@ -4,11 +4,19 @@
package compositedav
import (
"bytes"
"encoding/xml"
"log"
"net/http"
"sync"
"time"
"github.com/jellydator/ttlcache/v3"
"tailscale.com/drive/driveimpl/shared"
)
var (
notFound = newCacheEntry ( http . StatusNotFound , nil )
)
// StatCache provides a cache for directory listings and file metadata.
@ -18,12 +26,38 @@ import (
// This is similar to the DirectoryCacheLifetime setting of Windows' built-in
// SMB client, see
// https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-7/ff686200(v=ws.10)
//
// StatCache is built specifically to cache the results of PROPFIND requests,
// which come back as MultiStatus XML responses. Typical clients will issue two
// kinds of PROPFIND:
//
// The first kind of PROPFIND is a directory listing performed to depth 1. At
// this depth, the resulting XML will contain stats for the requested folder as
// well as for all children of that folder.
//
// The second kind of PROPFIND is a file listing performed to depth 0. At this
// depth, the resulting XML will contain stats only for the requested file.
//
// In order to avoid round-trips, when a PROPFIND at depth 0 is attempted, and
// the requested file is not in the cache, StatCache will check to see if the
// parent folder of that file is cached. If so, StatCache infers the correct
// MultiStatus for the file according to the following logic:
//
// 1. If the parent folder is NotFound (404), treat the file itself as NotFound
// 2. If the parent folder's XML doesn't contain the file, treat it as
// NotFound.
// 3. If the parent folder's XML contains the file, build a MultiStatus for the
// file based on the parent's XML.
//
// To avoid inconsistencies from the perspective of the client, any operations
// that modify the filesystem (e.g. PUT, MKDIR, etc.) should call invalidate()
// to invalidate the cache.
type StatCache struct {
TTL time . Duration
// mu guards the below values.
mu sync . Mutex
cachesByDepthAndPath map [ int ] * ttlcache . Cache [ string , [ ] byte ]
cachesByDepthAndPath map [ int ] * ttlcache . Cache [ string , * cacheEntry ]
}
// getOr checks the cache for the named value at the given depth. If a cached
@ -32,25 +66,57 @@ type StatCache struct {
// status and value. If the function returned http.StatusMultiStatus, getOr
// caches the resulting value at the given name and depth before returning.
func ( c * StatCache ) getOr ( name string , depth int , or func ( ) ( int , [ ] byte ) ) ( int , [ ] byte ) {
cached := c . get ( name , depth )
if cached != nil {
return http . StatusMultiStatus , cached
}
status , next := or ( )
if c != nil && status == http . StatusMultiStatus && next != nil {
c . set ( name , depth , next )
ce := c . get ( name , depth )
if ce == nil {
// Not cached, fetch value.
status , raw := or ( )
ce = newCacheEntry ( status , raw )
if status == http . StatusMultiStatus || status == http . StatusNotFound {
// Got a legit status, cache value
c . set ( name , depth , ce )
}
}
return status , next
return ce. Status , ce . Raw
}
func ( c * StatCache ) get ( name string , depth int ) [ ] byte {
// get retrieves the entry for the named file at the given depth. If no entry
// is found, and depth == 0, get will check to see if the parent path of name
// is present in the cache at depth 1. If so, it will infer that the child does
// not exist and return notFound (404).
func ( c * StatCache ) get ( name string , depth int ) * cacheEntry {
if c == nil {
return nil
}
name = shared . Normalize ( name )
c . mu . Lock ( )
defer c . mu . Unlock ( )
ce := c . tryGetLocked ( name , depth )
if ce != nil {
// Cache hit.
return ce
}
if depth > 0 {
// Cache miss.
return nil
}
// At depth 0, if child's parent is in the cache, and the child isn't
// cached, we can infer that the child is notFound.
p := c . tryGetLocked ( shared . Parent ( name ) , 1 )
if p != nil {
return notFound
}
// No parent in cache, cache miss.
return nil
}
// tryGetLocked requires that c.mu be held.
func ( c * StatCache ) tryGetLocked ( name string , depth int ) * cacheEntry {
if c . cachesByDepthAndPath == nil {
return nil
}
@ -65,28 +131,80 @@ func (c *StatCache) get(name string, depth int) []byte {
return item . Value ( )
}
func ( c * StatCache ) set ( name string , depth int , value [ ] byte ) {
// set stores the given cacheEntry in the cache at the given name and depth. If
// the depth is 1, set also populates depth 0 entries in the cache for the bare
// name. If status is StatusMultiStatus, set will parse the PROPFIND result and
// store depth 0 entries for all children. If parsing the result fails, nothing
// is cached.
