readautocloser: only close once (fixes #250)

README.md

@@ -391,6 +391,7 @@ Sinks are methods that return some data from a pipe, ending the pipeline and ext
 
 | Version | New |
 | ----------- | ------- |
+| 0.25.2  | Fixed bug where [`Post`](https://pkg.go.dev/github.com/bitfield/script#Pipe.Post) would error on posting a file ([#250](https://github.com/bitfield/script/issues/250))|
 | 0.25.1  | [`Unique`](https://pkg.go.dev/github.com/bitfield/script#Pipe.Unique) |
 | 0.25.0  | [`ExecCommand`](https://pkg.go.dev/github.com/bitfield/script#Pipe.ExecCommand) / [`Shell`](https://pkg.go.dev/github.com/bitfield/script#Pipe.Shell) supersede `Exec` (thanks [Dhanalakshmi-D04](https://github.com/Dhanalakshmi-D04)) |
 |         | [`WithContext`](https://pkg.go.dev/github.com/bitfield/script#Pipe.WithContext) (thanks [billvamva](https://github.com/billvamva)) |

script.go

@@ -1203,6 +1203,18 @@ type ReadAutoCloser struct {
 	r io.ReadCloser
 }
 
+// onceCloser makes Close safe to call more than once.
+type onceCloser struct {
+	io.ReadCloser
+	once sync.Once
+	err  error
+}
+
+func (c *onceCloser) Close() error {
+	c.once.Do(func() { c.err = c.ReadCloser.Close() })
+	return c.err
+}
+
 // NewReadAutoCloser returns a [ReadAutoCloser] wrapping the reader r.
 func NewReadAutoCloser(r io.Reader) ReadAutoCloser {
 	if _, ok := r.(io.Closer); !ok {
@@ -1213,7 +1225,7 @@ func NewReadAutoCloser(r io.Reader) ReadAutoCloser {
 		// This can never happen, but just in case it does...
 		panic("internal error: type assertion to io.ReadCloser failed")
 	}
-	return ReadAutoCloser{rc}
+	return ReadAutoCloser{&onceCloser{ReadCloser: rc}}
 }
 
 // Close closes ra's reader, returning any resulting error.

script_test.go

@@ -1029,6 +1029,18 @@ func TestPostPostsToGivenURLUsingPipeAsRequestBody(t *testing.T) {
 	}
 }
 
+func TestPostDoesNotErrorWhenFileAutoClosed(t *testing.T) {
+	t.Parallel()
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		io.Copy(w, r.Body)
+	}))
+	defer ts.Close()
+	_, err := script.File("testdata/hello.txt").Post(ts.URL).String()
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestRejectRegexp_DropsMatchingLinesFromInput(t *testing.T) {
 	t.Parallel()
 	input := "hello world"
@@ -1477,6 +1489,27 @@ func TestReadAutoCloser_ReadsAllDataFromSourceAndClosesItAutomatically(t *testin
 	}
 }
 
+type mockCloser struct {
+	io.Reader
+	closed bool
+	t      *testing.T
+}
+
+func (mc *mockCloser) Close() error {
+	if mc.closed {
+		mc.t.Fatal("source closed twice")
+	}
+	mc.closed = true
+	return nil
+}
+
+func TestReadAutoCloser_OnlyClosesSourceOnce(t *testing.T) {
+	t.Parallel()
+	acr := script.NewReadAutoCloser(&mockCloser{t: t})
+	acr.Close()
+	acr.Close()
+}
+
 func TestSliceProducesElementsOfSpecifiedSliceOnePerLine(t *testing.T) {
 	t.Parallel()
 	want := "1\n2\n3\n"