// Copyright (C) The Arvados Authors. All rights reserved. // // SPDX-License-Identifier: AGPL-3.0 // Package webdavfs adds special behaviors to an arvados.FileSystem so // it's suitable to use with a webdav server. package webdavfs import ( "context" "crypto/rand" "errors" "fmt" "io" prand "math/rand" "os" "strings" "sync/atomic" "time" "git.arvados.org/arvados.git/sdk/go/arvados" "golang.org/x/net/webdav" ) var ( lockPrefix string = uuid() nextLockSuffix int64 = prand.Int63() ErrReadOnly = errors.New("read-only filesystem") ) // FS implements a webdav.FileSystem by wrapping an // arvados.CollectionFilesystem. type FS struct { FileSystem arvados.FileSystem // Prefix works like fs.Sub: Stat(name) calls // Stat(prefix+name) in the wrapped filesystem. Prefix string // If Writing is false, all write operations return errors. // (Opening a file for writing succeeds -- otherwise webdav // would return 404 -- but writing to it fails.) Writing bool // webdav PROPFIND reads the first few bytes of each file // whose filename extension isn't recognized, which is // prohibitively expensive: we end up fetching multiple 64MiB // blocks. Avoid this by returning EOF on all reads when // handling a PROPFIND. AlwaysReadEOF bool } func (fs *FS) Mkdir(ctx context.Context, name string, perm os.FileMode) error { if !fs.Writing { return ErrReadOnly } name = strings.TrimRight(name, "/") return fs.FileSystem.Mkdir(fs.Prefix+name, 0755) } func (fs *FS) OpenFile(ctx context.Context, name string, flag int, perm os.FileMode) (f webdav.File, err error) { writing := flag&(os.O_WRONLY|os.O_RDWR|os.O_TRUNC) != 0 f, err = fs.FileSystem.OpenFile(fs.Prefix+name, flag, perm) if !fs.Writing { // webdav module returns 404 on all OpenFile errors, // but returns 405 Method Not Allowed if OpenFile() // succeeds but Write() or Close() fails. We'd rather // have 405. writeFailer ensures Close() fails if the // file is opened for writing *or* Write() is called. var err error if writing { err = ErrReadOnly } f = writeFailer{File: f, err: err} } if fs.AlwaysReadEOF { f = readEOF{File: f} } return } func (fs *FS) RemoveAll(ctx context.Context, name string) error { return fs.FileSystem.RemoveAll(fs.Prefix + name) } func (fs *FS) Rename(ctx context.Context, oldName, newName string) error { if !fs.Writing { return ErrReadOnly } if strings.HasSuffix(oldName, "/") { // WebDAV "MOVE foo/ bar/" means rename foo to bar. oldName = oldName[:len(oldName)-1] newName = strings.TrimSuffix(newName, "/") } return fs.FileSystem.Rename(fs.Prefix+oldName, fs.Prefix+newName) } func (fs *FS) Stat(ctx context.Context, name string) (os.FileInfo, error) { return fs.FileSystem.Stat(fs.Prefix + name) } type writeFailer struct { webdav.File err error } func (wf writeFailer) Write([]byte) (int, error) { wf.err = ErrReadOnly return 0, wf.err } func (wf writeFailer) Close() error { err := wf.File.Close() if err != nil { wf.err = err } return wf.err } type readEOF struct { webdav.File } func (readEOF) Read(p []byte) (int, error) { return 0, io.EOF } // NoLockSystem implements webdav.LockSystem by returning success for // every possible locking operation, even though it has no side // effects such as actually locking anything. This works for a // read-only webdav filesystem because webdav locks only apply to // writes. // // This is more suitable than webdav.NewMemLS() for two reasons: // First, it allows keep-web to use one locker for all collections // even though coll1.vhost/foo and coll2.vhost/foo have the same path // but represent different resources. Additionally, it returns valid // tokens (rfc2518 specifies that tokens are represented as URIs and // are unique across all resources for all time), which might improve // client compatibility. // // However, it does also permit impossible operations, like acquiring // conflicting locks and releasing non-existent locks. This might // confuse some clients if they try to probe for correctness. // // Currently this is a moot point: the LOCK and UNLOCK methods are not // accepted by keep-web, so it suffices to implement the // webdav.LockSystem interface. var NoLockSystem = noLockSystem{} type noLockSystem struct{} func (noLockSystem) Confirm(time.Time, string, string, ...webdav.Condition) (func(), error) { return noop, nil } func (noLockSystem) Create(now time.Time, details webdav.LockDetails) (token string, err error) { return fmt.Sprintf("opaquelocktoken:%s-%x", lockPrefix, atomic.AddInt64(&nextLockSuffix, 1)), nil } func (noLockSystem) Refresh(now time.Time, token string, duration time.Duration) (webdav.LockDetails, error) { return webdav.LockDetails{}, nil } func (noLockSystem) Unlock(now time.Time, token string) error { return nil } func noop() {} // Return a version 1 variant 4 UUID, meaning all bits are random // except the ones indicating the version and variant. func uuid() string { var data [16]byte if _, err := rand.Read(data[:]); err != nil { panic(err) } // variant 1: N=10xx data[8] = data[8]&0x3f | 0x80 // version 4: M=0100 data[6] = data[6]&0x0f | 0x40 return fmt.Sprintf("%x-%x-%x-%x-%x", data[0:4], data[4:6], data[6:8], data[8:10], data[10:]) }