helper: stub helper for tests

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

helper/export_test.go

@@ -0,0 +1,18 @@
+package helper
+
+import (
+	"os"
+	"os/exec"
+	"testing"
+)
+
+// replace execCommand to have the resulting *exec.Cmd launch TestHelperChildStub
+func ReplaceExecCommand(t *testing.T) {
+	t.Cleanup(func() {
+		execCommand = exec.Command
+	})
+
+	execCommand = func(name string, arg ...string) *exec.Cmd {
+		return exec.Command(os.Args[0], append([]string{"-test.run=TestHelperChildStub", "--", name}, arg...)...)
+	}
+}

helper/helper.go

@@ -16,6 +16,11 @@ var (
 	ErrStatusRead  = errors.New("unexpected status response")
 )
 
+const (
+	FortifyHelper = "FORTIFY_HELPER"
+	FortifyStatus = "FORTIFY_STATUS"
+)
+
 // Helper wraps *exec.Cmd and manages status and args fd.
 // Args is always 3 and status if set is always 4.
 type Helper struct {
@@ -52,15 +57,20 @@ func (h *Helper) StartNotify(ready chan error) error {
 		h.argsP[0], h.argsP[1] = pr, pw
 	}
 	// create status pipes if ready signal is requested
+	var sv string
 	if ready != nil {
 		if pr, pw, err := os.Pipe(); err != nil {
 			return err
 		} else {
 			h.statP[0], h.statP[1] = pr, pw
 		}
+
+		sv = FortifyStatus + "=1"
+	} else {
+		sv = FortifyStatus + "=0"
 	}
 
-	// prepare extra files
+	// prepare extra files from caller
 	el := len(h.ExtraFiles)
 	if ready != nil {
 		el += 2
@@ -76,6 +86,7 @@ func (h *Helper) StartNotify(ready chan error) error {
 
 	// prepare and start process
 	h.Cmd.ExtraFiles = ef
+	h.Cmd.Env = append(h.Cmd.Env, FortifyHelper+"=1", sv)
 	if err := h.Cmd.Start(); err != nil {
 		return err
 	}
@@ -175,10 +186,12 @@ func (h *Helper) Start() error {
 	return h.StartNotify(nil)
 }
 
+var execCommand = exec.Command
+
 func New(wt io.WriterTo, name string, arg ...string) *Helper {
 	if wt == nil {
 		panic("attempted to create helper with invalid argument writer")
 	}
 
-	return &Helper{args: wt, Cmd: exec.Command(name, arg...)}
+	return &Helper{args: wt, Cmd: execCommand(name, arg...)}
 }

helper/stub_test.go

@@ -0,0 +1,75 @@
+package helper_test
+
+import (
+	"io"
+	"os"
+	"strconv"
+	"syscall"
+	"testing"
+
+	"git.ophivana.moe/cat/fortify/helper"
+)
+
+func TestHelperChildStub(t *testing.T) {
+	// this test mocks the helper process
+	if os.Getenv(helper.FortifyHelper) != "1" {
+		return
+	}
+	// simulate args pipe behaviour
+	func() {
+		f := os.NewFile(3, "|0")
+		if f == nil {
+			panic("attempted to start helper without args pipe")
+		}
+
+		if _, err := io.Copy(os.Stdout, f); err != nil {
+			panic("cannot read args: " + err.Error())
+		}
+	}()
+
+	var wait chan struct{}
+
+	// simulate status pipe behaviour
+	if os.Getenv(helper.FortifyStatus) == "1" {
+		wait = make(chan struct{})
+		go func() {
+			f := os.NewFile(4, "|1")
+			if f == nil {
+				panic("attempted to start with status reporting without status pipe")
+			}
+
+			if _, err := f.Write([]byte{'x'}); err != nil {
+				panic("cannot write to status pipe: " + err.Error())
+			}
+
+			// wait for status pipe close
+			var epoll int
+			if fd, err := syscall.EpollCreate1(0); err != nil {
+				panic("cannot open epoll fd: " + err.Error())
+			} else {
+				defer func() {
+					if err = syscall.Close(fd); err != nil {
+						panic("cannot close epoll fd: " + err.Error())
+					}
+				}()
+				epoll = fd
+			}
+			if err := syscall.EpollCtl(epoll, syscall.EPOLL_CTL_ADD, int(f.Fd()), &syscall.EpollEvent{}); err != nil {
+				panic("cannot add status pipe to epoll: " + err.Error())
+			}
+			events := make([]syscall.EpollEvent, 1)
+			if _, err := syscall.EpollWait(epoll, events, -1); err != nil {
+				panic("cannot poll status pipe: " + err.Error())
+			}
+			if events[0].Events != syscall.EPOLLERR {
+				panic(strconv.Itoa(int(events[0].Events)))
+
+			}
+			close(wait)
+		}()
+	}
+
+	if wait != nil {
+		<-wait
+	}
+}