []generator.File) (_ []byte, err error) {
generator, err := template.New("html_page").Parse(htmlPageTemplate)
if err != nil {
err = fmt.Errorf("failed to parse HTML page template: %w", err)
return
}
type file struct {
Filename string
PngLink string
SvgLink string
}
var templateInfo = struct{ Files []file }{Files: make([]file, len(files))}
for idx, f := range files {
templateInfo.Files[idx].Filename = f.Filename
templateInfo.Files[idx].PngLink = createLink(defaultServer, formatPNG, f.Encoded)
templateInfo.Files[idx].SvgLink = createLink(defaultServer, formatSVG, f.Encoded)
}
var buffer bytes.Buffer
if err = generator.Execute(&buffer, templateInfo); err != nil {
err = fmt.Errorf("failed to execute generator: %w", err)
return
}
return buffer.Bytes(), nil
}
const htmlPageTemplate = `<!DOCTYPE html>
<html lang=en>
<head>
<title>gopuml</title>
<meta name='generator' content='github.com/lonnblad/gopuml'>
</head>
<body onload="javascript:checkReload();" style="width:100vw;height:100vh;background-color:lightgrey;">
<div style="margin: 0px 20px;width:100%">
{{range .Files}}
<h2>{{.Filename}}</h2>
<h3>.png</h3>
Static <a href="{{.PngLink}}">.png link</a> from plantuml.com.
<p>
<img style="object-fit:contain;" src="{{.PngLink}}" alt=".png" />
</p>
<h3>.svg</h3>
Static <a href="{{.SvgLink}}">.svg link</a> from plantuml.com.
<p>
<img style="object-fit:contain;" src="{{.SvgLink}}" alt=".svg" />
</p>
{{end}}
</div>
<script>
function checkReload() {
const timestamp = new Date().toUTCString();
fetch('/', {method: 'HEAD', headers: {'If-Modified-Since': timestamp}})
.then(response => {
if (response.status === 200) {
location.reload(true)
} else {
checkReload()
}
})
.catch(err => console.log(err));
}
</script>
</body>
</html>`