From f97494e89bff7b15d1be5f4b2d047382a54e6094 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Wed, 6 Dec 2017 21:07:24 +0100
Subject: syscallcompat: add Readlinkat
We need readlinkat to implement Readlink
symlink-race-free.
---
internal/syscallcompat/sys_common.go | 23 +++++++++++++++++++++++
internal/syscallcompat/sys_common_test.go | 29 +++++++++++++++++++++++++++++
2 files changed, 52 insertions(+)
create mode 100644 internal/syscallcompat/sys_common.go
create mode 100644 internal/syscallcompat/sys_common_test.go
(limited to 'internal')
diff --git a/internal/syscallcompat/sys_common.go b/internal/syscallcompat/sys_common.go
new file mode 100644
index 0000000..440b42f
--- /dev/null
+++ b/internal/syscallcompat/sys_common.go
@@ -0,0 +1,23 @@
+package syscallcompat
+
+import (
+ "golang.org/x/sys/unix"
+)
+
+// Readlinkat exists both in Linux and in MacOS 10.10+. We may add an
+// emulated version for users on older MacOS versions if there is
+// demand.
+// Buffer allocation is handled internally, unlike the bare unix.Readlinkat.
+func Readlinkat(dirfd int, path string) (string, error) {
+ // Allocate the buffer exponentially like os.Readlink does.
+ for bufsz := 128; ; bufsz *= 2 {
+ buf := make([]byte, bufsz)
+ n, err := unix.Readlinkat(dirfd, path, buf)
+ if err != nil {
+ return "", err
+ }
+ if n < bufsz {
+ return string(buf[0:n]), nil
+ }
+ }
+}
diff --git a/internal/syscallcompat/sys_common_test.go b/internal/syscallcompat/sys_common_test.go
new file mode 100644
index 0000000..bc694ba
--- /dev/null
+++ b/internal/syscallcompat/sys_common_test.go
@@ -0,0 +1,29 @@
+package syscallcompat
+
+import (
+ "bytes"
+ "os"
+ "syscall"
+ "testing"
+)
+
+func TestReadlinkat(t *testing.T) {
+ for _, targetLen := range []int{100, 500, 4000} {
+ target := string(bytes.Repeat([]byte("x"), targetLen))
+ err := os.Symlink(target, tmpDir+"/readlinkat")
+ if err != nil {
+ t.Fatal(err)
+ }
+ target2, err := Readlinkat(tmpDirFd, "readlinkat")
+ if err != nil {
+ t.Fatal(err)
+ }
+ if target != target2 {
+ t.Errorf("target=%q != target2=%q", target, target2)
+ }
+ err = syscall.Unlink(tmpDir + "/readlinkat")
+ if err != nil {
+ t.Fatal(err)
+ }
+ }
+}
--
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