continuserv: Live serves updates to the spec

.gitignore

@@ -1,4 +1,5 @@
 scripts/gen
+scripts/continuserv/continuserv
 templating/out
 *.pyc
 supporting-docs/_site

scripts/continuserv/main.go

@@ -0,0 +1,129 @@
+// continuserv proactively re-generates the spec on filesystem changes, and serves it over HTTP.
+// It will always serve the most recent version of the spec, and may block an HTTP request until regeneration is finished.
+// It does not currently pre-empt stale generations, but will block until they are complete.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"path"
+	"path/filepath"
+	"strings"
+	"sync"
+	"sync/atomic"
+
+	fsnotify "gopkg.in/fsnotify.v1"
+)
+
+var toServe atomic.Value // Always contains valid []byte to serve. May be stale unless wg is zero.
+var wg sync.WaitGroup    // Indicates how many updates are pending.
+var mu sync.Mutex        // Prevent multiple updates in parallel.
+
+func main() {
+	w, err := fsnotify.NewWatcher()
+	if err != nil {
+		log.Fatalf("Error making watcher: %v", err)
+	}
+
+	dir, err := os.Getwd()
+	if err != nil {
+		log.Fatalf("Error getting wd: %v", err)
+	}
+	for ; !exists(path.Join(dir, ".git")); dir = path.Dir(dir) {
+		if dir == "/" {
+			log.Fatalf("Could not find git root")
+		}
+	}
+
+	filepath.Walk(dir, makeWalker(w))
+
+	wg.Add(1)
+	populateOnce(dir)
+
+	ch := make(chan struct{}, 100) // Buffered to ensure we can multiple-increment wg for pending writes
+	go doPopulate(ch, dir)
+
+	http.HandleFunc("/", serve)
+	go http.ListenAndServe(":8000", nil)
+
+	for {
+		select {
+		case e := <-w.Events:
+			if filter(e) {
+				wg.Add(1)
+				ch <- struct{}{}
+			}
+		}
+	}
+}
+
+func makeWalker(w *fsnotify.Watcher) filepath.WalkFunc {
+	return func(path string, _ os.FileInfo, err error) error {
+		if err != nil {
+			log.Fatalf("Error walking: %v", err)
+		}
+		w.Add(path)
+		return nil
+	}
+}
+
+// Return true if event should trigger re-population
+func filter(e fsnotify.Event) bool {
+	// vim is *really* noisy about how it writes files
+	if e.Op != fsnotify.Write {
+		return false
+	}
+	// Avoid some temp files that vim writes
+	if strings.HasSuffix(e.Name, "~") || strings.HasSuffix(e.Name, ".swp") || strings.HasPrefix(e.Name, ".") {
+		return false
+	}
+
+	// Avoid infinite cycles being caused by writing actual output
+	if strings.Contains(e.Name, "/tmp/") || strings.Contains(e.Name, "/gen/") {
+		return false
+	}
+	return true
+}
+
+func serve(w http.ResponseWriter, req *http.Request) {
+	wg.Wait()
+	b := toServe.Load().([]byte)
+	w.Write(b)
+}
+
+func populateOnce(dir string) {
+	defer wg.Done()
+	mu.Lock()
+	defer mu.Unlock()
+	cmd := exec.Command("python", "gendoc.py")
+	cmd.Dir = path.Join(dir, "scripts")
+	var b bytes.Buffer
+	cmd.Stderr = &b
+	err := cmd.Run()
+	if err != nil {
+		toServe.Store([]byte(fmt.Errorf("error generating spec: %v\nOutput from gendoc:\n%v", err, b.String()).Error()))
+		return
+	}
+	specBytes, err := ioutil.ReadFile(path.Join(dir, "scripts", "gen", "specification.html"))
+	if err != nil {
+		toServe.Store([]byte(fmt.Errorf("error reading spec: %v", err).Error()))
+		return
+	}
+	toServe.Store(specBytes)
+}
+
+func doPopulate(ch chan struct{}, dir string) {
+	for _ = range ch {
+		populateOnce(dir)
+	}
+}
+
+func exists(path string) bool {
+	_, err := os.Stat(path)
+	return !os.IsNotExist(err)
+}