func ( c * StatCache ) set ( name string , depth int , ce * cacheEntry ) {
if c == nil {
return
}
name = shared . Normalize ( name )
var self * cacheEntry
var children map [ string ] * cacheEntry
if depth == 1 {
switch ce . Status {
case http . StatusNotFound :
// Record notFound as the self entry.
self = ce
case http . StatusMultiStatus :
// Parse the raw MultiStatus and extract specific responses
// corresponding to the self entry (e.g. the directory, but at depth 0)
// and children (e.g. files within the directory) so that subsequent
// requests for these can be satisfied from the cache.
var ms multiStatus
err := xml . Unmarshal ( ce . Raw , & ms )
if err != nil {
// unparseable MultiStatus response, don't cache
log . Printf ( "statcache.set error: %s" , err )
return
}
children = make ( map [ string ] * cacheEntry , len ( ms . Responses ) - 1 )
for i := 0 ; i < len ( ms . Responses ) ; i ++ {
response := ms . Responses [ i ]
name := shared . Normalize ( response . Href )
raw := marshalMultiStatus ( response )
entry := newCacheEntry ( ce . Status , raw )
if i == 0 {
self = entry
} else {
children [ name ] = entry
}
}
}
}
c . mu . Lock ( )
defer c . mu . Unlock ( )
c . setLocked ( name , depth , ce )
if self != nil {
c . setLocked ( name , 0 , self )
}
for childName , child := range children {
c . setLocked ( childName , 0 , child )
}
}
// setLocked requires that c.mu be held.
func ( c * StatCache ) setLocked ( name string , depth int , ce * cacheEntry ) {
if c . cachesByDepthAndPath == nil {
c . cachesByDepthAndPath = make ( map [ int ] * ttlcache . Cache [ string , [ ] byte ] )
c . cachesByDepthAndPath = make ( map [ int ] * ttlcache . Cache [ string , * cacheEntry ] )
}
cache := c . cachesByDepthAndPath [ depth ]
if cache == nil {
cache = ttlcache . New (
ttlcache . WithTTL [ string , [ ] byte ] ( c . TTL ) ,
ttlcache . WithTTL [ string , * cacheEntry ] ( c . TTL ) ,
)
go cache . Start ( )
c . cachesByDepthAndPath [ depth ] = cache
}
cache . Set ( name , value , ttlcache . DefaultTTL )
cache . Set ( name , c e, ttlcache . DefaultTTL )
}
// invalidate invalidates the entire cache.
func ( c * StatCache ) invalidate ( ) {
if c == nil {
return
@ -108,3 +226,54 @@ func (c *StatCache) stop() {
cache . Stop ( )
}
}
type cacheEntry struct {
Status int
Raw [ ] byte
}
func newCacheEntry ( status int , raw [ ] byte ) * cacheEntry {
return & cacheEntry { Status : status , Raw : raw }
}
type propStat struct {
InnerXML [ ] byte ` xml:",innerxml" `
}
type response struct {
XMLName xml . Name ` xml:"response" `
Href string ` xml:"href" `
PropStats [ ] * propStat ` xml:"propstat" `
}
type multiStatus struct {
XMLName xml . Name ` xml:"multistatus" `
Responses [ ] * response ` xml:"response" `
}
// marshalMultiStatus performs custom marshalling of a MultiStatus to preserve
// the original formatting, namespacing, etc. Doing this with Go's XML encoder
// is somewhere between difficult and impossible, which is why we use this more
// manual approach.
func marshalMultiStatus ( response * response ) [ ] byte {
// TODO(percy): maybe pool these buffers
var buf bytes . Buffer
buf . WriteString ( multistatusTemplateStart )
buf . WriteString ( response . Href )
buf . WriteString ( hrefEnd )
for _ , propStat := range response . PropStats {
buf . WriteString ( propstatStart )
buf . Write ( propStat . InnerXML )
buf . WriteString ( propstatEnd )
}
buf . WriteString ( multistatusTemplateEnd )
return buf . Bytes ( )
}
const (
multistatusTemplateStart = ` <?xml version="1.0" encoding="UTF-8"?><D:multistatus xmlns:D="DAV:"><D:response><D:href> `
hrefEnd = ` </D:href> `
propstatStart = ` <D:propstat> `
propstatEnd = ` </D:propstat> `
multistatusTemplateEnd = ` </D:response></D:multistatus> `
)
Percy Wegmann
6 months ago
committed by