findbase: walk up tree to find a suitable base dir

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

base/findbase.go

@@ -0,0 +1,67 @@
+package base
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"syscall"
+)
+
+// FindBase steps up the directory tree to find the top-level that is still on
+// the same device as the path provided
+func FindBase(path string) (string, error) {
+	stat, err := os.Lstat(path)
+	if err != nil {
+		return "", err
+	}
+	if stat.IsDir() {
+		return findBaseInfo(stat)
+	}
+
+	return FindBase(filepath.Dir(path))
+}
+
+func findBaseInfo(stat os.FileInfo) (string, error) {
+	dirstat, err := os.Lstat(filepath.Dir(stat.Name()))
+	if err != nil {
+		return "", err
+	}
+	if stat.Name() == dirstat.Name() {
+		return stat.Name(), nil
+	}
+
+	if sameDevice(stat, dirstat) {
+		return findBaseInfo(dirstat)
+	}
+	return stat.Name(), nil
+}
+
+func hasPermission(path string) bool {
+	stat, err := os.Lstat(path)
+	if err != nil {
+		return false
+	}
+	if !stat.IsDir() {
+		path = filepath.Dir(path)
+	}
+	fh, err := ioutil.TempFile(path, "perm.test.")
+	if err != nil {
+		return false
+	}
+	os.Remove(fh.Name())
+	return true
+}
+
+func sameDevice(file1, file2 os.FileInfo) bool {
+	sys1 := file1.Sys().(*syscall.Stat_t)
+	sys2 := file2.Sys().(*syscall.Stat_t)
+	return ((major(sys1.Dev) == major(sys2.Dev)) && (minor(sys1.Dev) == minor(sys2.Dev)))
+}
+
+func major(n uint64) uint64 {
+	return uint64(n / 256)
+}
+
+func minor(n uint64) uint64 {
+	return uint64(n % 256)
+}

base/findbase_test.go

@@ -0,0 +1,75 @@
+package base
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestHasPermission(t *testing.T) {
+	if !hasPermission("/tmp") {
+		t.Error("expected to have permission to /tmp, but did not")
+	}
+
+	if hasPermission("/") {
+		t.Error("expected to not have permission to /, but did")
+	}
+}
+
+func TestSameDev(t *testing.T) {
+	file1, err := ioutil.TempFile("", "test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file1.Close()
+	file2, err := ioutil.TempFile("", "test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file2.Close()
+
+	stat1, err := file1.Stat()
+	if err != nil {
+		t.Fatal(err)
+	}
+	stat2, err := file2.Stat()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !sameDevice(stat1, stat2) {
+		t.Errorf("expected the two files to be on same device. But %q and %q are not", file1.Name(), file2.Name())
+	} else {
+		os.Remove(stat1.Name())
+		os.Remove(stat2.Name())
+	}
+}
+
+func TestNotSameDev(t *testing.T) {
+	file1, err := ioutil.TempFile("/tmp", "test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file1.Close()
+	file2, err := ioutil.TempFile("/home/vbatts", "test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file2.Close()
+
+	stat1, err := file1.Stat()
+	if err != nil {
+		t.Fatal(err)
+	}
+	stat2, err := file2.Stat()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if sameDevice(stat1, stat2) {
+		t.Errorf("expected the two files _not_ to be on same device. But %q and %q are not", file1.Name(), file2.Name())
+	} else {
+		os.Remove(stat1.Name())
+		os.Remove(stat2.Name())
+	}
+}