From efb60afdee168d8eab9defb06d6d0ae2965201ec Mon Sep 17 00:00:00 2001
From: Lisa Ugray <lisa.ugray@gmail.com>
Date: Mon, 1 Apr 2024 12:07:14 -0400
Subject: [PATCH] Allow overwriting symlinks

When extracting regular files, the file is opened for writing with
os.O_TRUNC, making it suitable to extract over an existing file. This
allows updating a local copy from an updated archive by extracting over
it. If a link is added to the archive though, the second time it's
extracted, an error occurs since os.Link and os.Symlink will not
overwrite. This removes any file currently in place before attempting to
write a link.
---
 extract.go      |  2 ++
 extract_test.go | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/extract.go b/extract.go
index 5c68e0f..1a74094 100644
--- a/extract.go
+++ b/extract.go
@@ -116,6 +116,7 @@ func Zip(ctx context.Context, body io.Reader, location string, rename Renamer) e
 type fs struct{}
 
 func (f fs) Link(oldname, newname string) error {
+	_ = os.Remove(newname) // Ignore error. We don't care if the file doesn't exist.
 	return os.Link(oldname, newname)
 }
 
@@ -124,6 +125,7 @@ func (f fs) MkdirAll(path string, perm os.FileMode) error {
 }
 
 func (f fs) Symlink(oldname, newname string) error {
+	_ = os.Remove(newname) // Ignore error. We don't care if the file doesn't exist.
 	return os.Symlink(oldname, newname)
 }
 
diff --git a/extract_test.go b/extract_test.go
index 3ad01f2..7b088c1 100644
--- a/extract_test.go
+++ b/extract_test.go
@@ -220,6 +220,48 @@ func TestExtract(t *testing.T) {
 	}
 }
 
+func TestExtractIdempotency(t *testing.T) {
+	for _, test := range ExtractCases {
+		dir, _ := os.MkdirTemp("", "")
+		dir = filepath.Join(dir, "test")
+		data, err := os.ReadFile(test.Archive)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		var extractFn func(context.Context, io.Reader, string, extract.Renamer) error
+		switch filepath.Ext(test.Archive) {
+		case ".bz2":
+			extractFn = extract.Bz2
+		case ".gz":
+			extractFn = extract.Gz
+		case ".zip":
+			extractFn = extract.Zip
+		case ".mistery":
+			extractFn = extract.Archive
+		default:
+			t.Fatal("unknown error")
+		}
+
+		buffer := bytes.NewBuffer(data)
+		if err = extractFn(context.Background(), buffer, dir, test.Renamer); err != nil {
+			t.Fatal(test.Name, ": Should not fail first extraction: "+err.Error())
+		}
+
+		buffer = bytes.NewBuffer(data)
+		if err = extractFn(context.Background(), buffer, dir, test.Renamer); err != nil {
+			t.Fatal(test.Name, ": Should not fail second extraction: "+err.Error())
+		}
+
+		testWalk(t, dir, test.Files)
+
+		err = os.RemoveAll(dir)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
 func BenchmarkArchive(b *testing.B) {
 	dir, _ := os.MkdirTemp("", "")
 	data, _ := os.ReadFile("testdata/archive.tar.bz2")