Handle absolute paths in relationships file, prevent panic on closing…

… unopened files (#23)

* Handle absolute paths in relationships file

* Prevent closing an unopened file panicing

file.go

@@ -54,6 +54,9 @@ func readFile(file *zip.File) ([]byte, error) {
 
 // Close closes the XlsxFile, rendering it unusable for I/O.
 func (xl *XlsxFileCloser) Close() error {
+	if xl == nil {
+		return nil
+	}
 	return xl.zipReadCloser.Close()
 }
 

file_test.go

@@ -33,17 +33,24 @@ func TestGettingFileByNameFailure(t *testing.T) {
 }
 
 func TestOpeningMissingFile(t *testing.T) {
-	_, err := OpenFile("this_doesnt_exist.zip")
+	f, err := OpenFile("this_doesnt_exist.zip")
+	defer f.Close()
 
 	require.EqualError(t, err, "open this_doesnt_exist.zip: no such file or directory")
 }
 
+func TestHandlingSpuriousWorkbookLinks(t *testing.T) {
+	f, err := OpenFile("./test/test-xl-relationship-prefix.xlsx")
+	defer f.Close()
+	require.NoError(t, err)
+}
+
 func TestOpeningXlsxFile(t *testing.T) {
-	actual, err := OpenFile("./test/test-small.xlsx")
-	defer actual.Close()
+	f, err := OpenFile("./test/test-small.xlsx")
+	defer f.Close()
 
 	require.NoError(t, err)
-	require.Equal(t, []string{"datarefinery_groundtruth_400000"}, actual.Sheets)
+	require.Equal(t, []string{"datarefinery_groundtruth_400000"}, f.Sheets)
 }
 
 func TestClosingFile(t *testing.T) {

sheets.go

@@ -4,6 +4,7 @@ import (
 	"archive/zip"
 	"encoding/xml"
 	"fmt"
+	"strings"
 )
 
 // workbook is a struct representing the data we care about from the workbook.xml file.
@@ -30,6 +31,11 @@ type relationship struct {
 func getFileNameFromRelationships(rels []relationship, s sheet) (string, error) {
 	for _, rel := range rels {
 		if rel.ID == s.RelationshipID {
+			if strings.HasPrefix(rel.Target, "/") {
+				// path is absolute, take all but the leading slash
+				return rel.Target[1:], nil
+			}
+			// path is relative, so needs xl/ adding
 			return "xl/" + rel.Target, nil
 		}
 	}