From d2e0fd2af0e90eb9b01816064bcd2fb59dfb362d Mon Sep 17 00:00:00 2001
From: eleksir <eleksir@exs-elm.ru>
Date: Sat, 18 Apr 2026 09:17:16 +0300
Subject: [PATCH] There was a bug where all files treated as hardlinks in
 resulting tar archive, now it was hopefully fixed

---
 internal/backer/archive.go              | 21 +++++-----
 internal/backer/utils_test.go           | 53 +++++++++++++++++++++++++
 test_data/test1/hardlinks/hardlink1.txt |  1 +
 test_data/test1/hardlinks/hardlink2.txt |  1 +
 test_data/test1/hardlinks/original.txt  |  1 +
 5 files changed, 66 insertions(+), 11 deletions(-)
 create mode 100644 test_data/test1/hardlinks/hardlink1.txt
 create mode 100644 test_data/test1/hardlinks/hardlink2.txt
 create mode 100644 test_data/test1/hardlinks/original.txt

diff --git a/internal/backer/archive.go b/internal/backer/archive.go
index 75aac24..fe71e16 100644
--- a/internal/backer/archive.go
+++ b/internal/backer/archive.go
@@ -9,6 +9,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"syscall"
 
 	"backer/internal/log"
 )
@@ -149,6 +150,7 @@ func writeFilesToTar(ctx context.Context, filepaths []string, tw *tar.Writer, cl
 		// If linkTarget is set, ensure the header is marked as a link.
 		if linkTarget != "" {
 			header.Typeflag = tar.TypeLink
+			header.Linkname = linkTarget
 		}
 
 		header.Format = tar.FormatGNU
@@ -164,8 +166,8 @@ func writeFilesToTar(ctx context.Context, filepaths []string, tw *tar.Writer, cl
 			return
 		}
 
-		// Only stream file contents for regular files.
-		if mode.IsRegular() {
+		// Only stream file contents for regular files that are not hard links.
+		if mode.IsRegular() && linkTarget == "" {
 			f, err := os.Open(fpath)
 			if err != nil {
 				log.Warnf("Skipping %s: open failed: %v", fpath, err)
@@ -195,15 +197,12 @@ func getInode(fi os.FileInfo) uint64 {
 		return 0
 	}
 
-	// Use type assertion to get inode - works on Unix, returns 0 on Windows.
-	type inodeGetter interface {
-		Dev() uint64
-		Ino() uint64
-	}
-
-	if ig, ok := fi.Sys().(inodeGetter); ok {
-		// Combine device and inode for uniqueness across file systems.
-		return (ig.Dev() << 32) | ig.Ino()
+	// Use reflection to get Dev and Ino fields from the syscall.Stat_t struct.
+	st := fi.Sys()
+	// Try type assertion for the struct with fields.
+	switch v := st.(type) {
+	case *syscall.Stat_t:
+		return (v.Dev << 32) | v.Ino
 	}
 
 	return 0
diff --git a/internal/backer/utils_test.go b/internal/backer/utils_test.go
index e18f9f8..5ef5529 100644
--- a/internal/backer/utils_test.go
+++ b/internal/backer/utils_test.go
@@ -247,6 +247,59 @@ func TestCreateTarGzStreamHardLink(t *testing.T) {
 	}
 }
 
+// TestCreateTarGzStreamHardLinkFromTestData tests hard link handling with test data.
+func TestCreateTarGzStreamHardLinkFromTestData(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("Hard link detection not supported on Windows (inodes unavailable)")
+	}
+
+	testDataPath := filepath.Join("../../test_data", "test1", "hardlinks")
+	filepaths, err := GetFilesFromDirectories(context.Background(), []string{testDataPath})
+	if err != nil {
+		t.Fatalf("Failed to get files from directory: %v", err)
+	}
+
+	ctx := context.Background()
+	reader := CreateTarGzStream(ctx, filepaths)
+	defer reader.Close()
+
+	gzReader, err := gzip.NewReader(reader)
+	if err != nil {
+		t.Fatalf("Failed to create gzip reader: %v", err)
+	}
+	defer gzReader.Close()
+
+	tarReader := tar.NewReader(gzReader)
+
+	entries := 0
+	linkCount := 0
+
+	for {
+		header, err := tarReader.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Fatalf("Failed to read tar entry: %v", err)
+		}
+
+		entries++
+		t.Logf("Entry %d: name=%s typeflag=%c linkname=%s", entries, header.Name, header.Typeflag, header.Linkname)
+
+		if header.Typeflag == tar.TypeLink {
+			linkCount++
+		}
+	}
+
+	if entries != 4 {
+		t.Errorf("Expected 4 entries (dir + 1 original + 2 hardlinks), got %d", entries)
+	}
+
+	if linkCount != 2 {
+		t.Errorf("Expected 2 hard link entries, got %d", linkCount)
+	}
+}
+
 // TestCreateTarGzStreamCancellation tests context cancellation.
 func TestCreateTarGzStreamCancellation(t *testing.T) {
 	tmpDir := t.TempDir()
diff --git a/test_data/test1/hardlinks/hardlink1.txt b/test_data/test1/hardlinks/hardlink1.txt
new file mode 100644
index 0000000..508d3cf
--- /dev/null
+++ b/test_data/test1/hardlinks/hardlink1.txt
@@ -0,0 +1 @@
+shared content for hardlinks
diff --git a/test_data/test1/hardlinks/hardlink2.txt b/test_data/test1/hardlinks/hardlink2.txt
new file mode 100644
index 0000000..508d3cf
--- /dev/null
+++ b/test_data/test1/hardlinks/hardlink2.txt
@@ -0,0 +1 @@
+shared content for hardlinks
diff --git a/test_data/test1/hardlinks/original.txt b/test_data/test1/hardlinks/original.txt
new file mode 100644
index 0000000..508d3cf
--- /dev/null
+++ b/test_data/test1/hardlinks/original.txt
@@ -0,0 +1 @@
+shared content for hardlinks