feat: add live proxy

air_example.toml

@@ -73,3 +73,9 @@ clean_on_exit = true
 [screen]
 clear_on_rebuild = true
 keep_scroll = true
+
+# Enable live-reloading on the browser. This is useful when developing UI applications.
+[proxy]
+  enabled = true
+  proxy_port = 8090
+  app_port = 8080

runner/config.go

@@ -31,6 +31,7 @@ type Config struct {
 	Log         cfgLog    `toml:"log"`
 	Misc        cfgMisc   `toml:"misc"`
 	Screen      cfgScreen `toml:"screen"`
+	Proxy       cfgProxy  `toml:"proxy"`
 }
 
 type cfgBuild struct {
@@ -96,6 +97,12 @@ type cfgScreen struct {
 	KeepScroll     bool `toml:"keep_scroll"`
 }
 
+type cfgProxy struct {
+	Enabled bool `toml:"enabled"`
+	Port    int  `toml:"proxy_port"`
+	AppPort int  `toml:"app_port"`
+}
+
 type sliceTransformer struct{}
 
 func (t sliceTransformer) Transformer(typ reflect.Type) func(dst, src reflect.Value) error {
@@ -350,10 +357,9 @@ func (c *Config) killDelay() time.Duration {
 	// interpret as milliseconds if less than the value of 1 millisecond
 	if c.Build.KillDelay < time.Millisecond {
 		return c.Build.KillDelay * time.Millisecond
-	} else {
-		// normalize kill delay to milliseconds
-		return time.Duration(c.Build.KillDelay.Milliseconds()) * time.Millisecond
 	}
+	// normalize kill delay to milliseconds
+	return time.Duration(c.Build.KillDelay.Milliseconds()) * time.Millisecond
 }
 
 func (c *Config) binPath() string {

runner/engine.go

@@ -18,6 +18,7 @@ import (
 // Engine ...
 type Engine struct {
 	config    *Config
+	proxy     *Proxy
 	logger    *logger
 	watcher   filenotify.FileWatcher
 	debugMode bool
@@ -48,6 +49,7 @@ func NewEngineWithConfig(cfg *Config, debugMode bool) (*Engine, error) {
 	}
 	e := Engine{
 		config:         cfg,
+		proxy:          NewProxy(&cfg.Proxy),
 		logger:         logger,
 		watcher:        watcher,
 		debugMode:      debugMode,
@@ -310,6 +312,13 @@ func (e *Engine) isModified(filename string) bool {
 
 // Endless loop and never return
 func (e *Engine) start() {
+	if e.config.Proxy.Enabled {
+		go func() {
+			e.mainLog("Proxy server listening on %s", e.proxy.server.Addr)
+			e.proxy.Run()
+		}()
+	}
+
 	e.running = true
 	firstRunCh := make(chan bool, 1)
 	firstRunCh <- true
@@ -347,6 +356,9 @@ func (e *Engine) start() {
 				}
 			}
 
+			if e.config.Proxy.Enabled {
+				e.proxy.Reload()
+			}
 			e.mainLog("%s has changed", e.config.rel(filename))
 		case <-firstRunCh:
 			// go down
@@ -535,6 +547,9 @@ func (e *Engine) runBin() error {
 				cmd, stdout, stderr, _ := e.startCmd(command)
 				processExit := make(chan struct{})
 				e.mainDebug("running process pid %v", cmd.Process.Pid)
+				if e.proxy.config.Enabled {
+					e.proxy.Reload()
+				}
 
 				wg.Add(1)
 				atomic.AddUint64(&e.round, 1)
@@ -579,6 +594,11 @@ func (e *Engine) cleanup() {
 	e.mainLog("cleaning...")
 	defer e.mainLog("see you again~")
 
