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harness.go
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harness.go
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// The Harness for a Revel program.
//
// It has a couple responsibilities:
// 1. Parse the user program, generating a main.go file that registers
// controller classes and starts the user's server.
// 2. Build and run the user program. Show compile errors.
// 3. Monitor the user source and re-build / restart the program when necessary.
//
// Source files are generated in the app/tmp directory.
package harness
import (
"crypto/tls"
"fmt"
"github.com/revel/revel"
"go/build"
"io"
"net"
"net/http"
"net/http/httputil"
"net/url"
"os"
"os/signal"
"path"
"path/filepath"
"strings"
"sync/atomic"
)
var (
watcher *revel.Watcher
doNotWatch = []string{"tmp", "views", "routes"}
lastRequestHadError int32
)
// Harness reverse proxies requests to the application server.
// It builds / runs / rebuilds / restarts the server when code is changed.
type Harness struct {
app *App
serverHost string
port int
proxy *httputil.ReverseProxy
}
func renderError(w http.ResponseWriter, r *http.Request, err error) {
req, resp := revel.NewRequest(r), revel.NewResponse(w)
c := revel.NewController(req, resp)
c.RenderError(err).Apply(req, resp)
}
// ServeHTTP handles all requests.
// It checks for changes to app, rebuilds if necessary, and forwards the request.
func (hp *Harness) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Don't rebuild the app for favicon requests.
if lastRequestHadError > 0 && r.URL.Path == "/favicon.ico" {
return
}
// Flush any change events and rebuild app if necessary.
// Render an error page if the rebuild / restart failed.
err := watcher.Notify()
if err != nil {
atomic.CompareAndSwapInt32(&lastRequestHadError, 0, 1)
renderError(w, r, err)
return
}
atomic.CompareAndSwapInt32(&lastRequestHadError, 1, 0)
// Reverse proxy the request.
// (Need special code for websockets, courtesy of bradfitz)
if r.Header.Get("Upgrade") == "websocket" {
proxyWebsocket(w, r, hp.serverHost)
} else {
hp.proxy.ServeHTTP(w, r)
}
}
// Return a reverse proxy that forwards requests to the given port.
func NewHarness() *Harness {
// Get a template loader to render errors.
// Prefer the app's views/errors directory, and fall back to the stock error pages.
revel.MainTemplateLoader = revel.NewTemplateLoader(
[]string{path.Join(revel.RevelPath, "templates")})
revel.MainTemplateLoader.Refresh()
addr := revel.HttpAddr
port := revel.Config.IntDefault("harness.port", 0)
scheme := "http"
if revel.HttpSsl {
scheme = "https"
}
// If the server is running on the wildcard address, use "localhost"
if addr == "" {
addr = "localhost"
}
if port == 0 {
port = getFreePort()
}
serverUrl, _ := url.ParseRequestURI(fmt.Sprintf(scheme+"://%s:%d", addr, port))
harness := &Harness{
port: port,
serverHost: serverUrl.String()[len(scheme+"://"):],
proxy: httputil.NewSingleHostReverseProxy(serverUrl),
}
if revel.HttpSsl {
harness.proxy.Transport = &http.Transport{
TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
}
}
return harness
}
// Rebuild the Revel application and run it on the given port.
func (h *Harness) Refresh() (err *revel.Error) {
if h.app != nil {
h.app.Kill()
}
revel.TRACE.Println("Rebuild")
h.app, err = Build()
if err != nil {
return
}
h.app.Port = h.port
if err2 := h.app.Cmd().Start(); err2 != nil {
return &revel.Error{
Title: "App failed to start up",
Description: err2.Error(),
}
}
return
}
func (h *Harness) WatchDir(info os.FileInfo) bool {
return !revel.ContainsString(doNotWatch, info.Name())
}
func (h *Harness) WatchFile(filename string) bool {
return strings.HasSuffix(filename, ".go")
}
// Run the harness, which listens for requests and proxies them to the app
// server, which it runs and rebuilds as necessary.
func (h *Harness) Run() {
var paths []string
if revel.Config.BoolDefault("watch.gopath", false) {
gopaths := filepath.SplitList(build.Default.GOPATH)
paths = append(paths, gopaths...)
}
paths = append(paths, revel.CodePaths...)
watcher = revel.NewWatcher()
watcher.Listen(h, paths...)
go func() {
addr := fmt.Sprintf("%s:%d", revel.HttpAddr, revel.HttpPort)
revel.INFO.Printf("Listening on %s", addr)
var err error
if revel.HttpSsl {
err = http.ListenAndServeTLS(addr, revel.HttpSslCert,
revel.HttpSslKey, h)
} else {
err = http.ListenAndServe(addr, h)
}
if err != nil {
revel.ERROR.Fatalln("Failed to start reverse proxy:", err)
}
}()
// Kill the app on signal.
ch := make(chan os.Signal)
signal.Notify(ch, os.Interrupt, os.Kill)
<-ch
if h.app != nil {
h.app.Kill()
}
os.Exit(1)
}
// Find an unused port
func getFreePort() (port int) {
conn, err := net.Listen("tcp", ":0")
if err != nil {
revel.ERROR.Fatal(err)
}
port = conn.Addr().(*net.TCPAddr).Port
err = conn.Close()
if err != nil {
revel.ERROR.Fatal(err)
}
return port
}
// proxyWebsocket copies data between websocket client and server until one side
// closes the connection. (ReverseProxy doesn't work with websocket requests.)
func proxyWebsocket(w http.ResponseWriter, r *http.Request, host string) {
d, err := net.Dial("tcp", host)
if err != nil {
http.Error(w, "Error contacting backend server.", 500)
revel.ERROR.Printf("Error dialing websocket backend %s: %v", host, err)
return
}
hj, ok := w.(http.Hijacker)
if !ok {
http.Error(w, "Not a hijacker?", 500)
return
}
nc, _, err := hj.Hijack()
if err != nil {
revel.ERROR.Printf("Hijack error: %v", err)
return
}
defer nc.Close()
defer d.Close()
err = r.Write(d)
if err != nil {
revel.ERROR.Printf("Error copying request to target: %v", err)
return
}
errc := make(chan error, 2)
cp := func(dst io.Writer, src io.Reader) {
_, err := io.Copy(dst, src)
errc <- err
}
go cp(d, nc)
go cp(nc, d)
<-errc
}