archive: improve filter error reporting

pkg/archive/filter.go

@@ -26,6 +26,19 @@ func getFilterPath(name string) string {
 	return path.(string)
 }
 
+type errorRecordingReader struct {
+	r   io.Reader
+	err error
+}
+
+func (r *errorRecordingReader) Read(p []byte) (int, error) {
+	n, err := r.r.Read(p)
+	if r.err == nil && err != io.EOF {
+		r.err = err
+	}
+	return n, err
+}
+
 // tryProcFilter tries to run the command specified in args, passing input to its stdin and returning its stdout.
 // cleanup() is a caller provided function that will be called when the command finishes running, regardless of
 // whether it succeeds or fails.
@@ -38,22 +51,20 @@ func tryProcFilter(args []string, input io.Reader, cleanup func()) (io.ReadClose
 
 	var stderrBuf bytes.Buffer
 
+	inputWithError := &errorRecordingReader{r: input}
+
 	r, w := io.Pipe()
 	cmd := exec.Command(path, args[1:]...)
-	cmd.Stdin = input
+	cmd.Stdin = inputWithError
 	cmd.Stdout = w
 	cmd.Stderr = &stderrBuf
 	go func() {
 		err := cmd.Run()
-		if err != nil && stderrBuf.Len() > 0 {
-			b := make([]byte, 1)
-			// if there is an error reading from input, prefer to return that error
-			_, errRead := input.Read(b)
-			if errRead != nil && errRead != io.EOF {
-				err = errRead
-			} else {
-				err = fmt.Errorf("%s: %w", strings.TrimRight(stderrBuf.String(), "\n"), err)
-			}
+		// if there is an error reading from input, prefer to return that error
+		if inputWithError.err != nil {
+			err = inputWithError.err
+		} else if err != nil && stderrBuf.Len() > 0 {
+			err = fmt.Errorf("%s: %w", strings.TrimRight(stderrBuf.String(), "\n"), err)
 		}
 		w.CloseWithError(err) // CloseWithErr(nil) == Close()
 		cleanup()