+	if e.config.Proxy.Enabled {
+		e.mainDebug("powering down the proxy...")
+		e.proxy.Stop()
+	}
+
 	e.withLock(func() {
 		close(e.binStopCh)
 		e.binStopCh = make(chan bool)

runner/proxy.go

@@ -0,0 +1,155 @@
+package runner
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"strconv"
+	"strings"
+	"syscall"
+	"time"
+)
+
+type Reloader interface {
+	AddSubscriber() *Subscriber
+	RemoveSubscriber(id int)
+	Reload()
+	Stop()
+}
+
+type Proxy struct {
+	server *http.Server
+	config *cfgProxy
+	stream Reloader
+}
+
+func NewProxy(cfg *cfgProxy) *Proxy {
+	p := &Proxy{
+		config: cfg,
+		server: &http.Server{
+			Addr: fmt.Sprintf("localhost:%d", cfg.Port),
+		},
+		stream: NewProxyStream(),
+	}
+	return p
+}
+
+func (p *Proxy) Run() {
+	http.HandleFunc("/", p.proxyHandler)
+	http.HandleFunc("/internal/reload", p.reloadHandler)
+	log.Fatal(p.server.ListenAndServe())
+}
+
+func (p *Proxy) Stop() {
+	p.server.Close()
+	p.stream.Stop()
+}
+
+func (p *Proxy) Reload() {
+	p.stream.Reload()
+}
+
+func (p *Proxy) injectLiveReload(origURL string, respBody io.ReadCloser) string {
+	buf := new(bytes.Buffer)
+	if _, err := buf.ReadFrom(respBody); err != nil {
+		panic("failed to convert request body to bytes buffer")
+	}
+	s := buf.String()
+
+	body := strings.LastIndex(s, "</body>")
+	if body == -1 {
+		panic("invalid html")
+	}
+	script := `
+	<script>
+	const parser = new DOMParser();
+	const proxyURL = "http://localhost:%d";
+	new EventSource(proxyURL + "/internal/reload").onmessage = () => {
+		fetch(proxyURL + "%s").then(res => res.text()).then(resStr => {
+			const newPage = parser.parseFromString(resStr, "text/html");
+			document.replaceChild(newPage.documentElement, document.documentElement);
+		});
+	};
+	</script>
+	`
+	parsedScript := fmt.Sprintf(script, p.config.Port, origURL)
+
+	s = s[:body] + parsedScript + s[body:]
+	return s
+}
+
+func (p *Proxy) proxyHandler(w http.ResponseWriter, r *http.Request) {
+	url := fmt.Sprintf("http://localhost:%d", p.config.AppPort)
+	req, err := http.NewRequest(r.Method, url, r.Body)
+	if err != nil {
+		panic(err)
+	}
+	req.Header.Set("X-Forwarded-For", r.RemoteAddr)
+
+	client := &http.Client{}
+	var resp *http.Response
+	for i := 0; i < 10; i++ {
+		resp, err = client.Do(req)
+		if err == nil {
+			break
+		}
+		if !errors.Is(err, syscall.ECONNREFUSED) {
+			log.Fatalf("failed to call http://localhost:%d, err: %+v", p.config.AppPort, err)
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+	defer resp.Body.Close()
+
+	// copy all headers except Content-Length
+	for k, vv := range resp.Header {
+		for _, v := range vv {
+			if k == "Content-Length" {
+				continue
+			}
+			w.Header().Add(k, v)
+		}
+	}
+	w.WriteHeader(resp.StatusCode)
+
+	if strings.Contains(resp.Header.Get("Content-Type"), "text/html") {
+		s := p.injectLiveReload(r.URL.String(), resp.Body)
+		w.Header().Set("Content-Length", strconv.Itoa((len([]byte(s)))))
+		if _, err := io.WriteString(w, s); err != nil {
+			panic("failed to write injected payload")
+		}
+	} else {
+		w.Header().Set("Content-Length", resp.Header.Get("Content-Length"))
+		if _, err := io.Copy(w, resp.Body); err != nil {
+			panic("failed to write normal payload")
+		}
+	}
+}
+
+func (p *Proxy) reloadHandler(w http.ResponseWriter, r *http.Request) {
+	flusher, err := w.(http.Flusher)
+	if !err {
+		http.Error(w, "Streaming unsupported!", http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Type", "text/event-stream")
+	w.Header().Set("Cache-Control", "no-cache")
+	w.Header().Set("Connection", "keep-alive")
+
+	sub := p.stream.AddSubscriber()
+	go func() {
+		<-r.Context().Done()
+		p.stream.RemoveSubscriber(sub.id)
+	}()
+
+	w.WriteHeader(http.StatusOK)
+	flusher.Flush()
+
+	for range sub.reloadCh {
+		fmt.Fprintf(w, "data: reload\n\n")
+		flusher.Flush()
+	}
+}

