[WIP] Partial bot skeleton, non-functional though

vendor/github.com/cockroachdb/pebble/vfs/clone.go

@@ -0,0 +1,137 @@
+// Copyright 2019 The LevelDB-Go and Pebble Authors. All rights reserved. Use
+// of this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package vfs
+
+import (
+	"io"
+	"sort"
+
+	"github.com/cockroachdb/errors/oserror"
+)
+
+type cloneOpts struct {
+	skip    func(string) bool
+	sync    bool
+	tryLink bool
+}
+
+// A CloneOption configures the behavior of Clone.
+type CloneOption func(*cloneOpts)
+
+// CloneSkip configures Clone to skip files for which the provided function
+// returns true when passed the file's path.
+func CloneSkip(fn func(string) bool) CloneOption {
+	return func(co *cloneOpts) { co.skip = fn }
+}
+
+// CloneSync configures Clone to sync files and directories.
+var CloneSync CloneOption = func(o *cloneOpts) { o.sync = true }
+
+// CloneTryLink configures Clone to link files to the destination if the source and
+// destination filesystems are the same. If the source and destination
+// filesystems are not the same or the filesystem does not support linking, then
+// Clone falls back to copying.
+var CloneTryLink CloneOption = func(o *cloneOpts) { o.tryLink = true }
+
+// Clone recursively copies a directory structure from srcFS to dstFS. srcPath
+// specifies the path in srcFS to copy from and must be compatible with the
+// srcFS path format. dstDir is the target directory in dstFS and must be
+// compatible with the dstFS path format. Returns (true,nil) on a successful
+// copy, (false,nil) if srcPath does not exist, and (false,err) if an error
+// occurred.
+func Clone(srcFS, dstFS FS, srcPath, dstPath string, opts ...CloneOption) (bool, error) {
+	var o cloneOpts
+	for _, opt := range opts {
+		opt(&o)
+	}
+
+	srcFile, err := srcFS.Open(srcPath)
+	if err != nil {
+		if oserror.IsNotExist(err) {
+			// Ignore non-existent errors. Those will translate into non-existent
+			// files in the destination filesystem.
+			return false, nil
+		}
+		return false, err
+	}
+	defer srcFile.Close()
+
+	stat, err := srcFile.Stat()
+	if err != nil {
+		return false, err
+	}
+
+	if stat.IsDir() {
+		if err := dstFS.MkdirAll(dstPath, 0755); err != nil {
+			return false, err
+		}
+		list, err := srcFS.List(srcPath)
+		if err != nil {
+			return false, err
+		}
+		// Sort the paths so we get deterministic test output.
+		sort.Strings(list)
+		for _, name := range list {
+			if o.skip != nil && o.skip(srcFS.PathJoin(srcPath, name)) {
+				continue
+			}
+			_, err := Clone(srcFS, dstFS, srcFS.PathJoin(srcPath, name), dstFS.PathJoin(dstPath, name), opts...)
+			if err != nil {
+				return false, err
+			}
+		}
+
+		if o.sync {
+			dir, err := dstFS.OpenDir(dstPath)
+			if err != nil {
+				return false, err
+			}
+			if err := dir.Sync(); err != nil {
+				return false, err
+			}
+			if err := dir.Close(); err != nil {
+				return false, err
+			}
+		}
+
+		return true, nil
+	}
+
+	// If the source and destination filesystems are the same and the user
+	// specified they'd prefer to link if possible, try to use a hardlink,
+	// falling back to copying if it fails.
+	if srcFS == dstFS && o.tryLink {
+		if err := LinkOrCopy(srcFS, srcPath, dstPath); oserror.IsNotExist(err) {
+			// Clone's semantics are such that it returns (false,nil) if the
+			// source does not exist.
+			return false, nil
+		} else if err != nil {
+			return false, err
+		} else {
+			return true, nil
+		}
+	}
+
+	data, err := io.ReadAll(srcFile)
+	if err != nil {
+		return false, err
+	}
+	dstFile, err := dstFS.Create(dstPath)
+	if err != nil {
+		return false, err
+	}
+	if _, err = dstFile.Write(data); err != nil {
+		return false, err
+	}
+	if o.sync {
+		if err := dstFile.Sync(); err != nil {
+			return false, err
+		}
+	}
+	if err := dstFile.Close(); err != nil {
+		return false, err
+	}
+	return true, nil
+}