Fix failing tests on Windows

To simulate failures opening a cache file, fixtures are written without the read permission bits.
Since Unix permission bits have no meaning on Windows, a slightly more complicated solution is required to achieve the same permissions.
Thankfully, there's a library to abstract that already.

vendor/github.com/hectane/go-acl/api/acl.go

@@ -0,0 +1,98 @@
+//+build windows
+
+package api
+
+import (
+	"golang.org/x/sys/windows"
+
+	"unsafe"
+)
+
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa379284.aspx
+const (
+	NO_MULTIPLE_TRUSTEE = iota
+	TRUSTEE_IS_IMPERSONATE
+)
+
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa379638.aspx
+const (
+	TRUSTEE_IS_SID = iota
+	TRUSTEE_IS_NAME
+	TRUSTEE_BAD_FORM
+	TRUSTEE_IS_OBJECTS_AND_SID
+	TRUSTEE_IS_OBJECTS_AND_NAME
+)
+
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa379639.aspx
+const (
+	TRUSTEE_IS_UNKNOWN = iota
+	TRUSTEE_IS_USER
+	TRUSTEE_IS_GROUP
+	TRUSTEE_IS_DOMAIN
+	TRUSTEE_IS_ALIAS
+	TRUSTEE_IS_WELL_KNOWN_GROUP
+	TRUSTEE_IS_DELETED
+	TRUSTEE_IS_INVALID
+	TRUSTEE_IS_COMPUTER
+)
+
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa374899.aspx
+const (
+	NOT_USED_ACCESS = iota
+	GRANT_ACCESS
+	SET_ACCESS
+	DENY_ACCESS
+	REVOKE_ACCESS
+	SET_AUDIT_SUCCESS
+	SET_AUDIT_FAILURE
+)
+
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa446627.aspx
+const (
+	NO_INHERITANCE                     = 0x0
+	SUB_OBJECTS_ONLY_INHERIT           = 0x1
+	SUB_CONTAINERS_ONLY_INHERIT        = 0x2
+	SUB_CONTAINERS_AND_OBJECTS_INHERIT = 0x3
+	INHERIT_NO_PROPAGATE               = 0x4
+	INHERIT_ONLY                       = 0x8
+
+	OBJECT_INHERIT_ACE       = 0x1
+	CONTAINER_INHERIT_ACE    = 0x2
+	NO_PROPAGATE_INHERIT_ACE = 0x4
+	INHERIT_ONLY_ACE         = 0x8
+)
+
+var (
+	procSetEntriesInAclW = advapi32.MustFindProc("SetEntriesInAclW")
+)
+
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa379636.aspx
+type Trustee struct {
+	MultipleTrustee          *Trustee
+	MultipleTrusteeOperation int32
+	TrusteeForm              int32
+	TrusteeType              int32
+	Name                     *uint16
+}
+
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa446627.aspx
+type ExplicitAccess struct {
+	AccessPermissions uint32
+	AccessMode        int32
+	Inheritance       uint32
+	Trustee           Trustee
+}
+
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa379576.aspx
+func SetEntriesInAcl(entries []ExplicitAccess, oldAcl windows.Handle, newAcl *windows.Handle) error {
+	ret, _, err := procSetEntriesInAclW.Call(
+		uintptr(len(entries)),
+		uintptr(unsafe.Pointer(&entries[0])),
+		uintptr(oldAcl),
+		uintptr(unsafe.Pointer(newAcl)),
+	)
+	if ret != 0 {
+		return err
+	}
+	return nil
+}