func handleExec()

in cmd/buildlet/buildlet.go [847:993]
135 lines of code
30 McCabe index (conditional complexity)

func handleExec(w http.ResponseWriter, r *http.Request) {
	cn := w.(http.CloseNotifier)
	clientGone := cn.CloseNotify()
	handlerDone := make(chan bool)
	defer close(handlerDone)

	if r.Method != "POST" {
		http.Error(w, "requires POST method", http.StatusBadRequest)
		return
	}
	if r.ProtoMajor*10+r.ProtoMinor < 11 {
		// We need trailers, only available in HTTP/1.1 or HTTP/2.
		http.Error(w, "HTTP/1.1 or higher required", http.StatusBadRequest)
		return
	}
	// Create *workDir and (if needed) tmp and gocache.
	if !mkdirAllWorkdirOr500(w) {
		return
	}
	for _, dir := range []string{processTmpDirEnv, processGoCacheEnv} {
		if dir == "" {
			continue
		}
		if err := os.MkdirAll(dir, 0755); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	}
	if err := checkAndroidEmulator(); err != nil {
		http.Error(w, "android emulator not running: "+err.Error(), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Trailer", hdrProcessState) // declare it so we can set it

	cmdPath := r.FormValue("cmd") // required
	absCmd := cmdPath
	dir := r.FormValue("dir") // optional
	sysMode := r.FormValue("mode") == "sys"
	debug, _ := strconv.ParseBool(r.FormValue("debug"))

	if sysMode {
		if cmdPath == "" {
			http.Error(w, "requires 'cmd' parameter", http.StatusBadRequest)
			return
		}
		if dir == "" {
			dir = *workDir
		} else {
			dir = filepath.FromSlash(dir)
			if !filepath.IsAbs(dir) {
				dir = filepath.Join(*workDir, dir)
			}
		}
	} else {
		if !validRelPath(cmdPath) {
			http.Error(w, "requires 'cmd' parameter", http.StatusBadRequest)
			return
		}
		absCmd = filepath.Join(*workDir, filepath.FromSlash(cmdPath))
		if dir == "" {
			dir = filepath.Dir(absCmd)
		} else {
			if !validRelPath(dir) {
				http.Error(w, "bogus 'dir' parameter", http.StatusBadRequest)
				return
			}
			dir = filepath.Join(*workDir, filepath.FromSlash(dir))
		}
	}

	if f, ok := w.(http.Flusher); ok {
		f.Flush()
	}

	postEnv := r.PostForm["env"]

	goarch := "amd64" // unless we find otherwise
	if v := envutil.Get(runtime.GOOS, postEnv, "GOARCH"); v != "" {
		goarch = v
	}
	if v, _ := strconv.ParseBool(envutil.Get(runtime.GOOS, postEnv, "GO_DISABLE_OUTBOUND_NETWORK")); v {
		disableOutboundNetwork()
	}

	env := append(baseEnv(goarch), postEnv...)
	if v := processTmpDirEnv; v != "" {
		env = append(env, "TMPDIR="+v)
	}
	if v := processGoCacheEnv; v != "" {
		env = append(env, "GOCACHE="+v)
	}
	if path := r.PostForm["path"]; len(path) > 0 {
		if kv, ok := pathEnv(runtime.GOOS, env, path, *workDir); ok {
			env = append(env, kv)
		}
	}
	env = envutil.Dedup(runtime.GOOS, env)

	var cmd *exec.Cmd
	if needsBashWrapper(absCmd) {
		cmd = exec.Command("bash", absCmd)
	} else {
		cmd = exec.Command(absCmd)
	}
	cmd.Args = append(cmd.Args, r.PostForm["cmdArg"]...)
	cmd.Env = env
	envutil.SetDir(cmd, dir)
	cmdOutput := flushWriter{w}
	cmd.Stdout = cmdOutput
	cmd.Stderr = cmdOutput

	log.Printf("[%p] Running %s with args %q and env %q in dir %s",
		cmd, cmd.Path, cmd.Args, cmd.Env, cmd.Dir)

	if debug {
		fmt.Fprintf(cmdOutput, ":: Running %s with args %q and env %q in dir %s\n\n",
			cmd.Path, cmd.Args, cmd.Env, cmd.Dir)
	}

	t0 := time.Now()
	err := cmd.Start()
	if err == nil {
		go func() {
			select {
			case <-clientGone:
				err := killProcessTree(cmd.Process)
				if err != nil {
					log.Printf("Kill failed: %v", err)
				}
			case <-handlerDone:
				return
			}
		}()
		err = cmd.Wait()
	}
	state := "ok"
	if err != nil {
		if ps := cmd.ProcessState; ps != nil {
			state = ps.String()
		} else {
			state = err.Error()
		}
	}
	w.Header().Set(hdrProcessState, state)
	log.Printf("[%p] Run = %s, after %v", cmd, state, time.Since(t0))
}