runner/proxy_stream.go

@@ -0,0 +1,50 @@
+package runner
+
+import (
+	"sync"
+)
+
+type ProxyStream struct {
+	sync.Mutex
+	subscribers map[int]*Subscriber
+	count       int
+}
+
+type Subscriber struct {
+	id       int
+	reloadCh chan struct{}
+}
+
+func NewProxyStream() *ProxyStream {
+	return &ProxyStream{subscribers: make(map[int]*Subscriber)}
+}
+
+func (stream *ProxyStream) Stop() {
+	for id := range stream.subscribers {
+		stream.RemoveSubscriber(id)
+	}
+	stream.count = 0
+}
+
+func (stream *ProxyStream) AddSubscriber() *Subscriber {
+	stream.Lock()
+	defer stream.Unlock()
+	stream.count++
+
+	sub := &Subscriber{id: stream.count, reloadCh: make(chan struct{})}
+	stream.subscribers[stream.count] = sub
+	return sub
+}
+
+func (stream *ProxyStream) RemoveSubscriber(id int) {
+	stream.Lock()
+	defer stream.Unlock()
+	close(stream.subscribers[id].reloadCh)
+	delete(stream.subscribers, id)
+}
+
+func (stream *ProxyStream) Reload() {
+	for _, sub := range stream.subscribers {
+		sub.reloadCh <- struct{}{}
+	}
+}

runner/proxy_stream_test.go

@@ -0,0 +1,66 @@
+package runner
+
+import (
+	"sync"
+	"testing"
+)
+
+func find(s map[int]*Subscriber, id int) bool {
+	for _, sub := range s {
+		if sub.id == id {
+			return true
+		}
+	}
+	return false
+}
+
+func TestProxyStream(t *testing.T) {
+	stream := NewProxyStream()
+
+	var wg sync.WaitGroup
+	for i := 0; i < 10; i++ {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			_ = stream.AddSubscriber()
+		}(i)
+	}
+	wg.Wait()
+
+	if got, exp := len(stream.subscribers), 10; got != exp {
+		t.Errorf("expected %d but got %d", exp, got)
+	}
+
+	go func() {
+		stream.Reload()
+	}()
+
+	reloadCount := 0
+	for _, sub := range stream.subscribers {
+		wg.Add(1)
+		go func(sub *Subscriber) {
+			defer wg.Done()
+			<-sub.reloadCh
+			reloadCount++
+		}(sub)
+	}
+	wg.Wait()
+
+	if got, exp := reloadCount, 10; got != exp {
+		t.Errorf("expected %d but got %d", exp, got)
+	}
+
+	stream.RemoveSubscriber(2)
+	stream.AddSubscriber()
+	if got, exp := find(stream.subscribers, 2), false; got != exp {
+		t.Errorf("expected subscriber found to be %t but got %t", exp, got)
+	}
+	if got, exp := find(stream.subscribers, 11), true; got != exp {
+		t.Errorf("expected subscriber found to be %t but got %t", exp, got)
+	}
+
+	stream.Stop()
+	if got, exp := len(stream.subscribers), 0; got != exp {
+		t.Errorf("expected %d but got %d", exp, got)
+	}
+}