X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/654ee9154fe85832a0862c27fd7b982831a75a0d..0767da07b441afe6ec470ee9862c2fd2ee17c38a:/services/keep-web/webdav.go

diff --git a/services/keep-web/webdav.go b/services/keep-web/webdav.go
index 1b5811dad7..57f3f53a99 100644
--- a/services/keep-web/webdav.go
+++ b/services/keep-web/webdav.go
@@ -5,20 +5,32 @@
 package main
 
 import (
+	"crypto/rand"
 	"errors"
+	"fmt"
+	prand "math/rand"
 	"net/http"
 	"os"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"git.curoverse.com/arvados.git/sdk/go/arvados"
 
 	"golang.org/x/net/context"
 	"golang.org/x/net/webdav"
 )
 
-var errReadOnly = errors.New("read-only filesystem")
+var (
+	lockPrefix     string = uuid()
+	nextLockSuffix int64  = prand.Int63()
+	errReadOnly           = errors.New("read-only filesystem")
+)
 
-// webdavFS implements a read-only webdav.FileSystem by wrapping
-// http.Filesystem.
+// webdavFS implements a read-only webdav.FileSystem by wrapping an
+// arvados.CollectionFilesystem.
 type webdavFS struct {
-	httpfs http.FileSystem
+	collfs arvados.CollectionFileSystem
 }
 
 var _ webdav.FileSystem = &webdavFS{}
@@ -28,11 +40,11 @@ func (fs *webdavFS) Mkdir(ctx context.Context, name string, perm os.FileMode) er
 }
 
 func (fs *webdavFS) OpenFile(ctx context.Context, name string, flag int, perm os.FileMode) (webdav.File, error) {
-	f, err := fs.httpfs.Open(name)
+	fi, err := fs.collfs.Stat(name)
 	if err != nil {
 		return nil, err
 	}
-	return &webdavFile{File: f}, nil
+	return &webdavFile{collfs: fs.collfs, fileInfo: fi, name: name}, nil
 }
 
 func (fs *webdavFS) RemoveAll(ctx context.Context, name string) error {
@@ -44,19 +56,127 @@ func (fs *webdavFS) Rename(ctx context.Context, oldName, newName string) error {
 }
 
 func (fs *webdavFS) Stat(ctx context.Context, name string) (os.FileInfo, error) {
-	if f, err := fs.httpfs.Open(name); err != nil {
-		return nil, err
-	} else {
-		return f.Stat()
-	}
+	return fs.collfs.Stat(name)
 }
 
 // webdavFile implements a read-only webdav.File by wrapping
-// http.File. Writes fail.
+// http.File.
+//
+// The http.File is opened from an arvados.CollectionFileSystem, but
+// not until Seek, Read, or Readdir is called. This deferred-open
+// strategy makes webdav's OpenFile-Stat-Close cycle fast even though
+// the collfs's Open method is slow. This is relevant because webdav
+// does OpenFile-Stat-Close on each file when preparing directory
+// listings.
+//
+// Writes to a webdavFile always fail.
 type webdavFile struct {
-	http.File
+	// fields populated by (*webdavFS).OpenFile()
+	collfs   http.FileSystem
+	fileInfo os.FileInfo
+	name     string
+
+	// internal fields
+	file     http.File
+	loadOnce sync.Once
+	err      error
+}
+
+func (f *webdavFile) load() {
+	f.file, f.err = f.collfs.Open(f.name)
 }
 
 func (f *webdavFile) Write([]byte) (int, error) {
 	return 0, errReadOnly
 }
+
+func (f *webdavFile) Seek(offset int64, whence int) (int64, error) {
+	f.loadOnce.Do(f.load)
+	if f.err != nil {
+		return 0, f.err
+	}
+	return f.file.Seek(offset, whence)
+}
+
+func (f *webdavFile) Read(buf []byte) (int, error) {
+	f.loadOnce.Do(f.load)
+	if f.err != nil {
+		return 0, f.err
+	}
+	return f.file.Read(buf)
+}
+
+func (f *webdavFile) Close() error {
+	if f.file == nil {
+		// We never called load(), or load() failed
+		return f.err
+	}
+	return f.file.Close()
+}
+
+func (f *webdavFile) Readdir(n int) ([]os.FileInfo, error) {
+	f.loadOnce.Do(f.load)
+	if f.err != nil {
+		return nil, f.err
+	}
+	return f.file.Readdir(n)
+}
+
+func (f *webdavFile) Stat() (os.FileInfo, error) {
+	return f.fileInfo, nil
+}
+
+// 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.
+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:])
+}