From b4b149f834bfe497475c8f8ffc5857a670da891e Mon Sep 17 00:00:00 2001
From: Scott Owens <sdark.arrow@gmail.com>
Date: Tue, 10 Dec 2019 16:24:03 +1100
Subject: [PATCH] adding support for Linker and LinkReader

---
 basepath.go      | 26 ++++++++++++++++++++++++++
 copyOnWriteFs.go | 20 ++++++++++++++++++++
 os.go            |  8 ++++++++
 readonlyfs.go    | 12 ++++++++++++
 symlink.go       | 14 ++++++++++++++
 5 files changed, 80 insertions(+)

diff --git a/basepath.go b/basepath.go
index 616ff8f..3a14b83 100644
--- a/basepath.go
+++ b/basepath.go
@@ -177,4 +177,30 @@ func (b *BasePathFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
 	return fi, false, err
 }
 
+func (b *BasePathFs) SymlinkIfPossible(oldname, newname string) error {
+	oldname, err := b.RealPath(oldname)
+	if err != nil {
+		return &os.LinkError{Op: "symlink", Old: oldname, New: newname, Err: err}
+	}
+	newname, err = b.RealPath(newname)
+	if err != nil {
+		return &os.LinkError{Op: "symlink", Old: oldname, New: newname, Err: err}
+	}
+	if linker, ok := b.source.(Linker); ok {
+		return linker.SymlinkIfPossible(oldname, newname)
+	}
+	return &os.LinkError{Op: "symlink", Old: oldname, New: newname, Err: ErrNoSymlink}
+}
+
+func (b *BasePathFs) ReadlinkIfPossible(name string) (string, error) {
+	name, err := b.RealPath(name)
+	if err != nil {
+		return "", &os.PathError{Op: "readlink", Path: name, Err: err}
+	}
+	if reader, ok := b.source.(LinkReader); ok {
+		return reader.ReadlinkIfPossible(name)
+	}
+	return "", &os.PathError{Op: "readlink", Path: name, Err: ErrNoReadlink}
+}
+
 // vim: ts=4 sw=4 noexpandtab nolist syn=go
diff --git a/copyOnWriteFs.go b/copyOnWriteFs.go
index e8108a8..96b7701 100644
--- a/copyOnWriteFs.go
+++ b/copyOnWriteFs.go
@@ -117,6 +117,26 @@ func (u *CopyOnWriteFs) LstatIfPossible(name string) (os.FileInfo, bool, error)
 	return fi, false, err
 }
 
+func (u *CopyOnWriteFs) SymlinkIfPossible(oldname, newname string) error {
+	if slayer, ok := u.layer.(Linker); ok {
+		return slayer.SymlinkIfPossible(oldname, newname)
+	}
+
+	return &os.LinkError{Op: "symlink", Old: oldname, New: newname, Err: ErrNoSymlink}
+}
+
+func (u *CopyOnWriteFs) ReadlinkIfPossible(name string) (string, error) {
+	if rlayer, ok := u.layer.(LinkReader); ok {
+		return rlayer.ReadlinkIfPossible(name)
+	}
+
+	if rbase, ok := u.base.(LinkReader); ok {
+		return rbase.ReadlinkIfPossible(name)
+	}
+
+	return "", &os.PathError{Op: "readlink", Path: name, Err: ErrNoReadlink}
+}
+
 func (u *CopyOnWriteFs) isNotExist(err error) bool {
 	if e, ok := err.(*os.PathError); ok {
 		err = e.Err
diff --git a/os.go b/os.go
index 13cc1b8..4761db5 100644
--- a/os.go
+++ b/os.go
@@ -99,3 +99,11 @@ func (OsFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
 	fi, err := os.Lstat(name)
 	return fi, true, err
 }
+
+func (OsFs) SymlinkIfPossible(oldname, newname string) error {
+	return os.Symlink(oldname, newname)
+}
+
+func (OsFs) ReadlinkIfPossible(name string) (string, error) {
+	return os.Readlink(name)
+}
diff --git a/readonlyfs.go b/readonlyfs.go
index c6376ec..f94b181 100644
--- a/readonlyfs.go
+++ b/readonlyfs.go
@@ -44,6 +44,18 @@ func (r *ReadOnlyFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
 	return fi, false, err
 }
 
+func (r *ReadOnlyFs) SymlinkIfPossible(oldname, newname string) error {
+	return &os.LinkError{Op: "symlink", Old: oldname, New: newname, Err: ErrNoSymlink}
+}
+
+func (r *ReadOnlyFs) ReadlinkIfPossible(name string) (string, error) {
+	if srdr, ok := r.source.(LinkReader); ok {
+		return srdr.ReadlinkIfPossible(name)
+	}
+
+	return "", &os.PathError{Op: "readlink", Path: name, Err: ErrNoReadlink}
+}
+
 func (r *ReadOnlyFs) Rename(o, n string) error {
 	return syscall.EPERM
 }
diff --git a/symlink.go b/symlink.go
index ba9d179..d1c6ea5 100644
--- a/symlink.go
+++ b/symlink.go
@@ -13,6 +13,10 @@
 
 package afero
 
+import (
+	"errors"
+)
+
 // Symlinker is an optional interface in Afero. It is only implemented by the
 // filesystems saying so.
 // It indicates support for 3 symlink related interfaces that implement the
@@ -34,8 +38,18 @@ type Linker interface {
 	SymlinkIfPossible(oldname, newname string) error
 }
 
+// ErrNoSymlink is the error that will be wrapped in an os.LinkError if a file system
+// does not support Symlink's either directly or through its delegated filesystem.
+// As expressed by support for the Linker interface.
+var ErrNoSymlink = errors.New("symlink not supported")
+
 // LinkReader is an optional interface in Afero. It is only implemented by the
 // filesystems saying so.
 type LinkReader interface {
 	ReadlinkIfPossible(name string) (string, error)
 }
+
+// ErrNoReadlink is the error that will be wrapped in an os.Path if a file system
+// does not support the readlink operation either directly or through its delegated filesystem.
+// As expressed by support for the LinkReader interface.
+var ErrNoReadlink = errors.New("readlink not supported")